Cytoplasm Final
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- Pages: 128
By Dr Iram Iqbal
1
Cells are the basic structural and functional unit of all multicellular organisms. Cells can be divided into two major components: Cytoplasm Nucleus.
2
With the L/M, Cytoplasm generally has an even, homogenous, amorphous appearance but may show granular, fibrillar, or vacuolated areas. Cytoplasm contains “organelles” and “inclusions”in aqueous gel called cytoplasmic matrix,
3
Organelles are living, structural components of cell. Organelles are described as ◦ membranous (cell membrane – limited) ◦ non membranous.
4
1. Plasma (cell) membrane 2. rER 3. sER 4. Golgi apparatus 5. Endosomes 6. Lysosomes 7. Transport vesicles 8. Mitochondria 9. Peroxisomes
5
1. 2. 3. 4.
Microtubules Filaments Centrioles Ribosomes
6
MEMBRANOUS ORGANELES
7
Plasma
membrane is a lipid bilayered structure that form the cell boundary as well as the boundaries of many organelles within the cell. It is visible with TEM. It is a dynamic structure that actively participates in many physiologic and biochemical activities essential to cell function and survival. 8
When plasma membrane is properly fixed, sectioned, stained and viewed on edge with TEM, it appears as two electron dense layers separated by an intermediate, electron lucent (non staining) layer.
Total thickness is about 8 – 10 nm.
9
PROTIENS PHOSPHOLIPIDS CHOLESTEROL
10
11
Integral membrane proteins Peripheral membrane proteins
12
PRESENT ON ONE SIDE OF MEMBRANE
13
Inserted in membrane Some entirely extend through membrane Perform many important functions
14
Integral membrane proteins can be visualized with the special tissue preparation technique of freeze fracture.
Usually the P-face display more particles ,thus more protein ,than the E-face.
E face
P-face
Micro domains of plasma membrane known as lipid rafts control the movement and distribution of proteins within lipid bilayers.
16
Localized regions with in the plasma membrane contain high concentration of cholesterol and glycosphingolipids. These regions are called lipid rafts. Owing to high concentration of cholesterol and the presence of longer, highly saturated fatty acid chain, the lipid raft area is thicker and exhibits less fluidity than the plasma membrane.
17
Lipid rafts contain a verity of integral and peripheral membrane proteins involved in cell signalling. They can be viewed as “signalling platforms ” floating in the ocean of lipids. Signal transduction in lipid rafts occurs more rapidly and efficiently because of close proximity of interacting proteins.
18
Integral membrane proteins have important functions in cell metabolism, regulation and integration. Six broad categories of membrane proteins have been defined in terms of their function: 1. 2. 3. 4. 5. 6.
Pumps Channels Receptor proteins Linker proteins Enzymes Structural proteins
Integral membrane proteins move within lipid bilayers of membrane 19
TRANSPORT IONS serve to transport certain ions such as Na + actively across membrane. Also transport metabolic precursor of macromolecules, such as sugar and amino acid across membrane either by themselves or linked through Na+ pump.
20
Allow Passage of small ions and molecules,and water across the plasma membrane in either direction i.e ,passive diffusion
21
22
For recognition and binding of substances to the outer surface of plasma membrane Like hormonal stimulation and antibody recognition
23
Anchor the intracellular cytoskeleton to the extracellular matrix.e.g,family of integrins that link cytoplasmic actin filament to a extracellular matrix protein
24
Protineous structures which have specific roles in ion pumping and digestion
25
Found in epithelial cells Form junctional complexes with neighbouring cells Visualized by freeze fracture method.
26
Channel proteins Carrier proteins
27
Some substances (fat-soluble and small un charged molecules cross the plasma membrane by simple diffusion down their concentration gradient. All other molecules require membrane transport proteins to provide them with individual passage across the plasma membrane.
28
Carrier proteins
Transfer small watersoluble molecules. They are highly selective often transporting only one type of molecules. After binding to a molecule designated for transport, the carrier protein undergoes a series of conformational changes and releases the molecules on the other side of the membrane.
Channel proteins
Also transfer small, water soluble molecules. Channel proteins create hydrophilic channels through the plasma membrane that regulate the transport of the molecules. They are ion selective and are regulated on the basis of the cell's needs 29
VESICULAR
TRANSPORT process that involves configurational changes in the plasma membrane & also provides for the transfer of molecules b/w different cellular compartments It maintains the integrity of plasma membrane
30
EXOCYTOSIS ENDOCYTOSIS
31
Processes of vesicular transport in which substances enter the cell are termed as endocytosis Uptake of fluid and macromolecules during endocytosis depends on three different mechanisms 32
PHAGOCYTOSIS
PINOCYTOSIS
RECEPTOR MEDIATED ENDCYTOSIS
33
PHAGOCYTOSIS Also called cell eating It is ingestion of large particles, such as cell debris ,bacteria and other foreign materials In this nonselective process large vesicles(250nm) called phagosomes are produced Best seen in macrophages 34
PINOCYTOSIS Also called cell drinking Is the nonspecific ingestion of fluid and small protein molecules via small vesicles usually amaller than150nm in diameter.
35
cargo
dynamin
This is a receptor mediated mechanism that allows selected molecules to enter the cell.
36
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Exocytosis is the process by which a vesicle moves from the cytoplasm to the plasma membrane, where it discharges its contents to the extra cellular space. Two general pathways of exocytosis: Constitutive pathway Regulated secretory pathway
Ca+
37
These are the membrane enclosed compartments in the cytoplasm, associated with all the endocytotic pathways Endosomes can be viewed either as stable cytoplasmic organelles or as transient structures formed as the result of endocytosis.
38
Endosomes destined to become lysosomes receive newly synthesized lysosomal enzymes Early and late endosomes differ in their cellular localization, morphology and state of acidification and function.
39
Early endosomes are restricted to portion of cytoplasm near the cell membrane where vesicles originating from the cell membrane fuse. Large number of vesicles originating in early endosome travell to deeper structures in the cytoplasm called late endosomes. The late endosomes mature into lysosomes.
40
Major function of early endosomes is to sort and recycle proteins internalized by endocytotic pathways.
41
Early endosomes
Late endosomes
Found in more peripheral cytoplasm Have a tubovesicular structure. Lumen is subdivided in to cisternae PH 6.2 - 6.5
Found near the Golgi apparatus and the nucleus. More complex structure and often exhibit onionlike internal membrane. PH 5.5
42
Lysosomes are small membrane bound organelles that contain a variety of acid hydrolases. Ribosomes are composed of two different sized subunits. The RNA molecules of both subunits are synthesized in side the nucleus.
Their numerous proteins are synthesized in the cytoplasm and then enter the nucleus and associate with rRNA . Subunits then leave the nucleus via nuclear pores, to enter the cytoplasm and participate in protein synthesis.
44
They constitute an intracellular digestive system capable of breaking down material originating both outside and within the cell. Great variety of appearances or pleomorphism.
45
Usually range from 0.2 – 0.4 um in diameter. Have a unique membrane that is resistant to hydrolytic digestion occurring in their lumen. Lysosomal membrane has an unusual phospholipid structure that contain cholesterol and a unique lipid called lysophosphatidic acid which play an important role in restricting the activity of hydrolytic enzymes directed against the membrane.
46
Found in all cells except erythrocytes but are numerous particularly in: Macrophages Neutrophils Hepatic cells Cells of Proximal tubule of kidney
47
Identified by Electron cytochemistry Divided into main groups:
1. Primary lysosomes 2. Secondary lysosomes
48
Newly formed lysosomes that have pinched of from golgi cisternae Contain all enzymes that are used in cell digestion
49
Formed by fusion of primary lysosomes with the structure that contains material to be digested Also called phagosome.digestive vacuole or autophagic vacuole
50
Hydrolytic breakdown of the contents of the lisosomes often produced a debris-liked vacule called a Residual body.which may remain for the entire life eg residual bodies are a normal feature of the cell aging
51
Normal feature of cell aging Debris filled vacuole Produced by break down of contents of
secondary lysosomes Found as age pigment or lipofusin pigment
52
Depending on the nature of digested material, three different pathways deliver material for intracellular digestion in lysosomes: 1.Extra cellular large particles ….. Phagosome and Phagolysosome. 2.Extra cellular small particles …..Endocytotic pathway. 3.Intracellular particles ….. autophagy
53
54
55
With TEM, RER appears as a series of interconnected, membrane limited flattened sacs called cisternae, with particles studding the external surface of membrane (ribosomes).
56
Basophilic component of cytoplasm, ergastoplasm-----the areas of cytoplasm that stain blue with basic stains . Ergastoplasm indicates i.e. that component of cytoplasm involved in protein synthesis..
Protein synthesis system of the cell consists of rER and ribosomes
The particles called ribosomes are attached to the membrane of eRE by ribosomal docking proteins
58
Membrane of reticulum enclose an intracellular compartment that segregates newly synthesized products. Its main function is synthesis of a secretory protein Synthesis of phospholipids Glycosylation of glycoprotiens
59
On E/M, appear as small, dense particles of about 15 – 20 nm in diameter, roughly spherical but irregular, and each is formed by two subunits, one large and one small. Responsible for cytoplasmic basophilia and they contain RNA and protein. Are sites where amino acids are incorporated into peptides and proteins i.e. site of protein synthesis 60
Found in all cells except mature erythrocytes. May be attached to granular endoplasmic reticulum or may lie free within general cytoplasm. Polysomes or polyribosomes----a cluster of ribosomes along a single strand of mRNA that is engaged in the synthesis of protein.
61
Ribosomes are the sites where mRNA is translated into protein. Proteins destined for transport (secretory, membrane, and lysosomal) are synthesized on polyribosomes bound to rER . whereas proteins not destined for transport (for intracellular use) are synthesized on free polyribosomes in cytosol. Ribosomes are numerous in rapidly growing and dividing cells.
62
63
SER is an irregular network of membrane bounded channels that lacks ribosomes on its surface, which makes it appear smooth. SER consists of short anastomosing tubules
64
Membranes are 6 – 7 nm thick, and a tubular lumen of about 50 nm. May exhibit distinct cytoplasmic eosinophilia. Tubular elements may connect directly with rER and indirectly with golgi apparatus via small vesicles.
65
Cells with large amount of SER may exhibit distinct cytoplasmic eosinophilia when viewed under L/M. Biochemically similar to RER but lacks ribosome docking proteins
67
Abundant in cells that function in lipid metabolism, cells that synthesize and secrete steroids (e.g. adrenocortical cells and testicular cells of leydig, progesterone secreting cells of corpus luteum of ovary). Lipid and steroid metabolism Glycogen metabolism Membrane formation and recycling Synthesis of phospholipids of all cell membrane Drug detoxification Muscle contraction and relaxation (specialized form,sarcoplasmic reticulum)
68
Well developed in secretory cells and does not stain with H & E. May be visible by L/M as either a positive or negative image After routine H & E stains, in cells with intensely basophilic cytoplasm such as osteoblasts & plasma cells, golgi apparatus is indicated as a pale, clear area. This is negative image After silver impregnation or prolonged exposure to osmium tetra oxide, it is seen as darkly staining network of stacked, flattened, membrane limited sacs or cisternae and tubular extensions embedded in a network of microtubules near MTOC----Positive image 69
Small vesicles involved in vesicular transport are seen in associated with cisternae. Regions: Cis golgi network (CGN) Trans golgi network (TGN) Medial golgi
71
72
73
74
It is active in cells: That secrete protein by exocytosis In cells that synthesize large amounts of membrane and membrane associated proteins such as nerve cells.
It functions in post translational modification, storing and packaging of proteins. It is involved in membrane flow , in transport and concentration of secretory materials and their release from the cells, in synthesis of certain secretory products, particularly glycoproteins and mucopolysacchrides and probably in lysosome formation 75
Basolateral plasma membrane Apical plasma membrane Endosomes or Lysosomes Apical cytoplasm
76
Are membrane bound organelles and lie free within cytoplasm. Display a variety of shapes including spheres, rods, elongated filaments and even coiled structures. Present in all cells except RBSs and terminal keratinocytes Abundant in cells that generate large amounts of energy.
77
Each mitochondria is bounded by two unit membranes Inner membrane shows folds called cristae to increase the surface area The space b/w inner and outer membrane is continuous with the interstitial space within each crista The inner mitochondrial membrane surrounds the large intercristal space of mitochondrial matrix. 78
Outer mitochondrial membrane 6 – 7 nm thick smooth membrane Contains many anion channels Possess receptors for proteins and polypeptides
79
Inner mitochondrial membrane Thinner than outer one Arranged in cristae Rich in phospholipids Cardiolipin, which makes the membrane impermeable to ions The internal membrane and cristae are coated with small particles called elementary particles or globular units
80
These have special heads 9-10 nm in diameter attached to inner mitochondrial membrane by a narrow 5nm long stalk
Enzymes of phosphorylation and electron transfer system are located either on elementary particles or within the inner mitochondrial membrane that form cristae
Enzymes of Kreb,s cycle lies in mitochondrial matrix
The matrix also contain calcium salts, organic crystals, glycogen, and RNA, DNA,
81
1.
2. 3.
Performing the oxidative reactions of the respiratory electron transport chain Synthesizing ATP Regulating transport of metabolites into and out of the metrix.
82
Intermembranous space Contain specific enzymes that use ATP generated in inner mitochondrial membrane (e.g. creatine kinase, adenylate kinase and cytochrome C)
83
Store house for energy, metabolites within the cell are utilized by Kreb,s citric acid cycle and energy released is captured through oxidative phosphorylation. thus ATPs are formed which are high energy compound. Involved in fatty acid B – oxidation. Source of electron for electron transport chain Store Ca++ and other divalent and trivalent cations. Synthesis of steroid hormons
84
Small (0.5 µm in dia.) membrane bounded spherical organelles containing oxidative enzymes (particularly catalases and other peroxidases)
85
Abundant in liver and kidney cells, but found in most other cells Do not contain hydrolases
86
Oxidative enzymes are perform a variety of detoxification processes. β oxidation of fatly acids is also a major function of peroxisosomes
87
88
These are nonbranching and rigid hollow tubes of protein that can rapidly disassemble in one location and reassemble in another. In general, they grow from MTOC located near nucleus and extend toward the cell periphery.
89
The region of the cell containing the centrioles and pericentriolar material is called MTOC or Centrosome. The MTOC is the region where most microtubules are formed and from which they are directed to specific destinations within the cell. The structures present in MTOC are cilia, basal bodies and centrosomes
90
Development of MTOC itself depend on presence of centrioles. When centrioles are missing MTOCs disappear ,and formation of microtubules is severely impaired.
91
Complex structure of tubulin 92
These are elongated polymeric structures composed of equal parts of α tubulin and β tubulin. Under appropriate conditions tubulin subunits polimerize to form microtubules Microtubules grow from γ tubulin ring within the MTOC that serve as nucleation sites for each microtubule. Each microtubule possesses a minus (non-growing) end and a plus (growing) end. 93
Polymerization and depolymerization are in equilibrium. Length of microtubules changes dynamically as tubulin dimers are added or removed in a process of dynamic instability. These can be visualized in L/M and are involved in intracellular transport and cell motility
94
95
The figure shows the 3-dimensional view of a microtubule being formed. The tubulin molecules are the bead like structures and combine to form long hollow, dynamic polymers, microtubules 96
In general, microtubules are found in: Cytoplasm (where they originate from MTOC) Cilia and flagella (where they form axoneme and its anchoring basal body). Centrioles and mitotic spindle. Elongation processes of cells (such as those in growing axons)
97
Microtubules are involved in numerous essential cellular functions:
Intracellular vesicular transport Attachment of chromosomes to the mitotic spindle and their movement during mitosis and meioses. Cell elongation and movement. Maintenance of cell shape, particularly its asymmetry. Movement of cilia and flagella
98
Movement of intracellular organelles is generated by molecular motor proteins (associated with microtubules) Dyneins Kinesins
Both dyneins and kinesins are involved in mitosis and meiosis. In these activities, dyneins move the chromosome along the microtubules of the mitotic spindle. Kinesins are simultaneously involved in movement of polar microtubule. 99
100
Present in virtually all cell types. Abundant and may constitute 20% of total protein of some non muscle cells. Similar to tubulin in microtubules actin molecules also assemble spontaneously by polymerization into a linear helical array to form filaments 6 – 8 nm in diameter. Thinner, shorter and more flexible than microtubules. 101
G – actin (globular actin),free actin molecule in the cytoplasm F – actin (filamentous actin) polymerized actin of the filament Plus or barbed end,fast growing end Minus or pointed end. slow growing end Polymerization of actin filaments requires K+, Mg2+, ATP Control and regulation of polymerization process depends on: Local concentration of G – actin Interaction of actin binding proteins (ABPs)
102
103
104
Anchorage and movement of membrane protein Formation of the structural core of microvilli Locomotion of cells Extension of cell processes
105
Play a supporting or general structural role.
Intermediate filaments are formed from non polar and highly variable intermediate filament subunits 106
These rope like filaments are called intermediate because their diameter is 8 – 10 nm (intermediate between actin filaments and microtubules). 107
Characterized by a highly variable central “rod shaped domain” with strictly conserved globular domains at either end. Although various classes of intermediate filaments differ in the amino acid sequence of rod shaped domain and may show variation in molecular weight, they all share a homogenous region that is important in filament self – assembly. 108
109
Usually found in close proximity to the nucleus, partially surrounded by golgi apparatus and associated with a zone of amorphous, dense pericentriolar material
110
Centrioles represent the focal point around which the MTOC assembles. Visible in L/M, are paired short, rod like cytoplasmic cylinders built from nine microtubule triplets. 111
Arranged at right angle to each other but are not connected with one another
112
The dominant feature of centrioles is the cylindrical array of triplet microtubules with associated proteins. TEM reveals that each rod shaped centriole is about 0.2 µm long and consists of nine triplets of microtubules that are oriented parallel to the long axis of organelle and run in slightly twisted bundles. 113
Functions of the centrioles can be organized into two catagories. ◦ Basal body formation ◦ Mitotic spindle formation
The core structure of the cilium is composed of a complex set of microtubules consisting of two central microtubules surrounded by nine microtubules doublets. 115
One of the important function ot the centriole is to provide basal body. Which are necessary for the assembly of cilia and flagella. Basal bodies are formed by the replication of centrioles and give rise to multiple precentrioles . Each precentriole migrate to appropriate site on the surface of the cell where it become a basal body. The basal body act as a organizing center for cilium
116
Microtubules grow upward from the basal body,pushing the cell membrane outward,and alongated to form the mature cilium.
117
Inclusions contain products of metabolic activity of the cell and consist largely of pigment granules, lipid droplets and glycogen. Lipofuscin Hemosiderin Glycogen Lipid inclusions (fat droplets) Crystalline inclusions
118
Lipofuscin, is con glo me rate of lipid,metals and organic molecules that accumulate within the cell as a result of oxidative degradation of mitochondria and lysosomal digestion.
Hemosiderin , it is most likely formed by the indigestible residues of hemoglobin,and its presence is related to phagocytosis of RBCs.
Glycogen, is highly branched polymer used as a storage material for glucose. Fat droplets, are nutritive inclusion that provide energy for cellular metabolism.
119
120
Hemosiderin inside macrophages
121
Glycogen in liver cells
122
Lipid droplets
123
They are surrounded by membrane Usually present in apical portion of cell
124
A concentrated aqueous solution containing molecules of different sizes and shape( e.g, electrolytes, metabolites ,RNA and synthesized proteins) The cytoplasm matrix is the site of physiological processes that are fundamental to cell's existence (protein synthesis, breakdown of nutrients)
125
The network provides a structural substratum on which cytoplasmic reactions occur.
126
Text and Atlas of Histology by Michael H. Ross, 5th edition. Text book of Histology by Leeson Leeson Paparo, 5th edition. Image Results --------www.google.com
127
128
1
Cells are the basic structural and functional unit of all multicellular organisms. Cells can be divided into two major components: Cytoplasm Nucleus.
2
With the L/M, Cytoplasm generally has an even, homogenous, amorphous appearance but may show granular, fibrillar, or vacuolated areas. Cytoplasm contains “organelles” and “inclusions”in aqueous gel called cytoplasmic matrix,
3
Organelles are living, structural components of cell. Organelles are described as ◦ membranous (cell membrane – limited) ◦ non membranous.
4
1. Plasma (cell) membrane 2. rER 3. sER 4. Golgi apparatus 5. Endosomes 6. Lysosomes 7. Transport vesicles 8. Mitochondria 9. Peroxisomes
5
1. 2. 3. 4.
Microtubules Filaments Centrioles Ribosomes
6
MEMBRANOUS ORGANELES
7
Plasma
membrane is a lipid bilayered structure that form the cell boundary as well as the boundaries of many organelles within the cell. It is visible with TEM. It is a dynamic structure that actively participates in many physiologic and biochemical activities essential to cell function and survival. 8
When plasma membrane is properly fixed, sectioned, stained and viewed on edge with TEM, it appears as two electron dense layers separated by an intermediate, electron lucent (non staining) layer.
Total thickness is about 8 – 10 nm.
9
PROTIENS PHOSPHOLIPIDS CHOLESTEROL
10
11
Integral membrane proteins Peripheral membrane proteins
12
PRESENT ON ONE SIDE OF MEMBRANE
13
Inserted in membrane Some entirely extend through membrane Perform many important functions
14
Integral membrane proteins can be visualized with the special tissue preparation technique of freeze fracture.
Usually the P-face display more particles ,thus more protein ,than the E-face.
E face
P-face
Micro domains of plasma membrane known as lipid rafts control the movement and distribution of proteins within lipid bilayers.
16
Localized regions with in the plasma membrane contain high concentration of cholesterol and glycosphingolipids. These regions are called lipid rafts. Owing to high concentration of cholesterol and the presence of longer, highly saturated fatty acid chain, the lipid raft area is thicker and exhibits less fluidity than the plasma membrane.
17
Lipid rafts contain a verity of integral and peripheral membrane proteins involved in cell signalling. They can be viewed as “signalling platforms ” floating in the ocean of lipids. Signal transduction in lipid rafts occurs more rapidly and efficiently because of close proximity of interacting proteins.
18
Integral membrane proteins have important functions in cell metabolism, regulation and integration. Six broad categories of membrane proteins have been defined in terms of their function: 1. 2. 3. 4. 5. 6.
Pumps Channels Receptor proteins Linker proteins Enzymes Structural proteins
Integral membrane proteins move within lipid bilayers of membrane 19
TRANSPORT IONS serve to transport certain ions such as Na + actively across membrane. Also transport metabolic precursor of macromolecules, such as sugar and amino acid across membrane either by themselves or linked through Na+ pump.
20
Allow Passage of small ions and molecules,and water across the plasma membrane in either direction i.e ,passive diffusion
21
22
For recognition and binding of substances to the outer surface of plasma membrane Like hormonal stimulation and antibody recognition
23
Anchor the intracellular cytoskeleton to the extracellular matrix.e.g,family of integrins that link cytoplasmic actin filament to a extracellular matrix protein
24
Protineous structures which have specific roles in ion pumping and digestion
25
Found in epithelial cells Form junctional complexes with neighbouring cells Visualized by freeze fracture method.
26
Channel proteins Carrier proteins
27
Some substances (fat-soluble and small un charged molecules cross the plasma membrane by simple diffusion down their concentration gradient. All other molecules require membrane transport proteins to provide them with individual passage across the plasma membrane.
28
Carrier proteins
Transfer small watersoluble molecules. They are highly selective often transporting only one type of molecules. After binding to a molecule designated for transport, the carrier protein undergoes a series of conformational changes and releases the molecules on the other side of the membrane.
Channel proteins
Also transfer small, water soluble molecules. Channel proteins create hydrophilic channels through the plasma membrane that regulate the transport of the molecules. They are ion selective and are regulated on the basis of the cell's needs 29
VESICULAR
TRANSPORT process that involves configurational changes in the plasma membrane & also provides for the transfer of molecules b/w different cellular compartments It maintains the integrity of plasma membrane
30
EXOCYTOSIS ENDOCYTOSIS
31
Processes of vesicular transport in which substances enter the cell are termed as endocytosis Uptake of fluid and macromolecules during endocytosis depends on three different mechanisms 32
PHAGOCYTOSIS
PINOCYTOSIS
RECEPTOR MEDIATED ENDCYTOSIS
33
PHAGOCYTOSIS Also called cell eating It is ingestion of large particles, such as cell debris ,bacteria and other foreign materials In this nonselective process large vesicles(250nm) called phagosomes are produced Best seen in macrophages 34
PINOCYTOSIS Also called cell drinking Is the nonspecific ingestion of fluid and small protein molecules via small vesicles usually amaller than150nm in diameter.
35
cargo
dynamin
This is a receptor mediated mechanism that allows selected molecules to enter the cell.
36
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Exocytosis is the process by which a vesicle moves from the cytoplasm to the plasma membrane, where it discharges its contents to the extra cellular space. Two general pathways of exocytosis: Constitutive pathway Regulated secretory pathway
Ca+
37
These are the membrane enclosed compartments in the cytoplasm, associated with all the endocytotic pathways Endosomes can be viewed either as stable cytoplasmic organelles or as transient structures formed as the result of endocytosis.
38
Endosomes destined to become lysosomes receive newly synthesized lysosomal enzymes Early and late endosomes differ in their cellular localization, morphology and state of acidification and function.
39
Early endosomes are restricted to portion of cytoplasm near the cell membrane where vesicles originating from the cell membrane fuse. Large number of vesicles originating in early endosome travell to deeper structures in the cytoplasm called late endosomes. The late endosomes mature into lysosomes.
40
Major function of early endosomes is to sort and recycle proteins internalized by endocytotic pathways.
41
Early endosomes
Late endosomes
Found in more peripheral cytoplasm Have a tubovesicular structure. Lumen is subdivided in to cisternae PH 6.2 - 6.5
Found near the Golgi apparatus and the nucleus. More complex structure and often exhibit onionlike internal membrane. PH 5.5
42
Lysosomes are small membrane bound organelles that contain a variety of acid hydrolases. Ribosomes are composed of two different sized subunits. The RNA molecules of both subunits are synthesized in side the nucleus.
Their numerous proteins are synthesized in the cytoplasm and then enter the nucleus and associate with rRNA . Subunits then leave the nucleus via nuclear pores, to enter the cytoplasm and participate in protein synthesis.
44
They constitute an intracellular digestive system capable of breaking down material originating both outside and within the cell. Great variety of appearances or pleomorphism.
45
Usually range from 0.2 – 0.4 um in diameter. Have a unique membrane that is resistant to hydrolytic digestion occurring in their lumen. Lysosomal membrane has an unusual phospholipid structure that contain cholesterol and a unique lipid called lysophosphatidic acid which play an important role in restricting the activity of hydrolytic enzymes directed against the membrane.
46
Found in all cells except erythrocytes but are numerous particularly in: Macrophages Neutrophils Hepatic cells Cells of Proximal tubule of kidney
47
Identified by Electron cytochemistry Divided into main groups:
1. Primary lysosomes 2. Secondary lysosomes
48
Newly formed lysosomes that have pinched of from golgi cisternae Contain all enzymes that are used in cell digestion
49
Formed by fusion of primary lysosomes with the structure that contains material to be digested Also called phagosome.digestive vacuole or autophagic vacuole
50
Hydrolytic breakdown of the contents of the lisosomes often produced a debris-liked vacule called a Residual body.which may remain for the entire life eg residual bodies are a normal feature of the cell aging
51
Normal feature of cell aging Debris filled vacuole Produced by break down of contents of
secondary lysosomes Found as age pigment or lipofusin pigment
52
Depending on the nature of digested material, three different pathways deliver material for intracellular digestion in lysosomes: 1.Extra cellular large particles ….. Phagosome and Phagolysosome. 2.Extra cellular small particles …..Endocytotic pathway. 3.Intracellular particles ….. autophagy
53
54
55
With TEM, RER appears as a series of interconnected, membrane limited flattened sacs called cisternae, with particles studding the external surface of membrane (ribosomes).
56
Basophilic component of cytoplasm, ergastoplasm-----the areas of cytoplasm that stain blue with basic stains . Ergastoplasm indicates i.e. that component of cytoplasm involved in protein synthesis..
Protein synthesis system of the cell consists of rER and ribosomes
The particles called ribosomes are attached to the membrane of eRE by ribosomal docking proteins
58
Membrane of reticulum enclose an intracellular compartment that segregates newly synthesized products. Its main function is synthesis of a secretory protein Synthesis of phospholipids Glycosylation of glycoprotiens
59
On E/M, appear as small, dense particles of about 15 – 20 nm in diameter, roughly spherical but irregular, and each is formed by two subunits, one large and one small. Responsible for cytoplasmic basophilia and they contain RNA and protein. Are sites where amino acids are incorporated into peptides and proteins i.e. site of protein synthesis 60
Found in all cells except mature erythrocytes. May be attached to granular endoplasmic reticulum or may lie free within general cytoplasm. Polysomes or polyribosomes----a cluster of ribosomes along a single strand of mRNA that is engaged in the synthesis of protein.
61
Ribosomes are the sites where mRNA is translated into protein. Proteins destined for transport (secretory, membrane, and lysosomal) are synthesized on polyribosomes bound to rER . whereas proteins not destined for transport (for intracellular use) are synthesized on free polyribosomes in cytosol. Ribosomes are numerous in rapidly growing and dividing cells.
62
63
SER is an irregular network of membrane bounded channels that lacks ribosomes on its surface, which makes it appear smooth. SER consists of short anastomosing tubules
64
Membranes are 6 – 7 nm thick, and a tubular lumen of about 50 nm. May exhibit distinct cytoplasmic eosinophilia. Tubular elements may connect directly with rER and indirectly with golgi apparatus via small vesicles.
65
Cells with large amount of SER may exhibit distinct cytoplasmic eosinophilia when viewed under L/M. Biochemically similar to RER but lacks ribosome docking proteins
67
Abundant in cells that function in lipid metabolism, cells that synthesize and secrete steroids (e.g. adrenocortical cells and testicular cells of leydig, progesterone secreting cells of corpus luteum of ovary). Lipid and steroid metabolism Glycogen metabolism Membrane formation and recycling Synthesis of phospholipids of all cell membrane Drug detoxification Muscle contraction and relaxation (specialized form,sarcoplasmic reticulum)
68
Well developed in secretory cells and does not stain with H & E. May be visible by L/M as either a positive or negative image After routine H & E stains, in cells with intensely basophilic cytoplasm such as osteoblasts & plasma cells, golgi apparatus is indicated as a pale, clear area. This is negative image After silver impregnation or prolonged exposure to osmium tetra oxide, it is seen as darkly staining network of stacked, flattened, membrane limited sacs or cisternae and tubular extensions embedded in a network of microtubules near MTOC----Positive image 69
Small vesicles involved in vesicular transport are seen in associated with cisternae. Regions: Cis golgi network (CGN) Trans golgi network (TGN) Medial golgi
71
72
73
74
It is active in cells: That secrete protein by exocytosis In cells that synthesize large amounts of membrane and membrane associated proteins such as nerve cells.
It functions in post translational modification, storing and packaging of proteins. It is involved in membrane flow , in transport and concentration of secretory materials and their release from the cells, in synthesis of certain secretory products, particularly glycoproteins and mucopolysacchrides and probably in lysosome formation 75
Basolateral plasma membrane Apical plasma membrane Endosomes or Lysosomes Apical cytoplasm
76
Are membrane bound organelles and lie free within cytoplasm. Display a variety of shapes including spheres, rods, elongated filaments and even coiled structures. Present in all cells except RBSs and terminal keratinocytes Abundant in cells that generate large amounts of energy.
77
Each mitochondria is bounded by two unit membranes Inner membrane shows folds called cristae to increase the surface area The space b/w inner and outer membrane is continuous with the interstitial space within each crista The inner mitochondrial membrane surrounds the large intercristal space of mitochondrial matrix. 78
Outer mitochondrial membrane 6 – 7 nm thick smooth membrane Contains many anion channels Possess receptors for proteins and polypeptides
79
Inner mitochondrial membrane Thinner than outer one Arranged in cristae Rich in phospholipids Cardiolipin, which makes the membrane impermeable to ions The internal membrane and cristae are coated with small particles called elementary particles or globular units
80
These have special heads 9-10 nm in diameter attached to inner mitochondrial membrane by a narrow 5nm long stalk
Enzymes of phosphorylation and electron transfer system are located either on elementary particles or within the inner mitochondrial membrane that form cristae
Enzymes of Kreb,s cycle lies in mitochondrial matrix
The matrix also contain calcium salts, organic crystals, glycogen, and RNA, DNA,
81
1.
2. 3.
Performing the oxidative reactions of the respiratory electron transport chain Synthesizing ATP Regulating transport of metabolites into and out of the metrix.
82
Intermembranous space Contain specific enzymes that use ATP generated in inner mitochondrial membrane (e.g. creatine kinase, adenylate kinase and cytochrome C)
83
Store house for energy, metabolites within the cell are utilized by Kreb,s citric acid cycle and energy released is captured through oxidative phosphorylation. thus ATPs are formed which are high energy compound. Involved in fatty acid B – oxidation. Source of electron for electron transport chain Store Ca++ and other divalent and trivalent cations. Synthesis of steroid hormons
84
Small (0.5 µm in dia.) membrane bounded spherical organelles containing oxidative enzymes (particularly catalases and other peroxidases)
85
Abundant in liver and kidney cells, but found in most other cells Do not contain hydrolases
86
Oxidative enzymes are perform a variety of detoxification processes. β oxidation of fatly acids is also a major function of peroxisosomes
87
88
These are nonbranching and rigid hollow tubes of protein that can rapidly disassemble in one location and reassemble in another. In general, they grow from MTOC located near nucleus and extend toward the cell periphery.
89
The region of the cell containing the centrioles and pericentriolar material is called MTOC or Centrosome. The MTOC is the region where most microtubules are formed and from which they are directed to specific destinations within the cell. The structures present in MTOC are cilia, basal bodies and centrosomes
90
Development of MTOC itself depend on presence of centrioles. When centrioles are missing MTOCs disappear ,and formation of microtubules is severely impaired.
91
Complex structure of tubulin 92
These are elongated polymeric structures composed of equal parts of α tubulin and β tubulin. Under appropriate conditions tubulin subunits polimerize to form microtubules Microtubules grow from γ tubulin ring within the MTOC that serve as nucleation sites for each microtubule. Each microtubule possesses a minus (non-growing) end and a plus (growing) end. 93
Polymerization and depolymerization are in equilibrium. Length of microtubules changes dynamically as tubulin dimers are added or removed in a process of dynamic instability. These can be visualized in L/M and are involved in intracellular transport and cell motility
94
95
The figure shows the 3-dimensional view of a microtubule being formed. The tubulin molecules are the bead like structures and combine to form long hollow, dynamic polymers, microtubules 96
In general, microtubules are found in: Cytoplasm (where they originate from MTOC) Cilia and flagella (where they form axoneme and its anchoring basal body). Centrioles and mitotic spindle. Elongation processes of cells (such as those in growing axons)
97
Microtubules are involved in numerous essential cellular functions:
Intracellular vesicular transport Attachment of chromosomes to the mitotic spindle and their movement during mitosis and meioses. Cell elongation and movement. Maintenance of cell shape, particularly its asymmetry. Movement of cilia and flagella
98
Movement of intracellular organelles is generated by molecular motor proteins (associated with microtubules) Dyneins Kinesins
Both dyneins and kinesins are involved in mitosis and meiosis. In these activities, dyneins move the chromosome along the microtubules of the mitotic spindle. Kinesins are simultaneously involved in movement of polar microtubule. 99
100
Present in virtually all cell types. Abundant and may constitute 20% of total protein of some non muscle cells. Similar to tubulin in microtubules actin molecules also assemble spontaneously by polymerization into a linear helical array to form filaments 6 – 8 nm in diameter. Thinner, shorter and more flexible than microtubules. 101
G – actin (globular actin),free actin molecule in the cytoplasm F – actin (filamentous actin) polymerized actin of the filament Plus or barbed end,fast growing end Minus or pointed end. slow growing end Polymerization of actin filaments requires K+, Mg2+, ATP Control and regulation of polymerization process depends on: Local concentration of G – actin Interaction of actin binding proteins (ABPs)
102
103
104
Anchorage and movement of membrane protein Formation of the structural core of microvilli Locomotion of cells Extension of cell processes
105
Play a supporting or general structural role.
Intermediate filaments are formed from non polar and highly variable intermediate filament subunits 106
These rope like filaments are called intermediate because their diameter is 8 – 10 nm (intermediate between actin filaments and microtubules). 107
Characterized by a highly variable central “rod shaped domain” with strictly conserved globular domains at either end. Although various classes of intermediate filaments differ in the amino acid sequence of rod shaped domain and may show variation in molecular weight, they all share a homogenous region that is important in filament self – assembly. 108
109
Usually found in close proximity to the nucleus, partially surrounded by golgi apparatus and associated with a zone of amorphous, dense pericentriolar material
110
Centrioles represent the focal point around which the MTOC assembles. Visible in L/M, are paired short, rod like cytoplasmic cylinders built from nine microtubule triplets. 111
Arranged at right angle to each other but are not connected with one another
112
The dominant feature of centrioles is the cylindrical array of triplet microtubules with associated proteins. TEM reveals that each rod shaped centriole is about 0.2 µm long and consists of nine triplets of microtubules that are oriented parallel to the long axis of organelle and run in slightly twisted bundles. 113
Functions of the centrioles can be organized into two catagories. ◦ Basal body formation ◦ Mitotic spindle formation
The core structure of the cilium is composed of a complex set of microtubules consisting of two central microtubules surrounded by nine microtubules doublets. 115
One of the important function ot the centriole is to provide basal body. Which are necessary for the assembly of cilia and flagella. Basal bodies are formed by the replication of centrioles and give rise to multiple precentrioles . Each precentriole migrate to appropriate site on the surface of the cell where it become a basal body. The basal body act as a organizing center for cilium
116
Microtubules grow upward from the basal body,pushing the cell membrane outward,and alongated to form the mature cilium.
117
Inclusions contain products of metabolic activity of the cell and consist largely of pigment granules, lipid droplets and glycogen. Lipofuscin Hemosiderin Glycogen Lipid inclusions (fat droplets) Crystalline inclusions
118
Lipofuscin, is con glo me rate of lipid,metals and organic molecules that accumulate within the cell as a result of oxidative degradation of mitochondria and lysosomal digestion.
Hemosiderin , it is most likely formed by the indigestible residues of hemoglobin,and its presence is related to phagocytosis of RBCs.
Glycogen, is highly branched polymer used as a storage material for glucose. Fat droplets, are nutritive inclusion that provide energy for cellular metabolism.
119
120
Hemosiderin inside macrophages
121
Glycogen in liver cells
122
Lipid droplets
123
They are surrounded by membrane Usually present in apical portion of cell
124
A concentrated aqueous solution containing molecules of different sizes and shape( e.g, electrolytes, metabolites ,RNA and synthesized proteins) The cytoplasm matrix is the site of physiological processes that are fundamental to cell's existence (protein synthesis, breakdown of nutrients)
125
The network provides a structural substratum on which cytoplasmic reactions occur.
126
Text and Atlas of Histology by Michael H. Ross, 5th edition. Text book of Histology by Leeson Leeson Paparo, 5th edition. Image Results --------www.google.com
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