Chap 2 - Organelles And Their Functions

CHAPTER 2 PROKARYOTIC AND EUKARYOTIC CELLS

Cell Theory 1965

- Robert Hooke, an English scientist, observed a thin slice of cork under a compound microscope which consists of small boxes and named it as cells.

1838

- Matthias Schleiden, German botanist, suggested that all plants consists of cells.

1839

- Theodore Schwann, a German zoologist, suggested that animals also consists of cells. He came up with two theories: a.

All organisms consists of one or more cells.

b. A cell is the basic unit of structure and function for all living organisms 1849

- Rudolf Virchow, a German scientist, came up with another theory : all cells originate from pre-existing cells.

a.

b.

Robert Hooke’s compound microscope

a) The small units of a thin slice of cork observed by Hooke. b) The plant cell

Cellular Structure and Function Cytology - the study of cells and their submicroscopic structure By using electron microscope, the microscopic structure of cells can be observed. Two types of cell: 1. Prokaryotic cell ‘pro’ – before ; ‘karyon’ – nucleus Prokaryotic cell, the DNA is concentrated in a region called the nucleoid with no membrane enclosed it. ex. Bacterial cell and Cyanobacteria 2. Eukaryotic cell ‘eu’ – true It has true nucleus bounded by a membranous nuclear envelope. ex. Fungal cells, animal cells and plant cells

A comparison between Prokaryotic Cell and Eukaryotic Cell

All cells have the following structures:

i. Plasma membrane which functions as a barrier between external and internal parts of a cell. ii. Nucleus which contains genetic information and controls cell activities. iii. Cytoplasma which is a liquid medium where chemical reactions and metabolism occurs, the site for synthesis of enzyme, proteins and other materials needed by the cell.

A view of the Eukaryotic Cells A N I M A L C E L L

P L A N T C E L L

Nucleus •

Contains most of the genes

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~5µ mØ

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Nuclear envelope encloses the nucleus

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Chromosomes, a structure that carries genetic information

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Chromatin, a complex of proteins and DNA that builds up chromosome

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Nucleolus a mass of densely stained granules and fibers adjoining part of the chromatin

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Nuclear matrix a framework of fibers extending throughout the nuclear interior

Nuclear envelope •

Double membrane, each a lipid bilayer with associated proteins, separated by a space of 20-40 nm

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Perforated by micropores ~ 100nm Ø that regulates the entry and exit of certain large macromolecules and particles

Chromosomes •

An organized unit of DNA, carries the genetic information

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Each chromosome is made up of a material called chromatin a complex of proteins and DNA

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A typical human cell has 46 chromosomes – a combination of 23 chromosomes of egg and sperm cells

Nucleolus •

a mass of densely stained granules and fibers adjoining part of the chromatin

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rRNA is synthesized from instructions in the DNA with the protein from cytoplasm, into its small and large ribosomal subunit in nucleolus

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It will exit the nucleus to the cytoplasm and assemble to become the ribosome

Ribosomes: Protein factories in the cell •

Made of ribosomal RNA and protein that carry out protein synthesis

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Cells that have a high protein synthesis have a large number of this cell

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Not enclosed in membrane

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2 types of ribosome based on its location: 1. Free ribosomes : suspended in the cytosol and build protein that function in the cytosol. Ex: enzyme for sugar breakdown 2. Bounded ribosomes : attached to the outside of the endoplasmic reticulum or nuclear envelope; make proteins for insertion into membranes, for packaging within certain organelles such as lysosomes

Endoplasmic Reticulum (ER) : Biosynthetic Factory •

Latin words – little net within the cytoplasm ; a membranous system

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Consists of a network of membranous tubules and sacs called cisternae

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ER membrane separates the internal compartment of the ER – ER lumen or cisternal space from the cytosol

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Provides skeletal support in a cell

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Continuous with nuclear envelope

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Two types of ER: 1. Smooth ER : outer surface lack of ribosomes - synthesis of lipid 2. Rough ER : it has ribosomes on the outer surface - synthesis of protein

The Golgi Apparatus (GA) : Shipping and receiving center •

Functions: Center for manufacturing, warehousing, sorting and shipping

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Consists of flattened membranous sacs – cisternae that stack together

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Vesicles concentrated in the vicinity of the GA are engaged in the transfer of material between GA and other structures.

Lysosomes : Digestive Compartments •

A membranous sac of hydrolytic enzymes that is used to digest macromolecules

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Lysosomal enzymes works in acidic environment and perform autodigestion which destroy the cell itself

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Hydrolytic enzymes and lysosomal membrane are made by RER and then transferred to the GA for processing

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Functions: 1.

Intracellular digestion 2. Involved in phagocytosis. Ex. In Amoeba 3. Autophagy – recycle of cell’s own organic materials

Vacuoles : Diverse Maintenance Compartments •

Found in plant or fungal cell

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In mature plant cells, vacuoles enclosed by a membrane called tonoplast which is selective in transporting solutes

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Functions: 1. Hydrolysis (=lysosomes) 2. As food vacuoles 3. Contractile vacuoles – regulates water in the cell 4. As a storage cells in seed 5. As disposal sites for metabolic by-products 6. Protect the plant by containing compounds that are poisonous

Mitochondria and chloroplasts: Change energy from one form to another •

Semiautonomous organelles that grow and reproduce within the cell

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Contains small amount of DNA that programs the synthesis of proteins

Chloroplast

Mitochondria

Mitochondria : Chemical energy Conversion • Functions : Sites of cellular respiration, the metabolic process that generates ATP from ADP by extracting energy from sugars, fats and other fuels with the help of oxygen. • Enclosed by two membranes, a phospholipid bilayer with embedded protein • The outer membrane is smooth, inner membrane is convoluted forming cristae that increase the surface area for cellular respiration • Consists of two compartments : intermembrane space and mitochondrial matrix • Mitochondrial matrix contains many enzymes, mitochondrial DNA and ribosomes

Chloroplasts : Capture of light energy •

A type of plastids

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3 types of plastids: 1. Amyloplasts – colourless plastids that store starch, particularly in root and tuber 2. Chromoplasts – contain pigments that give fruits and flowers their orange and yellow hues 3. Chloroplasts – contain the green pigment chlorophyll, along with enzymes and other molecules that function in photosynthetic production of sugars

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Lens-shaped, ~ 2µ m by 5µ m, enclosed by two membranes separated by intermembrane space

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Within the cell, there are thylakoids a flattened interconnected sacs; a stack of thylakoids is called granum

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The fluid outside the thylakoids is called stroma which contains the chloroplasts DNA, ribosomes, starch and lipid granules and some enzymes

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Three compartments : the intermembrane space, the stroma and the thylakoid space

Differences Between Animal and Plant cells Animal Cells

Plant Cells

Only have cell membrane.

Have cell membrane and the rigid cell wall.

Do not chloroplasts.

Have chloroplasts.

Have small or no vacuoles at all.

Have large vacuoles.

Have centrioles.

Do not have centrioles.

Food storage : glycogen

Food storage : starch

Unicellular and Multicellular Organisms

Two categories of cell 1. Unicellular organism Single-celled organisms which function as one unit to carry out activities like growth, reproduction. Motility, excretion, transportation, respiration and digestion. Ex. Paramesium 2. Multicellular organism Consists of multiple cells. They depend on coordination and cooperation between different types of cells for proper function. Ex. Human, Fish, Elephant.