Cell Biology Questions And Answers

Explaining terms  01.In silico cell  02.Ion channels  03.active transport  04.ATP-powered pump  05.Tight junctions  06.Gap junctions  07.Respiratory chain  08.Nuclear pore complex  09.Endomembrane system  10.The cytoskeleton  11.Elementary particle  12.Signal peptide  13.Nuclear pore  14.Degenerate  15.Cell cycle  16.Homologus chromosome  17.Sister chromatids  18.Pars granulosa  19.Hetero chromatin  20.Meiosis  21.Nuclearsome Questions  01.What are different between Eukaryotic cells and Prokaryotic cells ?  02.Please explain the statement: plasma membrane is asymmetrical membrane.  03. What is the Fluid Mosaic Model ?  04. Please explain the role of Cell junction and cell adhesion by use of examples  05.Comparing the difference in microtubule, microfilament, and intermediate filament.  06.Talk about the ultrastructure of mitochondria  07.Mitochondria is called semiautonomous organelle, why?  08.Talk about the process that secretory proteins are synthesized and transported  09. The difference between mitosis and meiosis  10. How many Checkpoints in cell cycle? What they check for?  11. Describe the two kinds of molecular mechanism in apoptosis.  12. Describe these 2 models of chromosome structure  13. what’s the Signal theory for the translocation of protein?  14. Describe the difference between apoptosis and Necrosis Cell-Cycle Checkpoints

G1 Checkpoint • �START in yeast • �Restriction Point in mammals • �Main step that commits a cell to division • �Sensitive to: • �� Cell size • �� Availability of nutrients • �� External growth factors G2 checkpoint � Error check: DNA replication must be complete � Detects unreplicated DNA, holds cell at G2 �� Detects damaged DNA, arrests cell in G2 until damage repaired Spindle Assembly Checkpoint • Boundary between metaphase and anaphase • All chromosomes must be properly attached to the spindle • MPF causes activation of anaphase promoting complex pathway that promotes anaphase

In silico cell--------Ion channels-------- Ion channels are usually small proteins that span the membrane and have central water-filled pores and its outside surface is hydrophobic and the inside hydrophilic. Most ion channels are gated and open transiently in response to a specific stimulus, such as a change in membrane potential or the binding of a ligand or a chemical (phosphorylation) or electrical stimulus.

active transport------- Often the transport has to happen in the direction opposite to the electrochemical or concentration gradient. In order to accomplish this, membranes have evolved elaborate schemes to pump the substance ( ions or moleciles) from the area of smaller concentration to a compartment with higher concen-tration. All these schemes cost the cell energy (hydrolysis of ATP or light energy) and thus are called active transport. It is sensitive to inhibitors that stop ATP synthesis. •

ATP-powered pump------ ATP-powered pump is an ATPase that use the energy of ATP hydrolysis to move ions or small molecules across a membrane against a chemical concentration or electric potential gradient or both. All ATP-powered pumps are transmembrane proteins with one or more binding sites for ATP located on the cytosolic face of the membrane. Although these proteins commonly are called ATPase, they normally do not hydrolyze ATP into ADP and Pi unless ions or other molecules are simultaneously transported.

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Tight junctions-------- Tight junctions, also called Occluding junctions, form a physical barrier that prevents the leakage of even small molecules between cells. Tight junctions are located between neighboring cells at the most apical region of the cells and appear as points where the cell membranes come into direct contact with each other. Tight junctions are composed of anastomosing strands of transmembrane proteins that completely encircle the cell. Tight junctions can regulate the passage of molecules across these natural barriers. It restrict foodstuffs to the lumen and allow amino acids, sugars, and other molecules, to be directly routed to the circulatory system.

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Gap junctions------- Gap junctions, such as the Communicating junctions, attach cells together in a manner that allows the transfer of chemical or electrical signals between neighboring cells. Gap junctions are formed by a grouping of transmembrane proteins into a structure called a connexon.

Respiratory chain------- Respiratory chain is composed of a series of substance which can accept and release electron or proton reversibly. They are a group of lipid protein complex which are all existing on the inner membrane of

mitochondria associatly and orderly, and coupling oxidative phosphorylation. So respiratory chain can also be called electron transport chain. Respiratory chain includes four complex NADH-dehydrogenase complex ; Succinate-CoQ dehydrogenase complex; CoQ-cytochrome c dehydrogenase complex; cytochrome c oxidase complex; Nuclear pore complex-------- Nuclear pore structure is conferred by a set of protein granule subunits, which are arranged in an octagonal pattern, and form the boundaries of the pore complex. It appears as if the two membranes are pinched at that site, leaving a space filled with filamentous material. Sometimes a thin diaphragm may be seen running horizontally through the pore. It contains 8 subunits that "clamp" over region of the inner and outer membrane where they join. Actually, they form a ring of subunits 15-20 nm in diameter. Each subunit projects a spoke-like unit into the center so that the pore looks like a wheel with 8 spokes from the top. Inside is a central "plug". The next (left) figure shows a cross section of the pore with the clamp-like complex adjacent to the membranes. The projected spoke is directed towards the central "plug' or granule.

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Endomembrane system------- The endomembrane system is a collection of membranous structures involved in transport within the cell. The main components of the endo-membrane system are the endoplasmic reticulum, Golgi bodies, vesicles, lysosomes, peroxisomes and nuclear envelope. These compartments are involved in the processing of proteins for export from the cell, proteins destined for lysosomes, and proteins entering the cell from the cell surface. Once proteins enter the endoplasmic reticulum they never return to the cytosol compartment; they are carried by vesicle transport to the other compartments of the system. This flow of vesicles is highly regulated.

The cytoskeleton----------The cytoskeleton is that the maintenance of structure by the cytosol arises from a complex network of protein filaments that traverse the cell cytoplasm . Elementary particle---------the elementary particle protein is composed of two large oligomeric complexes. F0 is an integral membrane protein containing a, b,

c subunits. F1 is an peripheral protein that associates with the membrane through F0. F1 contains nine subunits. Signal peptide---------The mitochondrial signal peptides are stretches of 20 to 80 amino acids, at the NH2-terminus of the protein, that have the characteristic of forming an amphipathic a-helix where one side of the helix is nonpolar and the other side contains positively charged amino acids. The signal peptide binds to a putative signal receptor on the outer membrane , and the complex moves laterally across the outer membrane until it reaches a contact site at which the inner and outer membranes are joined. •

Nuclear pore------- There are many small pores on the nuclear envelope ,which is called nuclear pore. It is formed by the two membranes fusion in some places. The diameter of nuclear pore is about 40-100nm, average diameter is 80nm.The number of nuclear pores is different with the cell type and the physiological conditions. Nuclear pores allow communication between the nucleus and cytosol.

Degenerate---------Cell cycle------------------Homologus chromosome---------Sister chromatids-----------Pars granulose----------Hetero chromatin-------------Heterochromatin is the condensed form of chromatin organization. It is seen as dense patches of chromatin. Sometimes it lines the nuclear membrane, however, it is broken by clear areas at the pores so that transport is allowed. Sometimes, the heterochromatin forms a "cartwheel" pattern. Abundant heterochromatin is seen in resting, or reserve cells such as small lymphocytes (memory cells) waiting for exposure to a foreign antigen. Heterochromatin is considered transcriptionally inactive. Meiosis--------------Meiosis is a special type of nuclear division which segregates one copy of each homologous chromosome into each new "gamete". It reduces the number of sets of chromosomes by half, so that when gametic recombination (fertilization) occurs the ploidy of the parents will be reestablished

Nucleosome------------it is the lowest level of chromosome organization. The fundamental histone-containing structural subunit of eukaryotic chromosomes. In most eukaryotic organisms, nuclear deoxyribonucleic acid (DNA) is complexed with an approximately equal mass of histone protein. The nucleosome is organized so that the DNA is exterior and the histones interior. The DNA makes two turns around a core of eight histone molecules The nucleus is only 6 micrometers in diameter. The total length of DNA in the human genome is 1.8 meters. Thus, in order to pack the DNA into the nucleus as in the photograph of the metaphase chromosome , there must be several levels of coiling and supercoiling. There is nearly a 10,000-fold reduction in length in an interphase nucleus. Each chromosome contains 1 long molecule of DNA plus associated histones (basic proteins) which help in the condensation and regulation processes. These basic structures are known as nucleosome. histone octomer + DNA = nucleosome

different between Eukaryotic cells and Prokaryotic cells Prokaryotic cells Eukaryotic cells size: 1-10µm includes bacteria and bluegreen algae no true nucleus DNA circular and free no membrane-bound organelles

size: 1-100µm four major groups: Protista, fungi, plants and animals true nucleus DNA linear and in nucleus internal compartmentalization with organelles, hence division of labour (specialization)

simple binary reproduction no development of tissues multicellular types rare

mitotic reproduction(and meiotic) tissue and organ systems common independent unicellular organism or part of multicellular organism

Fluid mosaic model The globular membrane proteins are embedded within the bilayer, with hydrophobic portions of the proteins buried within the hydrophobic core of the lipid bilayer, and hydrophilic portions of the proteins exposed to the aqueous environment, and the proteins float within the lipid bilayer.

Role of Cell junction and cell adhesion Cell adhesion plays a crucial role in embryogenesis, differentiation of adult tissues and wound healing. The function and regulation of intercellular junction molecules in desmosomes and adherens junctions act to mediate cell-cell adhesion and attachment of the cytoskeleton to the cell surface. Example 1 The importance of desmosomes in the maintenance of epithelial integrity is underscored in human patients with the autoimmune disease pemphigus. These patients produce autoantibodies that react specifically with the desmosomal transmembrane linker glycoproteins. This disrupts desmosomes in the skin, resulting in severe blistering and body fluid loss.

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Example 2 A family of genetic (inherited) blistering diseases of the skin that are caused by defective cell-ECM (cell extracellular matrix) adhesion. EB is divided into three main categories based on where the loss of adhesion occurs. EB simplex junctional EB dystrophic EB The 3 main types can be further sub-divided into at least 27 clinical variants.

difference in microtubule, microfilament, and intermediate filament 䦋㌌㏒ 䦋좈 ໱琰茞 microtubule ᓀ�Ü

microfilament

Intermediate filament

component

tubulin

actin

Intermediate filament monomer

diametr

22nm

7nm

10nm

structure

hollow tube

two strands helix rope-strands helix

polarity

yes

yes

no

treadmill action

yes

yes

no

Ultrastructure of mitochondria

Outer membrane Outer membrane is the outerest unit membrane enveloping the whole mitochondria. The width is 6nm. Its surface is smooth and elastical. Inner membrane The inner membrane has a very large surface area owing to its characteristic infolds ,which are called cristae. This membrane is composed of 75% proteins and is extremely active functionally. The inner membrane contains proteins involved in the respiratory chain ,ATP synthesis, and the transport of substrates and products of oxidative phosphorylation into and out of the mitochondria. The matrix contains enzymes involved in the oxidation of pyruvate and fatty acids ,as well as most of the enzymes of the citric acid cycle. In addition, the mitochondrial genome and mitochondrial ribosomes are located in the matrix.

semiautonomous organelle- mitochondrion  Mitochondria replicate much like bacterial cells. When they get too large, they undergo fission. This involves a furrowing of the inner and then the outer membrane as if someone was pinching the mitochondrion. Then the two daughter mitochondria split. Of course, the mitochondria must first replicate their DNA. An electron micrograph depicting the furrowing process is shown in these figures. Mitochondria have their own autonomous double-stranded circular DNA, and almost the entire genome is coding sequence. The human mitochondrial genome contains 16569 nucleotides which encode 13 proteins, 2 rRNA genes and 22 tRNA genes. Many of them are subunits of protein complexes involved in electron transport and oxidative phosphorylation .

The difference between mitosis and meiosis 䦋㌌㏒䦋좈໱琰茞 ᓀ Mitosis �Ü

Meiosis

Number of divisions

1

2

Number of daughter cells

2

4

Genetically identical?

Yes

No

Chromosome #

Same as parent

Half of parent

Where

Somatic cells

Germline cells

When

Throughout life

At sexual maturity

Role

Growth and repair

Sexual reproduction

Difference in apoptosis and necrosis Apoptosis • Chromatin condensation • Cell Shrinkage • Preservation of Organelles and cell membranes • Rapid engulfment by neighboring cells preventing inflammation • Biochemical Hallmark: DNA FRAGMENTATION Necrosis • Nuclear swelling • Cell Swelling • Disruption of Organelles • Rupture of cell and release of cellular contents

• Inflammatory response 2 models of chromosome structure  Solenoid Model of Chromosome Structure first level : nuclearsome (packing ratio -7) 2nd level: 6 nulearsomes coiling into a helical array - 30nm solenoid (packaging ratio -6) 3rd level : Solenoid coiling into a 400nm supersolenoid (packaging ratio -40) 4th level: chromotids (packaging ratio -5) Scaffold-radial loop structure model

Two kinds of molecular mechanism in apoptosis • Intrinsic/ Mitochondrial Apoptosis – Regulated by Mitochondria – Cytochrome c release • Extrinsic/ Death Receptor Apoptosis – Activated by ligation of Death Receptors – Fas, TNF alpha • These pathways intersect at the effector caspases.

Intrinsic/Mitochondrial Pathway

Extrinsic/ Death Receptor apoptosis