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Molecular and Cell Biology: Proteins, Enzymes, Synthesis and Division

Question 1:
a) What role do microtubules play in intracellular transport?
b) Describe the structure of microfilaments and microfilament networks and explain how they are assembled and disassembled within a cell.
c) Outline two functions that microfilament networks play in cell motility.
d) What function of intermediate filaments have in eukaryotic cells?

Question 3:
a) What two key factors determine the specificity of Watson-Crick base pairing in B-DNA? For each of these factors, explain why this is the case.
b) What activity of E.coli DNA polymerase 1 is responsible for ensuring correct Watso-Crick pairing during DNAS synthesis?
c) Outline briefly how this activity (given in your answer to part (b)) is achieved by this enzyme.

Question 5:
a) What is a mitotic spindle?
b) Which to classes of motor proteins interact with spindle microtubules during mitosis?
c) What role do these motor proteins play in the process of mitosis?
d) A drug that prevents the assembly of microtubules is applied to a culture of dividing cells for four hours. How will the culture treated with the drug differ from an untreated culture of the same cells, in terms of the numbers of cells in different stages of the cell cycle? In your answer, you should explain how the difference in appearance arises.

Question 6:
a) Describe the cellular location and function of the following membrane-bound vesicles: (i) synaptic vesicle, (ii) phagosome.
b) Describe the roles of two of the following proteins associated with the formation of transport vesicles: Epsin, Dynamin, GGA-proteins, GTP-binding adapter proteins.
c) Give one example of a transport vesicle that moves between the ER and the Golgi apparatus, indicating its coat protein and its direction of movement.

Solution Preview

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Molecular Biology
Question 1:
a. The role of Microtubules in intracellular support is: To help define the cell structure and movement. They transport organelles, such as vesicles or mitochondria. In non-dividing cells, microtubule networks radiate out from the centrosome to provide the basic organization of the cytoplasm, including the positioning of organelles.

b. Describe the structure of microfilaments and microfilament networks and explain how they are assembled and disassembled within a cell: Microfilaments are formed from pools of actin monomers, which associate non-covalently and can grow or shrink or remain stable. The microfilament network is formed from polymerized or fibrous actin (F-actin) extends throughout the cytoplasm, but its organization, the length of the filaments and their degree of branching depend very much on the type of cell, its shape, and how it is interacting with the extracellular matrix.

Microtubules (tubulin) or bundles of microfilaments (actin) cause movement, in some instances, by disassembly or assembly of subunits. Possible examples are the pulling of a chromosome toward a pole in mitosis (anaphase) or the deformation of a cell membrane to change the shape of a cell. Reorganization of the microfilament network can take place both locally (affecting only part of the cell) and globally (across the whole cell). In particular, cells that are moving rearrange their entire cytoskeleton as the cell becomes polarized, with engagement of microfilaments required for movement of the cell, and microtubules involved in moving the organelles.

c. Two of the functions that microfilaments networks play in cell motility are:
They help to generate the forces used in cellular contraction and basic cell movements. The filaments also enable a dividing cell to pinch off into two cells and are involved in amoeboid movements of certain types of cells. In association with myosin, microfilaments help to generate the forces used in cellular contraction and ...

Solution Summary

The solution discusses molecular and cell biology including proteins, enzymes, synthesis and division.