Question

1. What is NOT TRUE regarding the structure of actin filaments?

Group of answer choices

A. The actin filament is formed from one type of protein monomer.

B. The filament structure is helical.

C. The ends of the filament are the same.

D. The filament can breakdown once formed.

2. The concentration of cytoplasmic actin monomers is greater than what is necessary for actin filament polymerization. However, most of the actin protein in the cytoplasm remains in monomer form. Why is this?

Group of answer choices

A. Because the actin is stored in the ER, where it can’t polymerize.

B. Because the actin isn’t phosphorylated, which stops it from polymerizing.

C. Because various proteins bind to the actin and keep it from polymerizing.

D. Because the actin can’t exchange GDP for GTP.

3. The regulation of cell movement often involves an increase in what ion?

Group of answer choices

A. Ca2+

B. Na+

C. H+

D. K+

4. Microtubules are formed from the tubulin heterodimers. These include the nucleotide-binding __________________tubulin protein. The heterodimers form ______ (number) individual protofilament to form a microtubule.

Group of answer choices

A. beta-tubulin; 9

B. alpha-tubulin; 13

C. beta-tubulin; 13

D. gamma-tubulin;13

5. For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______.

Group of answer choices

A. stabilizing the filaments once they are formed.

B. increasing the rate at which subunits are added to the filaments.

C. promoting initial formation of filaments.

D. decreasing the binding strength between subunits on filaments.

6. Which of the situations below will enhance microtubule shrinkage?

Group of answer choices

A. addition of a drug that inhibits GDP/GTP exchange on free tubulin dimers

B. addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers

C. addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules

D. addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin

7. Which type of junction are intermediate fibers usually associated with?

Group of answer choices

A. desmosome

B. tight junction

C. gap junction

D. adheren junction

8. What is NOT TRUE of the extracellular matrix protein collagen?

Group of answer choices

A. It is secreted as procollagen and is assembled in the extracellular environment.

B. It is secreted as a single stranded molecule.

C. It first forms as a triple-stranded molecule, then a fibril.

D. It is primarily synthesized by fibroblast cells.

8. What is the molecular basis of the human genetic disease Hutchinson Guilford Progeria Syndrome?

Group of answer choices

A. defect in vimentin gene

B. defect in tubulin gene

C. defect in lamin A gene

D. defect in keratin gene

10. The movement of vesicles containing neurotransmitters towards the axon terminals involves the cytoplasmic structural element _________ and the protein ______________________.

Group of answer choices

A. keratin; kinesins

B. microtubules; dyneins

C. microtubules; kinesins

D. actin filaments; kinesins

Answer 1

1. (C) The ends of the filament are the same.

Actin filaments are made up of monomeric units of actin proteins which are spirally arranged. Actin filaments has 2 ends- Minus end and Plus end. The plus end is fast growing end of filament while minus end is slow growing one. This difference occurs because a conformational change is required for addition of ATP at minus end. The elongation of filament occurs when free actin associates with ATP.

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