Cytoskeleton and Motor Proteins

Question 1

Most eukaryotic cells contain a complex network of protein fibers calledthe cytoskeleton. What are the components of the cytoskeleton?

Answer 1

1. Microtubules
2. Microfilaments
3. Intermediate filaments

Question 2

Describe the structure of microtubules.

Answer 2

long, slender, hollow tubes composed of tubulin molecules

tubulin is a globular protein with α and β subunits.

Question 3

State the functions of microtubules.

Answer 3

• maintain asymmetric cell shapes
• are conveyer belts inside the cells because they move vesicles, granules, organelles like mitochondria, and chromosomes via special attachment proteins, from one point of the cell to another
• may join with other proteins to form complex structures called cilia, flagella or centrioles. Flagella and cilia are used for locomotion. They form the spindle fibres for separating the chromosomes during mitosis.

Question 4

Describe the structure of microfilaments.

Answer 4

intertwined helical chains of actin molecules; microfilaments components of myosin molecules are present in muscle cells

Question 5

State the functions of microfilaments.

Answer 5

• play a vital role in various cellular contractile systems, including muscle contraction and amoeboid movement
• serve as a mechanical stiffener for microvilli

Question 6

Name two diseases resulting from defects of the cytoskeleton which contribute to neurodegeneration.

Answer 6

1. Alzheimer’s disease
2. Parkinson’s disease
3. Amyotrophic Lateral Sclerosis (ALS)/Lou Gehrig’s disease/Motor Neuron Disease

Question 7

What are molecular motors/motor proteins?

Answer 7

They are biologicalmolecularmachines that are the essential agents of movement in living organisms.

for example, manyprotein-based molecular motors harness the chemicalfree energyreleased by thehydrolysisof ATPin order to perform mechanical work

Question 8

List three cytoskeletal motors.

Answer 8

a) Myosins are responsible for muscle contraction, intracellular cargo transport, and producing cellular tension.
b) Kinesinmoves cargo inside cells away from the nucleus alongmicrotubules.
c) Dyneinproduces theaxonemalbeating ofciliaandflagella and also transports cargo along microtubules towards the cell nucleus.

Question 9

List three polymerization motors.

Answer 9

a) Actin polymerization generates forces and can be used for propulsion.ATPis used.
b) Microtubule polymerization usingGTP.
c) Dynamin is responsible for the separation ofclathrinbuds from the plasma membrane.GTPis used.

Question 10

List the rotary motors.

Answer 10

FoF1-ATP synthase
Bacterial flagellum

Question 11

State the nucleic acid motors.

Question 12

What is a molecular motor? What are four broad categories of molecular motors?

Answer 12

(a) These are biological molecular machines that are essential agents of movement in living organisms.
(b) 1. Cytoskeletal motors, 2. Polymerisation motors, 3. Rotary motors, 4. Nucleic acid motors

Manyprotein-based molecular motors harness the chemicalfree energyreleased by thehydrolysisof ATPin order to perform mechanical work.

Question 13

Name three cytoskeletal motors and state their functions.

Answer 13

1. Dynein - produces the axonemal beating of cilia and flagella and also transports cargo along microtubules towards the cell nucleus
2. Kinesin - moves cargo inside cells away from the nucleus along microtubules
3. Myosins - responsible for muscle contraction, intracellular cargo transport, and producing cellular tension

Question 14

State the functions of the following nucleic acid motors:
1) RNA polymerase
2) DNA polymerase
3) Helicases
4) Structural Maintenance of Chromosome (SMC) proteins

Answer 14

1) transcribes RNA from a DNA template
2) turns single-stranded DNA into double-stranded DNA
3) they separate double strands of nucleic acids prior to transcription or replication
4) they are responsible for chromosome condensation in eukaryotic cells