Actin Filaments And Force Generation

Question 1

Give examples of polymerisation of actin generating force

Answer 1

• Acrosomal process of invertebrate sperm and pathogenic bacteria
• Llamelipodium (advancing region) of vertebrate tissue cells such as fibroblasts

Question 2

How do thyone sperm enter the egg cell?

Answer 2

• Actin and profilin held behind acrosomal vesicle
• profilin drives assembly of actin filaments
• rod of actin (90um) penetrates egg jelly layer

Question 3

Which bacteria hijack the host actin cytoskeleton?

Answer 3

Listeria

Shigella

Question 4

How do amoeba move?

Answer 4

• Actin filaments polymerise
• Pseudopodium anchored and extended
• Actin-myosin contraction = rail retraction

Question 5

Give example of interaction with myosin generating force and describe it

Answer 5

Muscle contraction:

Myosin II- two heads interact with Actin. Tail forms bipolar filament with another tail

Question 6

How many classes of myosin are there? How many in mice?

Answer 6

At least 15 classes

26 myosin genes in mice, 7 classes

Question 7

Which mysosin is conventional myosin?

Answer 7

Myosin II

Question 8

Which myosin is an organelle motor?

Answer 8

Myosin V

Question 9

Which myosin is involved with hearing?

Answer 9

Myosin VI and VII

Question 10

What functions do F-Actin myosin interactions have in the cell?

Answer 10

• F-Actin gliding
• Vesicle, organelle transport
• Tension, cleavage furrow
• Capping of surface receptors

Question 11

Which cell processes use a combination of polymerisation and actin-myosin interaction?

Answer 11

• Cilia and flagella
• Intracellular transport
• Mitotic spindle

Question 12

How do Cilia and flagella work?

Answer 12

sliding between adjacent doublets of microtubules causes waveform movement of axoneme

Question 13

Outline mucus propelling Cilia

Answer 13

6um, ~200/Cell
•Nasal passages and sinuses
•Eustachian tubes and middle ear
•pharynx, trachea, bronchi, bronchioles

Question 14

Outline fluid propelling cilia

Answer 14

13um, ~200/cell
•Ependymal lining of brain
•Testes, cervix and oviduct

Question 15

Outline sensory cilia

Answer 15

• Rods and comes of retina
• Hair cells of inner ear
• Olfactory cells (~17/cell)

Question 16

How long are flagella in spermatozoa?

Answer 16

~60um long

Question 17

What does kinesin do in axonal transport?

Answer 17

Moves organelles towards +ve end of microtubule

Question 18

What does dynein do in axonal transport?

Answer 18

Moves organelles towards -ve end of microtubule

Question 19

What is FtsZ?

Answer 19

Associated with division ring of bacteria and chloroplasts

Question 20

What is the mitotic apparatus?

Answer 20

Transient cytoskeletal apparatus based on microtubules and motor proteins
-> separation of chromosomes

Question 21

How is cytoplasm cleaved in mitosis in animal cells?

Answer 21

By a ring of actin microfilaments and myosin II

Question 22

Describe the mitotic spindle

Answer 22

• Centrosome duplicates and each forms pile of spindle

* Has 3 sets of microtubules- astral, kinetochore, polar

Question 23

Outline mitosis

Answer 23

1. Prophase- CHR condense
2. Prometaphase- nuclear envelope breaks down, CHR associate with mitotic spindle
3. Metaphase- CHR align at equator of mitotic spindle
4. Anaphase- separation of CHR then of spindle poles
5. Telophase- CHR decondense, nuclear envelope reforms

Question 24

When will anaphase start?

Answer 24

When all chromosomes are correctly attached to the spindle, so the forces on the chromatids are balanced

Question 25

How does anaphase happen?

Answer 25

• Loss of cohesion between sister chromatids
• Dynein moves chromosomes to poles at kinetichore and k microtubules shorten
• Kinesin pushes overlapping polar microtubules apart