Cytoskeleton And Apoptosis

Question 1

What is the cytoskeleton?

Answer 1

Dynamic network of proteins that quickly assemble and disassemble to respond to cell needs. Needed for: structure, intracellular transport, movement, and cell division.

Question 2

Name and explain 4 functions of the cytoskeleton.

Answer 2

1. maintaining cell shape- provides mechanical support allowing cells to adopt various shapes.
2. Facilitating cell movement- due to cytoskeleton components cells like sperm/WBC can swing or crawl.
3. Organising intracellular contents- help arrange organelles and other structures in cell to ensure efficient function.
4. Supporting intracellular transport- motor proteins uses cytoskeleton ‘tracks’ to transport vesicles, organelles and proteins across the cell.

Question 3

Name 3 protein components of the cytoskeleton.

Answer 3

1. Microfilaments (actin)
2. Microtubules
   E. Intermediate filament

Question 4

Describe and explain the functions of actin/microfilaments.

Answer 4

• thinnest fiber
  -made up of twisted strands of actin proteins

Functions include;
1. Structural support at cells edges
2. Key role in muscle contractions and cytokinesis (division of cytoplasm)
3. Help form cellular extensions like pseudopia that the cells move/engulf particles.

Question 5

Describe and explain microtubules.

Answer 5

• hollow tubes made from tublin protein subunits.
• thickest filament

Functions include:
1. Provide scaffolding to maintain cell shape
2. Form mistik spindle taht separates chromosomes in cell division
3. Act as a track for motor proteins allowing movement of organelles, vesicles, and other substances in the cells
4. Key component in cilia (move fluids across surface of tissues) and flagella (propel cells like in sperm).

Question 6

Describe and explain the functions of intermediate filaments.

Answer 6

• 8-12 nm in diameter.
• tensil strength for cells
• more stable
• less dynamic
• made from many proteins like keratin. Mutations in keratin gene can lead to conditions like epidermolysis bullosa simplex causes skin blisters.

Functions include:
1. Reinforce cell structure, help withstand mechanical stress
2. Anchor organelles and help maintain cells internal organisation

Question 7

Explain what microtubules role is in cell division.

Answer 7

• they form spindle fibres in mitosis, it attaches to chromosomes and pull them apart to form daughter cells.
• centromere is near the nucleus. Act as the organising centre for microtubules during mitosis.
• centrioles. Structure in centrome that replicate and migrates to opp.ends of the cell to form spindle fibres

Question 8

How is microtubules arranged in cilia and flagella?

Answer 8

Both made up of microtubules which are arranged in a ‘9+2’ structure where a pair of microtubules surround 2 central microtubules.
Movement of these structures is powered by Dynein.

Question 9

What is dynein?

Answer 9

Mono protein that causes microtubules to slide against each other.

Question 10

What does cilia do?

Answer 10

Sweep mucus and traps debris out of the lungs.

Question 11

What does flagella do?

Answer 11

Enables sperms to swim towards egg.

Question 12

What is actin polymerisation?

Answer 12

Actin/microfilaments form a structure like pseudophilia that allows cells to move by pushing CM outwards. Process is called ‘cell crawling’. It’s needed for WBS’s to move toward infected sites and engulfing pathogens.

Question 13

Name 2 motor proteins and explain what they do.

Answer 13

Kinesin and dynein.

They travel along the microtubules to move cellular cargo. They use ATP to move along cytoskeleton tracks, moving vesicles, residue, organelles and chromosomes to their location in the cells.

Kindsin moves cargo along cells periphery while dynein moves it towards cell center.

Question 14

Define and explain apoptosis.

Answer 14

Programmed cell death.
Neurosis results from injury/damage.

A process that allows the body to remove unwanted/damaged cells without causing harm to surrounding tissues.

Question 15

Functions of apoptosis.

Answer 15

1. Development- apoptosis sculpts tissues and organs during embryonic development. Eg. Apoptosis controls the separation of toes and fingers during foetus development.
2. Homeostasis- ensure body maintains proper balance of cell numbers in tissues.
3. elimination of damage/dangerous cells- cells with damage DNA, infected or potential to be cancerous is removed.

Question 16

What are the cells changes during apoptosis?

Answer 16

• cell shrinks, rounds up cytoskeleton and nucleus is broken down.
• plasma membrane forms plebs (small profusions) that soon break off.
• DNA is fragmented, intracellular proteins degraded by enzyme (caspase).

Question 17

Name two pathways apoptosis is initiated through.

Answer 17

Insintric and exsintric.

Question 18

Describe the insintric pathway of apoptosis.

Answer 18

1. Activated by internal signals like DNA damage/oxidation stress.
2. Mitochondria releases proteins like cytochromes C which activates cascade of capsases leading to cell death.

Question 19

Describe the exsintric pathway of apoptosis.

Answer 19

1. Triggered by external signals like death ligands binding to receptors on cell surface.
2. Activates death domains which further activates initiator capsase.
3. Capsase activates executioner capsase which breaks down cell proteins leading to its destruction.