Cell polarity and cytoskeleton and GTPase signalling

Question 1

What is cell polarity and why is it important?

Answer 1

Cell polarity is the asymmetrical organization of cellular components. It is essential for functions such as nutrient absorption (gut cells), electrical signal transmission (neurons), and directed migration (neutrophils)​

Question 2

What are the two main types of cell polarity?

Answer 2

Front-rear polarity in migrating cells like neutrophils.

Apico-basal polarity in epithelial cells, where the apical side faces the lumen and the basal side anchors to the basement membrane​.

Question 3

How is polarity linked to the cytoskeleton?

Answer 3

Polarity is generated by the cytoskeleton. For example, neutrophils form lamellipodia (branched actin) at the front and contractile actomyosin at the rear, enabling directed movement

Question 3

What proteins determine apico-basal polarity?

Answer 3

Crumbs and PAR define the apical domain; Scribble, DLG, and LGL define the basal domain. They operate via mutual exclusion

Question 4

What happens when apico-basal polarity is lost in epithelial cells?

Answer 4

It can lead to loss of tissue organization, contributing to diseases like acute tubular necrosis or cancer development​

Question 4

How do small G-proteins affect cell migration?

Answer 4

They link external signals (e.g., chemoattractants) via receptors like GPCRs to cytoskeletal changes, enabling directed migration such as neutrophil chemotaxis to wounds​

Question 5

What structures do Rho, Rac, and cdc42 help form?

Answer 5

Rho → Stress fibres

Rac → Lamellipodia (branched actin)

Cdc42 → Filopodia (linear actin

Question 5

What is the role of small G-proteins in the cell?

Answer 5

Small G-proteins like Rho, Rac, and cdc42 regulate actin dynamics via a GTP-GDP switch, allowing the cell to respond to external signals​

Question 6

What molecules regulate the GTP-GDP switch in G-proteins?

Answer 6

GEFs (Guanine nucleotide Exchange Factors) turn G-proteins ON (GDP → GTP).

GAPs (GTPase Activating Proteins) turn them OFF (GTP → GDP)​

Question 7

What is prenylation and why is it important?

Answer 7

It is the addition of a lipid group that anchors G-proteins to the inner leaflet of the plasma membrane, crucial for their localization and function​