cellular organisation

Question 1

What are the basic types of animal tissues?

Answer 1

Epithelial: High cell density, less ECM (gut lining, skin)
Muscular: Enables movement
Nervous: Transmits signals
Connective: Low cell density, more ECM (e.g., bone, cartilage)

Question 2

Why do animal cells form tissues?

Answer 2

1. For structural strength and support
2. To enable specialised functions
3. To allow force transmission via cell-cell or cell-ECM interactions

Question 3

What is the structural polarity in epithelial cells?

Answer 3

Apical side: Faces the lumen or external environment
Basal side: Attached to the ECM or basal lamina

Question 4

What is the basal lamina?

Answer 4

A thin layer of ECM under epithelial cells, providing structural support and anchoring cells

Question 5

How do epithelial and connective tissues differ in cell-to-ECM ratios?

Answer 5

Epithelial: High cell density, low ECM
Connective: Low cell density, high ECM

Question 6

What are the four types of cell junctions?

Answer 6

Adherens junctions: Cadherin-mediated, connect to actin filaments
Desmosomes: Cadherins link to intermediate filaments
Tight junctions: Act as selective permeability barriers.
Gap junctions: Water-filled channels for cell communication

Question 7

How do adherens junctions work?

Answer 7

Cadherins form homophilic, Ca2+- dependent bonds.
Linked to actin filaments via catenins and adapter proteins like vinculin

Question 8

What are desmosomes?

Answer 8

Similar to adherens junctions, but connect intermediate filaments using specialised cadherins, providing mechanical strength

Question 9

What is the function of tight junctions?

Answer 9

Create a selective barrier in epithelial tissues.
Allow a differential transport across apical and basal membranes
(e.g., glucose transport in the intestine)

Question 10

What are gap junctions?

Answer 10

• Formed by connexins or innexins
• Enable direct communication via water-filled channels, allowing ions and small molecules to pass through.

Question 11

What role do cell junctions play in tissues?

Answer 11

Facilitate direct cell-cell interactions

Transmit mechanical forces via cytoskeletal filaments

Question 12

How do epithelial cancers affect adherens junctions?

Answer 12

Many epithelial cancers downregulate E-cadherin, reducing cell adhesion and enabling metastasis

Question 13

What is a specialised connective tissue example?

Answer 13

Bone or cartilage

Question 14

Why don’t animal cells have cell walls?

Answer 14

They rely on tissues instead to provide structural strength and allow force transmission

Question 15

What are examples of epithelial tissues?

Answer 15

Lining of the gut and epidermal layers of the skin

Question 16

How does calcium affect adherens junctions?

Answer 16

Calcium binding prevents cadherin flexing, stabilising homophilic cadherin-cadherin interactions

Question 17

What is the function of Rac and Rho in adherens junctions?

Answer 17

They regulate cytoskeletal dynamics and maintain junctional integrity under mechanical force

Question 18

How do tight junctions contribute to intestinal glucose transport?

Answer 18

Differential transporter molecules on apical (glucose uptake) and basal (glucose release) membranes mediate transport across the epithelium.

Question 19

How do gap junctions regulate communication?

Answer 19

Gap junctions can open or close in response to signals, such as dopamine reducing communication in retinal neurons

Question 20

What are the 2 main ways cells interact in tissues?

Answer 20

1. Directly via cell junctions
2. Indirectly via interactions with the ECM

Question 21

How does the ECM differ between tissues?

Answer 21

High ECM content in connective tissues
Low ECM content in epithelial tissues

Question 22

What are examples of muscular tissue?

Answer 22

Smooth muscle, skeletal muscle, and cardiac muscle

Question 23

How does the ECM support epithelial tissues?

Answer 23

It anchors epithelial cells and transmits forces through the basal lamina

Question 24

What structural components make desmosomes strong?

Answer 24

Specialised cadherins connect intermediate filaments, enabling resistance to mechanical stress

Question 25

Why are gap junctions size-restrictive?

Answer 25

Their small pore size prevents macromolecules from passing through, allowing only ions and small molecules to exchange

Question 26

How do cell junctions withstand mechanical force?

Answer 26

Membrane protrusions initiate cell-cell contact. **RAC:** Recruits actin and cadherins to expand junctions, recruiting more cadherins and catenins. **RHO: **Remodels actin and recruits myosin, forming contractile actin-myosin bundles that strengthen the junction.

Question 27

What is the function of RAC in adherens junctions?

Answer 27

RAC facilitates actin polymerisation and cadherin recruitment, expanding cell junctions.

Question 28

What role does RHO play in adherens junctions?

Answer 28

RHO supports actin remodelling and recruits myosin, creating contractile actin-myosin bundles for stronger junctions.

Question 29

What are the components of gap junctions?

Answer 29

1. Interacting plasma membranes of adjacent cells. 2. Water-filled channel (~1.5 nm diameter). 3. Connexon: Composed of six subunits. 4. Two connexons align to form an open channel.

Question 30

What is the size of a gap junction channel?

Answer 30

Approximately 1.5 nm in diameter.

Question 31

How is a connexon structured?

Answer 31

A connexon is composed of six protein subunits that form a circular structure, which pairs with another connexon from an adjacent cell to create a functional channel.

Question 32

What is the role of tight junctions?

Answer 32

Seal neighbouring cells in epithelial sheets, preventing extracellular molecule leakage. Help polarise cells by separating apical and basal membranes.

Question 33

What is the function of adherens junctions?

Answer 33

Join actin bundles in one cell to actin bundles in neighbouring cells, providing mechanical strength and coordination.

Question 34

What is the function of desmosomes?

Answer 34

Connect intermediate filaments between adjacent cells, providing structural integrity and resistance to mechanical stress.

Question 35

What is the function of gap junctions?

Answer 35

Form channels that allow the exchange of small, water-soluble molecules, inorganic ions, and metabolites between adjacent cells.

Question 36

How do hemidesmosomes function?

Answer 36

Anchor intermediate filaments in a cell to the extracellular matrix, stabilizing the cell within tissues.

Question 37

What is the function of actin-linked cell-matrix junctions?

Answer 37

Anchor actin filaments in a cell to the extracellular matrix, providing structural support and facilitating cell-ECM interactions.

Question 38

What are the four types of direct cell-cell interactions?

Answer 38

**Tight junctions:** Prevent leakage of extracellular molecules and polarise cells. **Adherens junctions:** Join actin bundles between cells. **Desmosomes: **Join intermediate filaments between cells. **Gap junctions:** Allow exchange of small molecules and ions.

Question 39

What is the diameter of gap junction channels, and why is this significant?

Answer 39

~1.5 nm, allowing passage of small molecules while preventing the movement of macromolecules.

Question 40

How do tight junctions help maintain cellular polarity?

Answer 40

By separating apical and basal membrane domains, ensuring selective transport and compartmentalisation.

Question 41

What proteins are involved in adherens junctions?

Answer 41

Cadherins and actin filaments, linked via adapter proteins like catenins.

Question 42

What is the key structural difference between desmosomes and adherens junctions?

Answer 42

Desmosomes connect intermediate filaments, while adherens junctions connect actin filaments.

Question 43

How are gap junctions regulated?

Answer 43

Gap junctions can open or close in response to cellular signals, such as neurotransmitters like dopamine.

Question 44

Why are hemidesmosomes important in tissue integrity?

Answer 44

They anchor cells to the ECM, ensuring mechanical stability and maintaining tissue organisation.

Question 45

What is the role of the extracellular matrix in actin-linked junctions?

Answer 45

It serves as the anchoring site for actin filaments, mediating force transmission and structural support for cells.