Cell structure and tissues

Question 1

What are the interactions between cells in multicellular organisms?

Answer 1

• Cell adhesion molecules
• tight junctions
• desmosomes
• gap junctions

Question 2

What are the interactions between cells and their surroundings in multicellular organisms?

Answer 2

• the basal lamina
• the extracellular matrix

Question 3

What are the requirements in multicellular organisms for cells?

Answer 3

• to stick together and to the basal lamina or extracellular matrix
• to communicate with each other
• to co ordinate their activities
• to interact with other cell types

Question 4

What are the requirements in multicellular organisms for epithelia and the typical junctions between epithelial cells?

Answer 4

• epithelia need to form impermeable barriers between body cavities eg gut lining, blood vessels

Junctions
- tight junctions
- gap junctions
- desmosomes
- adherens junctions

Question 5

What is the function of Tight junctions?

Answer 5

seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them

Question 6

What is the function of adherens junction

Answer 6

joins an actin bundle in one cell to a similar bundle in a neighbouring cell

Question 7

What is the function of desmosome

Answer 7

joins the intermediate filaments in one cell to those in a neighbour

Question 8

What is the function of gap junctions

Answer 8

forms channels that allow small water soluble molecules (including ions) to pass from cell to cell)

Question 9

What is the function of emidesmosome

Answer 9

anchors intermediate filaments in a cell to the basal lamina

Question 10

what are the properties of cell adhesion molecules?

Answer 10

• mosaics of multiple distinct domains
• clustered: cell junctions
• adhesions: strong and long lasting
• also present in immune system

Question 11

How are integrins activated?

Answer 11

by binding to a molecule on either side of the membrane

Question 12

What are the properties of tight junctions?

Answer 12

• intercellular adhesion complexes
- semipermeable
- size and charge selective

• control paracellular diffusion of ions and solutes

• border between the apical and basolateral domains of the plasma membrane
- establish and maintain compartments with different fluid compositions

Question 13

What do adherens junctions do?

Answer 13

• connect bundles of actin and myosin filaments running parallel to plasma membrane
• allows contraction of epithelial layers
• play a role in formation of epithelial tubes

Question 14

what type of junctions do cadherins and integrins contain?

Answer 14

• Cadherin: contains junctions connent cells to one another

• Integrins: contains junctions connect cells to the substratum

Question 15

What do desmosomes do?

Answer 15

• join cells together
• connect the intermediate filaments running parallel networks of adjacent cells
• anchor cytoskeleton to plasma membrane
• connect cytoskeleton of surrounding cells giving strength

Question 16

What do gap junctions do?

Answer 16

• pores connect adjoining cells to:
- allow ion movement between cells, chemical and electrical coupling between adjacent cqkles
- important for intercellular signalling

• allows co ordination of activities in a sheet of cells eg muscle contraction

• rapid transmission of nerve impulses bc it can pass directly through cells eg muscle

Question 17

What is the basement membrane and what does it do? (basal lamina)

Answer 17

• thin dense layer of ECM
• forms supporting structure and scaffolding for epithelial tissue (composition varies)
• separates organs and tissues, maintains tissue structure and function

• functions
- structural support
- prevention if tumor invasion
- regulation of cell behaviour

Question 18

The extracellular matrix is a fibrous network of proteins and polysaccharides that fills spaces between cells. what are these

Answer 18

• Glycosaminoglycans: form a hydrated gel like substance into which fibres are embedded
• when linked to proteins are then called proteoglycans
• fibrous proteins eg collagen for structural and fibronectin for adhesiveness

• Fibroblasts
- produces the components of ECM
- secreted into surrounding environment to assemble into final structure

• pre collagen
- does nor assemble, needs to be processed in the extra cellular space

Question 19

What is the extracellular matrix (ECM)

Answer 19

• helps hole cells and tissues together
• plays active role in embryogenesis, wound healing and cell migration

Question 20

How does collagen form a triple helix

Answer 20

• collagen fibrils form by lateral interactions of triple helices
• bundles of collagen fibrils run perpendicular to each other
• collagen orientation varies between the different tissues

Question 21

How is the ECM extracellular matrix used in health and diseases?

Answer 21

• ECM interacts with cells to regulate gene expression
- impacts on drug metabolism resistance
- understanding such interactions can hep develop personalised med

• changes to ECM components associated with disease

• implication in tumour development- therapeutic target?