Eukaryotic Cells - Cells in tissues - lecture 6

Question 1

What are the requirements in a multicellular organism i.e. what does the cell need to do?

Answer 1

cells need to

• stick together and to the basal lamina
• communicate with each other
• co-ordinate their activities
• interact with other types

Question 2

what is the purpose of tight cellular junctions

Answer 2

• cells may need to form an impermeable barrier
• tight junctions seal gaps between cells
• membranes are firmly pressed together and prevent leakage

Question 3

what are the 2 types of proteins involved in tight cellular junctions?

Answer 3

1 - claudins; important in structure and sealing

2 - occludins; determines junction permeability

Question 4

what are gap cellular junctions?

Answer 4

• a series of pores connecting adjoining cells and forming a cytoplasmic bridge
• provide a chemical and electrical coupling between adjacent cells
• permit the movement of ions and small molecules of MW less than 1200 between cells

Question 5

what is the purpose of gap junctions?

Answer 5

• allow co-ordination of activities in a sheet of cells
• allow rapid transmission of nerve impulses; impulses can pass directly through the cells, rather than having to jump across synpases
• important for intracellular singalling

Question 6

what are adherens junctions?

Answer 6

• connect the contractile bundles of actin and myosin filaments that run parallel to the plasma membrane
• allows contraction of epithelial layers
• plays a role in formation of epithelial tubes
• loss of cadherin (proteins involved in interaction) is associated with metastasis in cancer

Question 7

what are desmosomes

Answer 7

• button-like contact points that rivet cells together
• connect the intermediate filament networks of adjacent cells
• desmosomes anchor the cells cytoskeleton to the plasma membrne and connect the cytoskeleton of surrounding cells giving strength

Question 8

what is the basal lamina

Answer 8

• specialised region of extracellular matrix that provides a solid substratum to anchor epithelial cells
• forms a barrier between epithelial sheets and connective tissue
• can take different forms in different tissues
• it is a network of proteins and proteoglycans connected to the plasma membrane

Question 9

what is the extracellular matrix?

Answer 9

• fibrous network of proteins and polysaccharides that fills the spaces between cells
• helps hold cells and tissues together
• plays active role in embryogenesis, wound healing and cell migration

Question 10

what is the purpose of elastic fibres?

Answer 10

• allow tissues to stretch and recoil
• some tissues need both strength and velocity
• composed of elastin deposited on glycoprotein-based microfibrils with crosslinks
• interwoven with collagens to limit extent of stretching