L8-9: Cellular Organisation, Strucutre and Function of ECM

Question 1

What are the 4 major types of animal tissue?

Answer 1

• epithelial
• muscular
• nervous
  similar strucutre (high frq of cell/cell contact with limited cell/ECM contact)
• connective
  lower freq of cell/cell contact with higher frequency of cell/ECM contact

Question 2

Explain the strucuture of epithelial cells

Answer 2

• has lots of cell, less ECM
• cell junctions link individual cells
• cells attached to thin layer of connective tissue comprising mostly of ECM (basal lamina)
• cells are asymmetrical/ polarised and can be columnar, cuboidal, squamos & stratified

Question 3

How are mechanical forces transmitted in eptihelial cells?

Answer 3

Via cytoskeletal filaments

Question 4

How do tissus cells directly contact each other?

Answer 4

Via cell junctions

Question 5

What are the 4 major types of cell junctions in epithelial cells?

Answer 5

Adherens junctions (cadherin), desmosomes, tight junctions and gap junctions

Question 6

Give an example of an adheren junction and explain its binding

Answer 6

Cadherin: superfamily of Ca2+ dependent molecules with many classical and non members
- cadherin bnidnig is homophillic and Ca2+ dependent

Question 7

Describe the structure of cadherins

Answer 7

They have 5 extracellular domains, seperated by flexible hinge regions

Question 8

What is the purpose of Ca2+ binding in cadherins?

Answer 8

Binding prevents flexing so promotes homophillic binding to another cadherin

• intracellular domain of cadherins interact with actin
• caherin proteins bind these cadherins to the actin via vinculin
• this macro-assembly allows cell junctions to withstand chemical force

Question 9

How are desmosomes structured?

Answer 9

Similar to adherens junctions but contain specialised cadherins that connect with intermediate filaments

Question 10

What is the main role of desmosomes?

Answer 10

To allow junctions to have strength

Question 11

How are tight junctions structured?

Answer 11

Epithelial tissues act as a selective permeability barrier

Question 12

What is the main role of tight junctions?

Answer 12

They allow different specialised receptors to be found on gloculose receptors on apical part of cell

Question 13

How do tight junctinos allow selective transport across epithelial?

Answer 13

Different transporter molecules are expressed in apical and basal plasma membrane

Question 14

How are gap junctinos structured?

Answer 14

They are channels made from connexins and innexins

- are very small so won’t allow macromolecules through

Question 15

Gap junctions are insensitive. True or false?

Answer 15

False, they are very responsive so can open or close in response to signals

Question 16

Which types of animal cell tissues have a similar structure?

Answer 16

Epithelila, muscle and nervous cells

• have high freq of cell/cell interactions
• cells in these tissue often interact with a specialised form of ECM termed basal lamina (basement membrane)

Question 17

What does the ECM provide for the cell?

Answer 17

• support and strength
• extracellular communication (so molecules such as horones are allowed to interact with cells)
• cell migration, polarity and shape (important in embryonic development, angiogenesis and wound & tumour develoment)

Question 18

Describe the structure of the basal lamina

Answer 18

Has very thin layer of ECM produced by cells above and below which have been evolutionarily conserved
- composed of laminin, type IV, XVIII collagen, nidogen, perlecan and fibronectin

Question 19

What is the main role of the basal lamina?

Answer 19

Essential for maintaining epithelial tissue

Question 20

What types of cells can be found in connective tissue?

Answer 20

Indigenoius or immigrant cells

Question 21

Name 3 examples of indigenous cells

Answer 21

Primitive mesenchymal cells, fibroblasts and specialised cells (adipocytes, mast cells, chondrocytes, osteoblasts)

Question 22

What are primitive mesenchymal cells and their function?

Answer 22

They are undifferentiated cells that can lead to the generation of other connective cells, adipocytes and mast cells (release histamine)

Question 23

What is the function of fibroblasts?

Answer 23

They synthesise most of the molecules found in the ECM

Question 24

Give examples of where specialised connective cells can be found

Answer 24

Cartilliage, bone marrow

Question 25

Give an example of a type of immigrant cell

Answer 25

Immune cells

Question 26

Describe the composition of connective tissue ECM

Answer 26

• high MW, highy charged polysaccs (GAG) covalently attached to proteins (proteoglycans) bind lots of water
• fibrous proteins (members of collagen family)
• glycoproteins (not part of collagen family) e.g. elastins

Question 27

What can some specialised forms of connective tissue ECM develop into?

Answer 27

• they can become calcified and form bone

- can become transparent e.g. cornea

Question 28

What are GAGs

Answer 28

Glycosaminogylcans are mostly -vely charged anions produced by animals

• consists of repeating sulphated disacc units
• often linked to a core protein to form proteoglycans (PGs)

Question 29

Describe the structure of PGs

Answer 29

• they can be relatively simple or complex

- can also self-aggregate forming a large protein structure

Question 30

What protein type is the most abundant in mammals?

Answer 30

Fibrous proteins

Question 31

Describe the strucutre of fibrous proteins and how its provides function

Answer 31

Has long, stiff, triple stranded helical strucure which provides tensile (pulling) strength of tissues

Question 32

How are fibrous proteins synthesised?

Answer 32

By indigenous ECM cells (e.g. fibroblasts)

• 40 different types encoded by different genes
• 3 polypeptides (alpha chains rich in proline/ glycine) form a coil
• different alpha chian combos form different types of collagen (type I-XVIII) found in differing connective tissue e.g. type II, IX found in cartillage

Question 33

What is the role of elastin?

Answer 33

Provides elasticity to connective tissues

- dominant component of ECM found in arteries

Question 34

What is the role of fibronectins?

Answer 34

Bind other matrix/ cell membrane proteins, organise matrix and provide cell matrix link

Question 35

How do cell anchors themselves?

Answer 35

By expressing receptors that bind ECM component e.g. basal lamina

Question 36

How does the structure of integrins provide function?

Answer 36

• intergrins are key receptors that bind ECM components
• has an alpha and beta subunit with large N terminal domain, short intracellular domain that binds adaptors & 24 different integrins

Question 37

What is the key roles of integrins?

Answer 37

• To allow ECM to interact with the cytoskeleton and provides strength
• To mediate signalling leading to altered gene expression

Question 38

What is the purpose of Talin?

Answer 38

It’s an important adaptor molecule

-exists in inactive/ active conformation

Question 39

Why is the inactive conformation of talin needed?

Answer 39

• many cells in connective tissue aren’t stationary and migrate through ECM
• cells use integrins to pull themselves through ECM
• cell ECM conacts therefore need to be made and broken as cells move

Question 40

How are integrins activated?

Answer 40

Using intracellular signalling