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BB10005 COPY > Extracellular matrix > Flashcards

Extracellular matrix Flashcards

1
Q

What is the definition of an extracellular matrix?

A
  1. Any substance produced by cells and secreted into the extracellular space within the tissues.
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2
Q

Why is the the ECM important?

A
  1. Structural - ECM provides physical support for cells and a linkage between different cells or tissues
  2. Cell Motility – it forms a substrate on which cells can move and furthermore it provides cues that guide the direction of movement
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3
Q

What are connective tissues made up of?

A

It is mostly made up of ECM and consists of scattered cells such as fibroblasts.

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4
Q

What is the ECM in connective tissue made up of?

A
  1. Collagen fibres cross-linked by accessory proteins in a matrix of proteogylcans (protein and polysaccharides).
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5
Q

What is the structure of epithelial tissues?

A
  1. Scant ECM – consists of layers of cells closely bound to one another to form protective sheets
  2. ECM concentrated under epithelia (BASAL LAMINA) provides a base for the cells to sit on and acts as a molecular sieve and substrate for migrating cells
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6
Q

What is the ECM in plants made up of?

A
  1. Cellulose fibres that are cross-linked with hemicellulose in a matrix of highly branched polysarccharides, such as pectin.
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7
Q

What is the other name for the ECM in plants?

A

The cell wall.

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8
Q

How does plant ECM differ from animal ECM?

A
  1. Unlike plants – which contain polysaccharide fibres animal ECM has fibres made of protein
  2. Animal ECM contains collagen and elastin
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9
Q

What percentage of the protein mass does collagen make up?

A

25%.

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10
Q

How many different collagen genes are there in mammals?

A

42.

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11
Q

How is collagen formed

A
  1. Synthesise pro alpha chain
  2. Hydroxylation of selected prolines and lysines
  3. Glycolysation of selected hydroxylysines
  4. Self-assembly of three pro-a chains
  5. Procollagen triple-helix formation
  6. Transported into secretory vesicles and to plasma membrane
  7. Released from cells in an organised fashion which appears to guide the orientation of the collagen
  8. Cleave off polypeptides by protease
  9. Self-assembly into fibrils
    10 Aggregation of collagens to form a collagen fibre
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12
Q

What does fibre forming collagen do and what is its structure

A
  1. Forms long fibres
  2. At base there is a single collagen polypeptide chain
  3. Triple helical molecules
  4. Form collagen fibrils
  5. Fibrils group together to form fibres
  6. The fibres are cross-linked to form a network
  7. Give strength to the matrix- resistance to pulling forces
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13
Q

What is the structure of crosslinking fibres

A
  1. Fibres are formed of type IX collagen

2. Cross link the fibre forming collagen

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14
Q

What does the pro collagen fibre termini do

A
  1. Core of collagen

2. Termini are important for preventing the fibrils form self-assembling in the cell

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15
Q

What are the cross links between the components of tropocollagen?

A

Covalent cross links.

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16
Q

What are the cross links between fibrils and fibres?

A

Hydroxyproline cross-links.

17
Q

What is the amino acid repeat in collagen molecules?

A

GlycineXY where X and Y can be any amino acids, but are predominantly lysine, proline, hydroxylysine and hydroxyproline.

18
Q

What amino acids are the basis of cross-linking between the collagen molecules?

A

The hydroxified amino acids.

19
Q

What is the importance of the collagen structures that do not form fibrils or fibres?

A
  1. They are bundled up into secretory vesicles that are taken to the edge of the cell and fused with the plasma membrane and procollagen helices.
20
Q

What is the function of elastin?

A

It provides elasticity to tissues.

21
Q

What is elastin composed of?

A
  1. Large filaments with lots of random coils that can be compared to springs.
  2. It is connected by cross-linked lysine or hydroxylysines.
  3. Loose randomly folded structure which can elongate under tension and will recoil when tension is gone
22
Q

What happens when elastin stretches?

A

It flattens out, compared to its relaxed coiled state.

23
Q

How is the ECM in animals similar to that in plants?

A

Most of the matrix consists of polysaccharides.

24
Q

What is the protective structure in plant ECM and animal ECM?

A
  1. Plants= pectin- Forms a highly hydrated gel
  2. Animals= glycosaminoglycans (GAGS)
  3. GAGS- Hyaluronan, chondroitin sulphate, heparan sulphate
25
Q

What are some of the features of glycosaminoglycans?

A
  1. Polysaccharide
  2. Repeating disaccharide of N-acetylglucosamine or N-acetyl galactosamine and Glucoronic acid or iduronic acid
  3. Highly negatively charged
  4. Hydrophillic
  5. Linked to non-fibrous proteins non-covalent link- Proteoglycans
  6. Covalently linked to other GAGs
  7. Form enormous structure and fill up space with not a lot of molecules
26
Q

Why do lots of different types of connective tissue exist?

A
  1. There is variation in the proportion of fibres to cells within the ECM
  2. there is varying numbers and proportions of different cell types within the ECM
  3. there is varying proportions and arrangements of fibres in the ECM
  4. there is varying composition of the non-fibrous component of the ECM.
27
Q

What are the specialised cell types of fibroblasts?

A

Osteocytes (bone)

28
Q

What are the specialised cell types of macrophages?

A

Chondrocytes (cartilage)

29
Q

What are the specialised types of mast cells?

A

Adipocytes (adipose/fat) and blood cells (blood)

30
Q

Why did Mr Morris have such stretchy skin?

A
  1. Collagen limits amount of stretch
  2. His elastin fibres work fine
  3. His collagen doesn’t resist tension
  4. Failure of conversion of lysine to hydroxylysine by lysyl hydroxylase OR failure to cleave off peptide termini => fibrils and fibres don’t form
31
Q

What does areolar connective tissue contain and what is its function?

A 
1. Used to cushion organs in the body
Contains
2. Collagen fibres in random organisation
3. Elastin fibres
4. Fibroblasts
32
Q

What does adipose tissue contain?

A
  1. Dominated by cells not fibres
  2. Adipocytes- adipose cells
  3. Specialised for absorbing lipids
  4. Loosely held together by collagen fibres- reticular fibres.
33
Q

What do tendons and ligaments contain?

A
  1. Dominated by collagen fibres not cells
  2. Need to resist tension so tendons don’t carry on stretching
  3. Collagen fibres are very abundant and organised- elongated in one orientation
  4. Fibroblast nuclei
34
Q

What does the dermis of the skin and organ joint capsules contain?

A
  1. Need resistance to tensile forces
  2. Direction of tension is not predictable
  3. So collagen is organised in a variable way
  4. Different alternating layers of collagen in different orientations giving resistance to tension in different directions
  5. Fibroblast nuclei
35
Q

What does elastic cartilage contain?

A
  1. Highly elastic
  2. Elastin fibres dominant
  3. Chondrocytes in lacuna secrete the elastin
36
Q

What does bone contain?

A
  1. Specialised cells- osteocytes in lacuna
  2. Mineralised matrix- calcium rich and crystalline
    in lacuna.
37
Q

What is scurvy?

A
  1. Vit C (Ascorbic acid) is an essential cofactor for prolyl hydroxylases
  2. They hydroxylate hyrdoxyProline and –Lys which needed for crosslinking of collagen fibres
  3. Hydroxyproline stabilises triple stranded collagen
  4. lack of normal fibrils leads to fragility and bleeding and teeth loss
38
Q

What is fibrodysplasia ossificans progressiva?

A
  1. When muscle and connective tissue, such as tendons, are gradually replaced by bone (ossified)

BB10005 COPY (23 decks)

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