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Miscellaneous > MCB Lecture 38 Connective Tissue > Flashcards

MCB Lecture 38 Connective Tissue Flashcards

0
Q

What are the two structural proteins in the extracellular matrix?

A

Elastin

Collagen

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1
Q

Describe the contents of extracellular matrix

A

Fibrous proteins
Adhesive proteins
Ground substance: proteoglycans

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2
Q

What are the adhesive proteins in ECM?

A

Fibronectin

Laminin

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3
Q

What is the function of ECM? (2)

A
  1. Support

2. Regulation of cellular activities

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4
Q

Which cells produce ECM? (4)

A

Cells within the ECM, mysenchymal cells
Eg. Fibroblasts
Osteoblasts
Chondroblasts

Also epithelial cells

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5
Q

Describe the structure of collagen

A

Three alpha helices intertwine to becomes a Super helix (triple helix)

Super helices interact via cross linking to form fibrils

Fibril interact to form collagen fibres

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6
Q

Describe the synthesis of fibrillar collagen

A
  1. Helix translated into ER
  2. Three helices intertwine with disulfide bonds, propeptides present on the ends
    Q3. Triple helix packaged and exocytosed
  3. Outside the cell, the pro-peptides are cleaved, and fibrils form
  4. Fibres form by covalent cross links between fibrils
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7
Q

Where do collagen fibrils form?

A

Outside the cell

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8
Q

What are the three types of collagen?

A

Fibrillar
Fibrillar associated collagen
Sheet forming collagen

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9
Q

Describe the features of fibril associated collagen

A
  1. Flexible region where there is no helix
  2. Bind to fibrillar collagen
  3. Pro-peptides aren’t cleaved
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10
Q

What are propeptides?
Where are they cleaved?
What is their function?

A

These are peptide regions on the end of the triple helices

They are cleaved when the triple helix is exocytosed

Their function is to stop fibrils forming inside the cell. Only once the helices are outside the cells can fibrils form

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11
Q

How is tensile stretch in collagen regulated?

A

The number of cross links in the fibrils corresponds to the tensile strength

The more cross links, the stronger the fibre

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12
Q

What do defects in collagen cause? (4)

A
  1. Scurvy
  2. Ehlers Danlos syndrome
  3. Achondrogenesis
  4. Osteogenesis imperfecta
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13
Q

What are the features of elastin?

A
  1. Stretchy, provides elasticity
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14
Q

Where is elastin found?

A
  1. Arteries, especially the aorta

2. Lungs

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15
Q

Describe the structure of elastin

A

Covalently cross linked network of elastin molecules + fibrillin

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16
Q

What do defects in elastin cause?

A
  1. Marfan syndrome:
    Problems with vasculature: vasodilation, aneurysms
    Scoliosis
    Dislocated lens
17
Q

What causes Marfan syndrome?

A

Defects in fibrilhin, which is vital for elastin fibre formation

18
Q

What are the general features of adhesive proteins?

A
  1. They interact with integrins in focal adhesions and hemi desmosomes

Mediate the interaction between cells and the ECM

  1. Multiple binding domains
19
Q

What are the two forms of fibronectin?

A
  1. Soluble, present in plasma

2. Insoluble: binds to integrins

20
Q

What is the sequence on fibronectin that binds to integrins?

A

RGD sequence

Arg, Gly, Asp

21
Q

What are two defects in fibronectin?

A
  1. Fibronectin knockout: blood vessels can’t form because there is no cell migration
  2. Antibodies form to the RGD sequence
22
Q

What is the structure of laminin?

A
  1. 3 chains: alpha, beta, gamma
    The three chains are connected with disulfide bonds
  2. Multiple binding domains
23
Q

Where is laminin located?

A

In the basement membrane

24
Q

What do laminin mutations cause? (2)

A
  1. Muscular dystrophy

2. Problems with Neuromuscular junctions

25
Q

What are basement membranes?

A

This is the layer of proteins under the epithelial cells

Mediates the interaction between epithelial tissue and ECM

26
Q

What are the functions of basement membranes?

A
  1. Growth factors

2. Modulates cell behaviour

27
Q

Describe the structure of ground substance

A

Proteoglycans in an aqueous environment, forming a gel

28
Q

Describe the structure of proteoglycans

A

Protein core
Linker Tetrasaccharides
Glucosaminoglycans (GAGs)

29
Q

What are proteoglycan aggregates?

A

This is when a molecule such as Hyaluronan binds many protein cores of proteoglycans.

This creates a huge proteoglycans, comparable in size to a bacterium

30
Q

What is hyaluronan?

A

It is a molecule to which multiple proteoglycans bind (at the protein core), forming an aggregate

31
Q

What are the general features of proteoglycans? What does this mean for the composition of the ground substance?

A
  1. The sugars are negatively charged
    Na+ is attracted, pulling water with it.

The osmotic pressure brings about

  1. Resistance to compressive forces
  2. Gel like characteristic
32
Q

Describe how proteoglycans can inhibit and enhance ligand signalling on cells

A
  1. Bind to secreted proteins (ligands) and present them to receptors
  2. Bind to secreted proteins (ligands) and sequester them from receptors
  3. Enhance the diffusion of protein ligands
33
Q

What sort of bonds are between collagen fibrils?

A

Covalent

34
Q

What is the name of the collagen that is present in the ER?

What is its structure?

A

Pro collagen

It is the super helix of alpha helices, with propeptides attach

35
Q

What is the handedness of collagen helices?

A

Left handed

36
Q

Which type of bonding is present in elastin networks?

A

Covalent

37
Q

What makes up an elastic fibre?

A

Elastin and fibrillin

38
Q

A single collagen alpha helix is made up of…

A

Gly-X-Y triplets

39
Q

In a collagen alpha helix, the ‘X’ and ‘Y’ correspond to…

A

X: proline or lysine
Y: hydroxyproline or hydroxylysine

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