Structural Proteins

Question 1

List the intracellular structural protein(s)

Answer 1

Keratin

Question 2

List the extracellular structural protein(s)

Answer 2

• Collagen
• Elastin

Question 3

Keratin

Answer 3

• Structural protein
• Found in skin, hair, nails hoofs and feathers
• High stability from cysteine disulphide bonds

Question 4

Alpha-keratin

Answer 4

• Consist of alpha helices
• Forms b-keratin at high temp
• Stabilised by disulphide bonds
• Hair, wool, nail, hoof

Question 5

Beta-keratin

Answer 5

• Stronger than alpha-keratin
• Beta-pleated sheet
• Feathers and reptile scales

Question 6

Disulphide bonds in keratin can be reduced by…

Answer 6

Thioglycol

or another reducing agent

Question 7

Composition of wool

Answer 7

• 3 alpha keratin macromolecules → 1 Protofibril
• 11 protofibrils → 1 Microfibril
• Microfibril → Macrofibril
• Macrofibril → Wool fibre

Question 8

What stabilises the polypeptide chain of keratin?

Answer 8

Disulphide bonds

Question 9

Cells on the outer layer of the epidermis

Answer 9

• Dead cells
• Held together by a network of keratin fibres
  
  • Provided by keratinocytes

Question 10

Synthesis of keratin

Answer 10

1. Pre-keratin produced in cells
2. Skin cells mature and become keratinized
3. Cells of the stratum basale go upwards
4. Keratin-containing stratum corneum formed

Question 11

Keratin can be degraded by…

Answer 11

• Thioglycolates
• Keratinase (moth larvas)

Question 12

List the extracellular matrix components

Answer 12

• Collagen
• Elastin
• Fibronectin
• Laminin
• Proteoglycans

Question 13

Collagen (extracellular)

Answer 13

• Very abundant fibrous protein
• Insoluble in water
• Skin, bone tendon, cartilage blood vessels
• Not found in plants

Question 14

Structure of collagen

Answer 14

• Basic unit: Tropocollagen (triple helix structure)
• Striated
• Gly & Pro / hydroxyPro / hydroxyLys are prominant in the peptide chains

Question 15

How does a lack of vitamin C cause scurvey?

Answer 15

• Vitamin C needed for collagen synthesis
• Bleeding gums, loosening teeth

Question 16

• Process name
• Enzyme required

Answer 16

• Hydroxylation of Lysine
• Lysine hydroxylase (Requires vitamin-C)

Question 17

Answer 17

Question 18

End product name

Answer 18

5-OH-Lys (Hyl)

Question 19

End product name

Answer 19

4-OH-Pro (Hyp)

Question 20

• Process name
• Enzyme required

Answer 20

• Hydroxylation of Proline
• Proline hydroxylase (requires vitamin C)

Question 21

Due to the high level of Pro / hydroxyl-Pro, the polypeptide chains of collagen cannot…

Answer 21

• Form alpha-helix/B-sheet
• Left-handed helix conformation instead
• This conformation allows the 3 helices to interlock (tropocollagen)

Question 22

Structural units of collagen

Answer 22

Tropocollagens → microfibrils → macrofibrils → fibres

Question 23

What binds tropocollagen units?

Answer 23

• Cross links (C=C/C=N bonds)
• Disulphide bonds
• H-Bonds

Question 24

What is the purpose of Pro/Lys being converted to hydroxy-Pro/hydroxy-Lys?

Answer 24

• Pro/Lys cannot hydrogen bond
• Converted to hydroxy- in order to form hydrogen bonds

Question 25

Lys-aldehyde + Lys-aldehyde → | (Allysine + Allysine →)

Answer 25

Condensation: Cross linkage

Question 26

Give the varieties of collagen in order of abundance

Answer 26

* Collagen-I * Collagen-II-IV * Collagen-V-VII

Question 27

Every third amino acid in collagen is...

Answer 27

Glycine | (Forms a helix)

Question 28

What structural change does hydroxy-Lysine undergo during collagen synthesis?

Answer 28

hydroxy-Lysine is glycosylated (Gal-Gal-Glu) Chains twist together and form a triple helix (procollagen)

Question 29

Describe the stages of collagen synthesis

Answer 29

1. Transcription + Translation 2. Pro → OH-Pro, Lys → OH-Lys 3. OH-Lys glycosylated → procollagen 4. C and N-terminus propeptides removed 5. Tropocollagen 6. Cross linkage → Type I collagen

Question 30

Which enzyme removes the C- and N-terminus propeptides?

Answer 30

Procollagen peptidase enzyme

Question 31

What can degrade collagen?

Answer 31

* Collagenase enzyme * Microbial collagenase * *Clostridium* * Tissue collagenase * Tadpole tail resorption * Wound healing

Question 32

Elastin

Answer 32

* Protein in connective tissue * Important in arteries, lung, skin, bladder * Elastic and expansible * Primarily composed of Gly, Pro (Lys)

Question 33

Describe the structure of elastin

Answer 33

* Linking of soluble tropoelastin molecules * Cross-linked by H-bonds and covalent bonds * Insoluble, durable crosslinked array formed

Question 34

Synthesis of elastin

Answer 34

Begins in the cytoplasm of fibrocytes 1. Tropoelastin formation 2. Extracellular crossling formation 3. Elastin fibre production

Question 35

Degradation of elastin

Answer 35

1. Tropoelastin 2. Mature elastin + Elastase enzyme → 3. Elastin fragments

Question 36

Where is elastase formed and stored?

Answer 36

* Pancreas * Leucocytes, stored in granulocytes