Week 3

Question 1

How is primary structure made, what is its shape, and what bonds stabilize it?

Answer 1

Linear sequence of amino acids linked by peptide bonds; stabilized ONLY by covalent peptide bonds.

Question 2

What are the most common forms of secondary structure?

Answer 2

α-helix and β-pleated sheet.

Question 3

Which bonds stabilize secondary structure?

Answer 3

Hydrogen bonds between peptide backbone C=O and N–H groups.

Question 4

What bonds stabilize tertiary structure?

Answer 4

• Hydrogen bonds * Ionic (salt bridges) * Hydrophobic interactions * Covalent disulfide bonds (between cysteines)

Question 5

What is quaternary structure?

Answer 5

The arrangement and interaction of multiple polypeptide chains (subunits) in a protein.

Question 6

What bonds stabilize quaternary structure?

Answer 6

• Hydrophobic interactions * Ionic bonds * Hydrogen bonds * Sometimes disulfide bonds (SAME forces as tertiary structure)

Question 7

What is denaturation?

Answer 7

Loss of secondary, tertiary, and quaternary structure (unfolding) without breaking peptide bonds.

Question 8

What is renaturation?

Answer 8

Protein refolds back to functional structure after removal of denaturing agent.

Question 9

What are denaturation-causing factors?

Answer 9

Heat, pH extremes, organic solvents, urea, detergents, heavy metals.

Question 10

What are chaperones and their role?

Answer 10

Proteins that assist in proper folding and prevent aggregation (misfolding).

Question 11

What are normal prion proteins (PrPᶜ)?

Answer 11

Normal cellular proteins rich in α-helices; function in neuronal cell membrane stability.

Question 12

What are infectious prions (PrPˢᶜ)?

Answer 12

Misfolded β-sheet–rich prion isoforms that convert normal PrPᶜ into abnormal forms.

Question 13

Symptoms of Creutzfeldt–Jakob Disease (CJD)?

Answer 13

Rapid dementia, ataxia, memory loss, myoclonus, behavioral changes, fatal neurodegeneration.

Question 14

Transmission methods of CJD?

Answer 14

Sporadic, inherited mutations, contaminated surgical instruments, corneal transplants, infected food (variant CJD).

Question 15

Cure or prevention for CJD?

Answer 15

No cure. Prevention = avoiding contaminated materials; strict sterilization of surgical instruments.

Question 16

Amino acid composition of collagen?

Answer 16

Rich in glycine, proline, hydroxyproline, hydroxylysine. Repeating sequence Gly-X-Y.

Question 17

What are the three major groups of collagen types?

Answer 17

1. Fibril-forming (Type I, II, III). 2. Fibril-associated (Type IX, XII). 3. Network-forming (Type IV, VII).

Question 18

Functions of collagen?

Answer 18

Structural support → tensile strength (tendons, bone), transparency (cornea), resisting shear, ECM support.

Question 19

Collagen synthesis steps (intracellular + extracellular)?

Answer 19

Intracellular: 1. Synthesis of prepro-α chains 2. Hydroxylation of proline/lysine (requires vitamin C) 3. Glycosylation of hydroxylysine 4. Formation of procollagen triple helix Extracellular: 5. Exocytosis of procollagen 6. Cleavage → tropocollagen 7. Cross-linking via lysyl oxidase (Cu²⁺-dependent)

Question 20

What is scurvy?

Answer 20

Vitamin C deficiency → defective proline/lysine hydroxylation → unstable collagen.

Question 21

Who is at risk for scurvy?

Answer 21

Malnourished individuals, elderly, alcoholics, poor diet, people lacking fresh fruits/vegetables.

Question 22

Symptoms of scurvy?

Answer 22

Bleeding gums, bruising, poor wound healing, petechiae, cork-screw hairs, weak joints.

Question 23

Which tissues contain elastin the most?

Answer 23

Lungs, large arteries, elastic ligaments, skin.

Question 24

Amino acid composition of elastin?

Answer 24

Rich in proline and lysine, but contains little hydroxyproline or hydroxylysine.

Question 25

What is a desmosine cross-link and why is it important?

Answer 25

A cross-link formed from **4 lysine residues** (3 oxidized to allysine). It gives elastin its **elasticity and ability to stretch and recoil**.

Question 26

What is fibrillin?

Answer 26

A glycoprotein that forms **microfibril scaffolds** for elastin deposition.

Question 27

What causes Marfan syndrome?

Answer 27

Mutation in **FBN1 gene** encoding **fibrillin-1**.

Question 28

Inheritance pattern of Marfan syndrome?

Answer 28

**Autosomal dominant.**

Question 29

Symptoms of Marfan syndrome?

Answer 29

Tall stature, long limbs, arachnodactyly, hyperflexible joints, lens dislocation, aortic aneurysm/dilation.

Question 30

Most life-threatening complication of Marfan syndrome?

Answer 30

**Aortic aneurysm → aortic dissection/rupture.**

Question 31

Treatment approaches for Marfan syndrome?

Answer 31

* β-blockers (reduce aortic stress) * ARBs (losartan) * Regular cardiac imaging * Surgery for aortic dilation * Avoid high-intensity exercise