(Dr. Choy) (Unit A) Topic Note 4

Question 1

What does the value of dissociation constant (K) imply?

Answer 1

1. Low K = Ligand has high affinity for binding
2. High K = Ligand has low affinity for binding

Question 2

What is the shape of myoglobin?

Answer 2

• Single polypeptide
• 8 alpha-helices
• A single molecule of heme

Question 3

What is the structure of hemoglobin?

Answer 3

• Four polypeptides (2 alpha subunits and 2 beta subunits)
• Four heme groups

Question 4

What is myoglobin responsible for?

Answer 4

• Present in muscles
• Helps to distribute oxygen delivered by the bloodstream throughout muscle tissue

Question 5

What is hemoglobin responsible for?

Answer 5

• Present in RBCs
• Binds to oxygen in the lungs
• Transports oxygen through the bloodstream and delivers to tissues

Question 7

What two states does hemoglobin exist in?

Answer 7

1. Tense (T): Deoxygenated
2. Relaxed (R): Oxygenated

Question 8

When initially binding to oxygen, what is hemoglobin like?

Answer 8

In the T-state, binds to oxygen relatively weakly

Question 9

Once bound to the oxygen, what happens to the hemoglobin?

Answer 9

Conformation change occurs and the hemoglobin changes to R form allowing for 3 more oxygens to bind

Question 10

Why does hemoglobin have a S-shaped curve?

Answer 10

Allows oxygen to bind tightly enough to be carried, but still loose to allow for release into the muscles

Question 11

What is oxygen-binding influenced by?

Answer 11

1. Higher concentration of CO2
2. Lower pH in the tissues
3. Presence of bisphosphoglycerate (BPG) in RBCs

Question 12

What is the effect of pH on oxygen binding to hemoglobin known as?

Answer 12

Bohr Effect

Question 13

What is collagen?

Answer 13

• Fibrous protein
• Forms very strong fibrils
• Strengthen bone, skin and basement membranes of arteries, veins and many other tissues

Question 14

Is collagen one single protein?

Answer 14

It is a family of proteins
* Collagen I
* Collagen II
* Collagen III
* Collagen IV

Question 15

How is collagen amino acid composition unusual?

Answer 15

All 20 amino acids are present, but:
* Rich in glycine
* High proline content

Question 16

How rich in glycine is collagen?

Answer 16

Every third amino acid residue in the sequence is glycine

Question 17

What amino acids are modified by hydroxylation in collagen?

Answer 17

• Many prolines, giving hydroxyproline
• Some lysines, giving hydroxylysines

Question 18

How does collagen construction start?

Answer 18

Synthesis of an individual polypeptide
* Different lengths
* Often quite long (1000 residues)

Question 19

Does the initial polypeptide of collagen have N and C terminals?

Answer 19

Yes, but they are later removed
* Becomes propeptides

Question 20

Once the collagen chains are formed and become propeptides, what happens?

Answer 20

Hydroxylated in the endoplasmic reticulum
* Carried out by two different enzymes (one of them is prolyl hydroxylase)

Question 21

Why the deficiency of vitamin C affect collagen formation?

Answer 21

The enzyme required in collagen formation - prolyl hydroxylase - requires vitamin C to be functional

Question 22

After the chains are hydroxylated, what happens to collagen?

Answer 22

3 collagen strands assemble together
* Starts by associating at the C-terminal propeptide region

Question 23

What is the initial coiled structure of collagen known as? What characteristic does it have?

Answer 23

Procollagen
* Has uncoiled, frayed ends

Question 24

How can the 3 chains come so close together in procollagen?

Answer 24

1. Hydrogen bonds between hydroxyl groups of hydroxyproline
2. Small side chain of glycine at every third residue

Question 25

Does collagen form an alpha helix structure?

Answer 25

No, it forms a much more extended helical conformation

Question 26

Why are hydroxylysine residues necessary?

Answer 26

Sites of sugar addition that increase solubility

Question 27

What are sites of sugar addition known as?

Answer 27

Glycosylation

Question 28

What does lysyl oxidase do?

Answer 28

Modifies lysine to form allysine

Question 29

What does allysine do?

Answer 29

Participates in cross-linking reactions that create covalent bonds between collagen chains

Question 30

How is procollagen modified to have only the triple-stranded rope part?

Answer 30

Propeptides are trimmed off by specific proteases to leave only the triple-stranded rope part

Question 31

What is the trimmed procollagen known as?

Answer 31

Tropocollagen

Question 32

How does the collagen fibrils form?

Answer 32

Tropocollagen molecule assembles into ordered polymers

Question 33

Why is the final collagen fiber extremely strong?

Answer 33

Covalent crosslinks are formed between neighboring molecules