(Dr. Choy) (Unit A) Topic Note 4 Flashcards
What does the value of dissociation constant (K) imply?
- Low K = Ligand has high affinity for binding
- High K = Ligand has low affinity for binding
What is the shape of myoglobin?
- Single polypeptide
- 8 alpha-helices
- A single molecule of heme
What is the structure of hemoglobin?
- Four polypeptides (2 alpha subunits and 2 beta subunits)
- Four heme groups
What is myoglobin responsible for?
- Present in muscles
- Helps to distribute oxygen delivered by the bloodstream throughout muscle tissue
What is hemoglobin responsible for?
- Present in RBCs
- Binds to oxygen in the lungs
- Transports oxygen through the bloodstream and delivers to tissues
What two states does hemoglobin exist in?
- Tense (T): Deoxygenated
- Relaxed (R): Oxygenated
When initially binding to oxygen, what is hemoglobin like?
In the T-state, binds to oxygen relatively weakly
Once bound to the oxygen, what happens to the hemoglobin?
Conformation change occurs and the hemoglobin changes to R form allowing for 3 more oxygens to bind
Why does hemoglobin have a S-shaped curve?
Allows oxygen to bind tightly enough to be carried, but still loose to allow for release into the muscles
What is oxygen-binding influenced by?
- Higher concentration of CO2
- Lower pH in the tissues
- Presence of bisphosphoglycerate (BPG) in RBCs
What is the effect of pH on oxygen binding to hemoglobin known as?
Bohr Effect
What is collagen?
- Fibrous protein
- Forms very strong fibrils
- Strengthen bone, skin and basement membranes of arteries, veins and many other tissues
Is collagen one single protein?
It is a family of proteins
* Collagen I
* Collagen II
* Collagen III
* Collagen IV
How is collagen amino acid composition unusual?
All 20 amino acids are present, but:
* Rich in glycine
* High proline content
How rich in glycine is collagen?
Every third amino acid residue in the sequence is glycine
What amino acids are modified by hydroxylation in collagen?
- Many prolines, giving hydroxyproline
- Some lysines, giving hydroxylysines
How does collagen construction start?
Synthesis of an individual polypeptide
* Different lengths
* Often quite long (1000 residues)
Does the initial polypeptide of collagen have N and C terminals?
Yes, but they are later removed
* Becomes propeptides
Once the collagen chains are formed and become propeptides, what happens?
Hydroxylated in the endoplasmic reticulum
* Carried out by two different enzymes (one of them is prolyl hydroxylase)
Why the deficiency of vitamin C affect collagen formation?
The enzyme required in collagen formation - prolyl hydroxylase - requires vitamin C to be functional
After the chains are hydroxylated, what happens to collagen?
3 collagen strands assemble together
* Starts by associating at the C-terminal propeptide region
What is the initial coiled structure of collagen known as? What characteristic does it have?
Procollagen
* Has uncoiled, frayed ends
How can the 3 chains come so close together in procollagen?
- Hydrogen bonds between hydroxyl groups of hydroxyproline
- Small side chain of glycine at every third residue
