CW7: Collagen, oestrogen receptor, and myoglobin Flashcards
What is the most abundant protein in mammals?
Collagen
What is the size and shape of collagen?
300 nm
Rod-shaped
In what structures does collagen provide tensile strength?
Skin, bone, teeth, cartilage, etc.
How many polypeptides form collagen? How many amino acids are in each polypeptide chain?
3 polypeptide chains of approx. 1000 amino acids each
What is the repeating pattern of collagen?
–(Gly-X-Y)– where X is usually proline and Y is often hydroxyproline
Why is glycine needed in the third position?
It has a small side chain (H) so allows for tight packing
How do people acquire scurvy?
Hydroxyproline (4-HyP) is formed from proline under the action of the enzyme prolyl hydoxylase
The additional –OH group allows cross-links to form between chains, adding tensile strength
Prolyl hydroxylase requires ascorbic acid (vitamin C) as a co-factor
Insufficient vitamin C means proline not converted to 4-HyP so no cross-links so weak collagen so scurvy!
What is the abbreviation for ‘oestrogen receptor’?
ER
Describe the structure and function of an oestrogen receptor.
- Regulates the response to oestrogen
- It is a soluble protein – nuclear hormone receptor
- To achieve this effect it needs two key domains:
- Ligand-binding domain (binds hormone; ligand = oestrogen)
- DNA-binding domain
What is the role of the DNA-binding domain in the oestrogen receptor?
ER binds to specific DNA sequences (oestrogen response elements)
This affects the transcription of neighbouring genes, i.e. it switches them on or off
Why is hydroxyproline required at the third position?
Prolyl hydroxilase has a preference for hydroxylating a proline where there is a glycine just to the C-terminal side of the proline (N-terminal side of glycine)
What is oestrogen and where is it produced?
Is it hydrophilic or hydrophobic?
A hormone produced in the ovaries
It is hydrophobic so can cross membranes
How does tamoxifen work?
ER is overproduces in approx. 70% of breast cancers
Tamoxifen competes for binding to ER, but cannot activate it
Why was myoglobin one of the first proteins to be studied?
It is readily available
Where in the body is myoglobin mostly found? In what type of animals is it mostly found?
It is an oxygen-storing protein in muscles, especially in diving animals
How many amino acids are in myoglobin? What is this in kDa?
152 amino acids (18 kDa)
How many subunits are in myoglobin? What is the name for this?
One – it is a monomer
What is a prosthetic group? What is myoglobin’s prosthetic group?
A compound permanently associated with a protein that contributes to the protein’s function
Mb’s prosthetic group is haem with Fe2+
Which binds oxygen: Fe2+ or Fe3+?
Fe2+ – it binds oxygen until it is oxygenated itself!
Which type of motif is common in myoglobin?
Alpha helices
Why does breathing in carbon monoxide lead to carbon monoxide poisoning and death?
CO is a poison to the system
It binds more strongly to Hb and Mb than O2 does
It is irreversible and leads to less Hb/Mb to carry oxygen so organs are starved of oxygen
What type of structure is present in a haem prosthetic group?
Porphyrin ring
Describe the haem prosthetic group.
It is a planar (flat) porphyrin ring structure with eight alpha helices (A-F, starting at the N-terminus)
What is another name for His-E7 on the haem prosthetic group?
Distal histidine
What is another name for His-F8 on the haem prosthetic group?
Proximal histidine
What is the dissociation equilibrium constant for O2 binding to myoglobin?
What is the equation for fractional saturation (Y) of myoglobin?
What is the general equation for fractional saturation (Y)?
How can the equation for the fractional saturation of myoglobin be rearranged so it is more like the Michaelis-Menten equation?
What shape is the saturation curve for myoglobin?
Hyperbolic
