BIO130H1 Lecture Notes - Lecture 4: Alpha Helix, Coiled Coil, Opioid Peptide

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18 Jan 2019
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BIO130 Lecture 4 17/01/2019
Vasopressin vs Oxytocin:
Differences in primary amino acid (AA) sequence matter
Both are 9 AA long
Neuropeptide hormones
AA sequence is identical except at 2 positions
Vasopressin controls urine production rates
Oxytocin is involved in birth, lactation and pair bonding
NOTE: the order of the AA’s is just as important as their presence
e.g. Leu-Enkephalin is a natural opioid peptide which down modulates the perception
of pain.
If you change the order of the AA sequence, the pentapeptide would have no
function in the body
The alpha helix:
Example of secondary structure
Found in skin, hair
The R groups are not involved in hydrogen bonding
Alpha helix vs DNA helix:
o Alpha helix is single stranded, whereas the DNA helix is double
stranded
o In the alpha helix, the R groups are facing outwards
o In the DNA helix, the sugar-phosphate backbone is facing outwards
and the bases are on the inside
The hydrogen bonds are happening between the amide hydrogens and the
carbonyl oxygens of two AA’s
One turn is about 3.6 AA
Forms strong, cylindrical structure
The beta sheet:
2nd type of secondary structure
Composed of 2< peptide strands
The alpha carbons are sticking up and down, giving the molecule its pleated
shape
Hydrogen bonding between carbonyl oxygens and amide hydrogens
Two types:
o Anti-parallel
o Parallel
A super secondary structure coiled coil
Amphipathic alpha helix
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