Pop quiz: alpha helices are stabilized by hydrogen bonds between the carbonyl group of residues i and the amide group of residues i+4 of the next helical turn. but the first and last turns don’t have a turn before or after them, respectively, which leaves the usual alpha-helical interactions for several residues unfulfilled. based on the hydrogen bonding requirements at the beginning of an alpha helix, which of the following amino acids do you predict is very common just before the start of a helix to stabilize the first helical turn?
a) gly
b) phe
c) ser
d) arg
e) ala

e) Ala

Explanation:

Alpha helix is a secondary structure of proteins, it is made of 3.6 aminoacids residues per turn, this structure is possible thanks to local hydrogen bonding between C=O and N-h groups. The result is a cylindrical structure with a hydrogen-bonded backbone and the outside studded with side chains.

Glycin has an -H in its side chain, this makes it a too flexible molecule, therefore it's unusual to find them in alpha-helical structures because their presence could cause the helix to deform. Large R-groups can also affect this stability, phenylalanine has a bulky aromatic side group, this discards it as a stabilizer. Serine has a hydrogen bond donor or acceptor as a side chain, due to the proximity to the main chain it competes with the main chain to form NH and CO bonds. Alanine is the most common amino acid in alpha-helix structures because it has a short and no charged R group (unlike arginine that even when it's short it has a charged R-group), this makes it flexible enough to keep the structure stabilized.

Hope you find this information useful! good luck!

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

the answer would be..

b. sucking