Shown below are the sequences of two strands that are adjacent to each other in an antiparallel β-sheet.

The strands are labelled “A” and “B” and the amino acids are labelled A1-A2-A3…A8 and B1-B2-B3…B8 so that we can unambiguously refer to each amino acid.

The side chains of amino acids Asp-A3 and Lys-B6 (underlined) form a salt bridge on one face of the β-sheet.

Shown below is a ribbon representation of a protein.

Oh look, it's the same sequence again.

Suppose that an A was introduced after codon 2 but before codon 3.

Suppose also that the final nucleotide of codon 4 was deleted.

Which statement below is true?

The structure below is the phospholipid phosphatidylcholine.

Identify each labelled region.

Let's start easy with something easy.

Here's a coding strand sequence, with each codon helpfully spaced by spaces and each codon numbered by numbers and with me writing more words than are necessary as some introductory text.

Spot the stop.

Good, very good.

Let's remain with that same sequence, but crank things up a notch.

Change to a different branched amino acid. (We know which those are, right? ... Right?)

OK, so here's that same image again.

What amino acid is circled? Enter your answer as the full amino acid name. E.g. if you think it's F, then write Phenylalanine.

Note also that nitrogen is blue, oxygen is red. Carbons (in this bit) are green. No hydrogens are shown.

Here we are again, staring at an amino acid, its backbone emerging from the cartoon of the beta strand like a whale breaching the pristine seas.

What R group do you see here?

Let's make it a little trickier with this image:

Which option is the correct sequence of the three amino acids shown here, in N- to C- direction?

Take your time. Think about where you can look to work out the correct direction through the alpha helix. There's one specific location that gives you everything you need.

Here's an image from that same protein, zooming in on a beta turn and with four amino acids highlighted in ball and stick representation. I've drawn around one amino acid.

With respect to the beta turn, which statement describes the circled amino acid?