Amino acids, protein structure, haemoglobin and collagen
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The teaching part (2 min) is free to watch. A free account opens the whole lecture: 5 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Twenty letters, endless words
- The amino acid
- Four levels of structure
Read the transcript of the teaching part
Last time
Before we start: last time, in Microscopy, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Twenty letters, endless words
Only twenty different amino acids build every protein in your body. Join them in a different order and you get an enzyme, a hormone, or the rope-like protein in your tendons. The order sets the shape, and the shape sets the job. This lesson follows that chain, using haemoglobin and collagen as examples.
The amino acid
Every amino acid has a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom and a variable R group. The R group is what makes each of the twenty different. Some R groups are hydrophobic, some are polar, some are charged. Two amino acids join by condensation. The carboxyl group of one reacts with the amino group of the next, releasing a molecule of water. The new bond is a peptide bond. A chain of many amino acids is a polypeptide.
Four levels of structure
The primary structure is the sequence of amino acids in the polypeptide, held by peptide bonds. The secondary structure is the alpha helix or beta pleated sheet, held by hydrogen bonds between the backbone groups. The tertiary structure is the three dimensional folding, held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions between R groups. The quaternary structure is two or more polypeptides combined, as in haemoglobin, which has four.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Amino acids, peptide bonds and protein structure · Haemoglobin and collagen · Amino acids, peptide bonds and protein structure · Haemoglobin and collagen.
The whole chapter: Biological Molecules, Biological Molecules.
Chapter 2: Biological molecules
- Monomers, sugars and Benedict's test 6 min
- Polysaccharides, lipids and water 6 min
- Amino acids, protein structure, haemoglobin and collagen 6 min
Also for A Level Biology 9700
Which topics come up most in A Level Biology 9700 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency, Paper 4 topic frequency.