proteins sl & hl

Question 1

Generalized structure of an amino acid
- Students should be able to draw a diagram of a generalized amino acid showing the alpha carbon atom with amine group, carboxyl group, R-group and hydrogen attached.

Question 2

Condensation reactions forming dipeptides and longer chains of amino acids
- Students should be able to write the word equation for this reaction and draw a generalized dipeptide after modelling the reaction with molecular models.

Question 3

Dietary requirements for amino acids
- Essential amino acids cannot be synthesized and must be obtained from food. Non-essential amino acids can be made from other amino acids. Students are not required to give examples of essential and non- essential amino acids. Vegan diets require attention to ensure essential amino acids are consumed.

Question 4

Infinite variety of possible peptide chains
- Include the ideas that 20 amino acids are coded for in the genetic code, that peptide chains can have any number of amino acids, from a few to thousands, and that amino acids can be in any order. Students should be familiar with examples of polypeptides.

Answer 4

• The amino acid sequence of each polypeptide is stored in a coded form in the base sequence of a gene.
• Amino acids are added one by one to form a polypeptide. They are always added in the same sequence to make a particular polypeptide
• Depending on the type of amino acid used – each with a specific characteristic according to their R-groups - will cause an interaction within the amino acid sequence, and therefore a specific three dimensional constellation.
• Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.
• Most polypeptides consist of between 50 and 1000 amino acids.

Question 5

Effect of pH and temperature on protein structure
- Include the term “denaturation”.

Question 6

Chemical diversity in the R-groups of amino acids as a basis for the immense diversity in protein form and function
Students are not required to give specific examples of R-groups. However, students should understand that R-groups determine the properties of assembled polypeptides. Students should appreciate that R-groups are hydrophobic or hydrophilic and that hydrophilic R-groups are polar or charged, acidic or basic.

Question 7

Impact of primary structure on the conformation of proteins
Students should understand that the sequence of amino acids determines the three-dimensional shape of proteins and the precise position of each amino acid within a structure. Proteins therefore have precise, predictable and repeatable structures, despite their complexity.

Question 8

Pleating and coiling of secondary structure of proteins
Include hydrogen bonding in regular positions to stabilize alpha helices and beta-pleated sheets.

Question 9

Dependence of tertiary structure on hydrogen bonds, ionic bonds, disulfide covalent bonds and hydrophobic interactions
Students are not required to name examples of amino acids that participate in these types of bonding, apart from pairs of cysteines forming disulfide bonds. Students should understand that amine and carboxyl groups in R-groups can become positively or negatively charged by binding or dissociation of hydrogen ions and that they can then participate in ionic bonding.

Question 10

Effect of polar and non-polar amino acids on tertiary structure of proteins
In proteins that are soluble in water, hydrophobic amino acids are clustered in the core of globular proteins. Integral proteins have regions with hydrophobic amino acids, helping them to embed in membranes.

Question 11

Quaternary structure of non-conjugated and conjugated proteins
Include insulin and collagen as examples of non-conjugated proteins and haemoglobin as an example of a conjugated protein.