IB Docs (2) Team MC test: Proteins & enzymes
Multiple choice test on B.2 Proteins & enzymes
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. As this relates to a sub-topic on the options you may need access to the IB data booklet.
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
Which best explains why 2-amino acids are solids at room temperature and soluble in water?
2-amino acids exist as zwitterions, H3N+CHRCOO−, in the solid state and as ions in solution.
Which is a 2-amino acid?
2-amino acids have the amino group and the carboxyl group both bonded to the same carbon atom.
What will be the formula of serine in a solution with a pH of 7.0?
The isoelectric point of serine (from Section 33 in the data booklet) is 5.7. At pH values above this the carboxylic acid group will dissociate to lose a proton and form the carboxylate ion.
How many different tripeptides exist that contain the residues from glycine, serine and threonine after they have condensed together?
The six are: H2N−ser−thr−gly−COOH, H2N−ser−gly−thr−COOH, H2N−thr−ser−gly−COOH, H2N−thr−gly−ser−COOH, H2N−gly−thr−ser−COOH and H2N−gly−ser−thr−COOH.
Some proteins fold in a sheet-like manner known as β-pleated sheet. Which level describes this type of folding?
The secondary structure describes the folding of the chain of 2-amino acids due to intramolecular hydrogen bonding.
Which level describes the sequence of 2-amino acids in the protein chain?
The strict sequence of 2-amino acids in the protein chain(s) is known as the primary structure, e.g. −ser−his−glu−ala−ala−leu−his−tyr− etc.
What is the main type of interaction that may occur between a cysteine residue in one part of a protein with a cysteine residue in another part of the protein chain.
Cysteine contains −SH and can undergo oxidation to form an −S−S− bond between the two residues, which is known as a disulfide bridge.
Which is a globular protein
Keratin, collagen and elastin are all fibrous proteins and have mainly structural roles. Hemoglobin is more spherical in shape and because the hydrophobic side chains in globular proteins tend to be concentrated more in the centre of the structure rather than on the outside, it is soluble in water to some extent.
Which factors can affect the activity of enzymes?
I. pH
II. temperature
III. the presence of heavy metal ions
pH and an increase in temperature can alter the structure of the enzyme and heavy metal ions can poison the enzyme by reacting with the −SH groups in cysteine residues.
Which explains why the rate of an enzyme-catalysed reaction reaches a maximum at a certain substrate concentration?
Enzymes function by providing an active site to enable the substrate particles to react via a pathway with a lower activation energy than the non-catalysed reaction. Once all the active sites are occupied the enzyme becomes saturated and is working at its maximum rate.
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