These notes have been created for students enrolled in the BMI2601 module at the University of South Africa. It contains all of the previous examination and assignment questions and answers, both lengthy and short. This is an excellent resource for exam revision.
, BIOCHEMISTRY
LONG QUESTIONS AND ANSWERS
@sciencera. learntothink
QUESTION 1 [10]
1.1 Describe the different types of noncovalent bonds that are important
in stabilizing biomolecules. (4)
• Hydrophobic interactions– interactions between the nonpolar molecules.
• Electrostatic interactions – interaction between positive and negative
charges.
• Hydrogen bonding– formed when a hydrogen atom is bonded to a small but
highly electronegative atom.
• Van der Waals forces– weak, short range electrostatic force of attraction
between molecules.
1.2 Define the term dielectric constant. (2)
The large dielectric constant means that substances whose molecules contain
ionic bonds will tend to dissociate in water yielding solutions containing ions. This
occurs because water as a solvent opposes the electrostatic attraction between
positive and negative ions that would prevent ionic substances from dissolving
1.3 What is a strong acid and give an example of a strong acid. (2)
A strong acid, fully ionizes/dissociate completely producing high [H+] (aq) ions
from water.
1.4 Define pKa.
The pKa value of an acidic group is the pH at which the protonated and
unprotonated species are present at equal concentrations.
QUESTION 2 [18]
2.1 Define a peptide bond. (2)
A peptide bond is a type of a covalent bond that is formed between the carboxyl
group (COOH) of one amino acid and the amino group (NH2) of another amino
acid forming the sequence CONH and releasing water (H2O).
,2.2 Draw the structure of the tripeptide Val-Ser-Tyr and identify the amino acids
at the termini. (5)
2.3 Write the name of an amino acid capable of forming disulphide bridges. (1)
Cysteine
2.4 Explain why proteins have important functions within the cell and are
essential for most biological processes to take place. (10)
1. Proteins as enzymes catalyze biochemical reactions.
2. Regulatory molecules
3. Synthesis of DNA and RNA molecules
4. Protein forms antibodies and immune system elements as part of the
body’s
5. defense system that fights infections.
6. Structural make up body components, support body function, give cells
shape.
7. Movement cell or muscle movement.
8. Act as carriers and storage certain molecules.
9. Transport oxygen and allow passage across membrane or to other body
sites.
10. Hormones and signaling molecules.
11. Act as receptors.
, QUESTION 3 [17]
3.1 Explain why enzyme are classified as catalysts. (3)
Enzymes are soluble protein molecules that can speed up chemical reactions in
cells. These reactions include respiration, photosynthesis and making new
proteins. The fact that enzymes remain chemically unaltered by participating in a
biochemical reaction distinguishes catalysts from substrates. Without enzymes
life would be practically impossible. In addition, enzymes are highly specific for
substrate. For these reasons enzymes are sometimes called biological catalysts.
3.2 Distinguish between cofactors and coenzymes. (4)
Cofactor is a non-protein chemical compound that binds tightly to the enzyme,
aiding in the function of an enzyme.
Coenzyme is a small, organic, non-protein molecule that carry chemical groups
between enzymes.
3.3 Distinguish between a zymogen and a ribozyme. (2)
Zymogen, also called Proenzyme, any of a group of proteins that display no
catalytic activity but are transformed within an organism into functional enzymes,
especially those that catalyze reactions involving the breakdown of proteins such
as digestive enzymes. Zymogens are enzymes released in inactive forms,
necessary to prevent the enzymes from digesting the cells that produce them.
Ribozymes (ribonucleic acid enzymes) are RNA molecules that are capable of
catalyzing specific biochemical reactions, like the action of protein enzymes.
3.4 Describe the ways in which enzyme activity can be regulated in the cell. (8)
1. Compartmentalization/localization
2. Enzyme production and degradation
3. Irreversible or reversible covalent modification
4. Allosteric control (regulated by inhibitor or activator binding)
5. Activation owing to environmental change
6. Isozymes
7. Feedback activation or inhibition
8. Induction or repression
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