Biological molecules and enzymes

Written by Dr. Hira Salman (Biology)

MDCAT · Biology · 8 questions

Name: ____________________ Date: ____________

A peptide bond joins:
- A A fatty acid and glycerol
- B Two amino acids
- C Two glucose molecules
- D Two nucleotides
Which of the following is a disaccharide?
- A Glucose
- B Sucrose
- C Fructose
- D Ribose
Enzymes speed up reactions by:
- A Increasing the amount of substrate
- B Raising the temperature of the reaction
- C Lowering the activation energy
- D Changing the final products
Which lipid is the main structural component of the plasma membrane?
- A Triglycerides
- B Phospholipids
- C Steroids only
- D Waxes
Cellulose is a polymer of:
- A Beta glucose
- B Fructose
- C Alpha glucose
- D Amino acids
The primary structure of a protein is the:
- A Folding into a 3D shape
- B Joining of several polypeptide chains
- C Alpha helix
- D Sequence of amino acids
Nucleotides in one strand of DNA are joined by:
- A Glycosidic bonds between sugars only
- B Phosphodiester bonds
- C Hydrogen bonds
- D Peptide bonds
The active site of an enzyme is the region where:
- A The substrate binds
- B The enzyme is made
- C The coenzyme is destroyed
- D The enzyme is stored

Answer key

1. B, 2. B, 3. C, 4. B, 5. A, 6. D, 7. B, 8. A

A peptide bond forms between the carboxyl group of one amino acid and the amino group of the next, releasing water.
Sucrose is made of glucose and fructose. Glucose, fructose and ribose are monosaccharides.
An enzyme gives the reaction an easier path with a lower activation energy. It is not used up and does not change the products.
Phospholipids form the bilayer of the membrane, with water-loving heads facing outward and fatty tails facing inward.
Cellulose is made of beta-glucose units joined by beta 1,4 glycosidic bonds. Starch and glycogen use alpha glucose.
The primary structure is the order of amino acids in the chain. Helices and sheets are secondary structure, and the 3D fold is tertiary.
A phosphodiester bond links the phosphate of one nucleotide to the sugar of the next, forming the backbone. Hydrogen bonds hold the two strands together.
The substrate binds to the active site, where the reaction is catalysed. Its shape fits the substrate.