Question

1.	Enzymes________:
	A)	convert endergonic reactions into exergonic reactions
	B)	lower the heat released in a reaction
	C)	ensure that chemical reactions are "one-way"
	D)	catalyze reactions by lowering the activation energy requirement
	E)	change the energy content of the reactants

2.	Which of the following is not true of protein structure?
	A)	proteins have hydrophobic domains composed of charged amino acids
	B)	proteins may undergo changes in conformation as part of normal function
	C)	carbohydrate chains are attached to the polypeptide backbone of many proteins
	D)	both covalent and noncovalent bonds hold a protein in its proper conformation
	E)	hydrophobic interactions are important for the stability of a protein

3.	Proton gradients across the mitchondrial inner membrane are________:
	A)	formed from the oxidation of NADH and FADH
	B)	used to transport protein into the mitochondria
	C)	used to break ATP into ADP and phosphate
	D)	formed using the energy from hydrolysis of ATP
	E)	usually quickly dissipated by uncouplers in the inner membrane

Answer 1

1. Answer: D

• Enzymes are molecules that help in catalyzing biochemical reactions, by binding substrates to their active or catalytic site by lowereing the activation enrgy.
• Rate of enzyme activity may be related using Michalis-Menten equations
• 1. Decrease in enzyme quantity: decrease in enzyme will decrease the amount of product produced (till enzyme saturation point) and absorbance will decrease.
• 2. Decrease in substrate: decrease in substrate will decrease the amount of product produced (till enzyme saturation point) and absorbance will decrease.
• 3. Increase of temperature (above optimum level for the enzyme), will eventually degrade the enzyme, thus decreasing absorbance. This may be evaluated by boiling the enzyme.
• 4. Change in pH, from the optimum value, alters enzyme activity.
• 5. Addition of inhibitor: Inhibitors, inhibit enzyme activity, resulting in decrease of absorbance number. In case of peroxidase, hydroxylamine decreases enzyme activity, indicated by decreased absorbance.

2. Answer: A

• Amino acids are monomeric unit, that are linked together to form polypeptides or proteins.
• The bonding is formed by Amine (NH₂) group of one amino acid with Carboxyl (COOH) group of other amino acid to form a covalent bond called the peptide bond.
• The R- side chain charged, uncharged, polar or non-polar, or aromatic. (A is not true).
• Secondary structures of protein are Alpha helix and Beta Pleated sheet formed by beta strands and beta turns.
• Secondary structures are stabilized by hydrogen bonds C=O of a peptide bond to the N-H of adjacent peptide bond.
• The interactions include: Hydrophobic interactions, salt bridges, hydrogen bonds, ionic interactions, Stabilized by Di-sulfide linkages.(B and D are true)
• Quaternary structure is based on spatial arrangement, or a specific geometry. Related to allosteric properties with conformational variations
• Proteins may be associated carbohydrates, like in glycoproteins. (C is true)

3. Answer: E

• The mechanism of oxidative phosphorylation occurs in mitochondria of live cells.
• Electrons are transported across various components of electron transport chain (ETC), resulting in series of oxidation-reduction reactions within the membrane bound complexes in mitochondria (complex I, II, III, IV).
• Electrons are transported across various components of electron transport chain (ETC), resulting in series of oxidation-reduction reactions. NADH and FADH2 are electron donors, their oxidation creates high concentration energy from electrons.
• This energy is used to pump proton from matrix to inter membrane space. Flow of protons creates and electrochemical gradient, which is used to generate ATP.
• In presence of uncouplers, electron transport from electron donors from NADH to oxygen continues. But protons are transported from intra-membranous space to mitochondrial matrix.
• But the proton motive force is dissipated as heat, thus, there is no ATP production.