biology(enzymes)
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85 Terms
Which enzymes are not proteins?
Ribozymes (RNA molecules with catalytic activity).
What is metabolism?
The sum of all chemical reactions occurring in a living organism.
What are the two types of metabolism?
Catabolism (breaks molecules down) and anabolism (builds molecules).
What is activation energy?
The minimum energy required for a reaction to occur.
How do enzymes increase reaction rate?
By lowering the activation energy.
Do enzymes change the Gibbs free energy (ΔG) of a reaction?
No
Do enzymes change the equilibrium constant of a reaction?
No. They only help equilibrium be reached faster.
What is the transition state?
The unstable, high-energy intermediate formed during a chemical reaction
How do enzymes lower activation energy?
By stabilizing the transition state
What is the active site?
The specific three-dimensional region where the substrate binds and catalysis occurs.
What determines enzyme specificity?
Shape, charge, polarity, and the arrangement of amino acid side chains in the active site.
Why is the induced-fit model more accurate?
It explains enzyme flexibility and transition-state stabilization
Why don’t enzymes change the equilibrium position of a reaction?
Because they lower the activation energy of both the forward and reverse reactions equally, speeding up both directions without changing the final equilibrium.
What is the optimum temperature for most human enzymes?
Approximately 37°C.
Does denaturation break peptide bonds?
Usually no. It disrupts secondary, tertiary, and quaternary structure while the primary structure generally remains intact.
Why does pH affect enzyme activity?
It changes the protonation (charge) of amino acid side chains, altering the active site’s shape and chemical properties.
What is the optimum pH of pepsin?
About pH 2.
What is the optimum pH of trypsin?
About pH 8
What is Vmax?
The maximum reaction rate when all enzyme active sites are occupied.
What is Km (Michaelis constant)?
The substrate concentration at which the reaction reaches half of Vmax.
What does a low Km indicate?
High affinity between enzyme and substrate.
Why can competitive inhibition be overcome?
Increasing substrate concentration increases the chance that substrate binds instead of the inhibitor.
What happens to Km during competitive inhibition?
Km increases
What happens to Vmax during competitive inhibition?
Vmax remains unchanged
Can substrate still bind during noncompetitive inhibition?
Yes, but catalysis is reduced because the enzyme’s shape or function has changed
Can noncompetitive inhibition be overcome by increasing substrate concentration?
No
What happens to Vmax during noncompetitive inhibition?
Vmax decreases.
What happens to Km during classical noncompetitive inhibition?
Km remains approximately the same.
Why does noncompetitive inhibition lower Vmax?
Because it reduces the number of functional enzyme molecules, lowering the maximum possible reaction rate.
Why does competitive inhibition increase Km?
More substrate is needed to achieve half of Vmax because the inhibitor competes for the active site.
What is allosteric regulation?
Regulation of enzyme activity by molecules binding to an allosteric site.
Can allosteric molecules activate enzymes?
Yes. Some allosteric regulators increase enzyme activity, while others decrease it.
What is feedback inhibition?
The end product of a metabolic pathway inhibits an enzyme acting earlier in the pathway.
Give an example of a rate-limiting enzyme.
Phosphofructokinase-1 (PFK-1) in glycolysis.
What is a cofactor?
non-protein substance required for an enzyme to function properly.
What are the two major types of cofactors?
Inorganic cofactors and organic cofactors (coenzymes).
Give three examples of inorganic cofactors.
Mg²⁺, Zn²⁺, Fe²⁺
What is a coenzyme?
An organic cofactor that assists enzyme activity.
Give three examples of coenzymes
NAD⁺, FAD, Coenzyme A
What is the role of NAD⁺?
It accepts electrons during oxidation-reduction reactions
What is the role of FAD?
It accepts electrons during oxidation-reduction reactions.
What is the role of Coenzyme A?
It carries acetyl groups in metabolism
What is a prosthetic group?
A cofactor that is permanently attached to an enzyme.
Difference between a coenzyme and a prosthetic group?
Coenzymes usually bind temporarily, whereas prosthetic groups remain permanently attached.
What is an apoenzyme?
The inactive protein portion of an enzyme without its required cofactor.
What is a holoenzyme?
The complete, active enzyme consisting of the apoenzyme plus its required cofactor.
Why is an apoenzyme inactive?
Because it lacks the necessary cofactor required for catalysis.
Name the six enzyme classes.
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.
Which enzyme class catalyzes oxidation-reduction reactions?
Oxidoreductases
Which enzyme class transfers functional groups?
Transferases
Which enzyme class catalyzes hydrolysis?
Hydrolases
Which enzyme class rearranges atoms within a molecule?
Isomerases
Which enzyme class joins molecules together using ATP?
Ligases
What is the substrate of amylase?
Starch
What are the products of amylase?
Maltose and shorter polysaccharides (eventually glucose after further digestion).
Where is amylase produced?
Salivary glands and pancreas
What is the substrate of pepsin?
Proteins
Where does pepsin work?
Stomach
Why does pepsin work best in the stomach?
Because its optimum pH is about 2.
What is the substrate of trypsin?
Proteins and peptides
Where does trypsin work?
Small intestine.
What activates trypsinogen into trypsin?
Enteropeptidase (enterokinase), after which trypsin can activate more trypsinogen.
What is the substrate of lipase?
Triglycerides
What are the products of lipase?
Fatty acids and glycerol (or monoglycerides plus fatty acids, depending on the lipase).
Which digestive enzymes digest nucleic acids?
Nucleases
What is a zymogen?
An inactive enzyme precursor that must be activated.
Why are digestive enzymes often secreted as zymogens?
To prevent digestion of the cells and tissues that produce them.
Give two examples of zymogens.
Pepsinogen and trypsinogen.
What reaction does catalase catalyze?
2H₂O₂ → 2H₂O + O₂
Where is catalase found?
Peroxisomes
Why is catalase essential?
It rapidly breaks down toxic hydrogen peroxide.
What is the function of ATP synthase?
Synthesizes ATP using the energy stored in a proton gradient.
Where is ATP synthase found?
Inner mitochondrial membrane and thylakoid membrane of chloroplasts.
What is the function of RuBisCO?
Catalyzes carbon fixation by adding CO₂ to RuBP in the Calvin cycle.
Why is RuBisCO considered inefficient?
It can bind O₂ instead of CO₂, causing photorespiration.
What is the function of DNA polymerase?
Synthesizes new DNA strands during DNA replication.
In which direction does DNA polymerase synthesize DNA?
5’ → 3’
What is the function of RNA polymerase?
Synthesizes RNA from a DNA template during transcription.
What is the function of DNA ligase?
Joins DNA fragments by forming phosphodiester bonds.
What are restriction enzymes?
Bacterial enzymes that cut DNA at specific recognition sequences.
What is reverse transcriptase?
An enzyme that synthesizes DNA from an RNA template.