Enzymes and Metabolism Lecture Notes Review

Flashcards covering enzymes, metabolism, and related biochemical pathways.

What is the primary function of enzymes?

Enzymes act as biological catalysts, accelerating biochemical reactions by lowering activation energy without altering the reaction equilibrium.

What types of biomolecules can function as enzymes?

Proteins (majority of enzymes) and some RNA molecules (ribozymes) can act as enzymes.

What does a negative Gibbs free energy (ΔG < 0) indicate about a reaction?

A negative ΔG means the reaction is spontaneous and can occur without external energy input.

How does ATP hydrolysis contribute to cellular metabolism?

ATP hydrolysis releases energy that powers cellular processes like muscle contraction, active transport, and biosynthesis.

Describe the lock-and-key model of enzyme action.

The lock-and-key model suggests a rigid fit between the enzyme and substrate.

Describe the induced-fit model of enzyme action.

The induced-fit model describes a flexible interaction between enzyme and substrate.

How do changes in temperature affect enzyme activity?

Enzyme activity generally increases with temperature up to an optimal point, beyond which it denatures.

What role does pH play in enzyme function?

Each enzyme has an optimal pH range; deviations can lead to reduced activity or denaturation.

Why don’t enzymes alter the Gibbs free energy (ΔG) of a reaction?

Enzymes accelerate reactions but do not change the overall thermodynamics or energy difference between reactants and products.

What equation describes enzyme kinetics?

Michaelis-Menten equation

What factors influence enzyme activity?

pH and temperature, and effectors (Inhibitors / activators)

What does the Km value represent in enzyme kinetics?

The substrate concentration at half of Vmax (measure of enzyme affinity)

At very low substrate concentrations, a Michaelis Menten reaction follows which order?

first order

What is the fundamental assumption of the Michaelis-Menten equation regarding enzyme kinetics?

The Michaelis-Menten equation assumes that the enzyme-substrate complex reaches a steady state, where its formation and breakdown occur at the same rate.

Define Vmax and explain why it depends on enzyme concentration.

Vmax is the maximum reaction velocity when all enzyme active sites are occupied by substrate. It depends on enzyme concentration because more enzyme molecules lead to a higher total reaction rate.

What alternative methods can be used when Vmax cannot be directly observed?

When Vmax cannot be directly measured, alternative methods like Lineweaver-Burk plots or Eadie-Hofstee plots are used to estimate kinetic parameters.

What is the purpose of the Michaelis-Menten equation in enzyme kinetics?

The Michaelis-Menten equation describes how reaction velocity depends on substrate concentration and helps determine enzyme kinetics parameters like Vmax and Km.

What advantage does the Eadie-Hofstee plot have over the Lineweaver-Burk plot?

The Eadie-Hofstee plot avoids the error magnification of the Lineweaver-Burk plot and provides a more evenly distributed data representation.

Why is Vmax not a suitable parameter for comparing different enzymes?

Vmax depends on enzyme concentration, making it unsuitable for comparing different enzymes. Instead, enzyme-independent parameters like Kcat and specific activity are used.

What does Km represent in enzyme kinetics, and why is it considered enzyme-independent?

Km (Michaelis constant) represents substrate concentration at half Vmax and reflects enzyme-substrate affinity, independent of enzyme concentration.

Explain the concept of turnover number (Kcat) and its significance in enzyme efficiency.

Turnover number (Kcat) is the number of substrate molecules converted per second per enzyme molecule, reflecting intrinsic catalytic efficiency.

What are the two ways we can measure enzyme activity in a reaction?

Tracking substrate disappearance and measuring product formation

Why is a spectrophotometer useful in enzyme kinetics?

A spectrophotometer allows real-time monitoring of substrate or product concentration by measuring absorbance changes.

How does the Michaelis-Menten equation relate to initial rates in enzyme kinetics?

The Michaelis-Menten equation models enzyme kinetics, but initial rates must be used to avoid interference from product formation.

What are the three main types of multi-substrate enzyme mechanisms?

Ordered Ternary Complex, Random Ternary Complex, Ping-Pong Mechanism

In which form is Enzyme activity regulated?

by effectors, cooperativity, and inhibitors

How does product inhibition help regulate enzyme activity?

Product inhibition occurs when the final product of a pathway inhibits an earlier enzyme, preventing excessive accumulation.

What happens to Vmax and Km in uncompetitive inhibition?

Vmax decreases and Km decreases too.

How is rational drug design used to develop new enzyme inhibitors?

Rational drug design uses enzyme structure and computational modeling to develop inhibitors that specifically target active sites.

What are the two main types of metabolism, and how do they differ?

Catabolism – Breakdown of molecules to release energy and Anabolism – Synthesis of larger molecules using energy

How do kinases and phosphatases regulate enzyme activity through phosphorylation?

Kinases add phosphate groups, activating or deactivating proteins, and Phosphatases remove phosphate groups, reversing the effect.

What is the approximate ΔG°' for ATP hydrolysis under standard conditions?

-32 kJ/mol, but in cells, it can be as high as -50 to -75 kJ/mol due to non-standard conditions

How long does the creatine phosphate system provide energy?

~10-15 seconds

What is the net ATP yield from one molecule of glucose in glycolysis?

2 ATP (net), since 4 ATP are produced, but 2 ATP are used in the preparatory phase

What is the meaning of the term "glycolysis"?

"chopping sugar", as it involves breaking down glucose into smaller molecules

Under anaerobic conditions in muscles, what occurs to pyruvate ?

pyruvate is converted into lactate via the enzyme lactate dehydrogenase, regenerating NAD⁺ to sustain glycolysis

What are the final products of glycolysis?

2 pyruvate , 2 ATP (net gain), 2 NADH

What are the main products of the Krebs cycle per acetyl-CoA?

3 NADH, 1 FADH₂, 1 ATP (or GTP), 2 CO₂

Whats is the use of glycogenolysis in the body?

breaking down glycogen stores through glycogenolysis

What signals the release of fatty acids from adipose tissue during fasting?

Glucagon

Why do red blood cells rely exclusively on glucose for energy?

They lack mitochondria and can only metabolize glucose anaerobically.

During extended fasting, what fuel does the brain use?

Ketone bodies.

Which glycolytic step is bypassed by fructose-1,6-bisphosphatase in gluconeogenesis?

The conversion of fructose-1,6-bisphosphate to fructose-6-phosphate.

Where does gluconeogenesis primarily occur?

The liver and the kideny (cortex)

What is primarily in charge of promoting glucose storage in the body?

Insulin

Which energy molecules are required for glycogenesis?

ATP and UTP

What are the two primary products of the Pentose Phosphate Pathway (PPP)?

NADPH and ribose-5-phosphate

What is the main role of NADPH produced in the Pentose Phosphate Pathway?

To reduce oxidized glutathione and support biosynthesis