Enzymes: Structure and Function

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Questions and Answers

What is the product of pyruvate in lactic acid fermentation?

Oxygen

Acetic Acid

Ethanol

Lactic Acid (correct)

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

2 ATP (correct)

0 ATP

1 ATP

4 ATP

Which of the following describes oxidation in cellular respiration?

Conversion of glucose to lactic acid

Creation of ATP

Loss of electrons (correct)

Gain of protons

What role do NAD⁺ and FAD serve in cellular respiration?

They transport high-energy electrons. Signup and view all the answers

How do photosynthesis and cellular respiration connect in the ecosystem?

Photosynthesis consumes CO₂ while respiration produces CO₂. Signup and view all the answers

What effect does excessive heat have on enzymes?

Causes denaturation. Signup and view all the answers

Which pH range is optimal for the enzyme amylase?

6.7-7.0 Signup and view all the answers

What role do cofactors and coenzymes play in enzyme activity?

They are non-protein molecules that assist enzymes. Signup and view all the answers

What type of inhibitor binds to the active site of an enzyme?

Competitive inhibitor Signup and view all the answers

Which enzyme has an optimal pH of 8.0?

Lipase Signup and view all the answers

What is the primary role of peroxisomes in plants?

Manage photorespiration Signup and view all the answers

Which factor does NOT significantly affect enzyme activity?

Substrate color Signup and view all the answers

What is the main consequence of a lack of oxygen in cellular respiration?

Shift to anaerobic respiration Signup and view all the answers

What is the function of the enzyme lactase?

Break down lactose into glucose and galactose. Signup and view all the answers

Which process results in a higher yield of ATP?

Aerobic respiration Signup and view all the answers

What is a major consequence of enzyme denaturation?

Loss of biological activity. Signup and view all the answers

What are the primary inputs for aerobic cellular respiration?

Oxygen and glucose Signup and view all the answers

During glycolysis, glucose is split into which molecules?

Two molecules of pyruvate Signup and view all the answers

Why is ATP often likened to a rechargeable battery?

It can be converted back to ADP to release energy Signup and view all the answers

What by-products are produced during anaerobic respiration?

Lactic acid or ethanol Signup and view all the answers

What is the primary function of enzymes in biochemical reactions?

To act as biological catalysts that lower activation energy Signup and view all the answers

What is the effect of breathing on cellular respiration?

Supplies oxygen and removes carbon dioxide Signup and view all the answers

Which model describes the precise fit between an enzyme and its substrate?

Lock-and-Key Model Signup and view all the answers

What role does the active site of an enzyme play?

It facilitates the binding of the substrate Signup and view all the answers

In the enzymatic reaction catalyzed by amylase, what is the substrate?

Starch Signup and view all the answers

What happens to an enzyme after it catalyzes a reaction?

It returns to its original state, ready for another reaction Signup and view all the answers

How do enzymes effectively lower the activation energy?

By weakening the chemical bonds of substrates Signup and view all the answers

What characteristic of enzymes ensures they are highly specific for their substrates?

The shape and chemical properties of the active site Signup and view all the answers

Why are enzymes often given names ending in "-ase"?

To signify that they are catalysts for biochemical reactions Signup and view all the answers

What are the final products of glycolysis?

2 ATP, 2 NADH, 2 pyruvate, 2 water Signup and view all the answers

During pyruvate oxidation, which molecule is produced in addition to acetyl-CoA?

NADH Signup and view all the answers

What is produced for each turn of the citric acid cycle from one acetyl-CoA?

3 NADH, 1 FADH₂, 1 ATP, 2 CO₂ Signup and view all the answers

What is the primary function of the electron transport chain (ETC)?

To generate ATP using a proton gradient Signup and view all the answers

In the citric acid cycle, what does oxaloacetate combine with to initiate the cycle?

Acetyl-CoA Signup and view all the answers

What happens to the electrons as they move through the ETC?

They release energy to pump H⁺ ions Signup and view all the answers

What is the net ATP yield from glycolysis after accounting for consumed ATP?

2 ATP Signup and view all the answers

Which of the following is NOT a product of pyruvate oxidation?

FADH₂ Signup and view all the answers

Study Notes

Enzymes

Enzymes are proteins that act as biological catalysts, speeding up chemical reactions by lowering the activation energy.
Enzyme structure is tertiary or quaternary, creating a specific shape crucial for function.
Enzymes are highly specific for their substrates.
Enzymes are reusable, not consumed in reactions.
Enzyme names often end in "-ase" (e.g., lactase, sucrase).

Key Definitions in Enzymes and Reactions

Substrate: The reactant on which an enzyme acts. It binds to the enzyme's active site.
- Example: Starch in the reaction catalyzed by amylase.
Product: The molecule(s) formed after an enzyme catalyzes a reaction.
- Example: Maltose and other sugars are products when amylase breaks down starch.
Active Site: The specific region on an enzyme where the substrate binds. Its shape and chemical properties match the substrate, enabling specific function.
- It facilitates substrate conversion to product by lowering activation energy.

How Enzymes Work

Enzyme-Substrate Interaction: The enzyme binds to the specific substrate at its active site to form an enzyme-substrate complex.
Catalysis: Enzymes weaken substrate bonds, reducing required activation energy and speeding up reactions.
Product Formation: The enzyme releases the products and returns to its original state, ready for another reaction.

Enzyme Mechanism Explained

Lock-and-Key Model: Enzymes and substrates fit together precisely.
Induced Fit Model: The enzyme changes shape slightly to better accommodate the substrate, leading to enhanced efficiency.

Factors Affecting Enzyme Activity

Temperature: Optimal temperature for most human enzymes is 37°C (body temperature)
- High heat denatures enzymes.
pH Levels: Most enzymes work best at neutral pH (6-8). Extreme pH values cause denaturation.
Ionic Concentration: High salt concentrations disrupt enzyme functions.
Cofactors and Coenzymes: Non-protein molecules that assist enzymes.
- Cofactors: Inorganic ions (e.g., zinc, iron).
- Coenzymes: Organic molecules (e.g., vitamins).
Inhibitors: Molecules that bind to the enzyme and reduce its activity.
- Competitive Inhibitors: Bind to the active site, blocking substrate binding.
- Non-Competitive Inhibitors: Bind elsewhere on the enzyme, altering its shape and functionality.

Optimal pH Levels for Common Enzymes

Different enzymes have optimal pH levels for maximum activity.

Comparison of Catalase in Animals vs. Plants

Similarities: Found in peroxisomes, break down hydrogen peroxide into water and oxygen.
Differences: Plants: involved in photorespiration. Animals: detoxify hydrogen peroxide primarily in high-energy tissues (e.g., liver)

Cellular Respiration

Cellular respiration breaks down glucose to release energy, producing ATP.
Breathing supplies oxygen for aerobic respiration. Without oxygen, fermentation occurs, releasing less energy.
Aerobic Respiration: Requires oxygen, high ATP yield.
Anaerobic Respiration/Fermentation: Occurs without oxygen, lower ATP yield, produces byproducts like lactic acid or ethanol.
General Overview: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP (36-38)
Reactants: Glucose and oxygen.
Products: Carbon dioxide, water and ATP (energy).
ATP Importance: ATP powers cellular processes like active transport and muscle contraction.

Stages of Cellular Respiration in Detail

Glycolysis: Initial breakdown of glucose in the cytoplasm, producing ATP, NADH and pyruvate.
Pyruvate Oxidation (Link Reaction): Pyruvate is converted into Acetyl-CoA in the mitochondrial matrix, releasing CO2 and producing NADH.
Citric Acid Cycle (Krebs Cycle): Acetyl CoA is further broken down in the mitochondrial matrix, releasing CO2, producing NADH, FADH2, and ATP.
Electron Transport Chain (ETC) and Oxidative Phosphorylation: High-energy electrons carried by NADH and FADH2 are passed through a chain of proteins in the inner mitochondrial membrane, creating a proton gradient. ATP is generated through chemiosmosis as protons flow back into the matrix.

Fermentation

Lactic Acid Fermentation: Pyruvate is converted into lactic acid in muscle cells during low oxygen conditions.
Alcoholic Fermentation: Pyruvate is converted to ethanol and CO2 in some microorganisms.

Redox Reactions

Cellular Respiration: Involves redox reactions (oxidation and reduction). Oxidation leads to the loss of electrons, reduction entails gaining of electrons.
Electron Carriers: NAD+ → NADH and FAD → FADH2 transport high energy electrons to the electron transport chain.

ATP Yield Summary

Glycolysis: 2 ATP.
Pyruvate Oxidation: 2 NADH.
Citric Acid Cycle: 2 ATP, 6 NADH, 2 FADH2.
Electron Transport and Oxidative Phosphorylation: ~28-32 ATP.

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Description

Explore the fascinating world of enzymes, the biological catalysts that speed up chemical reactions. This quiz covers key definitions like substrate, product, and active site, highlighting the importance of enzyme specificity and structure. Test your understanding of how enzymes function and their role in biological processes.