Biochemistry: Metabolism and Enzymes

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Questions and Answers

What role does NAD play in metabolic reactions?

It carries hydrogens and electrons from dehydrogenation reactions. (correct)

It acts as a catalyst for chemical reactions.

It directly converts glucose into ATP.

It serves as a substrate for phosphorylation.

What is the consequence of the bulky negative charge of the phosphate group in ATP?

It creates a strain between the last two phosphate groups, leading to energy release. (correct)

It facilitates the easy transfer of phosphate groups.

It stabilizes the molecule, making it less reactive.

It enhances the binding affinity of ATP to enzymes.

Which of the following is NOT a method of ATP generation?

Electron affinity reaction. (correct)

Oxidative phosphorylation.

Photophosphorylation.

Substrate-level phosphorylation.

Which of the following processes involves the conversion of glucose to CO2 for energy recovery?

Aerobic respiration Signup and view all the answers

What do glycolysis, Krebs cycle, and phosphorylation have in common?

They are all stages in the breakdown of glucose. Signup and view all the answers

What is the primary difference between anaerobic respiration and fermentation?

Anaerobic respiration produces more ATP than fermentation. Signup and view all the answers

Which of the following accurately describes the product yields of the Krebs cycle?

4 CO2, 6 NADH, 2 FADH2, 2 ATP Signup and view all the answers

What role do NADH and FADH2 play in the electron transport system?

They donate electrons to the ETC to facilitate ATP synthesis. Signup and view all the answers

In prokaryotic cells, where does the electron transport system primarily take place?

In the cytoplasmic membrane Signup and view all the answers

What is the terminal electron acceptor in fermentation?

Organic compounds Signup and view all the answers

What is the primary role of the apoenzyme in a holoenzyme?

To bind the substrate at the active site Signup and view all the answers

Which of the following describes the function of metallic cofactors?

They assist with precise functions between enzymes and substrates Signup and view all the answers

What distinguishes endoenzymes from exoenzymes?

Endoenzymes are produced within the cell and function within it. Signup and view all the answers

Which class of enzymes is specifically responsible for transferring functional groups from one substrate to another?

Transferases Signup and view all the answers

What is a characteristic of constitutive enzymes?

They are produced in constant amounts regardless of environmental conditions. Signup and view all the answers

How do coenzymes alter the substrate?

By transferring hydrogen atoms and chemical groups between substrates Signup and view all the answers

What role do hydrolases play in biochemical reactions?

They cleave bonds by adding water to molecules. Signup and view all the answers

What mechanism do enzymes follow for substrate interaction?

Lock and key mechanism Signup and view all the answers

What role do electrons play in metabolic processes?

They are critical for metabolic reactions. Signup and view all the answers

Which statement best describes the process of anabolism?

It synthesizes larger molecules from smaller ones using energy. Signup and view all the answers

What distinguishes catabolism from anabolism?

Catabolism breaks down larger molecules to release energy. Signup and view all the answers

How do enzymes contribute to chemical reactions?

They catalyze reactions without being consumed or altered. Signup and view all the answers

What is a holoenzyme?

A conjugated enzyme containing both protein and a non-protein molecule. Signup and view all the answers

Which of the following best describes the impact of enzymes on reaction rates?

Enzymes can increase reaction rates by up to a million times. Signup and view all the answers

What happens to an enzyme when it denatures?

It changes shape and loses its functionality. Signup and view all the answers

Which of the following is a characteristic of enzymes?

They can be reused multiple times in reactions. Signup and view all the answers

What happens during enzyme repression?

The synthesis of an enzyme is halted at some point in its pathway. Signup and view all the answers

Which statement accurately describes competitive inhibition?

An inhibitor competes with the substrate for the active site of the enzyme. Signup and view all the answers

What is the role of phosphorylating ADP in cellular processes?

To store energy in a more accessible form like ATP. Signup and view all the answers

Which type of reaction consumes energy to proceed?

Endergonic reactions Signup and view all the answers

What is the relationship between oxidation and reduction?

Oxidation and reduction occur simultaneously, with one losing and one gaining electrons. Signup and view all the answers

What triggers the induction of enzymes?

The presence of a suitable substrate. Signup and view all the answers

What is a characteristic of noncompetitive inhibition?

The active site undergoes a chemical change due to an inhibitor binding. Signup and view all the answers

Which process is essential for linking exergonic and endergonic reactions in cells?

The coupling of energy release and usage. Signup and view all the answers

Study Notes

Metabolism

Metabolism is the sum of all chemical reactions within a cell.
Metabolism is categorized as anabolism and catabolism.
Anabolism builds larger molecules from smaller ones and requires energy.
Catabolism breaks down larger molecules to release energy.

Anabolism

Anabolism is also known as biosynthesis.
It involves the synthesis of cell molecules and structures.

Catabolism

Catabolism is the opposite of anabolism.
It breaks down larger molecules to release energy.
Catabolism is related to exergonic reactions, which release energy.

Enzymes

Enzymes are catalysts that speed up chemical reactions without being consumed or becoming part of the products.
They bind to substrates and participate in changing the substrate.
Enzymes are not consumed in the reaction and can function repeatedly until they denature or are shut off.
Substrates are the molecules that enzymes interact with.
Enzymes can be simple or conjugated.
Simple enzymes consist only of protein.
Conjugated enzymes, also known as holoenzymes, contain a protein and a non-protein molecule.
The protein portion of a conjugated (holoenzyme) is called the apoenzyme.
The active site or catalytic site is where the substrate binds to the apoenzyme.
The non-protein portion of holoenzymes is called a cofactor.
Organic cofactors are called coenzymes; inorganic cofactors are metallic cofactors.
Coenzymes work with the apoenzyme to alter the substrate.
Coenzymes can carry and transfer hydrogen atoms, electrons, carbon dioxide, and amino groups.
Metallic cofactors, such as iron, copper, magnesium, zinc, cobalt, selenium, etc., assist in precise functions between the enzyme and substrate.
Metallic cofactors help bring the substrate and active site together and participate directly in chemical reactions.
Enzymes have a unique active site specific to the substrate.
Enzymes follow a lock and key mechanism.
Enzyme processes are very rapid, occurring up to 1 million times per second.
There are six classes of enzymes: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

Location of Enzymes

Exoenzymes are transported extracellularly and break down large food molecules or harmful chemicals.
Exoenzymes are made within the cell and transported out of the cell.
Endoenzymes are made within the cell and function within the cell.
Most enzymes in metabolic pathways are endoenzymes.

Enzyme Regulation

Enzymes can be constitutive or regulated.
Constitutive enzymes are present in consistent amounts regardless of the cell's environment.
Regulated enzymes can be induced or repressed in response to changes in substrate concentration.
Enzyme repression stops the further synthesis of an enzyme in its pathway.
Types of enzyme inhibition/repression:
- Competitive inhibition occurs when a molecule resembling the substrate occupies the active site, preventing the substrate from binding.
- Noncompetitive inhibition occurs when a regulatory molecule binds to a site other than the active site, chemically altering the active site.
Enzyme induction occurs when enzymes appear only when a suitable substrate is present.

Energy in Cells

Exergonic reactions release energy as they proceed forward.
Endergonic reactions require the addition of energy to proceed forward.
Exergonic and endergonic reactions are coupled together, with energy released from exergonic reactions used for endergonic reactions.
Biological oxidation is the loss of electrons; the compound losing electrons is oxidized.
Reduction is the gain of electrons; the compound gaining electrons is reduced.
A reduced molecule generally has more energy than the oxidized molecule.
Phosphorylation is the energy captured in electron carriers used to add inorganic phosphate to ADP or another compound.
Phosphorylation stores energy in high-energy molecules like ATP.
NAD (nicotinamide adenine dinucleotide) is a common electron carrier.
NAD carries hydrogens and electrons from dehydrogenation reactions.
Dehydrogenation reactions occur during redox reactions when hydrogens are removed from a compound.

ATP

ATP (adenosine triphosphate) is the universal currency for energy.
ATP is composed of adenine (nitrogenous base), ribose (5-carbon sugar), and three phosphate groups bound to ribose.
The phosphate groups have a negative charge and repel each other, causing strain that releases a lot of energy when the bonds are broken.
ATP replenishment is an ongoing cycle because it must be replaced immediately after being used in a chemical reaction.
ATP has many metabolic roles:
- Substrate-level phosphorylation: ATP generation through direct transfer of a phosphate group from a phosphorylated compound to ADP.
- Oxidative phosphorylation: a series of redox reactions occurring during the final phase of the respiratory pathway.
- Photophosphorylation: ATP formed through a series of sunlight-driven reactions in phototrophs.

Catabolic Pathways

There are three basic catabolic pathways: aerobic respiration, anaerobic respiration, and fermentation.

Glycolysis

Glycolysis is the most commonly used pathway to break down glucose.
It converts glucose to pyruvic acid and synthesizes a small amount of ATP.

Aerobic Respiration

Aerobic respiration converts glucose to CO2 and allows the cell to recover significant amounts of energy.
Aerobic Respiration uses glycolysis, the Krebs cycle, and the electron transport chain (ETC).
It yields 36-38 ATPs.
Aerobic respiration is the energy-yielding scheme for aerobic heterotrophs.

Anaerobic Respiration

Anaerobic respiration utilizes glycolysis, the Krebs cycle, and the ETC, but yields 2-36 ATPs.
Anaerobic respiration uses NO3-, SO4 2-, CO3 2-, or other oxidized compounds as the final electron acceptor.

Fermentation

Fermentation uses only glycolysis and does not require oxygen.
It yields only 2 ATP.
The end products of alcoholic fermentation are ethanol and CO2.
Alcoholic fermentation occurs in yeast or bacterial species.

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Description

Explore the fundamental concepts of metabolism, including the roles of anabolism and catabolism, in this quiz. Understand how enzymes function as catalysts in chemical reactions and their importance in biological processes. Test your knowledge on these essential biochemical principles.