Metabolism and Bioenergetics Quiz

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Questions and Answers

What is the primary function of the pentose phosphate pathway?

To generate ATP for cellular energy

To synthesize acetyl-CoA for the Krebs cycle

To produce NADPH and pentoses (correct)

To breakdown fatty acids

Where does the pentose phosphate pathway primarily take place?

In the nucleus

In the endoplasmic reticulum

In the mitochondria

In the cytoplasm (correct)

Which of the following best describes the Krebs cycle?

A process that synthesizes glucose from non-carbohydrate precursors

A series of reactions that produce ATP and carbon dioxide (correct)

A cycle that occurs in anaerobic conditions

A pathway for oxidizing glucose to produce NADPH.

In which cellular location does the Krebs cycle occur?

In the mitochondria Signup and view all the answers

Which of these characteristics is specific to anaerobic respiration?

It occurs without the consumption of oxygen. Signup and view all the answers

Which scientist is credited with investigating the Krebs cycle?

Hans Krebs Signup and view all the answers

What is the primary role of metabolism?

To manage all chemical reactions in cells. Signup and view all the answers

What is meant by the 'amphibolic' nature of the Krebs cycle?

It is both catabolic and anabolic Signup and view all the answers

Which of the following is NOT a characteristic of the pentose phosphate pathway?

It takes place in skeletal muscle Signup and view all the answers

Which of the following statements accurately describes the function of digestion?

The transformation of complex compounds into absorbable forms. Signup and view all the answers

Which stage of metabolism directly involves the breakdown of large molecules into their monomeric subunits?

Initial breakdown of large molecules Signup and view all the answers

During which stage of metabolism is the majority of ATP produced from food?

The oxidation of acetyl-CoA. Signup and view all the answers

What is a defining characteristic of anabolism?

It utilizes simple molecules to build more complex structures. Signup and view all the answers

Which process is characterized by breaking down large molecules into smaller ones, often producing energy?

Catabolism Signup and view all the answers

What is the purpose of the 'transformation' phase of metabolism?

To change the chemical structure of absorbed substances Signup and view all the answers

During which metabolic phase do substances and energy enter the protoplasm?

Absorption Signup and view all the answers

Which statement best describes the Krebs cycle?

It’s a cyclical process that both produces and utilizes compounds. Signup and view all the answers

What is the primary initial substrate of the Krebs cycle?

Oxalacetate Signup and view all the answers

Which of the following correctly describes the process of glucogenolysis?

It's a catabolic process that releases glucose from glycogen. Signup and view all the answers

Which hormone does NOT stimulate glucogenolysis?

Insulin Signup and view all the answers

Which enzyme is NOT directly involved in glucogenolysis?

Glycogen synthase Signup and view all the answers

What is the primary function of gluconeogenesis?

To synthesize glycogen from glucose-6-phosphate Signup and view all the answers

What role does UDP-glucose play in gluconeogenesis?

It is the active form of glucose incorporated onto glycogen. Signup and view all the answers

Why is glycogen considered an important storage mechanism?

It prevents drastic changes in osmotic pressure by storing glucose. Signup and view all the answers

Which of the following is NOT a precursor for gluconeogenesis?

Leucine Signup and view all the answers

What is the main purpose of the Pentose Phosphate Pathway?

To provide precursors for the synthesis of nucleotides and NADPH. Signup and view all the answers

During intense anaerobic exercise, what compound is produced in large amounts by muscle cells, leading to the Cori cycle?

Lactate Signup and view all the answers

Which of these metabolic pathways is considered a linear pathway?

Pentose Phosphate Pathway Signup and view all the answers

Where does the majority of gluconeogenesis take place in the body?

Liver Signup and view all the answers

What is a primary role of gluconeogenesis during fasting?

To synthesize glucose from non-carbohydrate sources Signup and view all the answers

Which compound is made in the first part of the pentose phosphate pathway, from glucose?

Ribulose 5-P Signup and view all the answers

What is the primary fuel source for red blood cells?

Glucose Signup and view all the answers

What is the primary fate of lactate produced in muscle cells during the Cori cycle?

It diffuses into the bloodstream and is transported to the liver. Signup and view all the answers

Which enzyme is notably absent in muscle cells, preventing them from releasing glucose into the circulation?

Glucose-6-phosphatase Signup and view all the answers

What is one of the main purposes of the Cori cycle, particularly during intense exertion?

To prevent the build-up of lactic acid in muscle tissue. Signup and view all the answers

Which metabolic pathway is NOT directly connected to the Cori cycle?

Beta-oxidation Signup and view all the answers

During the muscle phase of the Cori cycle, how many ATP molecules are produced per glucose molecule consumed?

2 ATP Signup and view all the answers

In the liver phase of the Cori cycle, what molecule is pyruvate converted into as the first step for gluconeogenesis?

Oxaloacetate Signup and view all the answers

Which enzyme converts oxaloacetate to phosphoenolpyruvate (PEP) in the liver during gluconeogenesis?

Phosphoenolpyruvate carboxykinase (PEPCK) Signup and view all the answers

Fructose 1,6-bisphosphate is converted directly into which molecule by the enzyme fructose 1,6-bisphosphatase?

Fructose 6-phosphate Signup and view all the answers

What is the primary role of glucose 6-phosphatase in glucose metabolism?

To convert glucose 6-phosphate into free glucose. Signup and view all the answers

Which of the following is NOT a primary source of free amino acids in cells?

Direct absorption from blood plasma Signup and view all the answers

What is the role of pyridoxal phosphate in transamination reactions?

An acceptor and transporter of the amino group. Signup and view all the answers

In a transamination reaction, what happens to the original amino acid that donates its amino group?

It is converted into a ketoacid. Signup and view all the answers

Which enzyme catalyzes the transamination of glutamate with pyruvate?

ALT Signup and view all the answers

Which of the following statements about GPT/ALT is true?

It is a cytosolic enzyme. Signup and view all the answers

Where is GOT/AST found in the cell?

Both in the cytoplasm and mitochondria Signup and view all the answers

What effect does cortisol have on transaminase enzymes such as GPT/ALT and GOT/AST?

Induces their gene expression Signup and view all the answers

Study Notes

Introduction to Metabolism

Metabolism is the sum of all chemical reactions in cells.
It's a highly coordinated cellular activity with directionality and matter/energy exchange with the environment.
Specific functions include: obtaining energy from light or food, converting nutrients into cell components, assembling components into macromolecules, and forming/degrading specialized cellular molecules.

Digestion

Breaks down carbohydrates, lipids, and proteins into absorbable forms (glucose, fatty acids, amino acids).

Absorption

The absorption process moves digested products, along with vitamins, minerals, water, etc., from the digestive system into the body.

Metabolic Phases

Absorption: Substances and energy enter the cell protoplasm from the environment.
Transformation: The cell processes absorbed substances and energy, including secretion, digestion, assimilation, and dissimilation processes.
Excretion: Removal of substances not incorporated into the cell protoplasm.

Metabolic Stages

Stage 1: Large molecules are broken down into monomers (e.g., polysaccharides into glucose, lipids into glycerol and fatty acids, proteins into amino acids). This stage does not produce usable energy.
Stage 2: Monomers are further broken down into simpler molecules, a key one being acetyl CoA. A small amount of ATP (energy) is created during this stage.
Stage 3: Acetyl CoA is oxidized to water and carbon dioxide, resulting in the majority of ATP production from the food molecules.

Metabolism Divisions: Anabolism and Catabolism

Anabolism: Constructive, building large molecules from smaller ones, using energy (ATP). Used to make proteins from amino acids.
Catabolism: Degradative, breaking down large molecules from food or body stores into smaller ones, releasing energy. Energy is stored in special molecules for later use.
Amphibolic Pathways: Mixed pathways that interconvert intermediates between the start of anabolic pathways and the end of catabolic ones.

Energy

Energy is the capacity to do work. It exists as heat, light, electricity, and movement.

Metabolic Pathways

A sequence of linked chemical reactions, where the product of one reaction is the substrate for the next (e.g., glycolysis). Includes a series of reactions that convert an initial substrate to final products through a series of intermediate metabolites.

Types of Metabolic Pathways

Catabolic pathways: Oxidative pathways that release energy and reducing power, and create ATP (e.g., glycolysis, beta-oxidation).
Anabolic pathways: Reductive pathways that consume energy (ATP), and reducing power to build molecules (e.g., gluconeogenesis, Calvin cycle).
Amphibolic pathways: Mixed catabolic and anabolic pathways (e.g., Krebs cycle).

Glycolysis (Glycolysis)

The process to break down glucose for energy in cells.
10 enzymatic reactions turn glucose into two pyruvate molecules for further energy delivery or other metabolic pathways.
Produces ATP and NADH, and is involved in aerobic respiration (with oxygen) and fermentation (without oxygen).
Occurs in the cytoplasm.
Doesn't require oxygen.
Involves a 6-carbon glucose turning into two 3-carbon pyruvate molecules.

Pentose Phosphate Pathway

An alternative pathway for glucose catabolism (alternative to glycolysis).
Occurs in the cytoplasm.
Oxidizes glucose to provide reducing power (NADPH+H+) needed for anabolic processes and to act as an antioxidant in cells, primarily in red blood cells.
Also produces pentoses (ribose) needed for building nucleic acids and other important coenzymes.
Has two phases: oxidative and non-oxidative.

Krebs Cycle (Citric Acid Cycle)

A key part of cell respiration.
Occurs in the mitochondria (in cells).
Converts intermediate molecules in earlier steps into carbon dioxide and water.
Generates energy in the form of ATP and reducing power (molecules that can donate electrons). A complex route with multiple steps.

Cori Cycle

A metabolic cycle happening between muscle and liver.
During intense muscle activity, lactic acid forms from glucose, moving to the liver.
The liver converts the lactate (lactic acid) back to glucose, which returns to the muscle for energy.
Important for providing energy quickly during intense activities or low oxygen conditions.
Glucose-muscle-lactate-liver-glucose-muscle

Transamination

Transferring an amino group from an amino acid to a keto acid.
Amino acid becomes a keto acid; keto acid becomes the new amino acid.
Crucial for amino acid metabolism.
Uses a coenzyme, pyridoxal phosphate (vitamin B6).
Key amino acid donors: Glutamate, alanine, and aspartate.
Key keto acid acceptors: α-ketoglutarate, pyruvate, and oxaloacetate.

Oxidative Deamination

Removing an amino group from an amino acid, producing ammonia.
Carried out by glutamate dehydrogenase.
Part of amino acid catabolism.
The major source of ammonia in our bodies comes from this reaction.
Results in the production of ammonia and α-ketoglutarate.

Urea Cycle

Metabolic process for removing excess nitrogen from the body.
The breakdown of proteins produces ammonia; this cycle converts ammonia to urea.
Happens primarily in the liver.
Several enzymatic reactions are needed to produce urea from ammonia and other compounds.

Gluconeogenesis

The synthesis of glucose from non-carbohydrate sources (e.g. amino acids, lactate).
Crucial for maintaining blood glucose levels, especially between meals or during fasting.
Happens primarily in the liver, and partially in the kidneys.
Opposite of glycolysis (where glucose is broken down).
Involves eleven enzymatic reactions; seven are the reverse of the glycolytic pathway; four reactions are unique to gluconeogenesis.

Glycogenolysis

Breakdown of glycogen (stored glucose) to release glucose.
Important for maintaining blood glucose levels between meals.
Primarily uses the enzyme glycogen phosphorylase.

Glycogenesis

Production of glycogen from glucose.
Primarily in liver and muscles.
Key enzymes include UDP-glucose pyrophosphorylase, glycogen synthase, and glycogen branching enzymes.

Amino Acid Classification

Glucogenic amino acids: Produce intermediates used in gluconeogenesis.
Ketogenic amino acids: Produce ketone bodies.
Some amino acids can be both.
Important in metabolism due to variety of processes they enter.

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Description

Test your knowledge on key concepts of metabolism, including the pentose phosphate pathway and the Krebs cycle. This quiz covers fundamental processes of digestion, anaerobic respiration, and the role of ATP production in cellular activities.