Metabolism and Metabolic Pathways Quiz
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Questions and Answers

What is the MOST accurate description of metabolism?

  • The process of absorption through the digestive system.
  • The breakdown of large molecules in the third stage of cellular respiration.
  • The mechanical processes of breaking down food.
  • The sum of all chemical reactions occurring in cells including the interchange of matter and energy with the environment. (correct)

During the digestion process, which of the following transformations occur?

  • Amino acids to proteins
  • Monomers to polymers
  • Carbohydrates to glucose (correct)
  • Fatty acids to lipids

Which of the following correctly describes the 'absorption' phase in metabolism?

  • The chemical transformation of absorbed substances and energy within the cell.
  • The elimination of substances not incorporated into the protoplasm.
  • The process of breaking down large molecules into their monomers.
  • The passage of digested products, vitamins, minerals, and water into the organism. (correct)

What is unique about the first stage of metabolism?

<p>It breaks down large molecules into their monomers, and does not release usable energy. (A)</p> Signup and view all the answers

Which molecule is a central intermediate in the second stage of metabolism?

<p>Acetyl-CoA (C)</p> Signup and view all the answers

What is the primary function of the third phase of metabolism?

<p>To oxidize acetyl-CoA to produce water, carbon dioxide and most of the body's ATP. (D)</p> Signup and view all the answers

How does anabolism differ from catabolism?

<p>Anabolism consumes energy to build molecules; catabolism releases energy breaking them down. (A)</p> Signup and view all the answers

Which metabolic process is primarily associated with the breakdown of food molecules?

<p>Catabolism (B)</p> Signup and view all the answers

Which of the following best describes the role of an amphibolic pathway?

<p>Both catabolic and anabolic, involved in both the breakdown and synthesis of molecules. (B)</p> Signup and view all the answers

What is the primary function of catabolic pathways?

<p>To release energy by breaking down complex molecules. (A)</p> Signup and view all the answers

Which of the following is an example of an anabolic pathway?

<p>Gluconeogenesis (A)</p> Signup and view all the answers

What is the main characteristic of metabolic pathways in general?

<p>They consist on a sequence of ordered reactions. (A)</p> Signup and view all the answers

In the process of glycolysis, what is the initial substrate and final product?

<p>Initial substrate : Glucose; final product: Two pyruvate molecules. (C)</p> Signup and view all the answers

What is the net effect of glycolysis with respect to energy production?

<p>It directly produces ATP and NADH (reducing power). (D)</p> Signup and view all the answers

The cytosol is the location of which cellular pathway?

<p>Glycolysis (A)</p> Signup and view all the answers

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

<p>It directly produces ATP. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the nature of Glycolysis?

<p>It is considered to be an amphibolic pathway, with both catabolic and anabolic functions. (C)</p> Signup and view all the answers

What is the primary function of NADPH + H+ produced in the pentose phosphate pathway?

<p>To act as a reducing power for anabolic reactions and as an antioxidant in cells (B)</p> Signup and view all the answers

Which of these molecules is a main product of the non-oxidative stage of the pentose phosphate pathway?

<p>Ribose (B)</p> Signup and view all the answers

What is the initial substrate that is oxidised at the start of the Krebs Cycle?

<p>Pyruvate (D)</p> Signup and view all the answers

In which cellular compartment does the Krebs cycle primarily take place?

<p>Mitochondria (C)</p> Signup and view all the answers

Which process would be considered to be specific to prokaryotic cells?

<p>Anaerobic Respiration (B)</p> Signup and view all the answers

What term describes the Krebs cycle's ability to both consume and produce compounds?

<p>Amphibolic (D)</p> Signup and view all the answers

Which of these scientists was responsible for elucidating the metabolic reactions occurring in the Krebs cycle?

<p>Hans Krebs (A)</p> Signup and view all the answers

What is the primary function of the Krebs cycle regarding compound transformation?

<p>It consumes compounds and also produces compounds for other metabolic pathways. (B)</p> Signup and view all the answers

Which statement accurately describes the cyclical nature of the Krebs cycle?

<p>It starts and ends with the same compound, Oxalacetate. (A)</p> Signup and view all the answers

Where does glucogenolysis primarily occur within the cell?

<p>Cytosol (A)</p> Signup and view all the answers

What is the immediate product of glycogen breakdown during glucogenolysis, before it becomes glucose-6-phosphate?

<p>Glucose-1-phosphate (A)</p> Signup and view all the answers

Which of the following hormonal responses correctly describes glucogenolysis?

<p>Stimulated by glucagon, epinephrine, and inhibited by insulin. (B)</p> Signup and view all the answers

What is the primary role of UDP-glucose in glycogenesis?

<p>It is a precursor for glycogen synthesis. (C)</p> Signup and view all the answers

Which of the following best describes glycogenesis?

<p>It is the process of converting glucose into glycogen for storage. (C)</p> Signup and view all the answers

Why is glycogen important as a storage mechanism for glucose within cells?

<p>It prevents drastic changes in osmotic pressure that free glucose could cause. (C)</p> Signup and view all the answers

What is the role of oxaloacetate in the transamination reaction catalyzed by aminotransferases?

<p>It accepts an amino group, converting to aspartate. (C)</p> Signup and view all the answers

Which coenzymes are directly involved in the oxidative deamination reaction catalyzed by glutamate dehydrogenase?

<p>NAD and NADP (A)</p> Signup and view all the answers

Under what cellular conditions does glutamate dehydrogenase activity increase?

<p>High levels of ADP and GDP (B)</p> Signup and view all the answers

What is the toxic effect of high levels of NH3 in the body?

<p>It can readily cross the blood-brain barrier and cause neurological damage. (A)</p> Signup and view all the answers

Which of the following statements best describes the urea cycle?

<p>It occurs in the liver and is responsible for processing nitrogen-containing waste into urea. (B)</p> Signup and view all the answers

What is the first committed step of the urea cycle?

<p>Phosphorylation of carbamate using ATP to form carbamoyl phosphate (C)</p> Signup and view all the answers

Which type of organism excretes nitrogenous waste primarily as ammonia?

<p>Ammonotelic (C)</p> Signup and view all the answers

Which of the following is NOT a correct pairing of a nitrogen excretion type and an example of an animal that uses it?

<p>Ureotelic - Birds (B)</p> Signup and view all the answers

Which enzyme catalyzes the first committed step of the urea cycle, requiring the hydrolysis of two ATP molecules?

<p>Carbamoyl phosphate synthetase I (C)</p> Signup and view all the answers

What molecule allosterically activates carbamoyl phosphate synthetase I (CPS1)?

<p>N-acetylglutamate (A)</p> Signup and view all the answers

Which of the following molecules is formed from the condensation of carbamoyl phosphate and ornithine?

<p>Citrulline (A)</p> Signup and view all the answers

Which enzyme catalyzes the condensation of citrulline with aspartate to form argininosuccinate, using the hydrolysis of ATP?

<p>Argininosuccinate synthetase (B)</p> Signup and view all the answers

Which molecule is released when argininosuccinate is broken down by argininosuccinase?

<p>Fumarate (A)</p> Signup and view all the answers

What product is generated via the hydrolysis of arginine, in the fifth reaction of the urea cycle?

<p>Ornithine and urea (B)</p> Signup and view all the answers

How do terrestrial vertebrates primarily excrete nitrogenous waste?

<p>As urea (D)</p> Signup and view all the answers

What is a crucial purpose of metabolism in living organisms?

<p>To maintain a constant supply of energy. (D)</p> Signup and view all the answers

Flashcards

What is metabolism?

The sum of all chemical reactions occurring within cells.

What is catabolism?

The process of breaking down large molecules into smaller ones, releasing energy in the process.

What is anabolism?

The process of building large molecules from smaller ones, requiring energy.

What is digestion?

The process of converting food into absorbable compounds, such as glucose, fatty acids, and amino acids.

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What is absorption?

The passage of digested nutrients, vitamins, minerals, and water from the digestive system into the body.

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Stage 1 of metabolism

The stage in metabolism where large molecules are broken down into their monomers (building blocks).

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Stage 2 of metabolism

The stage in metabolism where monomers are further broken down into simpler molecules, converging towards acetyl-CoA.

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Stage 3 of metabolism

The stage in metabolism where acetyl-CoA is oxidized, generating ATP and releasing carbon dioxide and water.

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Energy

The ability to do work and cause change in matter. It takes various forms, like heat, light, electricity, and movement.

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Metabolic Pathway

A set of chemical reactions in a living organism that converts substances into other substances.

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Catabolic Pathways

Metabolic pathways that break down larger molecules into smaller ones, releasing energy in the process. They are often oxidative.

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Anabolic Pathways

Metabolic pathways that build up larger molecules from smaller ones, requiring energy input. They are often reductive.

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Amphibolic Pathways

Metabolic pathways that can both break down and build up molecules. These pathways are important for both energy production and the synthesis of new molecules.

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Glycolysis

The process of oxidizing glucose in order to obtain energy for the cell. It involves 10 enzymatic reactions that convert glucose into two pyruvate molecules.

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Pyruvate

An important intermediate produced during glycolysis. It can be further processed in different pathways depending on the cell's energy needs.

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Metabolic Intermediates

A set of central metabolic pathways that are involved in the synthesis, degradation, and conversion of important metabolites, including those involved in energy production.

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Krebs Cycle

A metabolic pathway occurring in mitochondria that involves a series of reactions that break down acetyl-CoA, generating ATP, NADH, and FADH2. It's crucial for energy production.

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Glycogenolysis

The breakdown of glycogen into glucose, mainly occurring in the liver and muscles. This process provides glucose for energy production when blood sugar levels are low.

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Gluconeogenesis

The synthesis of glycogen from glucose, primarily occurring in the liver. It stores glucose for later use when energy is needed.

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Glycogen

A branched polymer of glucose, acting as a storage form of glucose in the liver and muscles. It provides a readily available source of energy.

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Glucagon

A hormone that stimulates glycogenolysis in the liver, releasing glucose into the bloodstream.

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Insulin

A hormone that inhibits glycogenolysis, promoting glucose storage as glycogen.

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Glucose Regulation in the Liver

The conversion of liver glycogen into free glucose, which is released into the blood. This process is regulated by glucagon and adrenaline.

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Glycogen Phosphorylase

An enzyme that breaks down glycogen into glucose-1-phosphate, initiating glycogenolysis.

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Pentose Phosphate Pathway

An alternative pathway for glucose catabolism that produces NADPH and pentoses.

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Oxidative stage of the Pentose Phosphate Pathway

A series of enzyme-catalyzed reactions in the cytoplasm that involve the oxidation of glucose.

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Non-oxidative stage of the Pentose Phosphate Pathway

A series of enzyme-catalyzed reactions in the cytoplasm that involve the interconversion of sugars, including the production of pentoses like ribose.

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Oxidation of pyruvate to acetyl-CoA

The first stage of the Krebs Cycle, where pyruvate is converted into acetyl-CoA.

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Aerobic Respiration

Cellular respiration that requires the presence of oxygen.

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Anaerobic Respiration

Cellular respiration that doesn't require the presence of oxygen.

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Transamination

A reversible reaction that involves transferring the amino group from glutamate to oxaloacetate, resulting in aspartate and α-ketoglutarate.

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Oxidative Deamination

The removal of an amino group from glutamate, catalyzed by glutamate dehydrogenase, resulting in α-ketoglutarate and ammonia (NH3).

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NH3 Production

The primary source of NH3 in the body is from the tissues through a reaction that converts NH3 into ammonium (NH4+) by reacting with α-ketoglutarate.

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NH3 Disposal

The body's process of eliminating excess NH3.

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Urea Cycle

A metabolic cycle occurring in the liver that processes amino acids and produces urea as a waste product.

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Ammonotelic

Organisms that excrete ammonia as a primary waste product, often found in aquatic environments.

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Ureotelic

Organisms that excrete urea as a waste product, common in terrestrial animals.

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Uricotelic

Organisms that excrete uric acid as a waste product, typically found in birds and reptiles.

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What is the first step of the urea cycle?

The first step in the urea cycle. CPS1 combines ammonia, carbon dioxide, and ATP to form carbamoyl phosphate, releasing two inorganic phosphates. This reaction is regulated by N-acetylglutamate, which activates CPS1.

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What does ornithine transcarbamylase do?

This enzyme is responsible for catalyzing the second step in the urea cycle. It transfers the carbamoyl group from carbamoyl phosphate to ornithine, forming citrulline and releasing inorganic phosphate.

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What does argininosuccinate synthetase do?

The third step in the urea cycle. This enzyme combines citrulline with aspartate, forming argininosuccinate. This reaction also requires ATP and involves an intermediate called citrulil-AMP.

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What is the role of argininosuccinase?

The fourth step in the urea cycle. This enzyme breaks down argininosuccinate into arginine and fumarate. Fumarate is a key intermediate in the Krebs cycle.

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What does arginase do?

The final step in the urea cycle. This enzyme hydrolyzes arginine, releasing urea and regenerating ornithine. Ornithine is then recycled back to the mitochondria for further rounds of the cycle.

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Why is the Urea Cycle important?

It eliminates waste products and ammonia from the body. This process helps to maintain the pH balance of the blood and prevents ammonia toxicity.

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How do different organisms excrete nitrogen?

Terrestrial vertebrates excrete nitrogen mainly as urea. Fish excrete ammonia directly. Birds and reptiles excrete nitrogen as uric acid.

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Study Notes

Introduction to Metabolism

  • Metabolism is the sum of all chemical reactions in cells
  • It's a highly coordinated cellular activity with directionality
  • Involves numerous enzyme systems
  • Exchanges matter and energy with the environment

Specific Functions of Metabolism

  • Obtaining chemical energy from sunlight or food
  • Converting nutrients into cellular components
  • Assembling components into cellular macromolecules
  • Forming and degrading molecules for specialized cellular functions

Digestion

  • Transforms carbohydrates, lipids, and proteins into absorbable forms: glucose, fatty acids, and amino acids, respectively

Absorption

  • Involves the passage of digested products (along with vitamins, minerals, water) through the digestive system into the organism

Metabolic Phases

  • Absorption: Substances and energy enter the protoplasm from the environment
  • Transformation: Includes processes like secretion, digestion, assimilation, and dissimilation, where the protoplasm transforms absorbed substances and energy
  • Excretion: Removal of substances not incorporated into the protoplasm

Metabolic Stages

  • Stage 1: Breakdown of large molecules into monomers (e.g., polysaccharides to glucose, lipids to glycerol and fatty acids, proteins to amino acids). No usable energy released.
  • Stage 2: The many small molecules created in stage 1 are broken down into a few simpler molecules central to metabolism. The trend is to converge to the molecule called Acetyl CoA. A small amount of ATP is generated during this stage.
  • Stage 3: The acetyl CoA molecule is oxidized into water and carbon dioxide. Most of the energy from food is produced during this stage.

Anabolism and Catabolism

  • Anabolism: Constructive metabolic process; builds large molecules from smaller ones, consuming energy (e.g., proteins from amino acids).
  • Catabolism: Degradative metabolic process; breaks down larger molecules (from food or body reserves) into smaller ones, releasing energy, some stored in special high-energy molecules
  • Amphibolic pathways: Also called mixed pathways, they're interconversions between metabolic intermediates at the start of anabolic or the end of catabolic pathways.

Energy

  • Capacity to do work, produce changes in matter; takes forms like heat, light, electricity, and movement

Metabolic Pathways

  • Sequences of reactions involving intermediates where the product of one reaction becomes the substrate for the next.
  • Consists of a series of steps with an initial substrate and final products.
  • Examples include glycolysis
  • Includes intermediary metabolites that are crucial in synthesis, degradation, and energy conversion.

Glycolysis (or Glycolisis)

  • A metabolic pathway that oxidizes glucose to produce cellular energy
  • Consists of 10 enzymatic reactions to convert glucose to two pyruvate molecules, which can then enter further metabolic pathways
  • Function: Produces energy molecules (ATP and NADH), provides energy source for aerobic respiration and fermentation
  • Location: Cytosol
  • Characteristics: Doesn't require oxygen; glucose (6C) is the initial substrate; two Pyruvate (3C) molecules are the final products.

Pentose Phosphate Pathway

  • Alternative glucose breakdown pathway (alternative glucose catabolism).
  • Also known as the phosphogluconate pathway.
  • Glucose is oxidized, producing energy (but not as ATP), and NADPH (nicotinamide adenine dinucleotide phosphate reduced form)
  • Key location: Cytoplasm
  • Characteristics: Oxidative and reversible interconversions; more complex than glycolysis; not found in skeletal muscle.
  • Functions: Provides reducing power (NADPH) for anabolic reactions; crucial for antioxidant defense, especially in red blood cells; supplies pentoses for nucleotide and coenzyme synthesis.

Krebs Cycle (Citric Acid Cycle)

  • Oxidative pathway producing ATP and CO2.
  • Key location: Mitochondria

Glycogenolysis

  • Breakdown of glycogen (storage form of glucose) into glucose-1-phosphate, then glucose-6-phosphate
  • Enzymes involved: Glycogen phosphorylase, debranching enzyme, phosphoglucomutase
  • Hormonal regulation by glucagon and epinephrine, and inhibited by insulin
  • Maintains blood glucose levels between meals

Glycogenesis

  • Synthesis of glycogen from glucose-6-phosphate
  • Requires UDP-glucose as activated glucose form
  • Enzymes include UDP-glucose pyrophosphorylase, glycogen synthase, and branching enzyme
  • Primarily in liver and muscle, stimulated by insulin to store excess glucose

Gluconeogenesis

  • Anabolic pathway to synthesize glucose from noncarbohydrate precursors (e.g., amino acids, lactate, glycerol)
  • Primarily in liver and kidneys
  • Consumes energy (ATP and GTP)
  • Crucial in maintaining blood glucose levels during fasting

Cori Cycle

  • Cyclic flow of glucose & lactate between muscle and liver
  • Muscle utilizes glycogen and produces lactate during intense activity
  • Liver converts lactate back to glucose for reuse

Transamination

  • Transfer of an amino group from one molecule to another
  • Usually involving glutamic acid, its keto acid counterpart, pyruvate or oxaloacetate
  • Important in amino acid metabolism, often uses co-enzyme Vitamin B6

Oxidative Deamination

  • Removal of an amino group as ammonia (NH3) from a molecule, using Glutamate dehydrogenase

Urea Cycle

  • Metabolic pathway to eliminate excess nitrogen (from protein breakdown) by converting ammonia to urea
  • A series of reactions mainly in the liver, involving several enzymes and intermediates
  • Main method for mammals to eliminate nitrogen waste.

Amino Acid Classification

  • Glucogenic: Amino acids form precursors for gluconeogenesis (e.g., alanine, glycine)
  • Ketogenic: Amino acids form ketone bodies (e.g., leucine)
  • Both glucogenic and ketogenic: Can be either, depending on metabolic pathways (e.g., isoleucine, phenylalanine, threonine, tryptophan)

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Introduction to Metabolism PDF

Description

Test your knowledge on metabolism and its various stages, including digestion, absorption, and the roles of anabolic and catabolic pathways. This quiz explores key concepts such as glycolysis and metabolic intermediates, helping you understand the intricacies of metabolic processes.

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