Cellular Metabolism Quiz

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Questions and Answers

What is the primary end product of pyruvate metabolism in yeast under anaerobic conditions?

Lactate

Pyruvic Acid

Glucose

Carbon dioxide and ethanol (correct)

What is the role of pyruvate decarboxylase?

To convert pyruvate into carbon dioxide and ethanol (correct)

To convert glucose into ethanol

To convert glucose into pyruvate

To convert pyruvate into lactate

What is the primary function of the Cori cycle?

To prevent lactate accumulation (acidosis) in muscles during anaerobic respiration (correct)

To convert ethanol back to glucose

To directly transport pyruvate from muscle to liver

To convert glucose directly into pyruvate in the muscle

During anaerobic glycolysis in muscle cells, what molecule is produced from pyruvate and then released into the blood?

Lactate (C) Signup and view all the answers

In the Cori cycle, what transformation occurs in the liver, of the incoming lactate?

Lactate is converted to pyruvate and then glucose (B) Signup and view all the answers

What are the chemical species formed within a metabolic pathway called?

Metabolic intermediates (C) Signup and view all the answers

What is the role of metabolic enzymes in metabolic pathways?

To catalyze the reactions, and are subject to regulation according to physiological needs (C) Signup and view all the answers

What do some metabolic enzymes require to assist in their catalytic functions?

Co-enzymes (A) Signup and view all the answers

In the complete oxidation of glucose, which of the following is the initial stage?

Glycolysis (A) Signup and view all the answers

Which of the following processes directly involves the inner mitochondrial membrane?

Oxidative phosphorylation (B) Signup and view all the answers

What is the primary product of substrate-level phosphorylation?

ATP (B) Signup and view all the answers

In which cellular compartment does glycolysis occur?

Cytoplasm (A) Signup and view all the answers

What is the main function of glucose in cellular metabolism?

To produce ATP (C) Signup and view all the answers

What are the end products of the reaction where glucose and ATP are reactants?

Glucose 6-phosphate and ADP (B) Signup and view all the answers

Which metabolic process involves the breakdown of glycogen into glucose?

Glycogenolysis (D) Signup and view all the answers

In aerobic respiration, what is the intermediate molecule that pyruvate is converted into?

Acetyl CoA (A) Signup and view all the answers

Under what conditions is gluconeogenesis particularly important?

During periods of fasting or vigorous exercise (A) Signup and view all the answers

Besides the liver, which other organ plays a key role in gluconeogenesis?

Kidneys (B) Signup and view all the answers

Which of the following non-carbohydrate precursors is converted to pyruvate before going to glucose in liver during gluconeogenesis?

Lactate (A) Signup and view all the answers

What process breaks down proteins to amino acids that can be used for the formation of glucose?

Proteolysis (A) Signup and view all the answers

What is directly produced during anaerobic respiration of glucose?

Lactate (B) Signup and view all the answers

What is the primary storage form of lipids in the liver and muscle?

Triacylglycerols (D) Signup and view all the answers

During prolonged fasting, what process is stimulated in muscles to provide amino acids?

Proteolysis (B) Signup and view all the answers

In the context of lipid metabolism, where does β-oxidation of fatty acids primarily occur?

Mitochondria (A) Signup and view all the answers

What is glycerol converted to before entering glycolysis or gluconeogenesis?

Dihydroxyacetone phosphate (DHAP) (C) Signup and view all the answers

What is the primary fate of nitrogen removed from amino acids?

Converted to urea and excreted (A) Signup and view all the answers

Besides synthesis in the liver, which of these are also sources of triacylglycerol?

Adipose tissues and dietary fat (D) Signup and view all the answers

What is the product of fatty acid β-oxidation that provides energy, particularly during fasting?

Acetyl CoA (D) Signup and view all the answers

What can the carbon skeleton of amino acids contribute to after the removal of nitrogen?

TCA cycle (D) Signup and view all the answers

What physiological state promotes glycogenesis in skeletal muscle and liver?

Well-fed state (D) Signup and view all the answers

In a fasting state, which hormone's increase leads to glycogen breakdown in the liver?

Glucagon (B) Signup and view all the answers

What is the primary input for the TCA cycle?

Acetyl CoA (C) Signup and view all the answers

What happens to glucose utilization after prolonged fasting?

It decreases significantly (C) Signup and view all the answers

Which molecules are regenerated during the electron transport process?

NAD+ and FAD (C) Signup and view all the answers

Which metabolic process becomes more predominant as fasting duration increases?

Gluconeogenesis (C) Signup and view all the answers

What is the primary reason for decreased proteolysis during prolonged fasting?

Gluconeogenesis relies on glycerol (A) Signup and view all the answers

How many NADH molecules are produced in one cycle of the TCA cycle?

3 (A) Signup and view all the answers

What is the function of GTP in the TCA cycle?

Store energy (C) Signup and view all the answers

What component primarily composes fats?

Glycerol and three fatty acids (A) Signup and view all the answers

Which statement accurately describes the energy metabolism in well-fed states?

Protein synthesis is promoted (B) Signup and view all the answers

Which complex in the electron transport chain receives electrons from FADH2?

Complex II (C) Signup and view all the answers

What does the oxidation of CoQ lead to in the electron transport chain?

Reduction of cytochrome c (D) Signup and view all the answers

Which tissues primarily uptake glucose in fasting conditions?

Insulin-independent tissues (B) Signup and view all the answers

What substrate is needed for the enzyme pyruvate dehydrogenase to function?

NAD+ (D) Signup and view all the answers

What is produced as a byproduct in the conversion of pyruvate to Acetyl-CoA?

CO2 (B) Signup and view all the answers

Study Notes

Overview of the Living Cell (I)

Bioenergetics is the quantitative study of energy transformation in living cells. This includes changes in energy form, such as from light energy to chemical energy.
Cellular energy exists in two forms: potential energy (e.g., chemical bonds, concentration gradients, electrical charges) and kinetic energy (e.g., heat).
Metabolism is a series of chemical reactions within a living organism that sustain life. Metabolism involves energy flow during chemical processes.

Learning Objectives

Understand the principles of catabolism and anabolism.
Overview of the metabolisms of carbohydrates, proteins and lipids.
Recognize the role of ATP and mitochondria in the energy production processes in the human body.
Discuss the role of the liver in different metabolic processes.

Key Concepts on Metabolism

Metabolic pathways can be broadly divided into catabolism and anabolism.
Catabolism breaks down complex molecules into simpler ones, releasing energy (e.g., glycolysis, β-oxidation).
Anabolism builds complex molecules from simpler ones, storing energy (e.g., glycogenesis, protein synthesis).
Metabolic intermediates are the chemical species formed within metabolic pathways.
These reactions are catalyzed by metabolic enzymes.
Enzyme activity is regulated by physiological needs and changes.
Some metabolic enzymes require co-enzymes.

Glucose Metabolism

Glucose is the primary carbohydrate used to produce ATP (adenosine triphosphate).
Glucose oxidation happens in three stages: glycolysis, citric acid cycle, and oxidative phosphorylation.

Glycolysis

Glycolysis is the breakdown of glucose into pyruvate.
It takes place in the cytosol.
The starting molecule is glucose (1X), and the end product is pyruvate (2X).
It releases 2 ATP.
It also produces NADH (2X).

Glycolysis (complete steps)

Details about the steps of glycolysis, including enzymes involved (Hexokinase, phosphofructokinase, pyruvate kinase).
Explanation of the regulation of glycolysis, including how enzymes like hexokinase and phosphofructokinase are regulated.

Import notes of glycolysis

Glycolysis is a metabolic pathway that breaks down glucose into pyruvate, producing ATP and NADH.
Its primary function is generating energy (ATP) for other metabolic processes and the production of intermediates in cells.
It's the only metabolic pathway that happens in all body cells.
Critically important for cells without mitochondria, such as brain cells and red blood cells.
Glycolysis works under both aerobic and anaerobic conditions.

Glycolysis in anaerobic environment

Muscle cells convert pyruvate to lactic acid, regenerating NAD+.
Fermentation is a process that converts pyruvate into CO2 and ethanol in some cells, such as yeast.

Cori cycle

Lactate produced in muscles is transported to the liver.
Lactate is converted back to pyruvate and then to glucose in the liver.
The Cori cycle prevents lactate acidosis in muscles during anaerobic conditions.

Glycolysis in aerobic environment

Aerobic respiration is the breakdown of glucose to produce much more ATP, using oxygen.

Tricarboxylic acid (TCA) cycle

Pyruvate is converted to Acetyl-CoA inside mitochondria, acting as the entry point of the TCA cycle.
Acetyl-CoA undergoes an 8-step process, generating 3 NADH, 1 FADH2, 1 GTP and released CO2.

Oxidative phosphorylation (electron transport system)

Electrons from NADH and FADH2 are passed to an electron transport chain.
This generates a proton gradient across the mitochondrial inner membrane.
The proton gradient drives ATP synthesis.

Synthesis of ATP by ATP Synthase

Chemiosmosis is the movement of ions across a membrane.
The proton gradient formed by the electron transport chain drives ATP synthase to make ATP.

Comparison of energy released from glucose

Aerobic respiration yields 38 ATP per glucose molecule.
Anaerobic respiration (glycolysis) yields 8 ATP per glucose molecule.

ATP and GTP

ATP (adenosine triphosphate) and GTP (guanosine triphosphate) are energy-carrying molecules.
Hydrolysis of ATP (breaking the phosphate bonds) releases energy to drive endergonic processes.

Summary of glucose metabolism

Glucose can undergo glycolysis (anaerobic) or the aerobic pathways that include TCA cycle and oxidative phosphorylation to generate energy.

Gluconeogenesis

Gluconeogenesis is a metabolic pathway that synthesizes glucose from non-carbohydrate sources.
Important for maintaining blood glucose during fasting and exercise.
Key organs are the liver and kidneys.

Glycogenolysis

Glycogenolysis is the breakdown of glycogen into glucose.
Important for providing glucose during periods of fasting and exercise.

Glycogenesis

Glycogenesis is the synthesis of glycogen from glucose.
Important for storing glucose for later use.

Blood glucose homeostasis

Blood glucose levels are maintained at ~5 mM (3.9-7.1 mM) through the actions of insulin and glucagon.
Insulin stimulates glucose uptake, glycolysis, and glycogenesis, lowering blood glucose.
Glucagon stimulates glucose release, gluconeogenesis, and glycogenolysis - raising blood glucose.

Signaling pathways in response to insulin and glucagon

Describes how insulin and glucagon influence different metabolic processes in cells, influencing enzymes involved in glycolysis, glycogenesis and gluconeogenesis via hormones and signal pathways

Insulin actions in liver, muscle and adipose tissue

Insulin promotes glucose uptake and storage in muscles, liver and adipose tissue. It also promotes the synthesis of glycogen, proteins, lipids and inhibits gluconeogenesis.
These actions maintain blood glucose levels.

Physiological responses to energy supply (1 & 2 & 3)

Describes the body's response to different energy states.

Lipid metabolism – structure of fat

Fats are composed of glycerol and fatty acids. Triglycerides are the major storage and transport form.

Lipid metabolism

Triglycerides are broken down to glycerol and fatty acids.
Glycerol can enter glycolysis or gluconeogenesis.
Fatty acids undergo beta-oxidation in mitochondria producing Acetyl-CoA for energy.

B-oxidation of fatty acids

Describes the steps of beta-oxidation in fats to liberate energy in the form of Acetyl-CoA.

Nitrogen metabolism

Nitrogen is removed from amino acids to produce urea, an excreted product.
Amino acids contribute carbon skeletons for other metabolic pathways, such as TCA cycle
Describes the overall metabolic processes of protein catabolism to liberate energy

Example of amino acid metabolism

Shows specific pathways for the breakdown of isoleucine

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Description

Test your knowledge on cellular metabolism, including concepts like pyruvate metabolism, the Cori cycle, and the role of metabolic enzymes. This quiz covers essential processes in anaerobic glycolysis and the function of glucose in metabolism.