Biochemistry: Glycolysis and Energy Production

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Questions and Answers

What is the primary source of energy obtained from carbohydrates?

Fructose

Glucose (correct)

Pyruvate

Glycogen

Which of the following is NOT a direct product of the breakdown of complex carbohydrates in the diet?

Disaccharides

Glucose

Amino acids (correct)

Monosaccharides

Where does glycolysis primarily take place within a cell?

Nucleus

Golgi apparatus

Cytosol (correct)

Mitochondria

What is the name given to the process that converts glucose into pyruvate?

Glycolysis (B) Signup and view all the answers

What is the key characteristic of glycolysis?

Anaerobic process that can occur without oxygen (C) Signup and view all the answers

What is the net gain of ATP molecules produced during glycolysis?

2 (C) Signup and view all the answers

Which of the following is not a product of glycolysis?

CO2 (A) Signup and view all the answers

In the first phase of glycolysis, glucose is converted into what?

2 molecules of glyceraldehyde-3-P (C) Signup and view all the answers

Which of the following correctly describes the role of NAD+ in glycolysis?

NAD+ is reduced to NADH, carrying electrons and protons. (C) Signup and view all the answers

What is the fate of the pyruvate produced at the end of glycolysis?

It can enter the Krebs cycle for further energy production. (C) Signup and view all the answers

What is the final electron acceptor in the electron transport chain?

Oxygen (B) Signup and view all the answers

Which of the following is NOT a component of the electron transport chain?

ATP synthase (A) Signup and view all the answers

Where are the enzymes responsible for the citric acid cycle located within the mitochondria?

Matrix (C) Signup and view all the answers

What is the primary function of Coenzyme Q (UQ/CoQ) in the electron transport chain?

To act as a mobile electron carrier within the inner mitochondrial membrane (D) Signup and view all the answers

During electron transport, what happens to the oxidation-reduction potential of the electron carriers?

It decreases (B) Signup and view all the answers

Where is cytochrome c located within the mitochondria?

Inner membrane (A) Signup and view all the answers

Which molecule is directly responsible for the production of ATP in oxidative phosphorylation?

ATP synthase (B) Signup and view all the answers

What is the primary function of the electron transport chain in cellular respiration?

To convert the chemical energy of NADH and FADH2 into ATP (A) Signup and view all the answers

What is the function of Pyruvate dehydrogenase (PDH)?

To convert pyruvate into acetyl-CoA (B) Signup and view all the answers

Which of the following statements accurately describes the location of the Pyruvate dehydrogenase complex (PDC) in eukaryotic cells?

PDC is located in the mitochondria, specifically in the matrix. (B) Signup and view all the answers

What is the role of Pyruvate dehydrogenase kinase and Pyruvate dehydrogenase phosphatase in the Pyruvate dehydrogenase complex (PDC)?

They regulate the activity of the PDH enzyme by phosphorylation and dephosphorylation. (D) Signup and view all the answers

What is the main function of the Citric Acid Cycle (CAC)?

To shuffle carbon skeletons and generate reducing equivalents for later use in ATP production (A) Signup and view all the answers

What is the role of NADH and FADH2 in the Citric Acid Cycle (CAC)?

They are produced as byproducts of the CAC and later used to generate ATP in oxidative phosphorylation. (A) Signup and view all the answers

Which of the following reactions is catalyzed by isocitrate dehydrogenase in the Citric Acid Cycle (CAC)?

Oxidative decarboxylation of isocitrate to α-ketoglutarate and CO2 (A) Signup and view all the answers

Which enzyme in the Citric Acid Cycle (CAC) is responsible for the formation of citrate?

Citrate synthase (B) Signup and view all the answers

What is the role of succinate thiokinase in the Citric Acid Cycle (CAC)?

It hydrolyzes the thioester bond in succinyl-CoA to form succinate and CoA. (D) Signup and view all the answers

Which complex in the electron transport chain (ETC) directly uses succinate as a substrate?

Complex II (Succinate dehydrogenase) (C) Signup and view all the answers

Which complex in the ETC is responsible for the reduction of oxygen to water?

Complex IV (Cytochrome c oxidase) (B) Signup and view all the answers

Which of the following is NOT a prosthetic group found in Complex III (Ubiquinol-cytochrome c reductase)?

Hem a (A) Signup and view all the answers

What is the role of ubiquinone (UQ) in the ETC?

To act as a mobile electron carrier between complexes I and III (D) Signup and view all the answers

What is the direct product of the reaction catalyzed by Complex I (NADH dehydrogenase)?

Ubiquinol (UQH2) (B) Signup and view all the answers

In which direction are protons moved across the inner mitochondrial membrane during the ETC?

From the mitochondrial matrix to the intermembrane space (D) Signup and view all the answers

Which of the following is the final electron acceptor in the ETC?

Molecular oxygen (O2) (D) Signup and view all the answers

Which of the following statements accurately describes the relationship between the ETC and ATP synthesis?

The ETC provides the proton gradient that drives ATP synthesis by ATP synthase. (C) Signup and view all the answers

Which of the following is NOT a product of pyruvate dehydrogenase complex (PDC) activity?

ATP (D) Signup and view all the answers

What is the primary fate of pyruvate under anaerobic conditions in muscle cells?

Conversion to lactate (B) Signup and view all the answers

Which of the following is a correct statement about triphosphate/diphosphate?

The phosphate groups are joined to each other by multiple bonds. (B) Signup and view all the answers

What is the primary function of the citric acid cycle?

Oxidize acetyl-CoA to CO2 and H2O. (C) Signup and view all the answers

Which of the following is a reduced electron carrier generated during the citric acid cycle?

NADH (C) Signup and view all the answers

Which of the following statements about alcoholic fermentation is TRUE?

It is used in the production of beer and wine. (B) Signup and view all the answers

What is the role of NAD+ in the conversion of pyruvate to lactate?

NAD+ is reduced to NADH. (B) Signup and view all the answers

Which of the following molecules is a key intermediate in both glycolysis and gluconeogenesis?

Pyruvate (A) Signup and view all the answers

Which of the following describes the role of the pyruvate dehydrogenase complex (PDC) in the citric acid cycle?

It provides the starting molecule for the cycle, acetyl-CoA. (A) Signup and view all the answers

Why is the citric acid cycle considered a central pathway in metabolism?

It connects carbohydrate, lipid, and protein metabolism. (C) Signup and view all the answers

Study Notes

Biochemistry of Cell - Week 9 Lectures

Carbohydrates are the primary energy source in the diet.
Complex carbohydrates (disaccharides and polysaccharides) are broken down by enzymes and stomach acid into monosaccharides, primarily glucose.
Glucose is stored in the liver and muscles as glycogen until needed.
Monosaccharides can be used to build new oligo- and polysaccharides or for energy production through glycolysis.
Glycolysis is a metabolic pathway that converts glucose into pyruvate.

Glycolysis

Glycolysis occurs in the cytosol of cells.
It is primarily an anaerobic process, meaning it does not require oxygen.
The pathway is a stepwise degradation of glucose.
Glucose, a six-carbon molecule, is converted to two three-carbon molecules of pyruvate.
Glycolysis involves 10 enzyme-catalyzed steps and is also known as the Embden-Meyerhof pathway.
Glycolysis is the first metabolic pathway to be elucidated in detail, mostly by German scientists during the first half of the 20th century.

Major Pathways of Carbohydrate Metabolism

Various pathways interrelate in carbohydrate metabolism, including glycogenesis (glycogen synthesis), glycogenolysis (glycogen breakdown), the pentose phosphate pathway, gluconeogenesis (glucose synthesis), and the citric acid cycle.
These pathways determine how glucose is broken down, stored, and used for energy production as well as other metabolic functions.

Introduction to Glycolysis

Glycolysis occurs in the cytoplasm of cells.
It involves the conversion of glucose into pyruvate.
The process is anaerobic, no oxygen is needed.
The first step is the phosphorylation of glucose to form glucose-6-phosphate.
This process starts by the conversion of glucose to fructose 1, 6-bisphosphate which subsequently yields 2 molecules of triose phosphate, one molecule of glyceraldehyde-3-phosphate, and one molecule of dihydroxyacetone phosphate.
Subsequent reactions convert these to pyruvate.

Possible fates of pyruvate in glycolysis

Under aerobic conditions, pyruvate is converted to acetyl-CoA.
Pyruvate is oxidized by loss of carboxyl group as CO2, remaining two-carbon unit becomes the acetyl group of acetyl CoA.
This occurs via the pyruvate dehydrogenase (PDH), which is a multi-enzyme complex in the mitochondria.
Under anaerobic conditions, pyruvate undergoes either lactic acid fermentation or alcoholic fermentation.

The Citric Acid Cycle (CAC)

The CAC plays a central role in both catabolism (breakdown) and anabolism (building up) of macromolecules.
The cycle is also known as the Krebs cycle or the tricarboxylic acid cycle.
Some of the compounds in the cycle are organic acids with 3 carboxyl groups.
The CAC is a crucial pathway for energy production from carbohydrates, fats, and proteins.

Stages of CAC

Stage 1: Amino acids, fatty acids, and glucose can yield acetyl-CoA. Acetyl-CoA is oxidized to CO2 and H2O.
Stage 2: Acetyl-CoA enters the CAC.
Stage 3: High-energy electrons and protons from NAD+ and FAD are transferred to form NADH + H+ and FADH2. Electrons enter the electron transport chain.

Oxidative Phosphorylation

Oxidative phosphorylation is a process where energy from the electron transport chain is used to phosphorylate ADP to ATP.
Oxidative phosphorylation is tightly linked to the oxidation of NADH and FADH2 in the presence of oxygen.
Reduced coenzymes (NADH and FADH2) are oxidized, releasing the electrons and protons.
These electrons are transferred through a series of electron carriers, which pumps protons (H+) from the matrix to the intermembrane space in the mitochondria, creating a proton gradient
This proton gradient drives ATP synthesis through a protein called ATP synthase. The energy released during electron transport is used to generate a proton gradient across the inner membrane, driving ATP synthesis.

The Electron Transport Chain (ETC)

ETC is a series of electron carriers located in the inner mitochondrial membrane.
It involves the transfer of electrons from NADH and FADH2 to oxygen, yielding ATP.
It consists of four enzyme complexes, each containing various prosthetic groups.

Mitochondrial Function

Mitochondria have specific compartments where different metabolic processes occur.
Their various complexes and enzymes are related, and localized to different membranes, and spaces.

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Test your knowledge of glycolysis and energy metabolism in this quiz. Explore key concepts, processes, and components involved in carbohydrate breakdown. Ideal for students studying biochemistry or related fields.