Biochemistry Glycolysis Overview

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Questions and Answers

Which substrate is primarily used in the TCA cycle?

Glucose

Lactate

Fatty acids

Acetyl coenzyme A (correct)

What is the primary regulatory site in glycolysis?

Glyceraldehyde-3-phosphate dehydrogenase

Hexokinase

Phosphofructokinase-1 (PFK-1) (correct)

Pyruvate Dehydrogenase

Which molecule is produced as a result of the bisphosphoglycerate shunt?

2,3-Bisphosphoglycerate (correct)

1,3-Bisphosphoglycerate

Glycerol 3-phosphate

Ethanol

Which of the following pathways is activated when ATP needs are low?

Glycolysis Signup and view all the answers

How is ATP homeostasis primarily maintained in cells?

By adjusting glycolysis based on ATP needs Signup and view all the answers

Which of the following is a source of acetyl-CoA for the TCA cycle?

Amino acids Signup and view all the answers

What role does 2,3-BPG play in red blood cells?

Inhibits oxygen binding to heme Signup and view all the answers

What is the primary function of the enzyme pyruvate dehydrogenase in cellular metabolism?

Links glycolysis to the TCA cycle Signup and view all the answers

What is the primary function of anaerobic glycolysis in tissues with limited oxygen supply?

To oxidize NADH to NAD+. Signup and view all the answers

Which of the following is a net reaction of anaerobic glycolysis?

Glucose + 2 ADP + 2 Pi → 2 lactate + 2 ATP + 2 H2O + 2 H⁺ Signup and view all the answers

What is a consequence of excess lactate in the body?

Lowering blood pH leading to lactic acidosis. Signup and view all the answers

Which tissues primarily rely on anaerobic glycolysis due to their low oxygen supply?

Skeletal muscles and kidney medulla. Signup and view all the answers

Which enzyme is responsible for converting pyruvate to lactate in anaerobic glycolysis?

Lactate dehydrogenase (LDH). Signup and view all the answers

What intermediates are generated from glycolysis that can serve as precursors for nucleotide synthesis?

Ribose 5-phosphate. Signup and view all the answers

How does the liver utilize lactate produced during anaerobic glycolysis?

Converts it into glucose via the Cori cycle. Signup and view all the answers

Which of the following is NOT a role of glycolysis in the cell?

Directly synthesizing fatty acids. Signup and view all the answers

What reaction is catalyzed by glyceraldehyde-3-phosphate dehydrogenase in glycolysis?

Conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate Signup and view all the answers

Which enzyme is responsible for the final transfer of phosphate to ADP, producing ATP and pyruvate?

Pyruvate kinase Signup and view all the answers

What is produced during the oxidation of 1,3-bisphosphoglycerate in glycolysis?

NADH Signup and view all the answers

In anaerobic metabolism, what does lactate dehydrogenase convert pyruvate into?

Lactate Signup and view all the answers

Why is NADH reoxidized during glycolysis?

To ensure a continuous supply of NAD+ Signup and view all the answers

What is the primary fate of pyruvate in the presence of oxygen?

Oxidation to acetyl CoA Signup and view all the answers

Which compound is generated from the conversion of 3-phosphoglycerate in glycolysis?

Phosphoenolpyruvate Signup and view all the answers

What distinguishes aerobic glycolysis from anaerobic glycolysis?

Aerobic glycolysis allows for complete oxidation of pyruvate to CO2 Signup and view all the answers

Study Notes

Glycolysis Overview

Aldolase catalyzes aldol cleavage, forming a covalent bond with the substrate using a lysine residue.
Each glucose molecule yields two glyceraldehyde-3-phosphate (G3P) for glycolysis.

Glyceraldehyde-3-Phosphate Oxidation

Glyceraldehyde-3-phosphate dehydrogenase converts G3P to 1,3-bisphosphoglycerate (1,3-BPG).
NAD+ is reduced to NADH during this process, involving a high-energy thioester intermediate.
The reaction creates a high-energy acyl phosphate bond, initiating substrate-level phosphorylation.

ATP Formation

1,3-BPG donates a phosphate to ADP through 3-phosphoglycerate kinase, generating ATP and 3-phosphoglycerate.
The acyl phosphate bond's energy drives ATP synthesis.

Conversion to Phosphoenolpyruvate (PEP)

3-phosphoglycerate is converted to 2-phosphoglycerate, followed by dehydration to form PEP, which possesses a high-energy enol phosphate bond.

Final ATP Generation

PEP transfers its phosphate to ADP via pyruvate kinase, producing ATP and pyruvate.
This reaction is energetically favorable and irreversible.

Oxidative Fates of Pyruvate and NADH

NADH must be reoxidized to NAD+ for glycolysis to continue, achieved via two pathways: aerobic and anaerobic.

Aerobic Pathway

Electrons are transferred to the mitochondrial electron transport chain (ETC) using shuttles and oxygen, oxidizing pyruvate to acetyl CoA for the TCA cycle.

Anaerobic Pathway

NADH is reoxidized to NAD+ by converting pyruvate to lactate through lactate dehydrogenase (LDH), diverting pyruvate from the TCA cycle.

ATP Generation Comparison

Aerobic glycolysis produces more ATP than anaerobic glycolysis, with shuttle systems facilitating NADH oxidation.

Mitochondrial Membrane Characteristics

The inner mitochondrial membrane's impermeability to NADH necessitates shuttles to transfer electrons to the ETC.

Anaerobic Glycolysis Overview

Occurs under limited oxidative capacity (e.g., in red blood cells).
Results in the net reaction: Glucose + 2 ADP + 2 Pi → 2 lactate + 2 ATP + 2 H2O + 2 H⁺.

Acid Production

Glycolysis results in pyruvic acid, which is reduced to lactic acid, dissociating into lactate and H⁺.
High lactate levels can lower blood pH, leading to lactic acidosis.

Tissues Relying on Anaerobic Glycolysis

Red and white blood cells, kidney medulla, eye tissues, and skeletal muscles utilize anaerobic glycolysis due to high glycolytic enzyme levels and low ATP demands.

Role of Anaerobic Glycolysis

Provides ATP when oxygen is scarce; eye cells rely on it to prevent opacities in structures.

Fate of Lactate

Lactate can be converted back to pyruvate in the liver, heart, and muscle; in the liver, it can contribute to gluconeogenesis (Cori cycle).

LDH Isoenzymes

LDH consists of A (muscle) and B (heart) subunits, forming various tetramers (M4, M3H1, M2H2, M1H3, H4) that play roles in lactate and pyruvate conversions.

Other Functions of Glycolysis

Generates precursors for nucleotide synthesis, produces various sugars, and synthesizes amino acids like serine and alanine.

Liver Functions

Major biosynthetic site, converting pyruvate into fatty acids and synthesizing glucose from lactate, glycerol, and amino acids (gluconeogenesis).

Bisphosphoglycerate Shunt

Converts 1,3-BPG to 2,3-BPG in red blood cells, which inhibits oxygen binding to heme and reenters glycolysis as 3-phosphoglycerate.

Regulation of Glycolysis by ATP Needs

Regulation occurs at the rate-limiting steps, mainly via PFK-1 and pyruvate dehydrogenase, ensuring proper product flow into alternative pathways.

Major Regulatory Sites

PFK-1 serves as a primary control point in glycolysis, while pyruvate dehydrogenase links glycolysis to the TCA cycle.

Regulation Mechanisms

ATP homeostasis is maintained by adjusting glycolytic activity based on cellular ATP requirements.

Tissue-Specific Isoenzymes

Isoenzymes allow glycolysis regulation to adapt to tissue-specific conditions; liver pyruvate kinase isoenzyme inhibits glycolysis during active gluconeogenesis.

TCA Cycle Overview

Produces over two-thirds of ATP from oxidized fuel sources using acetyl CoA derived from fatty acids, glucose, amino acids, acetate, and ketone bodies.
Oxidation generates CO₂ and conserves energy as NADH, FAD(2H), and GTP, with NADH and FAD(2H) donating electrons to the ETC for ATP production via oxidative phosphorylation.
Also known as the Krebs cycle, named after Sir Hans Krebs.

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Description

This quiz explores key processes in glycolysis, focusing on the roles of aldolase and glyceraldehyde-3-phosphate dehydrogenase. You will learn how these enzymes facilitate substrate-level phosphorylation and oxidation of G3P to 1,3-bisphosphoglycerate, contributing to energy production in cells.