Bioenergetics and Redox Reactions

Questions and Answers

Reduction refers to the loss of electrons.

False

ATP is used in ligation reactions to break bonds between molecules.

False

Glycolysis includes an isomerization reaction that converts glucose-6-phosphate to fructose-6-phosphate.

True

Carbohydrates and fats release energy when they are reduced during metabolism.

False Signup and view all the answers

Monosaccharides are classified as long chains of sugar units.

False Signup and view all the answers

Fructose metabolism primarily occurs in the kidneys.

False Signup and view all the answers

Glyceraldehyde-3-phosphate can enter glycolysis after glyceraldehyde is phosphorylated.

True Signup and view all the answers

Galactose is converted directly to glucose without any intermediate forms.

False Signup and view all the answers

Sucrose is composed of glucose and maltose.

False Signup and view all the answers

Lactose intolerance occurs due to a deficiency in lactase.

True Signup and view all the answers

Study Notes

Redox Reactions

Reduction involves a gain of electrons, crucial for energy transfer in processes such as cellular respiration.
Cellular respiration transfers electrons from nutrients like glucose to oxygen, producing ATP.

Types of Reactions

Ligation Reactions: Use ATP to form bonds between molecules; example includes the synthesis of oxaloacetate from pyruvate and CO2.
Isomerization Reactions: Rearrange atoms within a molecule; in glycolysis, glucose-6-phosphate is converted to fructose-6-phosphate.
Group Transfer Reactions: Transfer a chemical group; phosphorylation is a common example.
Hydrolytic Reactions: Use water to break bonds, such as converting peptides into amino acids or ATP into ADP.

Oxidation States of Carbon

Carbon’s oxidation state varies with the number of electrons it has; more reduced carbons (like hydrocarbons) store more energy.
Nutrient oxidation releases energy, which is converted into ATP by cells.

High-Energy Compounds

Beyond ATP, creatine phosphate, acetyl-CoA, and NADH are vital for energy storage and transfer.
Creatine phosphate acts as an energy reserve in muscles; acetyl-CoA is crucial in many metabolic pathways.
NADH and FADH2 function as electron carriers in oxidative phosphorylation.

Carbohydrates Overview

Carbohydrates serve as energy sources, structural components, and signaling molecules.
Types include:
- Monosaccharides: Single sugar units (e.g., glucose, fructose).
- Disaccharides: Two sugar units (e.g., sucrose, lactose).
- Oligosaccharides: Chains of 3-10 monosaccharides.
- Polysaccharides: Long chains (e.g., starch, glycogen).

Fructose Metabolism

Primarily occurs in the liver.
Key steps include:
- Phosphorylation by fructokinase to form fructose-1-phosphate.
- Cleavage by aldolase B into glyceraldehyde and DHAP.
- Glyceraldehyde conversion to glyceraldehyde-3-phosphate for glycolysis.
Excessive fructose intake can lead to metabolic disorders like fructose intolerance.

Galactose Metabolism

Also metabolized in the liver.
Steps include:
- Phosphorylation to form galactose-1-phosphate.
- Conversion to UDP-galactose via specific enzymes.
- UDP-galactose to UDP-glucose for further metabolism.
Galactosemia, a genetic disorder, results from deficiencies in processing galactose, leading to severe health issues.

Disaccharide Metabolism

Composed of two monosaccharide units; primary types include sucrose, lactose, and maltose.
Key hydrolysis reactions convert these into monosaccharides:
- Sucrose produces glucose and fructose.
- Lactose yields glucose and galactose.
- Maltose generates glucose.
Lactose intolerance stems from lactase deficiency, impacting digestion.

Ribose-5-Phosphate Interconversion

Involves enzymes like transketolase and transaldolase.
Important for producing sugars that integrate into glycolysis and gluconeogenesis.

Functions of NADPH

Acts as a reducing agent in biosynthesis and detoxification:
- Supports fatty acid, cholesterol, and nucleic acid synthesis.
- Reduces reactive oxygen species (ROS) and aids drug detoxification.
- Generates ROS in immune cells for pathogen destruction.

Regulation of the Pentose Phosphate Pathway (PPP)

Regulation occurs by substrate availability and enzyme activity.
Glucose-6-Phosphate Dehydrogenase (G6PD) is the rate-limiting enzyme, activated by NADP+ and inhibited by NADPH.

Clinical Relevance of the Pentose Phosphate Pathway

G6PD Deficiency can lead to oxidative stress and hemolytic anemia.
Increased PPP activity in tumor cells supports growth by providing NADPH.
Altered PPP activity can influence glucose metabolism in diabetes.

Glycosaminoglycans (GAGs)

Long, unbranched polysaccharides made of repeating disaccharides.
Important for extracellular matrix and connective tissues.
Key GAGs include:
- Hyaluronic Acid: Lubricates and provides shock absorption.
- Chondroitin Sulfate: Offers tensile strength to cartilage.
- Heparin: Acts as an anticoagulant.

Proteoglycans

Glycoproteins with GAGs attached to a core protein, essential for tissue structure and function.
Provide support, modulate cell interactions, and regulate growth factors.

Glycoproteins

Proteins with oligosaccharide chains, involved in various biological functions:
- Mediate cell recognition and immune responses.
- Integral for hormone and enzyme stability.

Glycosylation

The addition of carbohydrate groups to proteins or lipids, categorized into N-linked and O-linked glycosylation based on the attachment location.

Clinical Relevance of Glycosylation

Disorders related to GAGs (mucopolysaccharidoses), proteoglycans (Osteoarthritis), and glycoproteins (congenital disorders) can have significant health impacts.

Integration with Other Metabolic Pathways

GAGs, proteoglycans, and glycoproteins play roles in metabolic pathways, influencing processes like cell signaling, immune function, and tissue repair.