Biochemistry: Metabolism Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the total ATP cost for glucose synthesis?

6 ATP

8 ATP

2 ATP

4 ATP (correct)

Which hormone stimulates the liver to release glucose during fasting?

Glucagon (correct)

Cortisol

Adrenaline

Insulin

What is used to produce ATP during intense activity before glycolysis kicks in?

Lactate

Fatty acids

Glycogen

Creatine phosphate (correct)

What happens when oxygen supply is limited during prolonged exercise?

Increase in lactate production Signup and view all the answers

What process allows lactate to be converted back to glucose in the liver?

Cori Cycle Signup and view all the answers

What is the primary purpose of catabolic reactions in metabolism?

To break down complex molecules and release energy Signup and view all the answers

Which stage of catabolism involves the breakdown of large polymers into monomers?

Stage 1: Digestion and hydrolysis Signup and view all the answers

Which molecule is hydrolyzed to form ADP and AMP, releasing energy?

ATP Signup and view all the answers

What is the role of coenzymes like NAD+ in metabolic reactions?

To gain hydrogen ions and electrons for reduction Signup and view all the answers

Which vitamin is associated with coenzyme FAD?

Vitamin B2 Signup and view all the answers

What is produced when coenzyme A reacts with small acyl groups?

Thioester acetyl CoA Signup and view all the answers

During which stage of catabolism do small molecules undergo oxidation in the citric acid cycle?

Stage 3: Oxidation Signup and view all the answers

What does the term 'metabolism' encompass?

All chemical reactions that provide energy and substances for cell growth Signup and view all the answers

What product is formed when aldolase acts on glucose?

Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate Signup and view all the answers

What occurs during the isomerization of dihydroxyacetone phosphate?

Glyceraldehyde-3-phosphate is produced Signup and view all the answers

What is produced when the aldehyde group of glyceraldehyde-3-phosphate is oxidized?

1,3-bisphosphoglycerate Signup and view all the answers

What process occurs when ATP is produced from 1,3-bisphosphoglycerate?

Substrate-level phosphorylation Signup and view all the answers

What molecule is formed from dehydration of 3-phosphoglycerate?

Phosphoenolpyruvate Signup and view all the answers

Which enzyme transfers a phosphate group from phosphoenolpyruvate to ADP?

Pyruvate kinase Signup and view all the answers

What is the net gain of ATP and NADH from glycolysis?

2 ATP and 2 NADH Signup and view all the answers

Which molecules enter the glycolysis pathway from fructose and galactose metabolism?

Intermediates of glycolysis Signup and view all the answers

What is the primary function of salivary α-amylase in the digestion process?

To catalyze hydrolysis of carbohydrates Signup and view all the answers

Which enzyme is responsible for converting glucose-6-phosphate to fructose-6-phosphate during glycolysis?

Phosphoglucose isomerase Signup and view all the answers

What occurs in the large intestine when lactose is not digested?

Bacteria ferment it, producing gases Signup and view all the answers

What is the outcome of glycolysis in terms of glucose metabolism?

Production of two pyruvate molecules Signup and view all the answers

Which component is added to fructose-6-phosphate during glycolysis to produce fructose-1,6-bisphosphate?

A phosphate group from ATP Signup and view all the answers

What is a recommended approach for individuals with lactose intolerance when consuming dairy?

Taking lactase enzyme with meals Signup and view all the answers

What happens to salivary α-amylase as food moves into the stomach?

It is denatured by stomach acid Signup and view all the answers

What is the primary site for the final conversion of polysaccharides to glucose?

Small intestine Signup and view all the answers

What is the effect of high levels of glucose-6-phosphate on hexokinase activity?

Inhibits hexokinase Signup and view all the answers

Which enzyme is activated by high levels of AMP during glycolysis?

Phosphofructokinase Signup and view all the answers

What is produced during anaerobic conditions as pyruvate is reduced?

Lactic acid and NAD+ Signup and view all the answers

During aerobic conditions, what happens to pyruvate once it enters the mitochondria?

It is oxidized to acetyl-CoA Signup and view all the answers

In gluconeogenesis, which of the following replaces the irreversible reaction of hexokinase?

Glucose-6-phosphatase Signup and view all the answers

What is the net gain of ATP during glycolysis under anaerobic conditions?

Two ATP Signup and view all the answers

Which molecules are primarily used in gluconeogenesis to synthesize glucose in the liver?

Pyruvate, amino acids, and glycerol Signup and view all the answers

What happens to ATP levels when high levels of ATP inhibit phosphofructokinase?

Glycolysis is halted Signup and view all the answers

Study Notes

Chapter Twenty Two: Metabolic Pathways for Carbohydrates

Metabolic pathways provide energy and substances for continued cell growth
Two types of metabolic reactions:
- Catabolic reactions: break down complex molecules into smaller ones, releasing energy
- Anabolic reactions: use energy to build larger molecules

Stages of Catabolism

Catabolism is organized into stages:
- Stage 1: Digestion and hydrolysis. Large polymers are broken down into monomers which then enter the bloodstream
- Stage 2:Cellular degradation. Each set of molecules is broken down differently into two- and three-carbon compounds.
- Stage 3: Oxidation. All the small molecules are oxidized in the citric acid cycle and electron transport to generate ATP energy.

Stages of Catabolism: From Digestion to Cell

A diagram showing the stages of catabolism, including proteins, polysaccharides, lipids, and the conversion to ATP
Breakdown of proteins into amino acids, polysaccharides into glucose, fructose, and galactose, lipids into fatty acids and entering cells
Oxidation to CO₂, H₂O, and energy for ATP synthesis

ATP, Adenosine Triphosphate

ATP is composed of adenine, a ribose sugar, and three phosphate groups
Hydrolysis of ATP to ADP and AMP releases energy
More phosphate groups mean more stored energy

ATP Drives Reactions

Catabolic reactions release energy, storing it in ATP
Anabolic reactions use energy from ATP hydrolysis
7.3 kcal/mole of energy (31 kJ/mole) is released when ATP is converted to ADP + P_i

Metabolic Reactions

A coenzyme that gains hydrogen ions and electrons is reduced and energy is stored
A coenzyme that loses hydrogen ions and electrons to a substrate is oxidized

Table 22.2: Characteristics of Oxidation and Reduction

Oxidation: loss of electrons, loss of hydrogen (H or H⁺ and e⁻), gain of oxygen, and release of energy.
Reduction: gain of electrons, gain of hydrogen (H or H⁺ and e⁻), loss of oxygen, and input of energy.

Structure of Coenzyme NAD+

NAD+ is nicotinamide adenine dinucleotide
Attached to a derivative of coenzyme niacin (vitamin B₃)
Collects an H⁺ and 2 electrons

Coenzyme NAD+ or NADP+

NAD+ is the oxidized form, NADH + H⁺ is the reduced form
NAD+ collects 2H⁺ + 2e⁻ forming NADH + H⁺ (reduced form)
NADPH is a derivative that collects H⁺ and 2e⁻

Coenzyme FAD

FAD is flavin adenine dinucleotide
Contains ADP and riboflavin (vitamin B₂)
Collects 2H⁺ atoms (+ 2e⁻), reducing it to FADH₂

Structure of Coenzyme A

Coenzyme A (CoA) is made up of pantothenic acid (vitamin B₅), phosphorylated ADP, and aminoethanethiol
Preparation of small acetyl groups for enzyme reactions
Production of the energy-rich thioester acetyl CoA

Function, Coenzyme A

Preparation of small acyl groups (like acetyl) for reactions with enzymes
Production of the energy-rich thioester acetyl CoA

Digestion of Carbohydrates

Stage 1 of catabolism is digestion, the breakdown of food into small molecules
In the mouth: physical grinding and mixing of food; chemical hydrolysis of carbohydrates
α-amylase in saliva catalyzes hydrolysis of glycosidic bonds in carbohydrates
Salivary α-amylase continues to act on polysaccharides in the stomach until denatured
In the small intestine: further hydrolysis by pancreatic α-amylase, maltase, sucrase, and lactase
Monosaccharides are absorbed into the bloodstream

Lactose Intolerance

Lactase production may cease after childhood
Lactose cannot be digested in the small intestine leading to fermentation
Bacteria in the large intestine use lactose to form CO₂, H₂, and CH₄ causing cramps and diarrhea
Milk products can be predigested with lactase enzyme

In The Cell Stage 2: Glycolysis

Glucose from the bloodstream enters cells for decomposition
Glucose (6C) is converted to 2 pyruvate (3C) through glycolysis (Stage 2 of catabolism).
ATP input is returned when the process is completed.
Glycolysis takes place in the cytosol of the cell

Glycolysis: Reaction 1

Phosphorylation: a phosphate group is transferred from ATP to glucose, forming glucose-6-phosphate and ADP
The enzyme hexokinase catalyzes this reaction

Glycolysis: Reaction 2

Isomerization: Glucose-6-phosphate is converted to fructose-6-phosphate by the enzyme phosphoglucose isomerase

Glycolysis: Reaction 3

Phosphorylation: fructose-6-phosphate is converted to fructose-1,6-bisphosphate by the enzyme phosphofructokinase

Glycolysis: Reaction 4

Cleavage: fructose-1,6-bisphosphate is split into two three-carbon phosphate isomers (DHAP and G3P) by the enzyme aldolase

Glycolysis: Reaction 5

Isomerization: dihydroxyacetone phosphate is converted to glyceraldehyde-3-phosphate by the enzyme triose phosphate isomerase.

Glycolysis: Reaction 6

Oxidation and phosphorylation: Glyceraldehyde-3-phosphate is oxidized to a 1,3-bisphosphoglycerate and NAD⁺ is reduced to NADH
The enzyme glyceraldehyde-3-phosphate dehydrogenase catalyzes this reaction.

Glycolysis: Reaction 7

Phosphate transfer: A phosphate group from 1,3-bisphosphoglycerate is transferred to ADP by phosphoglycerate kinase, forming ATP (x2).

Glycolysis: Reaction 8

Isomerization: 3-phosphoglycerate is converted to 2-phosphoglycerate by the enzyme phosphoglycerate mutase

Glycolysis: Reaction 9

Dehydration: 2-phosphoglycerate is converted to phosphoenolpyruvate by the enzyme enolase

Glycolysis: Reaction 10

Phosphate transfer: A phosphate group from phosphoenolpyruvate is transferred to ADP by pyruvate kinase, forming ATP (x2)

Glycolysis: Overall Reaction

Two ATP are used to phosphorylate glucose and fructose-6-phosphate
Four ATP are produced from direct transfers of phosphate groups to ADP
A net gain of 2 ATP and 2 NADH

Fructose and Galactose

Galactose and fructose are intermediates in the glycolysis pathway
They enter the pathway by forming glucose-6-phosphate or fructose-6-phosphate.

Regulation of Glycolysis

Hexokinase is inhibited by high levels of glucose-6-phosphate
Phosphofructokinase is inhibited by high levels of ATP and activated by high levels of AMP
Pyruvate kinase is inhibited by high levels of ATP and acetyl CoA

Fates of Pyruvate

Pyruvate can undergo fermentation or oxidation depending on oxygen availability.
Under anaerobic conditions, pyruvate is converted to lactate
Under aerobic conditions, pyruvate is converted to acetyl-CoA

Pyruvate: Anaerobic Conditions

NADH concentration rises, reducing NAD⁺ availability
Pyruvate is reduced to lactate by lactate dehydrogenase to regenerate NAD⁺
Glycolysis can continue with a small amount of ATP produced.

Pyruvate: Aerobic Conditions

Pyruvate moves to the mitochondria where it is oxidized to acetyl-CoA
NAD⁺ is reduced to NADH to generate energy
Acetyl-CoA enters the citric acid cycle, and NADH goes through the electron transport chain to produce ATP

Gluconeogenesis

Glucose is produced from other substances (e.g., pyruvate, amino acids, glycerol) in gluconeogenesis
Critical in fasting or starvation as the liver's glycogen stores become depleted
The liver cells synthesize glucose for other cells

Glycolysis and Gluconeogenesis

Glycolysis has 10 reactions
Gluconeogenesis has 4 bypassed regulated reactions
Key enzymes regulate both pathways, differing at specific points

Energy Cost of Gluconeogenesis

Gluconeogenesis is costly, requiring 4 ATP, 2 GTP, and 2 NADH to synthesize one molecule of glucose.

Regulation of Blood Glucose

Two pancreatic hormones, insulin and glucagon, regulate glucose levels
Insulin lowers blood glucose by promoting glucose uptake into cells
Glucagon raises blood glucose by signaling the liver to release stored glucose

Biochemistry of Extreme Activity

The energy needed comes from ATP, creatine phosphate followed by glycolysis
Oxygen is used at maximum capacity during extreme muscle exertion.
Anaerobic glycolysis suffices until lactate buildup causes muscle fatigue

Biochemistry of Longer Exercise

Oxygen supply in muscle tissues must be maintained for long-distance/time activity
Aerobic glycolysis produces ATP as oxygen-carrying blood flows more quickly to muscles.
Anaerobic threshold - Glycolysis and lactate recycling provide ATP when oxygen isn't sufficient.

Lactate and the Cori Cycle

Lactate from muscles flows to the liver
The liver converts pyruvate to glucose which is carried back to the muscles.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers essential concepts in biochemistry related to metabolism, including ATP synthesis, catabolic reactions, and the roles of various coenzymes. Test your knowledge on how glucose is metabolized in different conditions and the biochemical reactions involved in energy production. Perfect for students studying biochemistry or related fields.