Chem 45 Biochemistry: Stoker chapter 23 Metabolism Introduction

Chapter 23

Biochemical Energy Production

Chapter 23

Table of Contents

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23.1Metabolism

23.2 Metabolism and Cell Structure

23.3 Important Nucleotide-Containing Compounds in Metabolic Pathways

23.5 High-Energy Phosphate Compounds

23.6 An Overview of Biochemical Energy Production

23.7 Chemical Processes Prior to Metabolism

Metabolism

Section 23.1

• Sum total of all chemical reactions in a living organism

• The various chemical processes by which food is utilized by a living organism to provide energy, growth substance, and cell repair

• Metabolism will provide the source of energy we need for all our activities such as thinking, moving, breathing, walking, talking, etc.

• Energy is also needed for many of the cellular processes such as protein synthesis, DNA replication, RNA transcription and transport across the membrane, etc.


Metabolism

Section 23.1

Catabolism and Anabolism

• Catabolism: All metabolic reactions in which large biochemical molecules are broken down to smaller ones – Usually energy is released in

these reactions– Example: Oxidation of glucose

• Anabolism: All metabolic reactions in which small biochemical molecules are joined to form larger ones– Usually require energy– Example: The synthesis of

proteins


Metabolism

Section 23.1

• Metabolic Pathway: Series of consecutive biochemical reactions used to convert a starting material into an end product

• There are two types of metabolic pathways– Linear

– Cyclic

• The major pathways for all forms of life are similar:


A B DC

C

A B

D

Linear Pathway

Cyclic Pathway

Metabolism

Section 23.1

Practice Exercise

• Classify each of the following chemical processes as anabolic or catabolic.

a. Synthesis of a protein from amino acids

b. Formation of a triacylglycerol from glycerol and fatty acids

c. Hydrolysis of a polysaccharide to monosaccharides

d. Formation of a nucleic acid from nucleotides


Metabolism

Section 23.1

Practice Exercise

• Classify each of the following chemical processes as anabolic or catabolic.

a. Synthesis of a protein from amino acids

b. Formation of a triacylglycerol from glycerol and fatty acids

c. Hydrolysis of a polysaccharide to monosaccharides

d. Formation of a nucleic acid from nucleotides


Answers:

a. Anabolic

b. Anabolic

c. Catabolic

d. Anabolic

Section 23.2

Metabolism and Cell Structure


Eukaryotic Cell Organelles and Their Function

• Nucleus: DNA replication and RNA synthesis

• Plasma membrane: Cellular boundary

• Cytoplasm: The water-based material of a eukaryotic cell

• Mitochondria: Generates most of the energy needed for cell.

• Lysosome: Contain hydrolytic enzymes needed for cell rebuilding, repair and degradation

• Ribosome: Sites for protein synthesis

Section 23.2

Metabolism and Cell Structure


Mitochondria

• An organelle that is responsible for the generation of most of the energy for a cell:– Outer membrane:

Permeable to small molecules: 50% lipid, 50% protein

– Inner membrane: Highly impermeable to most substances: 20% lipid, 80% protein

– Inner membrane folded into cristae to increase surface area

– Synthesis of ATP occurs on the inner membrane

Section 23.3

Important Nucleotide-Containing Compounds in Metabolic Pathways


• Several phosphate containing compounds found in metabolic pathways are known as high energy compounds

• High energy compounds have greater free energy of hydrolysis than a typical compound:– They contain at least one reactive bond -- called strained bond– Energy to break these bonds is less than a normal bond --

hydrolysis of high energy compounds give more energy than normal compounds

– More negative the free energy of hydrolysis, greater the bond strain

– Typically the free energy release is greater than 6.0 kcal/mole (indicative of bond strain)

– Strained bonds are represented by sign ~ (squiggle bond)

High-energy Phosphate Compounds

Section 23.3



• AMP: Structural component of RNA• ADP and ATP: Key components of

metabolic pathways– Phosphate groups are connected to

AMP by strained bonds which require less than normal energy to hydrolyze them

ATP + H2O ADP + PO43- +

Energy

ADP + H2O AMP + PO43- +

Energy

Overall Reaction: ATP + 2H2O AMP + 2 PO4

3- + Energy

• The net energy produced in these reactions is used for cellular reactions

• e.g., conversion of glucose to glucose-6-phosphate

Adenosine Phosphates (ATP, ADP and AMP)

Section 23.3



Flavin Adenine Dinucleotide (FAD)

• A coenzyme required in numerous metabolic redox reactions

• FAD is oxidized form

• FADH2 is reduced form

• In enzyme reactions FAD goes back and forth (equilibrium) from oxidized to reduced form.

• A typical cellular reaction in which FAD serves as oxidizing agent involves conversion of an alkane to an alkene

Section 23.3



• NAD+: coenzyme• NADH is reduced form • 3 Subunit structure:

– Nicotinamide - ribose - ADP– 6 Subunit structure:

Nicotinamide -- ribose -phosphate --phosphate - ribose – adenine

• A typical cellular reaction in which NAD+ serves as the oxidizing agent is the oxidation of a secondary alcohol to give a ketone.

Nicotinamide Adenine Dinucleotide (NAD)

Section 23.3



Coenzyme A

• A derivative of vitamin B• Active form of coenzyme A is the sulfhydryl group (-SH group) in the

ethanethiol subunit of the coenzyme

• Acetyl-CoA (acetylated)

Section 23.3



Classification of Metabolic Intermediate Compounds

• Metabolic intermediate compounds can be classified into three groups based on their functions

Section 23.6

An Overview of Biochemical Energy Production


• Energy needed to run human body is obtained from food

• Multi-step process that involves several different catabolic pathways aid in this process

• There are four general stages in the biochemical energy production process:– Stage 1: Digestion– Stage 2: Acetyl group formation,

– Stage 3: Citric acid cycle

– Stage 4: Electron transport chain and Oxidative phosphorylation,

• Each stage also involves numerous reactions

Section 23.6



Stage 1. Digestion

• Begins in mouth (saliva contains starch digesting enzymes), continues in the stomach (gastric juice), completed in small intestine: – Results in small molecules that can cross intestinal

membrane into the blood• End Products of digestion:

– Glucose and monosaccharides from carbohydrates

– Amino acids from proteins– Fatty acids and glycerol from fats and oils

• The digestion products are absorbed into the blood and transported to body’s cells

Section 23.6



Stage 2. Acetyl Group Formation

• The small molecules from Stage 1 are further oxidized.• End product of these oxidations is acetyl CoA• Primary products include two-carbon acetyl units (which

become attached to coenzyme A to give acetyl CoA) and the reduced coenzyme NADH.

• Involves numerous reactions:

– Reactions occur both in cytosol (glucose metabolism) as well as mitochondria (fatty acid metabolism) of the cells.

Section 23.6



Stage 3. Citric Acid Cycle

• Takes place inside the mitochondria

• In this stage acetyl group is oxidized to produce CO2 (which we exhale during breathing) and energy

• Most energy is trapped and carried by the reduced coenzymes NADH and FADH2 to the fourth stage

• Some energy produced in this stage is lost in the form of heat

Section 23.6



Stage 4. Electron Transport Chain and Oxidative Phosphorylation

• Takes place in mitochondria

• NADH and FADH2 are oxidized to release H+ and electrons

• H+ are transported to the inter-membrane space in mitochondria

• Electrons are transferred to O2 and O2 is reduced to H2O

• H+ ions reenter the mitochondrial matrix and drive ATP-synthase reaction to produce ATP

• ATP is the primary energy carrier in metabolic pathways

• The reactions in stages 3 & 4 are common to the processing of carbohydrates, fats, and proteins

• Collectively known as the common metabolic pathways, i.e., the sum of the reactions that occur in the citric acid cycle, the electron transport chain, and the oxidative phosphorylation

Section 23.6



Section 23.6



Chemical Processes Prior to Metabolism

• A. Digestion• Breakdown of food molecules by

hydrolysis into simpler chemical units that can be used by cells in metabolic processes

• B. Absorption• The process of getting the digested

molecules into the bloodstream and ultimately into the cells where metabolism occurs

• Takes place in the small intestine through tiny, finger-like projections, called villi, that line the inner surface

• Each villus is richly supplied with a fine network of blood vessels and a central lymph vessel

Chem 45 Biochemistry: Stoker chapter 23 Metabolism Introduction

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