Chapter 4
Cellular Metabolism
4.1: Introduction
Metabolic processes:
All chemical reactions that occur in the body
There are two types of metabolic reactions:
Anabolism
Larger molecules are made from smaller ones
Requires energy
Catabolism
Larger molecules are broken down into smaller ones
Releases energy
2
Anabolism
Anabolism provides the materials needed for cellular growth and repair
Dehydration Synthesis
Type of anabolic process
Produces water
Used to make polysaccharides, triglycerides, nucleic acids & proteins
3
Catabolism
Catabolism breaks down larger molecules into smaller ones
Hydrolysis
A catabolic process
Used to decompose carbohydrates, lipids, and proteins
Water is used to split the substances
Reverse of dehydration synthesis
CH2OH
CH2OH
O
H
O
H
H
CH2OH
H
O
H
H
CH2OH
H
O
H
H
H
H
H
H2O
HO
OH
H
H
OH
HO
OH
Monosaccharide
+
OH
H
H
OH
Monosaccharide
OH
HO
OH
H
H
OH
O
Disaccharide
OH
H
H
OH
+
OH
4
Water
Anabolism & Catabolism
5
4.3: Control of Metabolic Reactions
Enzymes
Control rates of metabolic reactions
Lower activation energy needed to start reactions
Most are globular proteins with specific shapes
Not consumed in chemical reactions
Substrate specific
Shape of active site determines substrate
Substrate molecules
Product molecule
Active site
Enzyme
molecule
(a)
Enzyme-substrate
complex
(b)
(c)
Unaltered
enzyme
molecule
6
Enzyme Action
Metabolic pathways
Series of enzyme-controlled reactions leading to formation of a
product
Each new substrate is the product of the previous reaction
Substrate
1
Enzyme A
Enzyme B
Substrate
Enzyme names
commonly:
2
Substrate
3
Enzyme C
Substrate
4
Enzyme D
Product
Reflect the substrate
Have the suffix – ase
Examples: sucrase, lactase, protease, lipase
7
Cofactors and Coenzymes
Cofactors
Make some enzymes active
Non-protein component
Ions or coenzymes
Coenzymes
Organic molecules that act as cofactors
Vitamins
8
Factors That Alter Enzymes
Factors that alter enzymes:
Heat
Radiation
Electricity
Chemicals
Changes in pH
9
Animation:
How Enzymes Work
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Regulation of Metabolic
Pathways
Limited number of regulatory enzymes
Negative feedback
Inhibition
Rate-limiting
Enzyme A
Substrate
Substrate
2
1
Enzyme B
Substrate
3
Enzyme C
Substrate
4
Enzyme D
Product
11
4.4: Energy for Metabolic Reactions
Energy is the capacity to change something; it is
the ability to do work
Common forms of energy:
Heat
Light
Sound
Electrical energy
Mechanical energy
Chemical energy
12
ATP Molecules
Each ATP molecule has three parts:
An adenine molecule
A ribose molecule
Three phosphate molecules in a chain
Third phosphate attached by high-energy bond
When the bond is broken, energy is transferred
When the bond is broken, ATP becomes ADP
ADP becomes ATP through phosphorylation
Phosphorylation requires energy release from cellular respiration
4.5: Cellular Respiration
Occurs in a series of reactions:
Glycolysis
“Prep” steps or intermediate steps
Citric acid cycle (aka TCA or Kreb’s Cycle)
Electron transport system
14
Cellular Respiration
Produces:
Carbon dioxide
Water
ATP (chemical energy)
Heat
Includes:
Anaerobic reactions (without O2) - produce little ATP
Aerobic reactions (requires O2) - produce most ATP
15
Glycolysis
Series of ten reactions
Breaks down glucose into 2 pyruvic acid molecules
Occurs in cytosol
Anaerobic phase of cellular respiration
Yields two ATP molecules per glucose molecule
Summarized by 3 Events:
Phosphorylation
Splitting
Production of NADH and ATP
16
Glycolysis
Event 1 – Phosphorylation
Glucose
Phase 1
priming
Carbon atom
P Phosphate
Two phosphates added to glucose
Requires ATP
2 ATP
2 ADP
Fructose-1,6-diphosphate
P
P
Event 2 – Splitting (cleavage)
6-carbon glucose split into two 3carbon molecules
Phase 2
cleavage
Dihydroxyacetone
phosphate
P
Phase 3
oxidation and
formation of
ATP and release
of high energy
electrons
Glyceraldehyde
phosphate
P
P
2 NAD+
4 ADP
2 NADH + H+
4 ATP
2 Pyruvic acid
O2
O2
2 NADH + H+
2 NAD+
2 Lactic acid
To citric acid cycle
and electron transport
chain (aerobic pathway)
17
Glycolysis
Event 3:Production of NADH and ATP
Glucose
Phase 1
priming
Carbon atom
P Phosphate
Hydrogen atoms are released
Hydrogen atoms bind to NAD+ to produce
NADH
NADH delivers hydrogen atoms to electron
transport system if oxygen is available
ADP is phosphorylated to become ATP
Two molecules of pyruvic acid are produced
Two molecules of ATP are generated
2 ATP
2 ADP
Fructose-1,6-diphosphate
P
P
Phase 2
cleavage
Dihydroxyacetone
phosphate
P
Phase 3
oxidation and
formation of
ATP and release
of high energy
electrons
Glyceraldehyde
phosphate
P
P
2 NAD+
4 ADP
2 NADH + H+
4 ATP
2 Pyruvic acid
O2
O2
2 NADH + H+
2 NAD+
2 Lactic acid
To citric acid cycle
and electron transport
chain (aerobic pathway)
18
Anaerobic Reactions
If oxygen is NOT available:
Glucose
Phase 1
priming
Carbon atom
P Phosphate
2 ATP
Electron transport system
cannot accept new electrons
from NADH
2 ADP
Fructose-1,6-diphosphate
P
P
Phase 2
cleavage
Dihydroxyacetone
phosphate
P
Pyruvic acid is converted to
lactic acid
Phase 3
oxidation and
formation of
ATP and release
of high energy
electrons
Glyceraldehyde
phosphate
P
P
2 NAD+
4 ADP
2 NADH + H+
4 ATP
2 Pyruvic acid
O2
Glycolysis is inhibited
O2
2 NADH + H+
2 NAD+
2 Lactic acid
To citric acid cycle
and electron transport
chain (aerobic pathway)
19
Aerobic Reactions
If oxygen IS available:
Pyruvic acid is used to produce acetyl
CoA
Citric acid cycle begins
Electron transport system functions
Carbon dioxide and water are formed
34 molecules of ATP are produced per
each glucose molecule
Glucose
High energy
electrons (e–) and
hydrogen ions (H+)
2 ATP
Pyruvic acid Pyruvic acid
Cytosol
Mitochondrion
High energy
electrons (e–) and
hydrogen ions (h+)
CO2
Acetyl CoA
Oxaloacetic
acid
Citric acid
High energy
electrons (e–) and
hydrogen ions (H+)
2 CO2
2 ATP
Electron transport chain
32-34 ATP
O2
–
+
2e + 2H
H2O
20
Citric Acid Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Begins when acetyl CoA
combines with Oxaloacetic
acid to produce Citric acid
Citric acid is changed into
oxaloacetic acid through a
series of reactions
Cycle repeats as long as
pyruvic acid and oxygen are
available
For each citric acid
molecule: One ATP is
produced
Eight hydrogen atoms are
transferred to NAD+ and
FAD Two CO2 produced
Pyruvic acid from glycolysis
Cytosol
CO2
Carbon atom
P
NAD+
Phosphate
Mitochondrion CoA Coenzyme A
NADH + H+
Acetic acid
CoA
Acetyl CoA
(replenish molecule)
Oxaloacetic acid
Citric acid
(finish molecule)
(start molecule)
CoA
NADH + H+
NAD+
Malic acid
Isocitric acid
NAD+
Citric acid cycle
CO2
Fumaric acid
NADH + H+
-Ketoglutaric acid
CO2
CoA
NAD+
FADH2
NADH + H+
FAD
Succinic acid
CoA
Succinyl-CoA
ADP + P
ATP
21
Electron Transport System
NADH and FADH2 carry electrons to the ETS
ETS is a series of electron carriers located in cristae of mitochondria
Energy from electrons transferred to ATP synthase
ATP synthase catalyzes the phosphorylation of ADP to ATP
Water is formed
ADP + P
ATP synthase
ATP
Energy
NADH + H+
Energy
2H+ + 2e–
NAD+
Energy
FADH2
2H+ + 2e–
FAD
Electron transport chain
2e–
2H+
O2
22
H2O
Summary of Cellular
Respiration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glucose
Glycolysis
The 3-carbon pyruvic acids generated by glycolysis
enter the mitochondria. Each loses a carbon
(generating CO2 and
2 is combined with a coenzyme to
form a 2-carbon acetyl coenzyme A (acetyl CoA). More
high-energy electrons are released.
Each acetyl CoA combines with a 4-carbon oxaloacetic
acid to form the 6-carbon citric acid, for which the cycle
is named. For each citric acid, a series of reactions
3
removes 2 carbons (generating 2 CO2’s), synthesizes
1 ATP, and releases more high-energy electrons.
The figure shows 2 ATP, resulting directly from 2
turns of the cycle per glucose molecule that enters
glycolysis.
Electron Transport Chain
The high-energy electrons still contain most of the
chemical energy of the original glucose molecule.
Special carrier molecules bring the high-energy
electrons to a series4of enzymes that convert much of
the remaining energy to more ATP molecules. The
other products are heat and water. The function of
oxygen as the final electron acceptor in this last step is
why the overall process is called aerobic respiration.
High-energy electrons (e–)
2 ATP
Cytosol
Glycolysis
Pyruvic acid
Pyruvic acid
High-energy electrons (e–)
CO2
Acetyl CoA
Citric acid
Oxaloacetic acid
Mitochondrion
The 6-carbon sugar glucose is broken down in the
1
cytosol into two 3-carbon pyruvic acid molecules with
a net gain of 2 ATP and release of high-energy
electrons.
Citric Acid Cycle
Citric acid
cycle
High-energy electrons (e–)
2 CO2
2 ATP
Electron
transport
chain
32–34 ATP
2e– and 2H+
O2
H2O
23
Carbohydrate Storage
Carbohydrate molecules from foods can enter:
Catabolic pathways for energy production
Anabolic pathways for storage
24
Carbohydrate Storage
Excess glucose stored as:
Glycogen (primarily by liver and muscle cells)
Fat
Converted to amino acids
Carbohydrates
from foods
Hydrolysis
Monosaccharides
Catabolic
pathways
Anabolic
pathways
Energy + CO2 + H2O Glycogen or Fat
Amino acids
25
Summary of Catabolism of
Proteins, Carbohydrates, and Fats
29
4.6: Nucleic Acids and
Protein Synthesis
Instruction of cells to synthesize proteins
comes from a nucleic acid, DNA
27
Genetic Information
Genetic information – instructs cells how to
construct proteins; stored in DNA
Gene – segment of DNA that codes for one
protein
Genome – complete set of genes
Genetic Code – method used to translate a
sequence of nucleotides of DNA into a
sequence of amino acids
28
Structure of DNA
Two polynucleotide chains –
double-stranded
Hydrogen bonds hold nitrogenous bases
together
Bases pair specifically (A-T and C-G)
Forms a helix
DNA wrapped about histones forms
chromatin
chromosomes are condensed chromatin
Animation:DNA Structure
https://www.youtube.com/watch?v=qy8dk5iS1f0&safe=active
29
DNA Replication
Hydrogen bonds break between bases
Double strands unwind and pull apart
New nucleotides pair with exposed bases
Controlled by DNA polymerase
Animation:DNA Replication
https://www.youtube.com/watch?v=27TxKoFU2Nw
30
Genetic Code
Specification of
the correct
sequence of
amino acids in a
polypeptide chain
Each amino acid
is represented by
a triplet code
31
RNA Molecules
Single-standed
Ribose
Uracil Instead Of Thymine
32
RNA Molecules
Messenger RNA (mRNA):
Making of mRNA (copying of DNA) is transcription
Transfer RNA (tRNA):
Carries amino acids to mRNA
Carries anticodon to mRNA
Translates a codon of mRNA into an amino acid
Ribosomal RNA (rRNA):
Provides structure and enzyme activity for ribosomes
33
RNA Molecules
Messenger RNA (mRNA):
Delivers genetic information from
nucleus to the cytoplasm
Single polynucleotide chain
Formed beside a strand of DNA
RNA nucleotides are complementary to
DNA nucleotides (exception – no
thymine in RNA; replaced with uracil)
34
Animation:Stages of Transcription
https://www.youtube.com/watch?v=WsofH466lqk
35
Animation:How Translation Works
https://www.youtube.com/watch?v=5bLEDd-PSTQ
Protein Synthesis
The transfer RNA molecule
for the last amino acid added
holds the growing polypeptide
chain and is attached to its
complementary codon on mRNA.
1
2
3
Growing
polypeptide
chain
Anticodon
1
4
Next amino acid
5
6
Transfer
RNA
UGCCGU
AU GGGC U C CGC AA CGGCA GGC A A GC GU
1
2
3
4
5
6
7
Codons
1
2
Growing
polypeptide
chain
2
A second tRNA binds
complementarily to the
next codon, and in doing
so brings the next amino
acid into position on the
ribosome.
Peptide bond
3
4
Next amino acid
5
6
Transfer
RNA
Anticodon
UGCCGU
AU GGGC U C CGC AA CGGCA GGC A A GC GU
The tRNA molecule that
brought the last amino acid
to the ribosome is released
to the cytoplasm, and will be
used again. The ribosome
moves to a new position at
the next codon on mRNA.
1
2
3
2
3
4
5
6
Messenger
RNA
7
Codons
1
3
A
4
5
7
Next
amino acid
6
A peptide bond forms,
linking the new amino acid
to the growing polypeptide
chain
Transfer
RNA
CGU
AU GGGC U C CGC AA CGGCA GGC A A GC GU
1
2
3
4
5
6
7
Messenger
RNA
Ribosome
1
2
4
3
4
5
6
7
Next
amino acid
Transfer
RNA
CGU CCG
AU GGGC U C CGC AA CGGCA GGC A A GC GU
1
2
3
4
5
6
7
Messenger
RNA
A new tRNA
complementary tothe next
codon on mRNA brings the
next amino acid to be added
to the growing polypeptide
chain
36
.
Nature of Mutations
Mutations – change in genetic information
Result when:
Extra bases are added or deleted
Bases are changed
May or may not change the protein
37
Protection Against Mutation
Repair enzymes correct the mutations
Inborn Errors of Metabolism
Occurs from inheriting a mutation that then
alters an enzyme
This creates a block in an otherwise normal
biochemical pathway
38