Chapter 4
Energy and
Cellular Metabolism
About this Chapter
•
•
•
•
•
•
Energy in biological systems
Chemical reactions
Enzymes
Metabolism
ATP production
Synthetic pathways
Energy: Biological Systems
• Energy transfer in the environment
KEY
Transfer of radiant
or heat energy
Sun
Transfer of energy
in chemical bonds
Energy lost
to environment
Heat
energy
Radiant
energy
Energy for work
CO2
Photosynthesis
takes place in
plant cells, yielding:
CO2 +
Energy stored in
biomolecules
Respiration
takes place in
human cells, yielding:
+
Energy stored
in biomolecules
+
H2O
N2
CO2
H2O
Figure 4-1
Energy: Capacity to Do Work
• Chemical work
• Making and breaking of chemical bonds
• Transport work
• Moving ions, molecules, and larger particles
• Can create concentration gradients
• Mechanical work
• Used for movement
Kinetic and Potential Energy
Figure 4-2
Thermodynamic Energy
• First law of Thermodynamics
• Total amount of energy in the universe is
constant
• Second law of Thermodynamics
• Processes move from state of order to disorder
Chemical Reactions: Overview
• Activation
energy is the
energy that must
be put into
reactants before
a reaction can
proceed
• A+BC+D
Figure 4-3
Chemical Reactions: Exergonic and endergonic
Activation energy
Activation energy
G+H
A+B
Net free
energy
change
E+F
Net free
energy
change
C+D
(b) Endergonic reactions
(a) Exergonic reactions
KEY
Reactants
Activation of reaction
Reaction process
Products
Figure 4-4
Chemical Reactions: Coupling
Figure 4-5
Enzymes: Overview
• Isozymes
• Catalyze same reaction, but under different
conditions
• May be activated, inactivated, or modulated
• Coenzymes  vitamins
• Chemical modulators  temperature and pH
Enzymes: Lower activation energy
KEY
Reactants
Activation of reaction
Reaction process
Products
Activation energy
A+B
Net free
energy
change
C+D
Figure 4-6
Enzymes: Law of Mass Action
Figure 4-9a
Enzymes: Law of Mass Action
Figure 4-9b
Enzymes: Types of Reactions
Table 4-4
Metabolism: Overview
• A group of metabolic pathways resembles a
road map
Figure 4-10
Metabolism: Cell Regulation
1. Controlling enzyme concentrations
2. Producing allosteric and covalent modulators
3. Using different enzymes for reversible
reactions
4. Isolating enzymes within organelles
5. Maintaining optimum ratio of ATP to ADP
Metabolism: Cell Regulation
enzyme 1
enzyme 2
enzyme 3
Feedback inhibition
Figure 4-11
Metabolism: Cell Regulation
CO2
carbonic
anhydrase
+ H2O
carbonic
anhydrase
Glucose
hexokinase
Carbonic acid
(a)
+
PO4
glucose 6phosphatase
Glucose
PO4
hexokinase
Glucose 6-phosphate
(b)
+
Glucose 6-phosphate
(c)
Figure 4-12
ATP Production: Overview
Glucose
• Overview
of aerobic
pathways
for ATP
production
G
L
Y
C
O
L
Y
S
I
S
Glycerol
Amino
acids
Amino
acids
Fatty acids
ADP
ATP
Acetyl CoA
Citric acid
cycle
Pyruvate
Cytosol
Acetyl CoA
Mitochondrion
High-energy
electrons
ADP
Amino
acids
CITRIC
ACID
CYCLE
ATP
CO2
High-energy electrons
and H+
ADP
ELECTRON TRANSPORT SYSTEM
ATP
O2
H2O
Figure 4-13
ATP Production: Glycolysis
Glucose
ATP
ADP
Glucose
+ 2 NAD+
+ 2 ADP
+P

2 Pyruvate + 2 ATP
+ 2 NADH
+ 2 H+
+ 2 H20
Glucose 6-phosphate
Fructose 6-phosphate
ATP
ADP
Fructose 1,6-bisphosphate
Dihydroxyacetone
phosphate
KEY
= Carbon
= Oxygen
= Phosphate group
Glyceraldehyde 3-phosphate
NAD+
(side groups not shown)
NADH
1, 3-Bisphosphoglycerate
ADP
ATP
3-Phosphoglycerate
This section
happens twice
for each glucose
molecule that
begins glycolysis
2-Phosphoglycerate
H2O
Phosphoenol pyruvate
ADP
ATP
Pyruvate
Figure 4-14
ATP Production: Pyruvate Metabolism
• Pyruvate can be converted into lactate or
acetyl CoA
Anaerobic
Lactate
NAD+
NADH
Aerobic
Pyruvate
Pyruvate
Pyruvate
Acetyl CoA
Cytosol
NAD+
NADH
CO2
Mitochondrial
matrix
CoA
Acetyl CoA
CoA
Acyl unit
CITRIC ACID
CYCLE
KEY
= Carbon
= Oxygen
CoA = Coenzyme A
H and –OH not shown
Figure 4-15
ATP Production: Citric Acid Cycle
• Acetyl CoA
enters the
citric acid
cycle
producing
3 NADH,
1 FADH2,
and 1 ATP
KEY
= Carbon
= Oxygen
CoA = Coenzyme A
Side groups not shown
CoA
Acetyl CoA
CoA
Citrate (6C)
Oxaloacetate (4C)
NADH
Isocitrate (6C)
NAD+
Malate (4C)
NAD+
Acetyl CoA
Citric acid
cycle
High-energy
electrons
CITRIC ACID
CYCLE
H2 O
CO2
NADH
a Ketoglutarate (5C)
Fumarate (4C)
NAD+
FADH2
ATP
FAD
NADH
CoA
ADP
Succinate (4C)
GTP
CO2
GDP + Pi
Succinyl CoA (4C)
CoA
CoA
Figure 4-16
ATP Production: Electron Transport
Mitochondrial
matrix
CITRIC
ACID
CYCLE
2 H2O
e–
O2
3
Inner
mitochondrial
membrane
+ Matrix pool of H+
1
ATP
4e–
High-energy electrons
ADP
+ Pi
4
H+
2
H+
H+
H+ Intermembrane
space
H+
H+
H+
Outer
mitochondrial
membrane
High-energy electrons
from glycolysis
2
1 Energy released
during metabolism
is captured by
high-energy electrons
carried by NADH and
FADH2.
Cytosol
Energy from high-energy
electrons moving along
the electron transport
system pumps H+ from
the matrix into the
intermembrane space.
3
4
Electrons at the end of the
electron transport system
are back to their normal
energy state. They combine
with H+ and oxygen to
form water.
Potential energy captured in
the H+ concentration gradient
is converted to kinetic energy
when H+ ions pass through the
ATP synthase. Some of the kinetic
energy is captured as ATP.
Figure 4-17
ATP Production: Electron Transport
CITRIC
ACID
CYCLE
Mitochondrial
matrix
Inner
mitochondrial
membrane
e–
1
High-energy electrons
Intermembrane
space
Outer
mitochondrial
membrane
High-energy electrons
from glycolysis
Cytosol
1 Energy released
during metabolism
is captured by
high-energy electrons
carried by NADH and
FADH2.
Figure 4-17, step 1
ATP Production: Electron Transport
Mitochondrial
matrix
CITRIC
ACID
CYCLE
Inner
mitochondrial
membrane
e–
1
e–
High-energy electrons
H+
2
H+
H+
Intermembrane
space
H+
H+
H+
Outer
mitochondrial
membrane
High-energy electrons
from glycolysis
2
1 Energy released
during metabolism
is captured by
high-energy electrons
carried by NADH and
FADH2.
Cytosol
Energy from high-energy
electrons moving along
the electron transport
system pumps H+ from
the matrix into the
intermembrane space.
Figure 4-17, steps 1–2
ATP Production: Electron Transport
Mitochondrial
matrix
CITRIC
ACID
CYCLE
2 H2O
e–
O2
3
Inner
mitochondrial
membrane
+ Matrix pool of H+
1
4e–
High-energy electrons
H+
2
H+
H+
Intermembrane
space
H+
H+
H+
Outer
mitochondrial
membrane
High-energy electrons
from glycolysis
2
1 Energy released
during metabolism
is captured by
high-energy electrons
carried by NADH and
FADH2.
Cytosol
Energy from high-energy
electrons moving along
the electron transport
system pumps H+ from
the matrix into the
intermembrane space.
3
Electrons at the end of the
electron transport system
are back to their normal
energy state. They combine
with H+ and oxygen to
form water.
Figure 4-17, steps 1–3
ATP Production: Electron Transport
Mitochondrial
matrix
CITRIC
ACID
CYCLE
O2 +
2 H2O
e–
Inner
mitochondrial
membrane
3
Matrix pool of H+
1
ATP
4e–
High-energy electrons
ADP
+ Pi
4
H+
2
H+
H+
H+ Intermembrane
space
H+
H+
H+
Outer
mitochondrial
membrane
High-energy electrons
from glycolysis
2
1 Energy released
during metabolism
is captured by
high-energy electrons
carried by NADH and
FADH2.
Cytosol
Energy from high-energy
electrons moving along
the electron transport
system pumps H+ from
the matrix into the
intermembrane space.
3
Electrons at the end of the
electron transport system
are back to their normal
energy state. They combine
with H+ and oxygen to
form water.
4
Potential energy captured in
the H+ concentration gradient
is converted to kinetic energy
when H+ ions pass through the
ATP synthase. Some of the kinetic
energy is captured as ATP.
NADH and FADH2  ATP by oxidative phosphorylation
Figure 4-17, steps 1–4
ATP Production: Energy Yield
AEROBIC METABOLISM
C6H12O6 + 6 O2
6 CO2 + 6 H2O
NADH FADH2
1 Glucose
G
L
Y
C
O
L
Y
S
I
S
ATP
CO2
1 Glucose
+4
2*
C6H12O6
G
L
Y
C
O
L
Y
S
I
S
–2
2
NADH FADH2
ATP
CO2
4
–2
2
2 Acetyl CoA
2 C3H6O3 (Lactic acid)
2
2 Pyruvate
2 Pyruvate
–2
2 Lactic acid
TOTALS
Citric acid
cycle
6 O2
ANAEROBIC METABOLISM
6
2
2
4
0
NADH
2
ATP
High-energy electrons
and H+
ELECTRON TRANSPORT
SYSTEM
26-28
TOTALS
6
H2O
* Cytoplasmic NADH sometimes yield only
1.5 ATP/NADH instead of 2.5 ATP/NADH.
30-32
ATP
6
CO2
Figure 4-18
ATP Production: Large Biomolecules
• Glycogenolysis
• Glycogen
• Storage form of glucose in liver and skeletal
muscle
• Converted to glucose or glucose 6-phosphate
ATP Production: Protein Catabolism and
Deamination
(b) Deamination
(a) Protein catabolism
NAD + H2O
NADH + H+
Deamination
NH3
Ammonia
Organic acid
Amino acid
Protein or Peptide
H2O
Hydrolysis of
peptide bond
Peptide
+
Glycolysis or
citric acid cycle
+
Amino acid
(c)
NH3
Ammonia
H+
NH4+
Ammonium
Urea
Figure 4-20
ATP Production: Lipolysis
Triglyceride
1 Lipases digest triglycerides
into glycerol and 3 fatty acids.
Glucose
1
Glycerol
2 Glycerol becomes a
glycolysis substrate.
G
L
Y
C
O
L
Y
S
I
S
2
Fatty acid
Pyruvate
Cytosol
3 b-oxidation chops 2-carbon
acyl units off the fatty acids.
3 b-oxidation
CO2
4 Acyl units become acetyl
CoA and can be used in the
citric acid cycle.
Acyl unit 4
Mitochondrial
matrix
Acetyl CoA
CoA
CoA
CITRIC
ACID
CYCLE
Figure 4-21
Synthesis: Gluconeogenesis
Glucose
Liver, kidney
Glucose
synthesis
Glucose 6phosphate
GLYCEROL
G
L
U
C
O
N
E
O
G
E
N
E
S
I
S
AMINO ACIDS
Pyruvate
AMINO ACIDS
LACTATE
Figure 4-22
Synthesis: Lipids
Glucose
G
L
Y
C
O
L
Y
S
I
S
1
Glycerol
3
Pyruvate
Acetyl CoA
Triglyceride
Fatty acid
synthetase
2
CoA
Acyl
unit
1 Glycerol can be made from
glucose through glycolysis.
Fatty acids
2 Two-carbon acyl units from acetyl CoA
are linked together by fatty acid
synthetase to form fatty acids.
3 One glycerol plus 3 fatty acids
make a triglyceride.
Figure 4-23
Synthesis: Lipids
Glucose
G
L
Y
C
O
L
Y
S
I
S
1
Glycerol
Pyruvate
Acetyl CoA
CoA
Acyl
unit
1 Glycerol can be made from
glucose through glycolysis.
Figure 4-23, steps 1
Synthesis: Lipids
Glucose
G
L
Y
C
O
L
Y
S
I
S
1
Glycerol
Pyruvate
Acetyl CoA
Fatty acid
synthetase
2
CoA
Acyl
unit
1 Glycerol can be made from
glucose through glycolysis.
Fatty acids
2 Two-carbon acyl units from acetyl CoA
are linked together by fatty acid
synthetase to form fatty acids.
Figure 4-23, steps 1–2
Synthesis: Lipids
Glucose
G
L
Y
C
O
L
Y
S
I
S
1
Glycerol
3
Pyruvate
Acetyl CoA
Triglyceride
Fatty acid
synthetase
2
CoA
Acyl
unit
1 Glycerol can be made from
glucose through glycolysis.
Fatty acids
2 Two-carbon acyl units from acetyl CoA
are linked together by fatty acid
synthetase to form fatty acids.
3 One glycerol plus 3 fatty acids
make a triglyceride.
Figure 4-23, steps 1–3
Synthesis: DNA to Protein
Gene
Regulatory proteins
1 GENE ACTIVATION
Constitutively
active
Regulated
activity
Induction
Repression
2 TRANSCRIPTION
mRNA
3 mRNA PROCESSING
Alternative
splicing
siRNA
Interference
mRNA “silenced”
Processed
mRNA
Nucleus
• rRNA in ribosomes
• tRNA
• Amino acids
4 TRANSLATION
Cytoplasm
Protein chain
5 POST-TRANSLATIONAL
MODIFICATION
Folding and
cross-links
Cleavage into
smaller peptides
Addition of groups:
• sugars
• lipids
• -CH3
• phosphate
Assembly into
polymeric proteins
Figure 4-25
Synthesis: DNA to Protein
Gene
Regulatory proteins
1 GENE ACTIVATION
Constitutively
active
Regulated
activity
Induction
Repression
Nucleus
Cytoplasm
Figure 4-25, steps 1
Synthesis: DNA to Protein
Gene
Regulatory proteins
1 GENE ACTIVATION
Constitutively
active
Regulated
activity
Induction
Repression
2 TRANSCRIPTION
mRNA
Nucleus
Cytoplasm
Figure 4-25, steps 1–2
Synthesis: DNA to Protein
Gene
Regulatory proteins
1 GENE ACTIVATION
Constitutively
active
Regulated
activity
Induction
Repression
2 TRANSCRIPTION
mRNA
3 mRNA PROCESSING
Alternative
splicing
siRNA
Interference
mRNA “silenced”
Processed
mRNA
Nucleus
Cytoplasm
Figure 4-25, steps 1–3
Synthesis: DNA to Protein
Gene
Regulatory proteins
1 GENE ACTIVATION
Constitutively
active
Regulated
activity
Induction
Repression
2 TRANSCRIPTION
mRNA
3 mRNA PROCESSING
Alternative
splicing
siRNA
Interference
mRNA “silenced”
Processed
mRNA
Nucleus
4 TRANSLATION
• rRNA in ribosomes
• tRNA
• Amino acids
Cytoplasm
Protein chain
Figure 4-25, steps 1–4
Synthesis: DNA to Protein
Gene
Regulatory proteins
1 GENE ACTIVATION
Constitutively
active
Regulated
activity
Induction
Repression
2 TRANSCRIPTION
mRNA
3 mRNA PROCESSING
Alternative
splicing
siRNA
Interference
mRNA “silenced”
Processed
mRNA
Nucleus
• rRNA in ribosomes
• tRNA
• Amino acids
4 TRANSLATION
Cytoplasm
Protein chain
5 POST-TRANSLATIONAL
MODIFICATION
Folding and
cross-links
Cleavage into
smaller peptides
Addition of groups:
• sugars
• lipids
• -CH3
• phosphate
Assembly into
polymeric proteins
Figure 4-25, steps 1–5
Protein: Transcription
RNA
polymerase
1 RNA polymerase binds to DNA.
2 The section of DNA that contains
the gene unwinds.
RNA bases
3 RNA bases bind to DNA,
creating a single strand of mRNA.
Sense
strand
Site of
nucleotide assembly
DNA
Lengthening
mRNA strand
mRNA
transcript
Antisense
RNA
strand
polymerase
4 mRNA and the RNA polymerase
detach from DNA, and the mRNA
goes to the cytoplasm.
mRNA strand released
RNA
polymerase
Leaves nucleus
after processing
Figure 4-26
Protein: Transcription
Gene
Sense
strand
Antisense strand
Promoter
Transcribed section
DNA
TRANSCRIPTION
Unprocessed
mRNA
Introns removed
Exons for protein #1
Introns removed
Exons for protein #2
Figure 4-27
Protein: Transcription and Translation
DNA
1
2
Transcription
mRNA processing
RNA
polymerase
Nuclear
membrane
3 Attachment of
ribosomal subunits
Amino acid
4
tRNA
Growing
peptide
chain
Translation
Incoming tRNA
bound to an
amino acid
Outgoing
“empty” tRNA
Anticodon
mRNA
5
Ribosome
mRNA
Termination
Ribosomal
subunits
Completed
peptide
Figure 4-28
Protein: Transcription and Translation
DNA
1
Transcription
RNA
polymerase
Nuclear
membrane
Figure 4-28, steps 1
Protein: Transcription and Translation
DNA
1
2
Transcription
mRNA processing
RNA
polymerase
Nuclear
membrane
Figure 4-28, steps 1–2
Protein: Transcription and Translation
DNA
1
2
Transcription
mRNA processing
RNA
polymerase
Nuclear
membrane
3 Attachment of
ribosomal subunits
Figure 4-28, steps 1–3
Protein: Transcription and Translation
DNA
1
2
Transcription
mRNA processing
RNA
polymerase
Nuclear
membrane
3 Attachment of
ribosomal subunits
Amino acid
4
tRNA
Growing
peptide
chain
Translation
Incoming tRNA
bound to an
amino acid
Outgoing
“empty” tRNA
Anticodon
mRNA
Ribosome
Figure 4-28, steps 1–4
Protein: Transcription and Translation
DNA
1
2
Transcription
mRNA processing
RNA
polymerase
Nuclear
membrane
3 Attachment of
ribosomal subunits
Amino acid
4
tRNA
Growing
peptide
chain
Translation
Incoming tRNA
bound to an
amino acid
Outgoing
“empty” tRNA
Anticodon
mRNA
5
Ribosome
mRNA
Termination
Ribosomal
subunits
Completed
peptide
Figure 4-28, steps 1–5
Protein: Post-Translational Modification
•
•
•
•
•
Protein folding
Cross-linkage
Cleavage
Addition of other molecules or groups
Assembly into polymeric proteins
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
1 mRNA is transcribed from the
genes in the DNA.
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
5
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
Transport vesicle
6
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
7
Cisterna
8
6 Transport vesicles move the
proteins from the ER to the
Golgi complex.
7 Gogli cisternae migrate from
the cis-face toward the cell
membrane.
9
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
10
Cytosol
Cell
membrane
Extracellular space
8 Some vesicles bud off the
cisterna and move in a
retrograde fashion.
9 At the trans-face, some
vesicles bud off to form
lysosomes.
10 Other vesicles become
secretory vesicles that release
their contents outside the cell.
Figure 4-29
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
Targeted
proteins
mRNA
1
DNA
Growing
amino-acid
chain
Mitochondrion
Cytosolic
protein
Nuclear
pore
1 mRNA is transcribed from the
genes in the DNA.
Endoplasmic
reticulum
Transport vesicle
Cis-Golgi complex
Retrograde
Golgi-ER
transport
Cisterna
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
Targeted
proteins
mRNA
1
DNA
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
Nuclear
pore
1 mRNA is transcribed from the
genes in the DNA.
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
Endoplasmic
reticulum
Transport vesicle
Cis-Golgi complex
Retrograde
Golgi-ER
transport
Cisterna
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–2
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
Nuclear
pore
1 mRNA is transcribed from the
genes in the DNA.
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
Endoplasmic
reticulum
Transport vesicle
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
Cisterna
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–3
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
1 mRNA is transcribed from the
genes in the DNA.
Endoplasmic
reticulum
Transport vesicle
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
Cisterna
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–4
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
1 mRNA is transcribed from the
genes in the DNA.
5
Transport vesicle
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
Cisterna
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–5
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
1 mRNA is transcribed from the
genes in the DNA.
5
Transport vesicle
6
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
Cisterna
6 Transport vesicles move the
proteins from the ER to the
Golgi complex.
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–6
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
1 mRNA is transcribed from the
genes in the DNA.
5
Transport vesicle
6
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
7
Cisterna
6 Transport vesicles move the
proteins from the ER to the
Golgi complex.
7 Gogli cisternae migrate from
the cis-face toward the cell
membrane.
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–7
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
1 mRNA is transcribed from the
genes in the DNA.
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
5
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
Transport vesicle
6
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
7
Cisterna
8
6 Transport vesicles move the
proteins from the ER to the
Golgi complex.
7 Gogli cisternae migrate from
the cis-face toward the cell
membrane.
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
8 Some vesicles bud off the
cisterna and move in a
retrograde fashion.
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–8
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
1 mRNA is transcribed from the
genes in the DNA.
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
5
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
Transport vesicle
6
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
7
Cisterna
8
6 Transport vesicles move the
proteins from the ER to the
Golgi complex.
7 Gogli cisternae migrate from
the cis-face toward the cell
membrane.
9
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
8 Some vesicles bud off the
cisterna and move in a
retrograde fashion.
9 At the trans-face, some
vesicles bud off to form
lysosomes.
Cytosol
Cell
membrane
Extracellular space
Figure 4-29, steps 1–9
Protein: Post-Translational Modification
and the Secretory Pathway
Nucleus
Ribosome
Peroxisome
mRNA
3
1
DNA
Targeted
proteins
Growing
amino-acid
chain
2
Mitochondrion
Cytosolic
protein
1 mRNA is transcribed from the
genes in the DNA.
2 mRNA leaves the nucleus
and attaches to cytosolic
ribosomes, initiating translation
and protein synthesis.
4
Nuclear
pore
Endoplasmic
reticulum
5
3 Some proteins are released by
free ribosomes into the cytosol
or are targeted to specific
organelles.
Transport vesicle
6
4 Ribosomes attached to the
rough endoplasmic reticulum
direct proteins destined for
packaging into the lumen of
the RER.
Cis-Golgi complex
Retrograde
Golgi-ER
transport
5 Proteins are modified as they
pass through the lumen of
the ER.
7
Cisterna
8
6 Transport vesicles move the
proteins from the ER to the
Golgi complex.
7 Gogli cisternae migrate from
the cis-face toward the cell
membrane.
9
Lysosome or
storage vesicle
Trans-Golgi
complex
Secretory
vesicle
10
Cytosol
Cell
membrane
Extracellular space
8 Some vesicles bud off the
cisterna and move in a
retrograde fashion.
9 At the trans-face, some
vesicles bud off to form
lysosomes.
10 Other vesicles become
secretory vesicles that release
their contents outside the cell.
Figure 4-29, steps 1–10
Summary
• Energy
• Chemical
• Transport
• Mechanical
• Kinetic energy
• Potential energy
Summary
• Chemical reactions
• Reactants
• Products
• Reaction rate
• Free energy and activation energy
• Exergonic versus endergonic reactions
• Reversible versus irreversible reactions
Summary
• Enzymes
•
•
•
•
Definition
Characteristics
Law of mass action
Type of reactions
Summary
• Metabolism
• Catabolic versus anabolic reactions
• Control of metabolic pathways
• Aerobic versus anaerobic pathways
Summary
• ATP production
•
•
•
•
Glycolysis
Pyruvate metabolism
Citric acid cycle
Electron transport chain
• Glycogen, protein, and lipid metabolism
Summary
• Synthetic pathways
•
•
•
•
•
•
Gluconeogenesis
Lipid synthesis
Protein synthesis
Transcription
Translation
Post-translational modification