Transcript Metabolic Reactions

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Hole’s Essentials of Human
Anatomy & Physiology
David Shier
Jackie Butler
Ricki Lewis
Power Points prepared by Melanie Waite-Altringer
Biology Faculty Member of
Anoka-Ramsey Community College
APR Enhanced
Lecture Outlines
Chapter 4
Cellular
Metabolism
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Introduction
A.
A living cell is the site of enzyme-catalyzed
metabolic reactions that maintain life.
3
The Composite Cell
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Metabolic Reactions
A.
Metabolic reactions are of two types:
1.
anabolic reactions, larger molecules
are constructed from smaller ones,
a process requiring energy.
2.
catabolic reactions, larger molecules are
broken down, releasing energy. The
reactions of metabolism are often
reversible.
5
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B.
Anabolism
1.
Anabolism provides the substances
needed for growth and repair.
2.
These reactions occur by
dehydration synthesis, removing
a molecule of water to join two
smaller molecules.
6
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3.
Polysaccharides, lipids, and proteins
are constructed via dehydration
synthesis.
a.
To form fats, glycerol and
fatty acids bond.
b.
The bond between two amino
acids is a peptide bond; two
bound amino acids form a
dipeptide, while many joined
form a polypeptide.
7
Fig04.01
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CH2OH
CH2OH
O
H
HO OH
H
O
H
H
H
OH
H
H
+
H
OH
Monosaccharide
CH2OH
O
H
H
HO OH
OH
Monosaccharide
CH2OH
OH
H
O
H
H
HO OH
H
H
O
H
OH
Disaccharide
H
H
H2O
OH
H
H
OH
+
OH
Water
8
Fig04.02
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H
H
C
O
OH
HO
C
H
(CH 2)14 CH3
H
C
O
O
O
H
C
OH
HO
C
C
OH
HO
C
(CH 2)14 CH3
H
C
O
C
H2O
H2O
H2O
(CH2)14 CH3
O
(CH 2)14 CH3
H
Glycerol
(CH2)14 CH3
O
O
H
C
H
C
O
C
(CH2)14 CH3
H
+
3 fatty acid molecules
Fat molecule (triglyceride)
+
3 water
molecules
9
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C.
Catabolism
1.
Catabolism breaks apart larger
molecules into their building blocks.
2.
These reactions occur by hydrolysis,
wherein a molecule of water is
inserted into a polymer which is
split into two smaller molecules.
10
Fig04.03
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Peptide
bond
H
H
N
H
C
C
R
Amino acid
H
H
O
N
H
H
+
C
H
O
C
R
Amino acid
N
H
H
H
O
C
C
R
R
N
C
H
H
Dipeptide molecule
O
C
OH
H2O
+
Water
11
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Control of Metabolic Reactions:
A.
Enzymes control the rates of all the
metabolic reactions of the cell.
B.
Enzyme Action
1.
Enzymes are complex proteins that
function to lower the activation
energy of a reaction so it may begin
and proceed more rapidly. Enzymes
are called catalysts.
12
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2.
3.
4.
5.
Enzymes work in small quantities
and are recycled by the cell.
Each enzyme is specific, acting on
only one kind of substrate.
Active sites on the enzyme combine
with the substrate and a reaction
occurs.
The speed of enzymatic reactions
depends on the number of enzyme
and substrate molecules available.
13
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C.
Factors That Alter Enzymes
1.
Enzymes (proteins) can be denatured
by heat, pH extremes, chemicals,
electricity, radiation, and by other
causes. Enzymes that only become active
when they combine with a nonprotein
component are cofactors. Small organic
cofactors are called coenzymes.
14
Fig04.04
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Substrate molecules
Product molecule
Active site
Enzyme
molecule
(a)
Enzyme-substrate
complex
(b)
(c)
Unaltered
enzyme
molecule
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Energy for Metabolic Reactions:
A.
Energy is the capacity to do work.
B.
Common forms of energy include heat,
light, sound, electrical energy,
mechanical energy, and chemical energy.
16
C.
D.
Release of Chemical Energy 1.
Release of chemical energy in the
cell often occurs through the
oxidation of glucose.
Cellular Respiration consists of 3 reactions:
glycolysis, citric acid cycle & electron
transport chain
1.
ATP
a.
ATP molecules contain three
phosphates in a chain.
b.
A cell uses ATP for many
functions including active
transport and synthesis of
various compounds.
Fig04.05
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Glucose
High-energy electrons (e–)
Cytosol
Glycolysis
1 The 6-carbon sugar glucose is broken down in the cytosol
into two 3-carbon pyruvic acid molecules with a net gain
of 2 ATP and the release of high-energy electrons.
2 ATP
Glycolysis
2 Pyruvic acids
(Each enters separately)
3 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
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.
High-energy electrons (e–)
CO2
Mitochondrion
Citric Acid Cycle
2 The 3-carbon pyruvic acids generated by glycolysis enter
the mitochondria separately. Each loses a carbon
(generating CO2) and is combined with a coenzyme to
form a 2-carbon acetyl coenzyme A (acetyl CoA). More
high-energy electrons are released.
Acetyl CoA
Citric acid
Oxaloacetic acid
Citric acid
cycle
High-energy electrons (e–)
2 CO2
2 ATP
Electron Transport Chain
4 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 series of enzymes that store much of the remaining
energy in 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.
Electron
transport
chain
32–34 ATP
2e– and 2H+
½ O2
H2O
18
c.
Energy is stored in the last
phosphate bond of ATP.
d.
Energy is stored while
converting ADP to ATP; when
energy is released, ATP
becomes ADP, ready to be
regenerated into ATP.
19
Fig04.06
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P
ATP
P
P
Fig04.07
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P
Energy transferred
from cellular
respiration used
to reattach
phosphate
P
P
Energy transferred
and utilized by
metabolic
reactions when
phosphate bond
is broken
ATP
P
P
P
P
ADP
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2.
Glycolysis
a.
The first part of cellular respiration
is the splitting of 6-C glucose that
occurs through a series of enzymecatalyzed steps called glycolysis.
b.
Glycolysis occurs in the cytosol and
does not require oxygen (is
anaerobic).
c.
Energy from ATP is used to start the
process but there is a net gain of
energy as a result.
22
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3.
Aerobic Respiration
1.
Oxygen is needed for aerobic
respiration, which occurs within the
mitochondria.
2.
There is a much greater gain of ATP
molecules from aerobic respiration.
3.
The final products of glucose
oxidation are carbon dioxide, water,
and energy.
23
Mitochondrion
Cristae of Mitochondrion
Fig04.09
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Food
© Royalty-Free/Corbis
Proteins
(egg white)
Carbohydrates
(toast, hash browns)
Amino acids
Simple sugars
(glucose)
Glycolysis
Fats
(butter)
Glycerol
2 Breakdown of simple
molecules to acetyl
coenzyme A
accompanied by
production of limited
ATP and high-energy
electrons
Acetyl coenzyme A
3 Complete oxidation
of acetyl coenzyme A
to H2O and CO2 produces
high-energy electrons,
which yield much ATP
via the electron transport
chain
CO2
ATP
High-energy
electrons
Electron
transport
chain
Fatty acids
ATP
Pyruvic acid
Citric
acid
cycle
1 Breakdown of large
molecules to
simple molecules
ATP
2e– and 2H+
–NH2
CO2
½ O2
H2 O
Waste products
26
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Metabolic Pathways:
A.
B.
The enzymes controlling either an
anabolic or catabolic sequence of
reactions must act in a specific order.
A sequence of enzyme-controlled
reactions is called a metabolic pathway.
27
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C.
Regulation of Metabolic Pathways
1.
The rate of a metabolic pathway is
determined by a regulatory enzyme
responsible for one of its steps.
2.
A rate-limiting enzyme is the first
step in a series.
28
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DNA (Deoxyribonucleic acid):
A.
Deoxyribonucleic acid (DNA) contains the
genetic code needed for the synthesis of
each protein (including enzymes) required
by the cell.
B.
Genetic Information
1.
A gene is a portion of a DNA
molecule that contains the genetic
information for making a single
protein. The complete set of
instructions is the genome.
29
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C.
DNA Molecules
1.
The nucleotides of DNA form a
sugar-phosphate backbone with
bases extending into the interior
of the DNA molecule.
2.
The nucleotides of one DNA strand
are compatible to those in the other
strand (adenine pairs with thymine;
cytosine with guanine) and so
exhibit complementary base pairing.
30
Fig04.10
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3.
The DNA molecule twists
to form a double helix and
may be millions of base
pairs long.
A
T
C
G
G
C
C
G
T
A
C
G
C
G
A
T
C
G
A
T
G
C
T
A
T
A
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D.
DNA Replication
1.
Each new cell must be provided with
an exact replica of the parent cell's
DNA.
2.
DNA replication occurs during
interphase.
a.
The DNA molecule splits.
b.
Nucleotides form complementary
pairs with the original strands.
3.
Each new DNA molecule consists of
one parental strand and one newlysynthesized strand of DNA.
32
Fig04.11
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A
T
C
G
G
C
C
G
Original DNA
molecule
A
T
C
G
C
G
A
T
A
C
T
G
A
T
G
C
C
Region of
replication
G
T
A
A
T
A
T
A
G
C
C
A
G
A
T
T
T
C
T
A
T
T
G
A
G
G
A
Newly formed
DNA molecules
C
G
A
33
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Protein Synthesis:
A.
The Genetic Code- Instructions for making
proteins
1.
The genetic code is the
correspondence of gene and protein
building block sequences.
2.
DNA molecules are trapped within a cell’s
nucleus
3.
Protein synthesis occurs in the cytoplasm
4.
Genetic information must be carried from
the nucleus to the cytoplasm
34
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2.
Transcription
a.
RNA molecules are singlestranded and contain ribose
rather than deoxyribose, and
uracil rather than thymine.
b.
Messenger RNA (mRNA)
molecules are synthesized in
the nucleus in a sequence
complementary to the DNA
template in a process called
transcription.
35
Nucleus
Nuclear Pores
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3.
Translation
a.
Each amino acid corresponds
to a triplet of DNA nucleotides; a
triplet of nucleotides in
messenger RNA is called a codon.
b.
Messenger RNA can move out of
the nucleus and associate with
ribosomes in the cytoplasm where
the protein will be constructed in
a process called translation.
38
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c.
d.
In the cytoplasm, a second
kind of RNA, called transfer
RNA, has a triplet of nucleotides
called the anticodon, which is
complementary to nucleotides of
the messenger RNA codon.
The ribosome holds the
messenger RNA in position while
the transfer RNA carries in the
correct amino acid in sequence,
with anticodons matching up to
codons.
39
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e.
The ribosome contains
enzymes needed to join the
amino acids together.
f.
As the amino acids are joined,
the new protein molecule into
its unique shape.
40
Membrane-bound Ribosomes
Free Ribosomes
Rough Endoplasmic Reticulum
Fig04.13
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3 Translation begins as tRNA anticodons
recognize complementary mRNA codons,
thus bringing the correct amino acids into
position on the growing polypeptide chain
Cytoplasm
DNA
double
helix
T
Nucleus
A
T
G
A
C
T A
G
C G
T
A
G
C
A
T
C
T A
G C
A
T
G
C G
T
A
G
C
A
T
C
T A
A
T
G C
T
A
G C
A
T
G
DNA
strands
pulled
apart
C
T
A
T
G
G
G
C
T
C
C
G
C
A
A
C
G
G
C
A
G
G
C
T
C
C
A
T
G
A
C
G
C G
T
A
G
C
T
U
A
2 mRNA leaves
the nucleus
and attaches
Messenger
to a ribosome
RNA
6 tRNA molecules
can pick up another
molecule of the
same amino acid
and be reused
Polypeptide
chain
G
C
G C
G C
C G
U A
C G
C G
G C
C G
A T
A T
C G
G C
G C
C G
A T
G C
G C
C G
U A
C G
C G
A
U A
G C
A T
C G
C
5 At the end of the mRNA,
the ribosome releases
the new protein
Direction of “reading”
1 DNA
information
is copied, or
transcribed,
into mRNA
following
complementary
base pairing
4 As the ribosome
moves along the
mRNA, more amino
acids are added
Amino acids
represented
A
U
Codon 1
Methionine
Codon 2
Glycine
Codon 3
Serine
Codon 4
Alanine
Codon 5
Threonine
Codon 6
Alanine
Codon 7
Glycine
G
G
G
C
U
C
C
Messenger
RNA
A
G
Amino acids
attached to tRNA
C
A
G
C
A
C
G
C
A
T
G
G
C
G
C
C
G
A
G
Transcription
U
C
G
C
DNA
strand
C
A
G
Translation
G
G
C
44
Fig04.14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 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
Growing
polypeptide
chain
3
4
Next amino acid
5
6
Transfer
RNA
Anticodon
U G C C G U
A U G G G C U C C G C A A C G G C A G G C A A G C G U
1
2
3
4
5
6
Messenger
RNA
7
Codons
Peptide bond
1
2
2 A second tRNA binds
complementarily to the
next codon, and in doing
so brings the next amino
acid into position on the ribosome.
A peptide bond forms, linking
the new amino acid to the
growing polypeptide chain.
Growing
polypeptide
chain
3
Next amino acid
4
5
6
Transfer
RNA
Anticodon
U G C C G U
A U G G G C U C C G C A A C G G C A G G C A A G C G U
1
2
3
4
5
6
Messenger
RNA
7
Codons
1
2
3 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.
3
4
7
5
Next
amino acid
6
Transfer
RNA
C G U
A U
1
G G C U C C G C A A C G G C A G G C A A G C G U
2
3
4
5
6
7
Messenger
RNA
Ribosome
1
2
3
4 A new tRNA complementary to
the next codon on mRNA brings
the next amino acid to be added
to the growing polypeptide chain.
4
5
6
7
Next
amino acid
Transfer
RNA
C G U C C G
A U G G G C U C C G C A A C G G C A G G C A A G C G U
1
2
3
4
5
6
7
Messenger
RNA
45