Download Glucose

Parts of Chapter 2, and 24
Figure 2.11 Patterns of chemical reactions.
(a)
Synthesis reactions
Smaller particles are bonded
together to form larger,
more complex molecules.
(b)
Decomposition reactions
Bonds are broken in larger
molecules, resulting in smaller,
less complex molecules.
(c)
Exchange reactions
Bonds are both made and broken
(also called displacement reactions).
Example
Example
Example
Amino acids are joined together to
form a protein molecule.
Glycogen is broken down to release
glucose units.
ATP transfers its terminal phosphate
group to glucose to form glucose-phosphate.
+
Amino acid
molecules
Glycogen
Protein
molecule
Glucose
molecules
Glucose
Adenosine triphosphate (ATP)
+
Glucose
phosphate
Adenosine diphosphate (ADP)
(a) Synthesis reactions
Smaller particles are bonded
together to form larger,
more complex molecules.
Example
Amino acids are joined together to
form a protein molecule.
Amino acid
molecules
Protein
molecule
.
(b) Decomposition reactions
Bonds are broken in larger
molecules, resulting in smaller,
less complex molecules.
Example
Glycogen is broken down to release
glucose units.
Glycogen
Glucose
molecules
.
(c) Exchange reactions
Bonds are both made and broken
(also called displacement reactions).
Example
ATP transfers its terminal phosphate
group to glucose to form glucose-phosphate.
+
Glucose
Adenosine triphosphate (ATP)
+
Glucose
phosphate
Adenosine diphosphate (ADP)
.
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
(a) Primary structure:
The sequence of
amino acids forms the
polypeptide chain.
(b) Secondary structure:
The primary chain forms
spirals (-helices) and
sheets (-sheets).
-Helix: The primary chain is coiled
to form a spiral structure, which is
stabilized by hydrogen bonds.
-Sheet: The primary chain “zig-zags” back
and forth forming a “pleated” sheet. Adjacent
strands are held together by hydrogen bonds.
(c) Tertiary structure:
Superimposed on secondary structure.
-Helices and/or -sheets are folded up
to form a compact globular molecule
held together by intramolecular bonds.
(d) Quaternary structure:
Two or more polypeptide chains, each
with its own tertiary structure, combine
to form a functional protein.
Tertiary structure of prealbumin
(transthyretin), a protein that
transports the thyroid hormone
thyroxine in serum and cerebrospinal fluid.
Quaternary structure of a
functional prealbumin molecule.
Two identical prealbumin subunits
join head to tail to form the dimer.
Figure 2.19a Levels of protein
structure.
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
(a) Primary structure:
The sequence of amino acids forms the polypeptide chain.
Figure 2.19b Levels of protein
structure.
-Helix: The primary chain is coiled
to form a spiral structure, which is
stabilized by hydrogen bonds.
-Sheet: The primary chain “zig-zags” back
and forth forming a “pleated” sheet. Adjacent
strands are held together by hydrogen bonds.
(b) Secondary structure:
The primary chain forms spirals (-helices) and sheets (-sheets).
.
Tertiary structure of prealbumin
(transthyretin), a protein that
transports the thyroid hormone
thyroxine in serum and cerebrospinal fluid.
(c) Tertiary structure:
Superimposed on secondary structure. -Helices and/or -sheets are
folded up to form a compact globular molecule held together by
intramolecular bonds.
.
Quaternary structure of
a functional prealbumin
molecule. Two identical
prealbumin subunits
join head to tail to form
the dimer.
(d) Quaternary structure:
Two or more polypeptide chains, each with its own tertiary structure,
combine to form a functional protein.
Figure 2.20 Enzymes lower the activation energy required for a
reaction to proceed rapidly
.
WITHOUT ENZYME
WITH ENZYME
Activation
energy
required
Less activation
energy required
Reactants
Reactants
Product
Product
Figure 2.21 Mechanism of enzyme
action.
Substrates (S)
e.g., amino acids
+
Product (P)
e.g., dipeptide
Energy is
absorbed;
bond is
formed.
Water is
released.
Peptide
bond
Active site
Enzyme (E)
Enzyme-substrate
complex (E-S)
1 Substrates bind
2 Internal
at active site.
rearrangements
Enzyme changes
leading to
shape to hold
catalysis
substrates in
occur.
proper position.
Enzyme (E)
3 Product is
released. Enzyme
returns to original
shape and is
available to catalyze
another reaction.
.
Stage 1 Digestion in
GI tract lumen to
absorbable forms.
Transport via blood to
tissue cells.
PROTEINS
CARBOHYDRATES
Amino acids
Glucose and other sugars
Stage 2 Anabolism
Proteins
(incorporation into
molecules) and
catabolism of nutrients
NH3
to form intermediates
within tissue cells.
FATS
Glycogen
Glucose
Fatty acids
Glycerol
Fats
Pyruvic acid
Acetyl CoA
Stage 3 Oxidative breakdown
of products of stage 2 in
Infrequent
mitochondria of tissue cells.
CO2 is liberated, and H atoms
removed are ultimately delivered
to molecular oxygen, forming
water. Some energy released is
used to form ATP.
Catabolic reactions
Anabolic reactions
Krebs
cycle
H
CO2
Oxidative
phosphorylation
(in electron
transport chain)
O2
H2O
Chemical energy (high-energy electrons)
Chemical energy
Glycolysis
Glucose
Cytosol
Krebs
cycle
Pyruvic
acid
Mitochondrial
cristae
Via substrate-level
phosphorylation
1 During glycolysis,
each glucose
molecule is broken
down into two
molecules of pyruvic
acid in the cytosol.
Electron transport
chain and oxidative
phosphorylation
Mitochondrion
2 The pyruvic acid then enters
the mitochondrial matrix, where
the Krebs cycle decomposes it
to CO2. During glycolysis and
the Krebs cycle, small amounts
of ATP are formed by substratelevel phosphorylation.
Via oxidative
phosphorylation
3 Energy-rich electrons picked up by
coenzymes are transferred to the electron transport chain, built into the cristae
membrane. The electron transport chain
carries out oxidative phosphorylation,
which accounts for most of the ATP
generated by cellular respiration.
Glucose
Glycolysis
Krebs
cycle
Electron transport chain
and oxidative
phosphorylation
Carbon atom
Phosphate
Phase 1
Sugar
Activation
Glucose is
activated by
phosphorylation 2 ADP
and converted
to fructose-1,
Fructose-1,66-bisphosphate
bisphosphate
Phase 2
Sugar
Cleavage
Fructose-1,
6-bisphosphate
is cleaved into
two 3-carbon Dihydroxyacetone
fragments
phosphate
Glyceraldehyde
3-phosphate
Phase 3
Sugar oxidation
and formation
2 NAD+
of ATP
4 ADP
The 3-carbon frag2 NADH+H+
ments are oxidized
(by removal of
hydrogen) and 4 ATP
2 Pyruvic acid
molecules are formed
2 NADH+H+
2 NAD+
2 Lactic acid
To Krebs
cycle
(aerobic
pathway)
Glycolysis
Krebs
cycle
Electron transport chain
and oxidative
phosphorylation
Carbon atom
Inorganic phosphate
Coenzyme A
Cytosol
Pyruvic acid from glycolysis
Transitional
phase
Mitochondrion
(matrix)
NAD+
CO2
NADH+H+
Acetyl CoA
Oxaloacetic acid
NADH+H+
(pickup molecule)
Citric acid
(initial reactant)
NAD+
Malic acid
Isocitric acid
NAD+
Krebs cycle
CO2
NADH+H+
-Ketoglutaric acid
Fumaric acid
CO2
FADH2
Succinic acid
FAD
GTP
ADP
Succinyl-CoA
GDP +
NAD+
NADH+H+
Glycolysis
Krebs
cycle
Electron transport
chain and oxidative
phosphorylation
Intermembrane
space
Inner
mitochondrial
membrane
Mitochondrial
matrix
2 H+ +
FADH2
NADH +
(carrying
from food)
1
2
ATP
synthase
FAD
H+
NAD+
Electron Transport Chain
Electrons are transferred from complex to complex and
some of their energy is used to pump protons (H+) into the
intermembrane space, creating a proton gradient.
ADP +
Chemiosmosis
ATP synthesis is powered by the
flow of H+ back across the inner
mitochondrial membrane through
ATP synthase.
Krebs
cycle
NADH+H+
Electron transport chain
and oxidative
phosphorylation
FADH2
Free energy relative to O2 (kcal/mol)
Glycolysis
Enzyme
Complex I
Enzyme
Complex II
Enzyme
Complex III
Enzyme
Complex IV
Figure 24.12 Energy yield during cellular respiration.
Cytosol
Mitochondrion
2 NADH + H+
Electron
shuttle across
mitochondrial
membrane
Glycolysis
Glucose
Pyruvic
acid
2 NADH + H+
2
Acetyl
CoA
6 NADH + H+
Krebs
cycle
(4 ATP–2 ATP
used for
activation
energy)
Net +2 ATP
by substrate-level
phosphorylation
2 FADH2
Electron transport
chain and oxidative
phosphorylation
10 NADH + H+ x 2.5 ATP
2 FADH2 x 1.5 ATP
+2 ATP
by substrate-level
phosphorylation
About
32 ATP
Maximum
ATP yield
per glucose
+ about 28 ATP
by oxidative
phosphorylation
Figure 24.15 Metabolism of triglycerides.
Glycolysis
Glucose
Stored fats
in adipose
tissue
Dietary fats
Glycerol
Triglycerides
(neutral fats)
Lipogenesis
Fatty acids
Ketone
bodies
Ketogenesis (in liver)
Glyceraldehyde
phosphate
Pyruvic acid
Certain
amino
acids
Acetyl CoA
CO2 + H2O
+
Steroids
Bile salts
Catabolic reactions
Anabolic reactions
Cholesterol
Krebs
cycle
Electron
transport
Figure 24.16 Transamination, oxidative deamination, and keto acid
are utilized for
Transamination
modification: processes that occur
when amino acids
Amino acid + Keto acid
Keto acid + Amino acid
energy.
(-keto(glutamic acid)
Liver
3 During keto
acid modification
the keto acids
formed during
transamination are
altered so they can
easily enter the
Krebs cycle
pathways.
glutaric acid)
Oxidative
deamination
NH3 (ammonia)
Keto acid
modification
Urea
CO2
Modified
keto acid
Blood
Enter Krebs
cycle in body cells
Krebs
cycle
Urea
Kidney
Excreted in urine
1 During
transamination
an amine group
is switched from
an amino acid to
a keto acid.
2 In oxidative
deamination, the
amine group of
glutamic acid is
removed as
ammonia and
combined with CO2
to form urea.
Figure 24.18 Interconversion of carbohydrates, fats, and proteins.
Proteins
Carbohydrates
Fats
Proteins
Glycogen
Triglycerides (neutral fats)
Glucose
Amino acids
Glucose-6-phosphate
Keto acids
Glycerol and fatty acids
Glyceraldehyde phosphate
Pyruvic acid
Lactic acid
NH3
Acetyl CoA
Ketone
bodies
Urea
Excreted
in urine
Krebs
cycle
Figure 24.17 Carbohydrate-fat and amino acid pools.
Food intake
Dietary proteins
and amino acids
Pool of free
amino acids
Components
of structural
and functional
proteins
Nitrogen-containing
Urea
derivatives
(e.g., hormones,
neurotransmitters)
Some lost via cell
sloughing, hair loss
Excreted
in urine
Dietary carbohydrates
and lipids
NH3
Structural
components of
cells (membranes,
etc.)
Pool of
carbohydrates and fats
(carbohydrates fats)
Specialized derivatives
(e.g., steroids,
acetylcholine); bile
salts
Some lost via surface
secretion, cell sloughing
Catabolized Storage
for energy
forms
CO2
Excreted
via lungs
Figure 24.19a Major events and
principal metabolic pathways of the
absorptive state.
Major metabolic thrust:
anabolism and energy storage
Amino
acids
Glucose
Major energy fuel:
glucose (dietary)
Glycerol and
fatty acids
Glucose
Liver metabolism:
amino acids deaminated and
used for energy or stored as fat
Amino acids
CO2 + H2O
Keto acids
+
Proteins
Glycogen
Triglycerides
(a) Major events of the absorptive state
Fats
CO2 + H2O +
In all tissues:
In muscle:
Glycogen
Glucose
Gastrointestinal
tract
CO2 + H2O
Glucose
+
Protein
Amino acids
In liver:
Glucose
Fats
Glucose
Glycogen
Keto
acids
Fatty
acids
Glyceraldehydephosphate
Glycerol
Protein
CO2 + H2O
In adipose
tissue:
Fats
+
(b) Principal pathways of the absorptive state
Fatty
acids
Glycerol
Fats
Fatty
acids
Initial stimulus
Blood glucose
Physiological response
Stimulates
Result
Beta cells of
pancreatic islets
Blood insulin
Targets tissue cells
Active transport
of amino acids
into tissue cells
Facilitated diffusion
of glucose into
tissue cells
Protein synthesis
Enhances glucose
conversion to:
Cellular
respiration
CO2 + H2O
+
Fatty acids
+
glycerol
Glycogen
Figure 24.21a Major events and
principal metabolic pathways of the
postabsorptive state.
Major metabolic thrust:
catabolism and replacement of
fuels in blood
Proteins
Glycogen
Major energy fuels:
glucose provided by glycogenolysis
and gluconeogenesis, fatty acids,
and ketones
Triglycerides
Glucose
Liver metabolism:
amino acids converted to glucose
Amino acids
Fatty acids
and ketones
Keto acids
CO2 + H2O
Amino
acids
Glucose
Glycerol and
fatty acids
(a) Major events of the postabsorptive state
+
Glucose
Glycogen
2
In muscle:
In adipose
tissue:
CO2 + H2O
+
Fat
Protein Pyruvic and
lactic acids
4
3
Amino acids
In most tissues:
4
2
Fat 3
In liver:
Amino acids Pyruvic and
lactic acids
4
Keto acids
Fatty acids
Glycerol
CO2 + H2O
2
3
Fatty
acids +
glycerol
+
Glucose
CO2 + H2O
+
Ketone
bodies
Keto
acids
Blood glucose
1
Stored
glycogen
(b) Principal pathways of the postabsorptive state
In nervous
tissue:
CO2 + H2O
+
Increases, stimulates
Reduces, inhibits
Initial stimulus
Plasma glucose
(and rising amino
acid levels)
Physiological response
Result
Stimulates
Alpha cells of
pancreatic islets
Negative feedback:
rising glucose
levels shut off
initial stimulus Plasma glucagon
Stimulates
glycogenolysis
and gluconeogenesis
Liver
Stimulates
fat breakdown
Adipose tissue
Plasma fatty acids
Plasma glucose
(and insulin)
Fat used by tissue cells
= glucose sparing
Table 24.4 Thumbnail Summary of
Metabolic Reactions
Table 24.5 Profiles of the Major
Body Organs in Fuel Metabolism
Table 24.6 Summary of Normal Hormonal Influences on
Metabolism
Table 24.7 Summary of Metabolic Functions of the Liver (1 of 2)
Table 24.7 Summary of Metabolic Functions of the Liver (2 of 2)