Download Metabolism

Combined
Chapters
Carbohydrate, Lipid,
and Protein
Metabolism
Stage 1: Digestion of Carbohydrates
• In the mouth, salivary amylase hydrolyzes aglycosidic bonds in polysaccharides to give
smaller polysaccharides (dextrins), maltose, and
some glucose.
• In the small intestine, pancreatic amylase
hydrolyzes dextrins to maltose and glucose.
• The disaccharides maltose, lactose, and sucrose
are hydrolyzed to monosaccharides.
• The monosaccharides enter the bloodstream for
transport to the cells.
Metabolism | # 2
Summary of carbohydrate digestion
in the human body.
Metabolism | # 3
Metabolism
Section of the
small intestine,
showing its folds
and the villi that
cover the inner
surface of the
folds.
© Ed Reschke / Peter Arnold, Inc.
Metabolism | # 4
Glycolysis: Splitting Sugar
• In Stage 2, the metabolic pathway called glycolysis degrades
glucose (6C) obtained from digestion to pyruvate (3C)
Metabolism | # 5
Glycolysis: Energy-Investment
In reactions 1-5 of glycolysis:
• Energy is used to add phosphate
groups to glucose and fructose
• Glucose is converted to two
three-carbon molecules
Metabolism | # 6
Glycolysis: Energy-Production
• In reactions 7 and 10, the
hydrolysis of triose
phosphates generates four
ATP molecules
Metabolism | # 7
Step 1: Formation of Glucose 6-phosphate
Step 2: Formation of Fructose 6-Phosphate
O
OH
ATP
ADP
O H
H
H
H
HO
P
O
O H
OH H
H
H
HO
OH
OH
Hexokinase
H
HO
OH
Step 1
H
OH
OH
OH
O
HO
Step 2
P
O
O
O H
OH H
H
H
H
HO
HO
P
O
OH
O
H
HO
OH
OH
OH
OH
OH
H
phosphoglucoisomerase
OH
H
Metabolism | # 8
Step 3: Formation of Fructose 1,6-bisphosphate
Step 4: Formation of Triose Phosphates
ATP
O
Step 3
HO
O
P
P
OH
6
5 C
H
4
O
P
H
HO
C
C
OH
H
OH
3
O
OH
2 C
OH
HO
Aldolase
O
CH2
P
OH
H
O
O
1
P
OH
H
OH
H2C
C 2
O
O
H
HO
H
H2C
O
O
phosphofructokinase
O
O
P
O
OH
OH
OH
HO
HO
O
H
HO
H
1
O
OH
OH
O
ADP
OH
4 CH
5 HC
OH
+
H2C
6
OH
O
O
P
Step 4
OH
OH
3
Metabolism | # 9
OH
Step 5: Isomerization of Triose
Phosphates
Step 5
O
H2C
C
HO
O
O
CH2
P
OH
OH
+
O
O
CH
CH
HC
OH
O
H2C
O
P
OH
2
OH
Triosephosphate
isomerase
HC
OH
O
H2C
O
P
OH
OH
By the end of Step 5, we have:
1. Used two molecules of ATP so we can
2. Break Glucose (6C) into 2 3C units of
glyceraldehyde 3-phosphate
Metabolism | # 10
Step 6: Formation of 1,3-Bisphosphoglycerate
Step 7: Formation of 3-Phosphoglycerate
Step 6
+ 2NAD+ +2Pi
2
2
+ 2NADH + 2H+
Glyceraldehyde
3-phosphate dehydrogenase
Step 7
O
O
O
P
OH
OH
2
O
2ADP
2ATP
OH
2
O
O
P
OH
OH
O-
phosphoglycerokinase
OH
O
O
P
OH
OH
Metabolism | # 11
Step 8: Formation of 2-Phosphoglycerate
Step 9: Formation of Phosphoenolpyruvate
O
O-
O
OC
2
OH
O
O
P
2
OH
phosphoglyceromutas
e
OH
O
2
O
P
HC
H2C
OH
O
O
O
P
OH
OC
OH
2
OH
H2C
Step 8
OH
OH
OC
Step 9
HC
O
enolase
C
O
O
P
OH
OH
HC
H
+2H2O
Metabolism | # 12
Step 10: Formation of Pyruvate
O
OC
2
C
O
O
P
OH
HC
2ADP
H
O
2ATP
C
2
OH
pyruvate kinase
O-
C
O
CH3
By the end of Step 10, we have:
1. Generated 4 ATP molecules (2 net)
Metabolism | # 13
Glycolysis: Overall Reaction
• Glycolysis generates 2 ATP and 2 NADH
• Two ATP are used in energy-investment to add phosphate
groups to glucose and fructose-6-phosphate
• Four ATP are formed in energy-generation by direct
transfers of phosphate groups to four ADP.
Glucose + 2ADP + 2Pi + 2NAD+ 
2Pyruvate + 2ATP + 2NADH + 4H+
Metabolism | # 14
Metabolism
Metabolism | # 15
Regulation of Glycolysis
• Reaction 1 Hexokinase is inhibited by high levels
of glucose-6-phosphate (feedback)
• Reaction 3 Phosphofructokinase, an allosteric
enzyme, is inhibited by high levels of ATP and
activated by high levels of ADP and AMP
• Reaction 10 Pyruvate kinase, another allosteric
enzyme is inhibited by high levels of ATP or acetyl
CoA
Metabolism | # 16
Pathways for Pyruvate
When oxygen is present in the cell, pyruvate from
glycolysis is decarboxylated to produce acetyl CoA
(enters TCA cycle) and CO2
• Pyruvate + HS-CoA + NAD+ 
acetyl CoA + CO2 + NADH + H+
Metabolism | # 17
Lactate Formation
When oxygen is not available, pyruvate is reduced
to lactate, which replenishes NAD+ to continue
glycolysis
• Pyruvate + NADH + H+  lactate + NAD+
Metabolism | # 18
Lactate in Muscles
Under anaerobic conditions (strenuous exercise):
• Oxygen in the muscles is depleted
• Lactate accumulates in the muscles
• Muscles tire and become painful
• Rest is needed to repay the oxygen debt and to
reform pyruvate in the liver
Metabolism | # 19
Fermentation
Fermentation:
• Occurs in anaeobic microorganisms such as yeast
• Decarboxylates pyruvate to acetaldehyde, which is
reduced to ethanol.
• Regenerates NAD+ to continue glycolysis
• Pyruvate + NADH + H+  ethanol + NAD+ + CO2
Metabolism | # 20
All three of the common fates of pyruvate from glycolysis provide
for the regeneration of NAD+ from NADH.
Metabolism | # 21
Metabolism
Structural
relationships
among glycerol
and acetone and
the C3
intermediates.
Metabolism | # 22
Metabolism
Entry points for
fructose and
galactose into
the glycolysis
pathway.
Metabolism | # 23
Metabolism
The dihyroxyacetone
phosphate-glycerol 3phosphate shuttle.
Cytosolic NADH can not
cross mitochondrial
membrane.
Shuttle brings cytosolic
electrons into
mitochondria in form of
mitochondrial FADH2
Metabolism | # 24
Metabolism
The processes of
glycogenesis,
storage of
glucose and
glycogenolysis,
liberating glucose,
are contrasted.
Metabolism | # 25
Metabolism
The Cori Cycle
Metabolism | # 26
Metabolism
Metabolism | # 27
Metabolism
Saturn Stills / SPL / Photo Researchers
A diabetic giving himself a blood
glucose test.
Metabolism | # 28
Metabolism
The events that must occur before triacylglycerols can reach the
bloodstream through the digestive process.
Metabolism | # 29
Metabolism
Chylomicron, a
type of lipoprotein
Metabolism | # 30
Metabolism
Structural
characteristics of
the adipose cell.
Metabolism | # 31
Metabolism
Fatty acids are
transported across the
inner mitochondrial
membrane in the form
of acyl carnitine.
Metabolism | # 32
Reactions of the fatty
acid spiral for an 18:0
fatty acid.
Metabolism | # 33
Lipids cont’d
Metabolism | # 34
Metabolism
Summary of
protein
digestion in
human body.
Metabolism | # 35
Metabolism
Metabolism | # 36
Metabolism
Possible fates for
amino acid degradation
products.
Metabolism | # 37
Metabolism
Key compounds in the
transamination /
oxidative deamination
process include three
keto acid/amino acid
pairs.
Metabolism | # 38
The
fourstep
urea
cycle.
Metabolism | # 39
Metabolism
Fates of the carbon
skeletons of amino
acids.
Metabolism | # 40
Metabolism
The starting materials
for the biosynthesis of
the 11 nonessential
amino acids.
Metabolism | # 41
Metabolism | # 42
Human
body
response
to
feasting,
fasting,
and
starving.
Metabolism | # 43