Metabolism
Chapter 24
Biology 2122
1. Metabolism:
– Anabolic and Catabolic
Reactions
2. Cell respiration -catabolic
reaction
3. Metabolic pathways
4. Cell Respiration
– Digestion and absorption
of nutrients
– In the cell anabolic process
build up lipids, proteins,
glycogen
– Aerobic respiration in the
mitochondria will produce
ATP
Metabolism overview
Important Aspects of Metabolism
1. Metabolic pathways – enzyme mediated
2. Glucose is oxidized
– other compounds are reduced.
3. Coenzymes – become reduced
– compounds electron and proton carriers.
4. Phosphorylation
– Hydrolysis of ATP
– Transfer of an inorganic phosphate from ATP
Oxidation and reduction
1. Glucose - oxidized in the cell
– C6H12O6 + 6O2 --------- 6CO2 + 6H2O + ATP + Heat
• Oxidation
– gain of oxygen or loss of a hydrogen
– Loss of electrons
• Reduction - gain of hydrogen and electrons
– Cellular respiration oxygen is reduced
– Any compound that receives electrons and hydrogen’s are
reduced
– OIL RIG
• Dehydrogenases
– Enzymes that remove hydrogen atoms from organic
compounds
Role of coenzymes
1. When hydrogen and electrons are being transferred from
one compound to another, which compounds will accept
them?
2. Coenzymes
– Organic compounds (enzyme with a vitamin)
– NAD+ (nicotinamide adenine dinucleotide) (niacin)
– FAD – (flavin adenine dinucleotide) (flavin)
3. What will they do after they are reduced?
– Carry hydrogen and electrons to the ‘electron transport chain’ and
unload them
– Final production of ATP
Phosphorylation and ATP synthesis
• Transfer of a
phosphate group to
another compound
• Metabolic pathways
– Produce ATP
• Substrate-level
phosphorylation
• Oxidative
phosphorylation
ATP formation
Glycolysis
In the Box:
• Glucose (6-C) and
Oxygen
Out of the Box:
• Pyruvic Acid (3-C)
Glycolysis
1. Sugar Activation
2. Sugar Cleavage
– Fructose 1,6-bisphosphate splits
into (2) 3-C compounds
3. ATP and Pyruvate formation
– Final produce is (2) 3-C pyruvate
• Net Totals
– 2 ATP; 2 NADH + H+
Preparing for the Krebs cycle
1. What happens to the 3-C pyruvate?
2. If oxygen is not available (anaerobic)
– Undergo lactic acid fermentation
– Only 2 ATP produce and lactic acid which causes soreness
in the muscles
3. If oxygen is available (aerobic) then pyruvate is
processed
– In the cytosol of mitochondria pyruvate loses a C (CO2) and
becomes acetic acid “decarboxylation”
– Coenzyme A attaches to Acetic Acid ---2-C Acetyl CoA
Krebs cycle
In the Box:
• Acetyl CoA
Out of the Box:
• CO2
• FADH2
• NADH
• ATP
Krebs cycle
• 2-C acetyl CoA is picked up by 4-C
oxaloacetate
– 6-C compound - citric acid
• Formation of intermediates
1. Reactions
– Decarboxylation
– substrate-level phosphorylation produces ATP
– Reduction of FADH2 and NADH + H+
2. Net (Remember the cycle turns twice)
– 2 ATP, 8 NADH, 2 FADH2 , 6 CO2
Oxidative phosphorylation
In the Box:
• NADH
• FADH2
Out of the Box:
• ATP
Electron transport chain and oxidative
phosphorylation
1. NADH + H+ and FADH2 lose their electrons
1. Hydrogen
– When hydrogen ions are released they are move
through channel proteins from the mitochondrial
matrix to the intermembrane space
– They form an ‘electrochemical gradient’
• Electrons
– Accepted by flavins, proteins that contain Fe and
S, cytochromes (pigments with Fe)
– They are ‘passed’ from one to the other down the
chain
– Finally accepted by ½ O2 to produce water
– Movement of these electrons provide the energy
to drive the hydrogen ions across the membrane
Chemiosmosis
1. Hydrogen ions will move
passively through ‘ATP
synthase’
2. As they move through, the
protein ‘spins’ providing
energy to phosphorylate
ADP and produce ATP
3. A total of 34 ATP are produced
– 1 Glucose = 36 net ATP (2-Kreb’s;
2 Glycolysis)
Summary
Glycogenesis and Glycogenolysis
• Excess ATP is accumulated
– Glycolysis declines
– Excess glucose stored as
glycogen or fat
– Glycogenesis occurs
• Glycogenolysis
– Glucose blood levels drop
– Glycogen phosphorylase
• Muscle cells
– Glucose-6 phosphate cannot
move across the membrane
– Glucose-6-phosphatase
Gluconeogenesis/Lipid oxidation
• When glucose levels are very low the liver can
synthesize glucose
– Amino acids + glycerol to produce glucose
– Prevents hypoglycemia
• Lipid Metabolism
– More energy than carbohydrates (9 kcal/g)
– Glycerol (from neutral fats)-- glyceraldehyde phosphate --
Krebs (18 ATP/glycerol)
– F.A. (from neutral fats)----- 2-C acetic acid + CoA (coenzyme A)
--- acetyl CoA -------Krebs
• Beta oxidation
Lipid oxidation
TRIGLYCERIDE
METABOLISM
Animation
BETAOXIDATION
• Lipogenesis:
Lipid metabolism
– excess lipids are not metabolized will be stored as adipose
in the hypodermis (50%) as well as other parts of the body
• Lipogenesis or triglyceride synthesis
– occurs when ATP and glucose levels are high (enough
energy available to the cells)
• Lypolysis: breaking down of stored fats
– Glycerol converted to energy
– Fatty acids
What happens if you deny yourself carbohydrates?
1. If carbohydrate levels are low
2. Oxaloacetic acid is converted to glucose
(fuels the brain).
3. Oxaloacetic acid levels become low and
acetyl CoA cannot enter the Kreb’s
cycle
– Ketogenesis and ketone bodies
– Ketosis - ketone bodies accumulate in the
urine
– pH levels drops to dangerous levels
• Deamination: before
proteins can be oxidized
for energy must lose
ammine group
– Converted to pyruvate
or intermediates of the
Krebs
• Events (notes)
– 1. transamination
– 2. oxidative
deamination
– 3. ketoacid modification
Protein
metabolism
Interconversions
Absorptive states
Post-absorptive state
Insulin
Glucagon and glucose
Liver Metabolism and cholesterol
• Cholesterol - Animation
– is an important component of bile salts; formation of vitamin D,
plasma membrane and steroid hormones
– 15% from the diet - the rest is made from acetyl CoA in the liver,
intestinal cells
• Cholesterol and Triglycerides are insoluble in water
– Transported via lipoproteins
– Proteins regulate lipid entry and exit in the cells
• Types are: HDL (high protein); LDL (lower protein); VLDL;
Chylomicrons
Cholesterol transport
1. Liver produces VLDL --- transport triglycerides to
adipose and other tissues ------converted to
LDL (much cholesterol)------ transports
cholesterol to peripheral tissues
2. HDL transports excess cholesterol from peripheral
tissues to liver --- broken down and becomes
parts of bile
3. HDL is made in a collapsed form ----- moves from
liver to blood and picks up cholesterol from the
tissue cells and some pulled from artery walls
Cholesterol Levels
1. Liver will stimulate the production of a basal amount of
cholesterol (85%)
– Dieting will not override genetics up to a certain point
2. Saturated fats ------ stimulate liver production of
cholesterol and inhibit secretion
3. Unsaturated fats ------- increase excretion of
cholesterol
– Hydrogenation and trans-fatty acids
– Omega 3’s lower cholesterol levels – fatty fish
• Levels
– HDL (<130) is good; LDL (>60) is good
Feeding centers
Body temperature regulation