Transcript HUMAN PHYSIOLOGY

Chapter Goals (metabolism)
After studying this chapter, students should be able to
1. describe the steps of glycolysis and discuss the significance of this metabolic
pathway.
2. describe how lactic acid is formed and explain the physiological significance of this
pathway.
3. describe the pathway for the aerobic respiration of glucose through the steps of Krebs
cycle and account for the energy produced.
4. explain the functional significance of the Krebs cycle in relation to the electrontransport system.
5. describe the electron-transport system and oxidative phosphorylation.
6. describe the role of oxygen in aerobic respiration.
7. compare the lactic acid pathway and aerobic respiration in terms of initial substrates,
final products, cellular locations, and the total number of ATP molecules produced
per glucose respired.
8. explain how glucose and glycogen can be interconverted, and how the liver can
secrete free glucose derived from its stored glycogen.
VII. METABOLISM
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Overall Reaction
Glycolysis
Kreb’s Cycle
Electron Transport
Overall Reaction
C6H12O6 + 6O2 D 6H20 + 6CO2 + ENERGY
Biochemistry Conventions
Electron “Shuttles”
• NAD+ = Nicotinamide Adenine
Dinucleotide
• FAD = Flavin Adenine Dinucleotide
5.2
Branchpoint
• Anaerobic --> Lactic Acid
• Aerobic --> Acetyl COA
5.8
5.7
2.13a
2.13b
Overall ATP Production
• Anaerobic (All Substrate Level)
– Total = 4 ATP/glucose
– Net = 4 - 2 = 2 ATP/glucose
• Aerobic
– Substrate Level
• 3ATP/cycle * 2 cycle/glu = 6 ATP
– Oxidative Level
• 1 NADH/cyc from glycolysis * 2cyc/glu *
2ATP/NADH = 4 ATP
• 4 NADH/cyc from Krebs * 2 cyc/glu *
3ATP/NADH = 24 ATP
• 1 FADH2/cyc from Krebs * 2 cycl/glu * 2
ATP/FADH2 = 4 ATP
5.18
Quick Write (10 points)
• A “Health Food” store advertises a “New
miracle dietary supplement, NADH, which,
if taken orally, will put more ATP in your
system”.
• Will you buy the stuff? Why or why not.
Chapter Summary
Glycolysis and the Lactic Acid Pathway
I. Glycolysis refers to the conversion of glucose to two molecules of pyruvic
acid.
A. In the process, two molecules of ATP are consumed and four
molecules of ATP are formed. Thus there is a net gain of two ATP.
B. In the steps of glycolysis two pairs of hydrogens are released.
Electrons from these hydrogens reduce two molecules of NAD.
II. When respiration is anaerobic, reduced NAD is oxidized by pyruvic acid,
which accepts two hydrogen atoms and is thereby reduced to lactic acid.
A. Skeletal muscles use anaerobic respiration and thus produce lactic
acid during the exercise. Heart muscle respires anaerobically for just
a short time, under conditions of ischemia.
B. Lactic acid can be converted to glucose in the liver by a process
called gluconeogenesis.
Chapter Summary
Aerobic Respiration
I. The Krebs cycle begins when coenzyme A donates acetic acid to an enzyme
that adds it to oxaloacetic acid to form citric acid.
A. Acetyl CoA is formed from pyruvic acid by the removal of carbon dioxide and two
hydrogens.
B. The formation of citric acid begins a cyclic pathway that ultimately forms a new
molecule of oxaloacetic acid.
C. As the Krebs cycle progresses, one molecule ATP is formed, and three
molecules of NAD and one of FAD are reduced by hydrogens from the Krebs
cycle.
Chapter Summary
Aerobic Respiration
II. Reduced NAD and FAD donate their electrons to an electrontransport chain of molecules located in the cristae.
A. The electrons from NAD and FAD are passed from one cytochrome of the
electron-transport chain to the next in a series of coupled oxidation-reduction
reactions.
B. As each cytochrome iron gains an electron, it becomes reduced; as it passes the
electron to the next cytochrome, it becomes oxidized.
C. The last cytochrome becomes oxidized by donating its electron to oxygen, which
functions as the final electron acceptor.
D. When one oxygen atom accepts two electrons and two protons, it becomes
reduced to form water.
E. The energy provided by electron transport is used to form ATP from ADP and Pi,
this process is known as oxidative phosphorylation.
Chapter Summary
Aerobic Respiration
III. Thirty-six molecules ATP are produced by the aerobic respiration of one
glucose molecule. Of these, two are produced in the cytoplasm by glycolysis
and the remainder are produced in the mitochondria.
IV. The formation of glycogen from glucose is called glycogenesis, and the
breakdown of glycogen is called glycogenolysis.
A. Glycogenolysis yields glucose-6-phosphate, which can enter the pathway of
glycolysis.
B. The liver contains an enzyme (which skeletal muscles do not) that can produce
free glucose from glucose-6-phosphate. Thus, the liver can secrete glucose
derived from glycogen.
V. Carbohydrate metabolism is influenced by the availability of oxygen and by a
negative feedback effect of ATP on glycolysis and the Krebs cycle.
Chapter Summary
Metabolism of Lipids and Proteins
I. In lipolysis, triglycerides yield glycerol and fatty acids.
A. Glycerol can be converted to phosphoglyceraldehyde and used for energy.
B. In the process of the b-oxidation of fatty acid, a number of acetyl CoA molecules
are produced.
C. Processes that operate in the reverse direction can convert glucose to
triglycerides.
II. Amino acids derived from the hydrolysis of proteins can serve as sources of
energy.
A. Through transamination, a particular amino acid and a particular keto acid
(pyruvic acid or one of the Krebs cycle acids) can serve as substrates to form a
new amino acid and a new keto acid.
B. In oxidative deamination, amino acids are converted into keto acids as their
amino group is incorporated into urea.
III. Each organ uses certain blood-borne energy carriers as its preferred energy
source.
A. The brain has an almost absolute requirement for blood glucose as its energy
source.