Human Physiology Cell respiration and metabolism

1. Cell Respiration and Metabolism
Human
physiology

2. Metabolism
• All reactions that involve energy
transformations.
• Divided into 2 Categories:
▫ Catabolic:
 Release energy.
 Breakdown larger molecules into smaller
molecules.
▫ Anabolic:
 Require input of energy.
 Synthesis of large energy-storage molecules.

3. Aerobic Cell Respiration
• Oxidation-reduction reactions:
▫ Break down of molecules for energy.
▫ Electrons are transferred to
intermediate carriers, then to the final
electron acceptor: oxygen.
 Oxygen is obtained from the blood.

4. Glycolysis
• Breakdown of glucose for energy in the
cytoplasm.
• Glucose is converted to 2 molecules of pyruvic
acid (pyruvate).
• Each pyruvic acid contains:
▫ 3 carbons
▫ 3 oxygens
▫ 4 hydrogens
• 4 hydrogens are removed from intermediates.

6. Glycolysis
• Each pair of H+
reduces a molecule of NAD.
• Produces:
▫ 2 molecules of NADH and 2 unbound H+
▫ 2 ATP
• Glycolysis Pathway:
• Glucose + 2 NAD + 2 ADP + 2 Pi
2 pyruvic acid + 2 NADH and 2 ATP

7. Glycolysis
• Glycolysis is exergonic.
▫ Energy released used to drive endergonic reaction:
 ADP + Pi ATP
• Glucose must be activated first before energy
can be obtained.
▫ ATP consumed at the beginning of glycolysis.

8. Glycolysis
• ATP ADP + Pi
• Pi is not released but added to intermediate
molecules (phosphorylation).
• Phosphorylation of glucose, traps the glucose
inside the cell.
• Net gain of 2 ATP and 2 NADH.

10. Glycolysis

11. Lactic Acid Pathway
• Anaerobic respiration:
▫ Oxygen is not used in the process.
• NADH + H+
+ pyruvic acid
lactic acid and NAD.
• Produce 2 ATP/ glucose molecule.

12. Lactic Acid Pathway
• Some tissues adapted to anaerobic
metabolism:
▫ Skeletal muscle: normal daily
occurrence.
▫ RBCs do not contain mitochondria
and only use lactic acid pathway.
• Cardiac muscle: ischemia

14. Glycogenesis and
Glycogenolysis
• Increase glucose intracellularly,
would increase osmotic pressure.
• Must store carbohydrates in form
of glycogen.

15. • Glycogenesis: formation of glycogen from glucose.
• Glycogenolysis: conversion of glycogen to glucose-6-
phosphate.
▫ Glucose-6-phosphate can be utilized through glycolysis.

16. Glycogenesis and
Glycogenolysis
• Glucose-6-phosphate cannot leak out of the
cell.
• Skeletal muscles generate glucose-6-
phosphate for own glycolytic needs.
• Liver contains the enzyme glucose-6-
phosphatase that can remove the phosphate
group and produce free glucose.

17. Cori Cycle
• Lactic acid produced by anaerobic respiration
delivered to the liver.
• LDH converts lactic acid to pyruvic acid.
• Pyruvic acid converted to glucose-6-
phosphate:
▫ Intermediate for glycogen.
▫ Converted to free glucose.
• Gluconeogenesis: conversion to non-
carbohydrate molecules through pyruvic acid
to glucose.

19. Aerobic Respiration
• Aerobic respiration of glucose,
pyruvic acid is formed by
glycolysis, then converted into
acetyl coenzyme A (acetyl CoA).
• Energy is released in oxidative
reactions, and is captured as ATP.

20. Aerobic Respiration
• Pyruvic acid enters interior of
mitochondria.
• Converted to acetyl CoA and 2 C02.
• Acetyl CoA serves as substrate for
mitochondrial enzymes.

21. Acetyl CoA enters the Krebs Cycle.

22. overview

23. Krebs Cycle
• Acetyl CoA combines with oxaloacetic acid to
form citric acid.
• Citric acid enters the Krebs Cycle.
• Produces oxaloacetic acid to continue the
pathway.
• 1 GTP, 3 NADH, and 1 FADH2
• NADH and FADH2 transport electrons to
Electron Transport Cycle.

24. CAC

26. Electron Transport
• Cristae of inner mitochondrial
membrane contain molecules that
serve as electron transport system.
• Electron transport chain consists of
FMN, coenzyme Q, and cytochromes.

27. ETC Chain
• Each cytochrome transfers electron pairs from
NADH and FADH2 to next cytochrome.
• Oxidized NAD and FAD are regenerated and
shuttle electrons from the Krebs Cycle to the
ETC.
• Cytochrome receives a pair of electrons.
• Iron reduced, then oxidized as electrons are
transferred.

28. ETC Chain
• Cytochrome a3 transfers electrons to
O2 (final electron acceptor).
• Oxidative phosphorylation occurs:
▫ Energy derived is used to phosphorylate
ADP to ATP.

30. Coupling ETC to ATP
• Chemiosmotic theory:
• ETC powered by transport of
electrons, pumps H+
from
mitochondria matrix into space
between inner and outer
mitochondrial membranes.

31. Coupling ETC to ATP
• Proton pumps:
• NADH-coenzyme Q reductase complex:
▫ Transports 4 H+
for every pair of electrons.
• Cytochrome C reductase complex:
▫ Transports 4 H+
.
• Cytochrome C oxidase complex:
▫ Transports 2 H+
.

32. Coupling ETC to ATP
• Higher [H+
] in inter-membrane space.
• Respiratory assemblies:
▫ Permit the passage of H+
.
• Phosphorylation is coupled to oxidation, when
H+
diffuse through the respiratory assemblies:
▫ ADP and Pi ATP

33. Coupling ETC to ATP
• Oxygen functions as the last electron
acceptor.
▫ Oxidizes cytochrome a3.
• Oxygen accepts 2 electrons.
• O2 + 4 e-
+ 4 H+
2 H20

35. ATP Produced
• Direct phosphorylation:
• Glycolysis:
▫ 2 ATP
• Oxidative phosphorylation:
▫ 2.5 ATP produced for pair of electrons each
NADH donates.
▫ 1.5 ATP produced for each pair of electrons
FADH2 donates ((activates 2nd
and 3rd
proton
pumps).
▫ 26 ATP produced.

36. Metabolism of Lipids
• When more
energy is taken
in than
consumed,
glycolysis
inhibited.
• Glucose
converted into
glycogen and fat.

37. Lipogenesis
• Formation of
fat.
• Occurs mainly
in adipose
tissue and liver.
• Acetic acid
subunits from
acetyl CoA
converted into
various lipids.

38. Metabolism of Lipids
• Lipolysis:
▫ Breakdown of fat.
• Triglycerides glycerol + fa
• Free fatty acids (fa) serve as blood-
borne energy carriers.
lipase

39. Beta-oxidation
• Enzymes
remove
2-carbon
acetic acid
molecules
from acid end
of fa.
• Forms acetyl
CoA.
• Acetyl CoA
enters Krebs
Cycle.

40. Metabolism of Proteins
• Nitrogen is ingested primarily as protein.
• Excess nitrogen must be excreted.
• Nitrogen balance:
▫ Amount of nitrogen ingested minus amount
excreted.
• + N balance:
▫ Amount of nitrogen ingested more than amount excreted.
• - N balance:
▫ Amount of nitrogen excreted greater than ingested.

41. • Adequate amino acids are required for growth and repair. A
new amino acid can be obtained by:
• Transamination:
▫ Amino group (NH2) transferred from one amino acid to form another.

42. • Process by which excess amino acids are
eliminated.
• Amine group from glutamic acid removed, forming
ammonia and excreted as urea.

43. Deamination
• Energy
conversion:
amino acid is
deaminated.
• Ketoacid can
enter the Krebs
Cycle.

44. Use of different energy sources.