Cell Respiration and Metabolism | human physiology | PPT

December 18, 2012 | By | Reply More

Cell Respiration and Metabolism | human physiology | PPT

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Cell Respiration and Metabolism




All reactions that involve energy transformations.

Divided into 2 Categories:


Release energy.

Breakdown larger molecules into smaller molecules.


Require input of energy.

Synthesis of large energy-storage molecules.


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.



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.



Each pair of H+ reduces a molecule of NAD.


2 molecules of NADH and 2 unbound  H+


Glycolysis Pathway:

Glucose + 2 NAD + 2 ADP + 2 Pi                 

2 pyruvic acid + 2 NADH and 2 ATP


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.


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.



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.

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


Glycogenesis and Glycogenolysis

Increase glucose intracellularly, would increase osmotic pressure.

Must store carbohydrates in form of glycogen.

Glycogenesis: formation of glycogen from glucose.

Glycogenolysis: conversion of glycogen to glucose-6-phosphate.

Glucose-6-phosphate can be utilized through glycolysis.

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.


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.


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.

Aerobic Respiration

Pyruvic acid enters interior of mitochondria.

Converted to acetyl CoA and 2 C02.

Acetyl CoA serves as substrate for mitochondrial enzymes.



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.




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.


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.

ETC Chain

Cytochrome a3 transfers electrons to O2  (final electron acceptor).

Oxidative phosphorylation occurs:

Energy derived is used to phosphorylate ADP to ATP.


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.

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+.

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

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

ATP Produced

Direct phosphorylation:



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.



Metabolism of Lipids

When more energy is taken in than consumed, glycolysis inhibited.

Glucose converted into glycogen and fat.


Formation of fat.

Occurs mainly in adipose tissue and liver.

Acetic acid subunits from acetyl CoA converted into various lipids.

Metabolism of Lipids


Breakdown of fat.

Triglycerides            glycerol + fa


Free fatty acids (fa) serve as blood-borne energy carriers.



Enzymes remove
2-carbon acetic acid molecules from acid end of fa.

Forms acetyl CoA.

Acetyl CoA enters Krebs Cycle.


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.

Adequate amino acids are required for growth and repair.  A new amino acid can be obtained by:



Amino group (NH2) transferred from one amino acid to form another.

Process by which excess amino acids are eliminated.

Amine group from glutamic acid removed, forming ammonia and excreted as urea.



Energy conversion: amino acid is deaminated.

Ketoacid can enter the Krebs Cycle.

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