Transcript The Kreb`s Cycle

The Krebs
Cycle
Biology 11 Advanced
http://www.schooltube.com/vi
deo/22af9fa0535847978a08/
The Beginning
• Three major stages of cellular respiration:
• 1. Glycolysis (splitting of sugar)
• 2. The Citric Acid Cycle
• 3. Oxidative Phosphorylation (production of ATP): Electron
Transport and Chemiosmosis.
• Glycolysis, which occurs in the cytosol, begins the degradation
process by breaking down glucose into two molecules of a
compound called pyruvate.
• The citric acid cycle, which takes place in the mitochondrial matrix,
completes the breakdown of glucose by oxidizing a derivative of
pyruvate to carbon dioxide.
• In the third stage, the electron transport chain accepts electrons
from the breakdown products of the first two stages and passes
these electrons from one molecule to the other.
• The energy released at each step of the chain is stored in a form
the mitochondrion can use to make ATP.
Cellular Respiration theoretically produces 38 molecules of ATP
Stage 1 - Glycolysis
•
Glucose, a six carbon
sugar, is split into two three
carbon sugars. These
smaller sugars are then
oxidized and their
remaining atoms
rearranged to form two
molecules of pyruvate
(pyruvate is the ionized
form of pyruvic acid.)
•
You need to know that
during glycolysis, a glucose
molecule is broken down
into two pyruvate, or
pyruvic acid, molecules
and 2 ATP are formed.
Stage 2 - The Krebs Cycle
• Also known as the Citric Acid Cycle/Tricarboxylic Acid Cycle
• What is it? It is a chemical cycle involving eight steps that completes
the metabolic breakdown of glucose molecules to carbon dioxide;
occurs within the mitochondrion; the second major stage in cellular
respiration.
• Upon entering the mitochondrion via active transport, pyruvate is
first converted to a compound called acetyl coenzyme A, or acetyl
CoA.
8 Steps of the CAC
1. Acetyl CoA adds its two-carbon acetyl group to oxaloacetate,
producing citrate.
2. Citrate is converted to its isomer by the removal of one water
molecule and addition of another.
3. Citrate loses a CO2 molecule, and the resulting compound is
oxidized, reducing NAD+ to NADH.
4. Another CO2 is lost, and the resulting compound is oxidized,
reducing NAD+ to NADH. The remaining molecule is then attached
to coenzyme A by an unstable bond.
5. CoA is displaced by a phosphate group which is transferred to
GDP, for GTP, and then to ADP, forming ATP.
6. Two hydrogens are transferred to FAD, forming FADH2 and oxidizing
succinate.
7. Addition of a water molecule rearranges bonds in the substrate.
8. The substrate is oxidized, reducing NAD+ to NADH and regenerating
oxaloacetate.
http://www.youtube.com/watch?v=juM2ROSLWfw
http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter7/how_the_krebs_cy
cle_works.html
http://www.npr.org/blogs/krulwich/2011/09/14/140428189/lord-saveme-from-the-krebs-cycle
Short Summary
• Acetyl CoA starts the Krebs cycle by joining with Oxaloacetate.
• It is an 8 step process and involves the oxidization of NAD+ to NADH,
FAD to FADH2, GDP to GTP and ADP to ATP.
• During a redox reaction, there is a loss of electrons (oxidization).
• It occurs in the mitochondrial matrix of the cell.
Stage 3 – Oxidative Phosphorylation
• The production of ATP using energy derived from the oxidation &
reduction reactions of the electron transport chain; during
oxidative phosphorylation, chemiosmosis couples electron
transport to ATP synthesis.
• Electron transport chain – a collection of molecules embedded in
the inner membrane of the mitochondrion – known as the cristae.
The cristae allow for a greater surface area for chemical reactions
to occur. This is the part of cellular respiration that oxygen is used.
• Chemiosmosis – The process in which energy stored in the form of a
hydrogen ion gradient across a membrane is used to drive cellular
work, such as the synthesis of ATP.
• About 34 ATP are produced during stage 3, and are transported by
active transport from the mitochondrial matrix back into the
cytosol.
Conclusion!
• Cellular respiration is the most prevalent and efficient catabolic
pathway (a metabolic pathway that releases stored energy by
breaking down complex molecules.) Oxygen is consumed as a
reactant along with the organic fuel.
• Mitochondria house most of the metabolic equipment for cellular
respiration.
• C6H12O6 + 6O2  6CO2 + 6H2O + Energy (38 ATP + heat)
• The breakdown of glucose is exergonic; which means that energy
is released in the form of heat.
The Big Picture – Aerobic Respiration
• Cellular respiration, as we have talked about, occurs in the
presence of oxygen. This is know as aerobic respiration.
• The products of aerobic respiration are carbon dioxide, water, and
ATP (as was shown on the previous slide.)
• Oxygen is needed for aerobic respiration because it is the final
acceptor in the electron transport chain; without it the process
would stop.
The Big Picture – Anaerobic Respiration
• Anaerobic respiration takes place in the absence of oxygen and
occurs in two forms.
• Lactic Acid Fermentation – Occurs in the cells of animals,
particularly in the muscle tissue. Glucose is broken down into lactic
acid and energy is released in the process. 2 molecules of ATP are
produced during this process. Pain during exercise (a stitch) can
be caused due to insufficient oxygen getting to the muscles and a
build up of lactic acid.
• Alcoholic Fermentation – Occurs in the cytoplasm of yeast cells.
This also only produces 2 ATP molecules. An enzyme is used to
break down the glucose molecules into carbon dioxide and
alcohol. The carbon dioxide gas released during this process is
what causes things, such as bread, to rise during baking.