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Cellular Respiration

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Elizabeth Pierson

on 14 November 2018

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Transcript of Cellular Respiration

Chemoheterotrophic Energy Processing
A Quick Recap
Respiration
Glycolysis
Mitochondria*
*-if they are present
Fermentation
The Citric Acid Cycle
What happens:
Oxidative Phosphorylation
Cytoplasm
Intermembrane Space
Final Accounting
Matrix
Remember Redox?
There is a reciprocal relationship between chemoheterotrophic nutrition and photoautotrophic nutrition.


The inputs of one are the outputs of the other.
Aerobic Cellular Respiration:
Photosynthesis:
C H O + 6O
6CO + 6H O
2
2
2
6
6
12
6
6
2
C H O + 6O
12
2
2
6CO + 6H O
Control:
Metabolic reactions are tightly controlled in multi-step metabolic pathways.
Redox
: Chemical reactions where electrons are transfered from one atom to another atom.
C H O + 6O
2
6CO + 6H O
12
6
6
2
2
Oxidized
Reduced
Glucose will be oxidized (it is the "
reducing agent
").
Oxygen will be reduced (it is the "
oxidizing agent
").
Electron Shuttles
Instead of direct transfer of electrons from glucose to oxygen, cells decouple metabolic oxidation and reduction.

"
Electron Carriers
":
compounds that store electrons from food.
Exist in oxidized and reduced forms.
In cells, electrons come with protons.
Transfer electrons and protons to other areas of the cell to continue metabolism

Two Major Kinds:
NAD+ / NADH
FAD / FADH
2
General Overview
All respiration begins with
glycolysis
in the cytoplasm.

Anaerobic respiration
will then require
fermentation
(also in the cytoplasm).

Aerobic respiration will occur in a mitochondria*. It will involve the
citric acid cycle
, followed by
oxidative phosphorylation
.

The point of all of it is to make
ATP
Inputs
Outputs
What happens:
Glucose(6C) is cleaved into 2 molecules of pyruvate (3C).

This requires 2 ATP. It produces 4.

2 NAD+ are reduced to 2 NADH
2 Phases of glycolysis
Every reaction in glycolysis is mediated by an enzyme.
Substrate-level phosphorylation
Description for when ATP is produced by enzymatic phosphate transfer from another organic phosphate.

This is how ATP is produced in glycolysis and the citric acid cycle.
1 Glucose (6C)
2 NAD+
2 ATP
2 Pyruvate (3C)
2 NADH
4 ATP
Where To Next?
anaerobic
: Fermentation

aerobic
: Mitochondria
Big Question
What happens:
NADH is oxidized back into NAD+.

This will require pyruvate to be reduced into another compound (waste product).

This enables glycolysis to keep functioning.


Ethanol Fermentation:

Example Organism
: Yeast
2
Lactic Acid Fermentation:

Example Organism
: All Animals (muscle cells)
2 NAD+
Outputs
Inputs
2 Pyruvate (3C)
2 NADH
Various Carbon Waste Products
Following glycolysis, aerobic respiration in eukaryotes will take place in the mitochondrion.

The products of glycolysis are transported through both mitochondrial membranes into the
mitochondrial matrix
.

This is where the
citric acid cycle
occurs.


First: Acetyl-CoA
While being transported in to the mitochondrion, pyruvate is converted into an
acetyl group
(-CH CH ) and a molecule of CO

The CO is a waste product.

The acetyl group is attached to a molecule of
CoEnzyme-A
(CoA). This is the carbon input into the citric acid cycle.

What happens:
The acetyl group from pyruvate is attatched to
oxaloacetate
, forming citric acid (aka "
citrate
")

The carbons from the acetyl group are oxidized into 2 CO .

3 molecules of NAD+ are reduced into NADH

1 molecule of FAD is reduced into FADH

1 ATP is produced

The citrate is converted back in to oxaloacetate.

This cycle happens 2X per glucose.
Every reaction in the citric acid cycle is mediated by an enzyme.
1 Acetyl-CoA (2C from pyruvate
3 NAD+
1 FAD
1 ADP
2 CO
3 NADH
1 FADH
1 ATP
Inputs
Outputs
1 Pyruvate (3C)
2 NAD+
1 Acetyl-CoA (2C
from pyruvate)
1 CO
2 NADH
Inputs
Outputs
2
2
3
2
2
2
2
2
2
X 2 per glucose
X 2 per glucose
The reduced electron shuttles (NADH and FADH ) are oxidized at the "
electron transport chain
" (ETC): complexes of proteins embedded in the folds of the
inner mitochondrial membrane
("
cristae
").

Electrons flow through the proteins in the chain, driven by the increasing electronegativity of the members of the ETC.

As the electrons move through the chain, the free energy they release is used to pump protons (H+) through the ETC proteins from the matrix into
the intermembrane space
.

Oxygen serves as the "
terminal electron acceptor
". When O acquires 4 electrons and 2 protons, it is converted into water, which is released as a waste product.

The oxidized electron carriers are fed back into glycolysis, and the citric acid cycle.
Chemiosmosis!
How ATP is produced.

The ETC establishes a proton (aka "
electrochemical
") gradient.

Protons can only diffuse back in to the matrix through a protein channel.

ATP synthase
: The only proton channel available in the inner membrane.

As protons diffuse through ATP synthase, the free energy that is released is used to catalyze ATP formation from ADP and free phosphate groups ("
oxidative phosphorylation
")
Inputs
Outputs
10 NADH
2 FADH
O
per glucose
per glucose
2
2
~32-34 ATP
H O
10 NAD+
2 FAD+
2
Why it's impossible to get a straight answer
A natural question:
How much ATP is produced per glucose?

Can't be answered any more exactly than something like "32-36".

Roughly:
3 ATP per NADH
2 ATP per FADH
2
Efficiencies
Anaerobic < Aerobic
If we consider a hypothetical maximum of 38 ATP per glucose molecule, aerobic cellular respiration is 19X more efficient than anaerobic cellular respiration in terms of usable energy generated.
Aerobic In Depth
Aerobic cellular respiration is ~40% efficient in terms of converting chemical energy in glucose into chemical energy in ATP.

By comparison, your car is ~15% efficient at converting the chemical energy in gasoline into mechanical energy.
How do living systems process energy?
* eukaryotes only
Chloroplast
Mitochondria
Oxygen,
Organic Molecules (ex. glucose)
Carbon Dioxide,
Water
ATP
Heat
Light
Oxidation
Reduction
Combustion
Respiration is
catabolic
and
exergonic.
Oxidized form:
Reduced form:
Full transcript