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AP Bio- Energy 5: Chemoheterotrophic Nutrition

5 of 5 of my Energy Unit (two discussions). Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.
by David Knuffke on 14 October 2014

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Transcript of AP Bio- Energy 5: Chemoheterotrophic Nutrition

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?
Versatility and Regulation
Food Gives Us Energy!
There is a reciprocal relationship between chemoheterotrophic nutrition and photoautotrophic nutrition.


The inputs of one are the outputs of the other.
This explains this curious fact:
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.
So that this doesn't happen:
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 Shuttles
":
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.
Fun Fact:
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
Glycolysis is hypothesized to be the most ancient metabolic pathway present in modern organisms.
It happens in all organisms!
Where To Next?
anaerobic
: Fermentation

aerobic
: Mitochondria
Big Question
Make Sure You Can:
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.

There are hundreds of fermentation pathways. We'll look at two.
Ethanol Fermentation:
Pyruvate (3C) is converted to ethanol (2C) and a molecule of CO (1C)

Example Organism
: Yeast
2
Lactic Acid Fermentation:
Pyruvate (3C) is converted to lactate (3C)


Example Organism
: All Animals (muscle cells)
Fun Fact:
Ethanol fermentation is possibly the most commercially lucrative biological reaction.
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.

Prokaryotes that carry out aerobic respiration utilize specialized portions of their cell membrane.
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.

Another NAD+ is reduced to NADH
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.

Remember: 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
1 NADH
Inputs
Outputs
2
2
3
2
2
Fun Fact:
The Citric Acid Cycle was discovered by Hans Krebs, who won a Nobel Prize for his efforts in 1953.

It's also widely known as the "Krebs Cycle".
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
")
Fun Fact:
Chemiosmosis was proposed by Peter Mitchell, who won a Nobel Prize for his efforts in 1978.

It is the major mechanism by which ATP is produced in aerobic cellular respiration AND photosynthesis.
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".

Why?
Decoupling of glucose oxidation and oxidative phosphorylation.
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?
This chimpanzee would die if it didn't eat. You don't want a chimpanzee to die, do you? DO YOU?!?!?
While we focus on Glucose....
...you should be aware that all macromolecules can be used as substrates for respiration.

Different components will enter the process at different points.

If an animal is starving, the following order of digestion of stored molecules will occur:

Carbohydrates (3 days)
Fats (~3 weeks)
Proteins (only at the very end)
So many control points:
Since every step of respiration is mediated by enzymes, there are multiple opportunities for feedback to control the process.

Phosphofructokinase (a glycolysis enzyme) is a particularly studied control point. It is stimulated by AMP, and inhibited by ATP and citrate.
* eukaryotes only
Chloroplast
Mitochondria
Rest in Peep!
Explain how chemoheterotrophic energy processing allows for the production of useful energy for organisms.

Explain why and how chemoheterotrophic energy processing is controlled.

Identify the reduction and oxidation reactions that occur in cellular respiration.

Explain the processes and identify all inputs and outputs of all steps of anaerobic and aerobic cellular respiration.

Relate the different steps of chemoheterotrophic nutrition to their locations in the cell.
Oxygen,
Organic Molecules (ex. glucose)
Carbon Dioxide,
Water
ATP
Heat
Light
Oxidation
Reduction
Combustion
Respiration is
catabolic
and
exergonic.
Oxidized form:
Reduced form:
March!
On to the next one.
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