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Metabolism: Glycolysis and Respiration

Image 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. Adapted from work by David Knuffke.
by

Alan Allmen

on 14 February 2018

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Transcript of Metabolism: Glycolysis and Respiration

Metabolism: Energy Processing
A Quick Recap
Respiration
Glycolysis
Mitochondria*
*-if they are present
Fermentation
The Kreb's Cycle
What happens:
Oxidative Phosphorylation
Cytoplasm
Intermembrane Space
Final Accounting
Matrix
Versatility
Reaction types
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 regulated by feedback loops acting on enzymes, in multi-step metabolic pathways.
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
Kreb's cycle
, followed by
oxidative phosphorylation
.

The point of all of it is to make
ATP
Inputs
Outputs
What happens:
Glucose(6C) is oxidized & 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:
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 is universal to life!
Where To Next?
anaerobic: Fermentation

aerobic: Mitochondria
What happens:
No ATP production: purpose is to oxidize NADH back into NAD+ for reuse during glycolysis.

Pyruvate is reduced into a waste product.

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
Kreb's cycle
occurs.

Prokaryotes that carry out aerobic respiration utilize specialized portions of their cell membrane.
Link reaction
While being transported in to the mitochondrion, pyruvate is decarboxylated, oxidized, and combined with a molecule of
CoEnzyme-A
(CoA) to form Acetyl CoA. This is the carbon input into the Kreb's cycle.

A molecule of CO2 is released as a waste product.


What happens:

Acetyl CoA is combined with other carbon-containing molecules, which are then oxidized and decarboxylated - creating more NADH and FADH , which will be used to make ATP.


Remember: This cycle happens 2X per glucose.
Every reaction in the Kreb's 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
Pyruvate (3C)
NAD+
Acetyl-CoA (2C from pyruvate)
CO
NADH
Inputs
Outputs
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
NADH and FADH2 are oxidized.
Freed electrons are passed between a chain of integral proteins along the inner mitochondrial membrane (Electron Transport Chain)
Electron movement powers the pumping of protons into the intermembrane space.
Proton gradient is established.
Oxygen accepts the electrons and is reduced, with protons (H+), to make water.


Chemiosmosis!
Purpose: To use proton concentration gradient to form ATP from ADP + P.

Protons can only diffuse back in to the matrix through
ATP synthase.

As protons diffuse through ATP synthase, kinetic energy is converted into chemical potential energy to catalyze ATP formation from ADP.
Inputs
Outputs
10 NADH
2 FADH
O
per glucose
per glucose
2
2
~32-36 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 "32-38".

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.
OILRIG:
Oxidation
Is
Losing electrons,
Reduction
Is
Gaining electrons
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)
* eukaryotes only
Chloroplast
Mitochondria
In Glorious Computer Animation
Oxygen,
Organic Molecules (ex. glucose)
Carbon Dioxide,
Water
ATP
Heat
Light
Full transcript