Transcript Cellular Respiration chapt06

Biochemical Pathways:
Cellular Respiration
Chapter 6
2-
Energy and Organisms

Organisms are classified based on the kind of energy
they use.
•
Autotrophs


•
Heterotrophs



To use the energy from light to make organic molecules
All organisms use cellular respiration.
•
6-
Obtain organic molecules by eating the autotrophs
Use the energy in the organic molecules to make ATP
Autotrophs use photosynthesis.
•

Use the energy from sunlight to make organic molecules (sugar)
Use the energy in the organic molecules to make ATP
To harvest the energy from organic molecules and use it to
makeCopyright
ATP© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Energy Transformation
6-
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cellular Respiration
6-

Respiration is a metabolic pathway of Redox
Reactions

Respiration oxidizes carbohydrates and
transfers the energy to produce ATP

The type of molecule that is reduced
determines the type of respiration

The energy produced is in the form of ATP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cellular Respiration

Three Types of Respiration
1.Aerobic Respiration
- Oxygen is reduced to produce water
2.Anaerobic Respiration
- A molecule other that oxygen is reduced
- may produce acids, methane, etc.
3.Fermentation
- Another carbohydrate is reduced to
5-
produce alcohols
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Aerobic Respiration
Glucose is Oxidized to become Carbon
Dioxide
5-

Oxygen is reduced to become water

The protons and electrons from the oxidation
of glucose are used to produce ATPs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Aerobic Respiration


5-
C6H12O6 + 6 O2
C6H12O6 + 6O2 + 38 ADP + 38 P
6 H2O + 6 CO2 + Energy
6 H2O + 6CO2 + 38 ATP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Aerobic Respiration

Aerobic Respiration is a three stage process:
–
–
–
5-
Stage 1: Glycolysis
Stage 2: The Krebs Cycle
Stage 3: Oxidative Phosphorylation (Electron
Transport Chain)

Each of these stages produce ATP

At the end of all three stages, there is a net
gain of ~38 ATP’s
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 1: Glycolysis
6-

Glycolysis is a 10 step metabolic pathway
that cleaves glucose

Glyo-lysis = “splitting glucose”

Glycolysis occurs in the cell’s cytoplasm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 1: Glycolysis

Glycolysis splits glucose to make two
pyruvate molecules

Produces 4 ATP molecules
–

6-
4 ATP made -2 ATP invested = net production of
2 ATP
Reduces 2 NAD+ to make 2 NADH
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 1: Glycolysis
6-

During Glycolysis,
Glucose (a 6 carbon
molecule) is chopped
up into 2 Pyruvates
(pyruvate is a 3
carbon molecule)

This is a 9 step
metabolic process
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 6_07
9 Steps of Glycolysis Summary
1. Glucose is phosphorylated - costs 1 ATP to become
Glucose-6-Phosphate
2. Glucose-6-P is converted to Fructose-6-P
3. Fructose-6-P is phosphorylated - costs 1 ATP to
become Fructose-1,6-bisphosphate
4. Fructose-1,6-bisphosphate is split into two
molecules - each with 3 carbons and a phosphate:
–
–
6-
Dihydroxyacetone (DHAP)
Glyceraldehyde-3-Phoshate (G-3-P)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
9 Steps of Glycolysis Summary
G-3-P

5. G-3-P is phosphorylated to
5. DHAP is phosphorylated to become
1,3-bisphosphoglycerate become 1,3 bisphosphoglycerate

6. 1,3-bisphosphglycerate gives up 6. 1,3-bisphosphoglycerate gives up a
a phosphate to an ADP, G-3-P left
phosphate to an ADP, G-3-P left

7. G-3-P converted to

6-
DHAP
2-Phosphoglycerate
7. G-3-P converted to
2-Phospoglycerate

8. 2-Phosphoglycerate converted to
to Phosphoenolpyruvate
8. 2-Phosphoglycerate converted
Phosphoenolpyruvate

9. Phosphoenolpyruvate gives up
its phosphate to an ADP
9. Phosphoenolpyruvate gives up
its phosphate to an ADP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glucose
2 ATP
4 ATP, 2 NADH
Pyruvate1
Pyruvate 2
NAD+, NADH

NAD+ is an electron carrier for the redox
reactions of cellular respiration

NAD+ accepts 2 electrons and 1 proton to
become NADH

Functions of NAD+, NADH
–
–
6-
–
NAD+ is reduced so Redox reactions can occur
NAD+ is used to carry electrons from one part of
the cell to another
NAD+ keeps protons out of solution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+
NAD ,
NADH
+
NAD
Reduced to NADH
FAD, FADH2

FAD is very similar to NAD+

It has the same functions of collecting and
carrying electrons and protons

FAD can carry 2 Hydrogen atoms
–
6-
FAD is Reduced to FADH2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 2: Kreb’s Cycle




6-
Also known as The Citric Acid Cycle or the
Tricarboxylic Acid (TCA) Cycle
The Krebs cycle is a metabolic pathway that
further oxidizes pyruvate
The Krebs Cycle occurs in the Cell
membrane of Prokaryotic Cells and in the
mitochondria of Eukaryotic Cells
In mitochondria, a multienzyme complex
called pyruvate dehydrogenase catalyzes
the reaction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 2: Kreb’s Cycle



6-
The Krebs Cycle begins with pyruvate (from
Glycolysis)
Remember, there are 2 pyruvates made from
each Glucose, so there are 2 Krebs Cycles
for every glucose molecule
During a Kreb’s Cycle the pyruvate (a 3
carbon molecule) will be completely oxidized
to become 3 carbon dioxide molecules (one
carbon atom each)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cellular Respiration


C6H12O6 + 6O2
Glucose
Oxygen
6H2O + 6CO2 + Energy
Water Carbon Dioxide
The Kreb’s Cycle produces the CO2 that we
exhale
5-
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 2: Kreb’s Cycle

Important steps in the Kreb’s Cycle
–
–
–
6-
Pyruvate is converted to acetyl-CoA
Acetyl-CoA combine with Oxaloacetate (in the
mitochondria) to make Citrate
The cycle ends with the production of
oxaloacetate, ready for anther turn of the cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 6_05
Stage 2: Kreb’s Cycle

During the Kreb’s Cycle enough energy is
released from one pyruvic acid molecule to
produce:
–
–
–
6-
1 ATP
4 NADH from 4 NAD+
1 FADH2 from 1 FAD.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 6_08
Glucose
2 ATP
4 ATP, 2 NADH
Pyruvate1
Pyruvate 2
Pyruate converted to Acetyl Co-A
2 ATP
1 ATP, 2 CO2
4 NADH, 1 FADH2
Stage 2: Kreb’s Cycle



6-
After glycolysis and the Krebs cycle glucose has
been completely oxidized to form:
– 6 CO2
– ~5 ATP
– ~10 NADH
– ~2 FADH2
We are still short of our 36-38 ATP goal
The third stage of cellular respiration uses the
protons and electrons of the hydrogens on the
NADH’s and FADH2’s that were produced during the
first 2 stages
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glucose
2 ATP
4 ATP, 2 NADH
Pyruvate1
Pyruvate 2
Pyruate converted to Acetyl Co-A
2 ATP
2 ATP, CO2
8 NADH, 2 FADH2
34 ATP
Electron Transport Chain
NADH, FADH2
Stage 3: Electron-Transport
System
6-

The electron transport chain (ETC) is a
series of membrane-bound electron carrier
molecules called cytochromes embedded in
the mitochondrial inner membrane

Electrons from NADH and FADH2 are
transferred to cytochromes of the ETC

Each cytochrome transfers the electrons to
the next cytochromes in the chain
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 7.13a
Stage 3: Electron-Transport
System
6-

As the electrons are transferred, some
electron energy is released with each
transfer

This energy is used by the cytochromes to
pump protons (H+) across the membrane
from the matrix to the inner membrane space

A proton concentration gradient is
established
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Stage 3: Electron Transport
Chain
Figure 6_06
Stage 3: Electron-Transport
System
6-

There are other channel proteins in the
membrane known as ATP synthases

ATP synthases provide a channel for protons
to rush through by diffusion

The rushing protons provides the energy for
ATP synthase to phosphorylate ADP to ATP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 6_06
40
41
Figure 6_09
Cellular Respiration

Recall Three Types of Respiration
1.Aerobic Respiration
- Oxygen is reduced to produce water
2.Anaerobic Respiration
- A molecule other that oxygen is reduced
- may produce acids, methane, etc.
3.Fermentation
- Another carbohydrate is reduced to
5-
produce alcohols
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Aerobic Respiration

Oxygen is the final molecule to receive the
electrons as they are passed down the
Electron Transport Chain
–


6-
Oxygen is reduced with two electrons and picks
up two protons
The result is water:
 2O2 + 8e-’s and 8H+’s
4H2O
Oxygen is the Final Electron Acceptor in
Aerobic Respiration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Electron Transport Chain
Glucose
2 ATP
4 ATP, 2 NADH
Pyruvate1
Pyruvate 2
Pyruate converted to Acetyl Co-A
2 ATP
2 ATP, CO2
8 NADH, 2 FADH2
30+ ATP
And H2O
Electron Transport Chain
NADH, FADH2
Aerobic Cellular Respiration:
Overview
6-
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Total Yields for Aerobic Cellular
Respiration per Glucose Molecule

Glycolysis
–
–

Kreb’s cycle
–
–
–

2 ATP
2 NADH (converted to 2 FADH2)
2 ATP
8 NADH
2 FADH2
Electron transport chain
–
Each NADH fuels the formation of 3 ATP.

–
Each FADH2 fuels the formation of 2 ATP.


6-
8 NADH x 3 ATP = 24 ATP
4 FADH2 x 2 ATP = 8 ATP
Total ATP=2+2+24+8=36 ATP made from the metabolism of
one glucose molecule.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2. Anaerobic Cellular Respiration



6-
Some cells do not require O2 as the final
electron acceptor for the electron transport
chain
These cells perform Anaerobic Respiration
Anaerobic Respiration produces fewer ATPs
per glucose molecule compared to Aerobic
Respiration – it is not as efficient and the
exact amount of ATP production depends on
the organism and the electron acceptors that
are used
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2. Anaerobic Cellular Respiration

Anaerobic respiration by methanogens
–
–

Anaerobic respiration by sulfur bacteria
–
6-
methanogens use CO2
CO2 is reduced to CH4 (methane)
inorganic sulphate (SO4) is reduced to hydrogen
sulfide (H2S)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
3. Fermentation

Fermentation reduces organic molecules as
the final electron acceptors
–
Ethanol fermentation occurs in yeast

–
Lactic acid fermentation


6-
fermentation of sugars produces alcohol
occurs in animal cells (especially muscles)
electrons are transferred from NADH to pyruvate to
produce lactic acid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 6_10
Alcoholic Fermentation



6-
Starts with glycolysis
–
Glucose is metabolized to pyruvic
acid.
–
A net of 2 ATP is made.
During alcoholic fermentation
–
Pyruvic acid is reduced to form
ethanol.
–
Carbon dioxide is released.
Yeasts do this
–
Leavened bread
–
Sparkling wine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lactic Acid Fermentation

Starts with glycolysis
–

During lactic acid fermentation
–
–

Pyruvic acid is reduced to form lactic acid.
No carbon dioxide is released.
Muscle cells have the enzymes to do this, but brain
cells do not.
–
6-
Glucose is metabolized to pyruvic acid.
–
Muscle cells can survive brief periods of oxygen
deprivation, but brain cells cannot.
Lactic acid “burns” in muscles.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Metabolizing Other Molecules
6-

Cells will use the energy in carbohydrates first.
– Complex carbohydrates are metabolized into
simple sugars.

Cells can use the energy in fats and proteins as well.
– Fats are digested into fatty acids and glycerol.
– Proteins are digested into amino acids.

Cells must convert fats and proteins into molecules
that can enter and be metabolized by the enzymes
of glycolysis or the Kreb’s cycle.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fat Respiration

Fats are broken down into
–
–

Glycerol
–
–

–
Converted to acetylCoA
Enter the Kreb’s cycle
Each molecule of fat fuels the formation of many
more ATP than glucose.
–
6-
Converted to glyceraldehyde-3-phosphate
Enters glycolysis
Fatty acids
–

Glycerol
Fatty acids
This makes it a good energy storage molecule.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Amino
Acids
Lipids
Preparatory Steps
Protein Respiration


Proteins are digested into amino acids.
Then amino acids have the amino group
removed.
–
–
6-
Generates a keto acid (acetic acid, pyruvic acid,
etc.)
Enter the Kreb’s cycle at the appropriate place
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Interconversion of Fats,
Carbohydrates and Proteins
6-
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Energy Resources

Carbohydrates, fats and proteins can all be
used for energy.
–

Glycolysis and the Kreb’s cycle allow these types
of molecules to be interchanged.
If more calories are consumed than used
–
–
The excess food will be stored.
Once the organism has all of the proteins it needs


6-
And its carbohydrate stores are full
The remainder will be converted to and stored as fat.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.