30
Krebs Cycle (Citric Acid Cycle) & Quick and Long Energy

Cell respiration part 2

Embed Size (px)

Citation preview

Page 1: Cell respiration part 2

Krebs Cycle (Citric Acid Cycle)&

Quick and Long Energy

Page 2: Cell respiration part 2

Glycolysis

To the electron transport chain

2 molecules of pyruvate

Glucose

Page 3: Cell respiration part 2

Energy accounting of glycolysis

• Net gain = 2 ATP + 2 NADH– some energy investment (-2 ATP)– small energy return (4 ATP + 2 NADH)

• 1 6C sugar 2 3C sugars

2 ATP 2 ADP

4 ADP

glucose pyruvate2x6C 3C

All that work! And that’s all I get?

ATP4

2 NAD+ 2 Butglucose hasso much moreto give!

Page 4: Cell respiration part 2

Krebs Cycle

• British biochemist Hans Krebs, discovered 1937

• During Krebs cycle, PYRUVATE is broken down into CARBON DIOXIDE in a series of energy extracting reactions

• AKA the CITRIC ACID CYCLE because citrate (also called citric acid) is the first product of the cycle

Page 5: Cell respiration part 2

From Glycolysis comes the Pyruvates….

Page 6: Cell respiration part 2

Krebs Cycle

Page 7: Cell respiration part 2

Step 1• Citric Acid Production

– Pyruvate ( 3-carbons) enter mitochondria Matrix

– One carbon is removed as CO2 (WASTE product) and electrons are removed by NAD+ (making NADH which goes to the ETC)

– Co-enzyme A joins the 2-carbon molecule (that used to be pyruvate) making Acetyl-CoA

– Now Acetyl-CoA can enter the Krebs cycle

– Acetyl Co-A combines with 4-carbon molecule called OXALOACETATE , making citrate (citric acid), a 6-carbon molecule

Page 8: Cell respiration part 2

Step 2• Citric acid (6 carbon molecule) is

broken down into a few different 5-carbon compounds, then into a few different 4-carbon compounds.

• Each step releases CO2, NADH and FADH2, and ATP

– CO2 is a waste product (breath out!)

– NADH and FADH2 (taxi cabs) goes onto the ETC (where the party is at)

– ATP is used for cell to do work (mechanical, chemical, or transport)

Page 9: Cell respiration part 2

4C

6C

4C

4C

4C

2C

6C

5C

4C

CO2

CO2

citrate

acetyl CoACount the carbons!

3Cpyruvate

x2

oxidationof sugars

This happens twice for each glucose molecule

Page 10: Cell respiration part 2

4C

6C

4C

4C

4C

2C

6C

5C

4C

CO2

CO2

citrate

acetyl CoACount the electron carriers!

3Cpyruvate

reductionof electroncarriers

This happens twice for each glucose molecule x2

CO2

NADH

NADH

NADH

NADH

FADH2

ATP

Page 11: Cell respiration part 2

So we fully oxidized (broke down)

glucose

C6H12O6

CO2

& ended up with 4 ATP!

What’s the point?

Page 12: Cell respiration part 2

Krebs cycle produces large quantities of electron carriers NADH FADH2

go to Electron Transport Chain!

Electron Carriers = Hydrogen Carriers

What’s so important about electron carriers?

H+

H+H+

H+

H+ H+

H+H+H+

ATP

ADP+ Pi

Page 13: Cell respiration part 2

Energy accounting of Krebs cycle

Net gain = 2 ATP

= 8 NADH + 2 FADH2

1 ADP 1 ATPATP

2x

4 NAD + 1 FAD 4 NADH + 1 FADH2

pyruvate CO2

3C 3x 1C

Page 14: Cell respiration part 2

Value of Krebs cycle?• If the yield is only 2 ATP then how was the Krebs

cycle an adaptation?– value of NADH & FADH2

• electron carriers & H carriers• to be used in the Electron Transport Chain

like $$in the bank

Page 15: Cell respiration part 2
Page 16: Cell respiration part 2

Summary• In one turn of the Krebs

Cycle:– 3 CO2 (1 from right before

Krebs)• Released when we exhale

– 1 ATP (E for cell work)– 1 NADH from right before

Krebs– 3 NADH from Krebs (to

ETC)– 1 FADH2 (to ETC)

– Water leaves and then reenters so we don’t count it in the products

• For one Glucose molecule how many times does the Krebs Cycle turn?

• What are the totals from the Krebs Cycle for one Glucose molecule?– 6 CO2s

– 2 ATPs– 8 NADHS– 2 FADH2

Page 17: Cell respiration part 2

So we use Krebs if we have oxygen….what if there is NO

oxygen???• Then we can’t even enter the mitochondria

and go to the Krebs cycle…• We are stuck using Glycolysis…• Anaerobic respiration (NO oxygen)

– 2 types• Lactic acid fermentation• Alcohol fermentation

Page 18: Cell respiration part 2

Pyruvate is a branching pointPyruvate

O2O2

mitochondriaKrebs cycleaerobic respiration

fermentationanaerobicrespiration

Page 19: Cell respiration part 2

GlycolysisPyruvate ???

2or

Page 20: Cell respiration part 2

• Cells cannot get enough oxygen• Build up of pyruvic acid and NADH and no oxygen to break it down• Cells begin fermentation

– Lactic Acid fermentation• Pyruvic acid + NADH lactic acid + NAD+• Get about 90 seconds of energy without having to use oxygen• HOWEVER, oxygen will be paid back double when you are done

(think heavy breathing)• Occurs in muscle cells, and microorganisms, such as the ones that

turn milk into cheese and yogurt• Lactic acid causes muscle cramping and burning sensation• Oxygen is required to break down lactic acid and get it out of body

– Alcohol fermentation• Pyruvic acid + NADH ethyl alcohol + NAD+ + CO2

• Occurs in yeast cells and other microorganisms, such as the ones involved in the production of bread and wine

Page 21: Cell respiration part 2

NADH

pyruvate

acetyl-CoA

lactate

ethanol

NAD+

NAD+

NADH

NAD+

NADH

CO2

acetaldehyde

H2O

Krebscycle

O2

lactic acidfermentation

with oxygenaerobic respiration

without oxygenanaerobic respiration“fermentation”

How is NADH recycled to NAD+?Another molecule must accept H from NADH

recycleNADH

which path you use depends on who you are…

which path you use depends on who you are…

alcoholfermentation

Page 22: Cell respiration part 2

Fermentation (anaerobic)• Bacteria, yeast

1C3C 2Cpyruvate ethanol + CO2

Animals, some fungi

pyruvate lactic acid3C 3C

beer, wine, bread

cheese, anaerobic exercise (no O2)

NADH NAD+

NADH NAD+

back to glycolysis

back to glycolysis

Page 23: Cell respiration part 2

recycleNADH

Alcohol Fermentation

1C3C 2Cpyruvate ethanol + CO2

NADH NAD+

Count thecarbons!

Dead end process at ~12% ethanol,

kills yeast can’t reverse the

reaction

bacteria yeast

back to glycolysis

Page 24: Cell respiration part 2

recycleNADH

Reversible process once O2 is available,

lactate is converted back to pyruvate by the liver

Lactic Acid Fermentationpyruvate lactic acid

3C 3CNADH NAD+

Count thecarbons!

O2

animalssome fungi

back to glycolysis

Page 25: Cell respiration part 2

Quick Energy• 3 ways to obtain energy

– ATP stored in muscles (glycogen) (short)– ATP from lactic acid (short)– ATP from cellular respiration (long)

• Cells initially have small amount of ATP from cell resp. and glycolysis• Think of running a 200 m sprint

– Gun goes off• Muscles of runner contract, turning glycogen in muscle cells into glucose,

but this only provides for a few seconds of intense activity– You pass the 50m mark

• most ATP the was initially stored is now gone• Muscle cells are producing ATP from lactic acid fermentation• This lasts about 90 seconds

– End of Race• Lots of lactic acid build up• Only way to get rid of lactic acid is a chemical pathway that requires oxygen• Thus, at the end of the race, you are breathing heavily and you should follow

an intense work out with a slow jog

Page 26: Cell respiration part 2
Page 27: Cell respiration part 2
Page 28: Cell respiration part 2

Long Term• Energy for running long races or other endurance sports• Cellular respiration is the only way to get enough ATP to last the length of the race• Cellular respiration makes ATP more slowly than lactic acid fermentation• Athletes must pace themselves• Glycogen an important molecule

– Carbohydrate– Polysaccharide (monosaccharide is glucose)– Muscle and liver cells store E as glycogen– Glycogen is broken down by the hormone Glucagon– Glycogen break down is also stimulated by muscle contraction

• When you work out, muscles contract and they can use energy stored in glycogen

– Increase glycogen storage, increase the duration of exhaustive work your muscles can do– Stores of glycogen last about 15-20 minutes

• After glycogen is used up, body starts to break down other molecules to get energy– Fats and proteins– Fatty acids are broken down and carried to mitochondrial matrix and enter the membrane in fragments

as acetyl-CoA– Proteins are broken down into aa and the these modified aa’s are fed back into the Krebs cycle (NAD+

and FAD)

• Aerobic exercise is good for weight control because it leads to break down of fats

Page 29: Cell respiration part 2

Training to Improve Function of ATP production

• Anaerobic training– Increase levels of glycogen in muscle cells

and increase tolerance of lactic acid build up• Aerobic training

– Increases size and number of mitochondria in muscle cells and increase delivery of oxygen to muscle cells by improving heart and lung efficiency

Page 30: Cell respiration part 2

2007-2008

What’s thepoint?

The pointis to makeATP!

ATP