cell respiration part 2
TRANSCRIPT
Krebs Cycle (Citric Acid Cycle)&
Quick and Long Energy
Glycolysis
To the electron transport chain
2 molecules of pyruvate
Glucose
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!
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
From Glycolysis comes the Pyruvates….
Krebs Cycle
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
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)
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
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
So we fully oxidized (broke down)
glucose
C6H12O6
CO2
& ended up with 4 ATP!
What’s the point?
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
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
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
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
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
Pyruvate is a branching pointPyruvate
O2O2
mitochondriaKrebs cycleaerobic respiration
fermentationanaerobicrespiration
GlycolysisPyruvate ???
2or
• 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
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
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
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
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
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
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
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
2007-2008
What’s thepoint?
The pointis to makeATP!
ATP