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2005-2006AP Biology

Chapter 9.Cellular RespirationSTAGE 1: Glycolysis

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2005-2006AP Biology

The Point is to Make ATP!

ATP

What’s the point?

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2005-2006AP Biology

Glycolysis Breaking down glucose

“glyco – lysis” (splitting sugar)

most ancient form of energy capture starting point for all cellular respiration

inefficient generate only 2 ATP for every 1 glucose

in cytosol why does that make evolutionary sense?

glucose → → → → → pyruvate2x6C 3C

Why does it make sense that this happens in the cytosol?Who evolved first?

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2005-2006AP Biology

Evolutionary perspective Life on Earth first evolved without

free oxygen (O2) in atmosphere energy had to be captured from

organic molecules in absence of O2

Organisms that evolved glycolysisare ancestors of all modern life all organisms still utilize

glycolysis

You mean,I’m relatedto them?!

The enzymes of glycolysis are very similar among all organisms. Thegenes that code for them are highly conserved.They are a good measure for evolutionary studies. Compareeukaryotes, bacteria & archaea using glycolysis enzymes.Bacteria = 3.5 billion years ago

glycolysis in cytosol = doesn’t require a membrane-boundorganelle

O2 = 2.7 billion years ago photosynthetic bacteria / proto-blue-green algae

Eukaryotes = 1.5 billion years ago membrane-bound organelles!

Processes that all life/organisms share: Protein synthesis Glycolysis DNA replication

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2005-2006AP Biology

glucoseC-C-C-C-C-C

fructose-6PP-C-C-C-C-C-C-P

DHAPP-C-C-C

PGALC-C-C-P

pyruvateC-C-C

2 ATP2 ADP

2 NAD+

2 NADH4 ADP4 ATP

Overview10 reactions

convert6C glucose totwo 3C pyruvate

produce 2 ATP& 2 NADH

activationenergy

1st ATP used is like a match to light a fire…initiation energy / activation energy.

Destabilizes glucose enough to split it in two

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2005-2006AP Biology

Glycolysis summary

endergonicinvest some ATP

exergonicharvest a little more ATP& a little NADH

Glucose is a stable molecule it needs an activation energyto break it apart.

phosphorylate it = Pi comes from ATP.make NADH & put it in the bank for later.

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2005-2006AP Biology

1st half of glycolysis (5 reactions)Glucose

“priming” get glucose

ready to split phosphorylate

glucose rearrangement

splitdestabilizedglucose

Payattention tothe enzymes!

PGAL

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2005-2006AP Biology

2nd half of glycolysis (5 reactions) Oxidation

G3P donates H NAD → NADH

ATP generation G3P → pyruvate donates P ADP → ATP

Payola!Finally some

ATP!

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2005-2006AP Biology

OVERVIEW OF GLYCOLYSIS

1 2 3

(Starting material)

6-carbon sugar diphosphate

6-carbon glucose

2

P P

6-carbon sugar diphosphate

P P

3-carbon sugarphosphate

P P P P

Priming reactions. Primingreactions. Glycolysis begins withthe addition of energy. Two high-energy phosphates from twomolecules of ATP are added to thesix-carbon molecule glucose,producing a six-carbon moleculewith two phosphates.

3-carbonpyruvate

2

NADH

ATP

ATP 2

NADH

ATP

Cleavage reactions. Then, thesix-carbon molecule with twophosphates is split in two, formingtwo three-carbon sugarphosphates.

Energy-harvesting reactions.Finally, in a series of reactions,each of the two three-carbonsugar phosphates is converted topyruvate. In the process, anenergy-rich hydrogen is harvestedas NADH, and two ATP moleculesare formed.

3-carbon sugarphosphate

3-carbon sugarphosphate

3-carbon sugarphosphate

3-carbonpyruvate

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2005-2006AP Biology

Substrate-level Phosphorylation In the last step of glycolysis, where

did the P come from to make ATP?

P is transferredfrom PEP to ADP kinase enzyme ADP → ATP

I get it!The P camedirectly fromthe substrate!

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2005-2006AP Biology

Energy accounting of glycolysis

Net gain = 2 ATP some energy investment (2 ATP) small energy return (4 ATP)

1 6C sugar → 2 3C sugars

2 ATP 2 ADP

4 ADP 4 ATP

glucose → → → → → pyruvate2x6C 3C

All thatwork! Andthat’s all I

get?

And that’s how life subsisted for a billion years.Until a certain bacteria ”learned” how to metabolize O2; which waspreviously a poison.But now pyruvate is not the end of the process

Pyruvate still has a lot of energy in it that has not beencaptured.

It still has 3 carbons bonded together!There is still energy stored in those bonds.It can still be oxidized further.

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2005-2006AP Biology

Is that all there is? Not a lot of energy…

for 1 billon years+ this is how life onEarth survived only harvest 3.5% of energy stored in glucose slow growth, slow reproduction

Heck of away to make

a living!

So why does glycolysis still take place?

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2005-2006AP Biology

We can’t stop there….

Going to run out of NAD+

How is NADH recycled to NAD+? without regenerating NAD+,

energy production would stop another molecule must

accept H from NADH

glucose + 2ADP + 2Pi + 2 NAD+ → 2 pyruvate + 2ATP + 2NADH

Glycolysis

NADH

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2005-2006AP Biology

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

aerobic respiration ethanol fermentation lactic acid fermentation

aerobic respiration

NADH

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2005-2006AP Biology

Anaerobic ethanol fermentation Bacteria, yeast

1C3C 2Cpyruvate → ethanol + CO2

Animals, some fungipyruvate → lactic acid

3C 3C

beer, wine, bread at ~12% ethanol, kills yeast

cheese, yogurt, anaerobic exercise (no O2)

NADH NAD+

NADH NAD+

Count the carbons!!

Lactic acid is not a dead end like ethanol. Once you have O2 again,lactate is converted back to pyruvate by the liver and fed to the Kreb’scycle.

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2005-2006AP Biology

Pyruvate is a branching pointPyruvate

O2O2

Kreb’s cyclemitochondria

fermentation

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2005-2006AP Biology

The Point is to Make ATP!

ATP

What’s the point?

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2005-2006AP Biology

Any Questions??