&HOO5HVSLUDWLRQ What is Glycolysis? Breaking …...Answers must be in the essay form. Outline form is NOT acceptable. Labeled diagrams may be used to supplement discussion, but in

1

What is Glycolysis?

• Breaking down glucose: “glyco – lysis” (splitting sugar)

• Most ancient form of energy capture.

• Starting point for all cellular respiration.

• Inefficient: generates only 2 ATP for every 1 glucose.

• Happens in the cytosol. Why does that make evolutionary sense?

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 Glycolysis are ancestors of all modern life

• All organisms still utilize glycolysis.

Overview

• 10 reactions

• Convert 6C glucose to two 3C pyruvate

• Produce 2 ATP & 2 NADH

Glycolysis Summary

Endergonic

• Invest some ATP.

Exergonic

• Harvest a little ATP & a

little NADH.

Overall

2015 AP Biology - Cell Respiration

2

Glycolysis Reaction Overview

• 10 Reactions Total

• 9 Different Enzymes needed.

Cleavage reactions

Then, the six-carbon

molecule with two

phosphates is split in

two, forming two

three-carbon sugar

phosphates.

Priming reactions.

Glycolysis begins

with the addition of

energy. Two high

energy phosphates

from two molecules

of ATP are added to

the six-carbon

molecule glucose,

producing a six-

carbon molecule with

two phosphates.

Energy-harvesting

reactions.

Finally, in a series of

reactions, each of the

two three-carbon

sugar phosphates is

converted to

pyruvate. In the

process, an energy-

rich hydrogen is

harvested as NADH,

and two ATP

molecules are

formed.


3

Substrate-level Phosphorylation

• In the last step of glycolysis, where did the P come from to make ATP?

• P is transferred from PEP to ADP

o kinase enzyme

o ADP → ATP

Is that all there is?

• Not a lot of energy…

• For 1 billon years+ this is how life on Earth survived

• Only harvest 3.5% of energy stored in glucose

• Slow growth, slow reproduction

We can’t stop there…

• Going to run out of NAD+.

• How is NADH recycled to NAD+?

• Without regenerating NAD+, energy production would stop so another

molecule must accept H from NADH.


4

The answer? Fermentation.

• In Bacteria & Yeast.

o beer, wine, bread

o at ~12% ethanol, kills yeast

• In Animals & some Fungi.

o cheese, yogurt

o anaerobic exercise (no O2), this is why your legs burn when running.


1

Glycolysis is only the start

• Glycolysis

• Pyruvate has more energy to yield

• 3 more C to strip off (to oxidize)

• If O2 is available, pyruvate enters mitochondria

• Enzymes of Krebs cycle complete oxidation of sugar to CO2

What is the point? TO MAKE ATP!!!

Oxidation of pyruvate

• Pyruvate enters mitochondria

o 3 step oxidation process

o Releases 1 CO2 (count the carbons!)

o Reduces NAD → NADH (stores energy)

o Produces acetyl CoA

• Acetyl CoA enters Krebs cycle

o Where does CO2 go?


2

Pyruvate oxidized to Acetyl CoA

Yield = 2C sugar + CO2 + NADH

Krebs cycle

• Aka Citric Acid Cycle

o in mitochondrial matrix

o 8 step pathway

� each catalyzed by specific enzyme

� step-wise catabolism of 6C citrate molecule

• Evolved later than glycolysis

o Does that make evolutionary sense?

� bacteria →3.5 billion years ago (glycolysis)

� free O2 →2.7 billion years ago (photosynthesis)

� eukaryotes →1.5 billion years ago (aerobic respiration

(organelles)


3

So we fully

oxidized

glucose:

C6H12O6

↓

CO2

& ended

up with 4

ATP!


4

So why is the Citric Acid

Cycle so great?

Krebs cycle produces large

quantities of electron carriers

• NADH

• FADH2

• Stored energy!

• go to ETC (Electron

Transport Chain)

Energy accounting of Krebs Cycle

Net gain = 2 ATP

= 8 NADH + 2 FADH2

So why the Krebs cycle?

• If the yield is only 2 ATP, then why?

o Value of NADH & FADH2

� Electron carriers

� Reduced molecules store energy!

� To be used in the Electron Transport Chain


1

ATP accounting so far…

• Glycolysis → 2 ATP

• Kreb’s cycle → 2 ATP

• Life takes a lot of energy to run, need to extract more energy than 4 ATP!

• There’s got to be a better way!

There is a better way!

• Electron Transport Chain

o Series of molecules built into inner mitochondrial membrane

o Mostly transport proteins

o Transport of electrons down ETC linked to ATP synthesis

o Yields ~34 ATP from only 1 glucose!

o Only in presence of O2 (aerobic)

Mitochondria (Form fits function!)

� Double membrane

o outer membrane

o inner membrane

� highly folded cristae*

� fluid-filled space between membranes = intermembrane space

o matrix

� central fluid-filled space

Electron Transport Chain


2

Remember the NADH?

Glycolysis = 4 NADH Kreb’s Cycle = 8 NADH, 2 FADH2

lectron Transport Chain

: NADH passes electrons to ETC

Electron Transport Chain

� NADH passes electrons to ETC

o H cleaved off NADH &

FADH2

o electrons stripped from H

atoms → H+ (H ions)

o electrons passed from one

electron carrier to next in

mitochondrial membrane

(ETC)

o transport proteins in

membrane pump H+ across

inner membrane to

intermembrane space


3

But what “pulls” the electrons down the ETC?

Electrons flow downhill

� Electrons move in steps from

carrier to carrier downhill to

O2

o each carrier more

electronegative

o controlled oxidation

o controlled release of

energy


4

Why the build up H+?

� ATP synthase

o enzyme in inner membrane of

mitochondria

ADP + Pi → ATP

� only channel permeable to H+

� H+ flow down concentration gradient provides

energy for ATP synthesis

o molecular power generator!

o flow like water over water wheel

o flowing H+ cause change in

o shape of ATP synthase enzyme

ATP Synthesis

Chemiosmosis couples ETC to ATP synthesis

� build up of H+ gradient just so H+ could flow through ATP synthase enzyme to build ATP


5

Cellular respiration

Summary of cellular respiration

� Where did the glucose come from?

� Where did the O2 come from?

� Where did the CO2 come from?

� Where did the H2O come from?

� Where did the ATP come from?

� What else is produced that is not listed in this equation?

� Why do we breathe?

Taking it beyond…

� What is the final electron acceptor in electron transport chain?

O2

� So what happens if O2 unavailable?

o ETC backs up

o ATP production ceases

o Cells run out of energy and you die!


1

Beyond glucose: Other carbohydrates

• Glycolysis accepts a wide range of carbohydrates fuels

o Polysaccharides → → → glucose

(hydrolysis)

� ex. starch, glycogen

o Other 6C sugars → → → glucose

(modified)

� ex. galactose, fructose

Beyond glucose: Proteins

• Proteins → → → → → amino acids

(Hydrolysis)

• Fats → → → → → glycerol & fatty acids

(Hydrolysis)

o Glycerol (3C) → → PGAL → → glycolysis

o Fatty acids → 2C acetyl groups → acetyl coA →Krebs cycle

Carbohydrates vs. Fats

• Fat generates 2x ATP vs. carbohydrate

o More C in gram of fat

o More O in gram of carbohydrate so it’s already partly oxidized.


2

Respond to cell’s needs

• Key points of control

o Phosphofructokinase

� Allosteric regulation of enzyme

• “can’t turn back” step

before splitting glucose

� AMP & ADP stimulate

� ATP inhibits

� citrate inhibits

Why is this regulation important?

• Balancing act: Availability of raw materials vs.

Energy demands vs. Synthesis.


ATP Accounting (From G

lucose to ATP)

Glycolysis

Glucose + 2 ATP

= 2 Pyruvate

4 ATP

2 NADH

Oxidation of Pyruvate

2 Pyruvate

= 2 Acetyl CoA

2 CO

2

2 NADH

Kreb’s Cycle

2 Acetyl CoA

= 4 CO

2

2 ATP

2 FADH

2

6 NADH

ETC

10 NADH +

2 FADH

2= ~34 ATP

(~3 ATP per NADH &

~2 ATP per

FADH

2)

This yields approxim

ately 38 Total

ATP from 1 glucose m

olecule.

But why does the NADH from

Glycolysis make less ATP per

molecule than the NADH from the

Kreb’s Cycle during the ETC?



2014 According to the chemiosmotic model proposed by Peter Mitchell in 1961, an electrochemical gradient is linked to the synthesis of ATP in mitochondria. Construct an explanation of the chemiosmotic model by doing each of the following. (a) Make a claim about the role of the inner mitochondrial membrane in ATP synthesis. (b) Present ONE piece of evidence that supports the role you proposed in part (a). (c) Provide reasoning to explain how the evidence you presented in part (b) supports the claim you made

in part (a).


1990 The College Board

Advanced Placement Examination

BIOLOGY

SECTION II Time – 1 hour and 30 minutes

Answer all questions. Number your answer as the question is numbered below.

Answers must be in the essay form. Outline form is NOT acceptable. Labeled diagrams may be used to supplement discussion, but in no case will a diagram alone suffice. It is important that you read each question completely before you begin to write.

1. The results below are measurements of cumulative oxygen consumption by germinating anddry seeds. Gas volume measurements were corrected for changes in temperature and pressure.

Cumulative Oxygen Consumed (mL)

Time (minutes) 0 10 20 30 40

22° C Germinating Seeds 0.0 8.8 16.0 23.7 32.0

Dry Seeds 0.0 0.2 0.1 0.0 0.1

10° C Germinating Seeds 0.0 2.9 6.2 9.4 12.5

Dry Seeds 0.0 0.0 0.2 0.1 0.2

a. Using the graph paper provided, plot the results for the germinating seeds at22° C and at 10° C.

b. Calculate the rate of oxygen consumption for the germinating seeds at 22° C, using thetime interval between 10 and 20 minutes.

c. Account for the differences in oxygen consumption observed between:(1) germinating seeds at 22° C and at 10° C; (2) germinating seeds and dry seeds.

a. Describe the essential features of an experimental apparatus that could be used to measureoxygen consumption by a small organism. Explain why each of these features isnecessary.

Copyright © 1970 to 2004 by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face‐to‐face teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited.

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