Transcript 3 Option B Cell Respiration Glycolysis 2011

Cellular Respiration
STAGE 1: Glycolysis
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What’s the point?
ATP
The Point is to Make ATP!
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Glycolysis
• Breaking down glucose
– “glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C
– 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?
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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
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You mean,
I’m related
to them?!
SEE H.O.
E
SEE H.O F
NOTES!!!
Stage I – Glycolysis
1). One glucose
molecule is
phosphorylated by 2 ATP
molecules .
( formed from previous
glucose molecules).
In addition to this
phosphorylation, the
structure of the glucose
molecule is altered slightly
(It is now primed for a
split into (2) 3-C
compounds)
This converts the
glucose into a compound
called fructose diphosphate.
(symbolized as
P - FRUCTOSE - P )
2). The fructose
diphosphate is then
split in half to form 2
molecules of a
substance called
glyceraldehyde
phosphate.
( P - GAL & GAL - P )
3. EACH GLYCERALDEHYDE
PHOSPHATE WILL UNDERGO
THE FOLLOWING
CHANGES:
A). 2 H atoms are released
from each molecule (total = 4 H
atoms).
Each pair of H atoms is picked
up by an NAD+ (total = 2 NAD+).
The H atoms are transported
to the H / e´ T.C. and used to
form ATP.
B). Another phosphate is added
to each glyceraldehyde. The
phosphate is taken from
phosphoric acid, (already
present).
The substance formed is
glyceraldehyde diphosphate
( P - GAL - P )
4). 2 phosphates are
removed from each
glyceraldehyde
diphosphate molecule.
(T= 4 phosphates).
Each phosphate is
added to an ADP
forming 4 ATP.
The structure of each
remaining molecule is
altered again, forming a
pyruvic acid molecule
(pyruvate).
Energy accounting of glycolysis
2 ATP
2 ADP
glucose      pyruvate
2x 3C
6C
4 ADP
4 ATP
• Net gain = 2 ATP
– some energy investment (2 ATP)
– small energy return (4 ATP)
• 1 6C sugar  2 3C sugars
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All that
work! And
that’s all I
get?
Is that all of the energy that 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
Heck of a
way to make
a living!
In addition…by the end of Glycolysis,
two additional products
have been formed:
• 2 pyruvic acid molecules which will enter
Stage II
• 2 NADH + H + which will travel to the H / e´
T.C. to form ATP.
Where does the supply of NAD+ come from?
glucose + 2ADP + 2Pi + 2 NAD+ 
2 pyruvate + 2ATP + 2NADH
• NADH must be about to give its H to another
molecule
• without regenerating NAD+,
energy production would stop
NADH
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Problem solved with options!
1. anaerobic respiration (absence of oxygen)
• ethanol fermentation
• lactic acid fermentation
2. aerobic respiration
NADH
Ex. Anaerobic ethanol fermentation
• Bacteria, yeast
pyruvate  ethanol + CO2
3C
 beer, wine, bread NADH
 at ~12% ethanol, kills yeast
2C
NAD+
 Animals, some fungi
pyruvate  lactic acid
3C
NADH
3C
NAD+
 cheese, yogurt, anaerobic exercise (no O2)
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1C
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
Kreb’s cycle
mitochondria
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Glycolysis summary
endergonic
invest some ATP
exergonic
harvest a little
more ATP
& a little NADH
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Another View
OVERVIEW OF GLYCOLYSIS
1
2
3
6-carbon glucose
(Starting material)
2 ATP
P
P
6-carbon sugar diphosphate
P
P
6-carbon sugar diphosphate
P
3-carbon sugar
phosphate
P
3-carbon sugar
phosphate
P
3-carbon sugar
phosphate
NADH
P
3-carbon sugar
phosphate
NADH
2 ATP
2 ATP
3-carbon
pyruvate
Priming reactions. Priming reactions. Cleavage reactions. Then, the six-
Glycolysis begins with the addition of
carbon molecule with two phosphates
energy. Two high-energy phosphates
is split in two, forming two threefrom two molecules of ATP are added to carbon sugar phosphates.
the six-carbon molecule glucose,
producing a six-carbon molecule with two
phosphates.
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3-carbon
pyruvate
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.
Any Questions??
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