Download Cellular Respiration Harvesting Chemical Energy

2006-2007
Today I will…
1. Describe the process of glycolysis.
2. State the reactants and products of glycolysis.
Modified from Kim Foglia
What’s the point?
ATP
2006-2007

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
◦ occurs in cytosol
 why does that make evolutionary sense?

Life on Earth first evolved without
free oxygen (O2) in atmosphere
◦ energy had to be captured from
organic molecules in absence of O2

Prokaryotes that evolved glycolysis are
ancestors of all modern life
◦ ALL organisms still utilize
glycolysis
10 reactions
◦ convert
6C glucose to two
3C pyruvate
◦ produce 2 ATP & 2
NADH
glucose
C-C-C-C-C-C
2 ATP
2 ADP
fructose-6P
P-C-C-C-C-C-C-P
DHAP
P-C-C-C
2 Pi
G3P = glyceraldehyde-3-phosphate
DHAP = dihydroxyacetone phosphate
G3P (PGAL)
C-C-C-P 2 NAD+
pyruvate
C-C-C
2 NADH
4 ADP
4 ATP
endergonic
invest some ATP
exergonic
harvest a little
ATP & a little NADH
yield
2 ATP
2 NADH

Glucose “priming”
◦ get glucose ready
to split
 phosphorylate
glucose
 rearrangement
◦ split destabilized
glucose
PGAL

Energy Harvest
◦ NADH production




G3P donates H
oxidize sugar
reduce NAD+
NAD+  NADH
◦ ATP production
 G3P  pyruvate
 sugars donate P
 ADP  ATP
2 ATP
2 ADP
glucose     
pyruvate
6C
4 ADP
2x 3C
4 ATP

Net gain = 2 ATP

1 6C sugar  2 3C sugars
◦ some energy investment (-2 ATP)
◦ small energy return (+4 ATP)

Not a lot of energy…
◦ for 1 billon years+ this is how life on Earth
survived… Why?
 slow growth, slow reproduction
 only harvest 3.5% of energy stored in glucose
 more carbons to strip off = more energy to harvest
O2
O2
O2
O2
O2
glucose     pyruvate
2x 3C
6C
glucose + 2ADP + 2Pi + 2 NAD+ 
Glycolysis
2 pyruvate + 2ATP + 2NADH
glucose + 2ADP + 2Pi + 2 NAD+ 
2 pyruvate + 2ATP + 2NADH

Going to run out of NAD+
◦ without regenerating NAD+,
energy production would stop
◦ another molecule must accept
H from NADH
How is NADH recycled to NAD+?
NADH

Another molecule must accept H from NADH
◦ aerobic respiration
O2
 to Electron Transport Chain in mitochondria
◦ anaerobic respiration
 ethanol fermentation
 lactic acid fermentation
NADH
which path you
use depends on
who you are…
O2

Bacteria, yeast
pyruvate  ethanol + CO2
3C
NADH
 beer, wine, bread
2C
NAD+
to glycolysis
 Animals, some fungi
pyruvate  lactic acid
3C
NADH
3C
NAD+to glycolysis
 cheese, anaerobic exercise (no O 2)
1C
bacteria yeast
pyruvate  ethanol + CO2
3C
NADH
2C
NAD+
 Dead end process
 at ~12% ethanol,
kills yeast
 can’t reverse the
reaction
1C
animals
pyruvate  lactic acid
NADH

3C
NAD+
3C
 Reversible process
 once O2 is available,
lactate is converted
to pyruvate by liver
O2
Pyruvate
O2
O2
fermentation
Kreb’s cycle
mitochondria
What’s the point?
ATP
2006-2007
H+
H+


H+
H+
H+
H+
H+
H+
Set up a H+
gradient
Allow the H+
to flow through
ATP synthase
ADP + Pi  ATP
ADP + Pi
ATP
Have we done that yet?
H+