Energy
Cellular Respiration
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Harvesting Energy

Cells are open systems, requiring outside energy
to perform work

Look at how cells harvest chemical energy stored
in organic molecules and use it to regenerate
ATP
Types of Organisms

Autotrophs

organisms that build organic molecules from
inorganic compounds


examples: plants, algae, some bacteria
Heterotrophs

organisms that obtain organic molecules by eating
other organisms or their by-products

examples: animals, fungi, some bacteria
Energy flow and chemical recycling in
ecosystems

Photosynthesis


products of cellular
respiration are used
as raw materials
Cellular respiration

products of photosynthesis are used
as raw materials
Cellular Respiration

Carbohydrates, lipids, and proteins can all be
metabolized as fuel

Cellular respiration is most often described as
oxidation of glucose
gains hydrogen e⁻
becomes reduced
Equation

C6H12O6 + 6O2
reducing agent
oxidizing
agent
6CO2 + 6H2O + Energy
oxidized
looses hydrogen e⁻
becomes oxidized
In bomb calorimeter ΔG = -686 Kcal
reduced
Biochemical Pathway

Series of enzymatic catalyzed reactions

body has 2000 different kinds of enzymes

Cellular respiration
Phosphorylation

To add phosphate to a molecule


ADP + Pi
ΔG = +7.3 Kcal


ATP
endergonic
two ways:


1. substrate-level phosphorylation
2. chemiosmosis (coupled with Elec.Trans. Chain)


oxidative phosphorylation (animals)
Photophosphorylation (plants)
Substrate-level Phosphorylation

ATP made directly
substrate-phosphate
product
ADP
ATP
anabolism
Chemiosmotic Phosphorylation

Making of ATP by using energy from H+
gradient

ATP made indirectly

two sources of electrons:


oxidative phosphorylation at mitochondria (electrons
from food)
photophosphorylation at chloroplasts (electrons from
water)
Oxidative Phosphorylation
(mitochondria)


by all organisms (photosynthetic and nonphotosynthetic)
at mitochondria



cristae
energy comes from food
coenzymes:
NAD +
FAD
NADH (equivalent to 3ATP)
FADH2 (equivalent to 2ATP)
Photophosphorylation
(photosynthesis)

by photosynthetic organisms

thylakoid membrane

energy comes from sunlight

coenzyme: NADP + H+
NADPH
ACTIVITIES






Is phosphorilation anabolic or catabolic?
Where in the cell does oxidative phosphorilation
occur?
What organism(s) have ox. phosph.?
Where does photophosphorilation occur?
What organism(s) show photophosphorilation?
Write the formulas of both.
answers







Anabolic (uses energy from the sun)
Mitochondria
Autotrophs and heterotrophs
Chloroplast
Autotrophs
C6H12O6 + 6O2
6CO2 + 6H2O + ATP
6CO2 + 6H2O
C6H12O6 + 6O2
Coenzymes
High-energy electrons are extracted from
chemical bonds (of food) and carried by
coenzymes to proton pumps
NADH
NAD +

3 ATP
FADH2
FAD
2 ATP
Electron Transport Chain (ETC)

all carriers are proteins
(except Q, ubiquinone)

each carrier is more
electronegative than
the previous one

with each passing,
electrons lose potential
energy (pulls electrons
to a lower energy state)

-53 kcal/mole of NADH
ETC cont.

oxygen is the most electronegative, it accepts
the electrons and H+ to form water

Simplified:
2 e- + ½ O2 + 2H+
H2O
Electron Transport Chain
Intermembrane space
Inner mitochondrial
membrane
Matrix
ATP synthase

protein complex, in the cristae.

Actually makes ATP from ADP and Pi.

Proton gradient powers ATP synthesis.

This concentration of H+ is the protonmotive force.

The ATP synthase molecules are the only
place that will allow H+ to diffuse back to
the matrix.
Cellular Respiration (summary)

an ATP-producing catabolic process

ultimate electron acceptor is oxygen

transfers energy from food to ATP
Stages of Cellular Respiration
a. Glycolysis

breakdown of 1 glucose into 2 pyruvate

location: cytosol

Anaerobic


10 step process
produces 2 ATP
Glycolysis
Energy Input/Output

energy investment phase



energy payoff phase



phosphorylating glucose
requires 2 ATP per glucose
ATP is produced
NADH is produced
Total per glucose:

2 ATP (net)
2 NADH = 6ATP
b. Oxidation of Pyruvate

Breakdown of 2 pyruvate into 2 acetyl-CoA

Location: mitochondrial matrix

Aerobic, 3 step process
Oxidation of Pyruvate (cont.)

If oxygen is present, pyruvate enters the mitochondrion (via active
transport)

a multi-enzyme complex modifies pyruvate to acetyl CoA (3 reactions)

A carboxyl group is removed as CO2.

A pair of electrons is transferred from the remaining two-carbon
fragment to NAD+ to form NADH.

The oxidized
fragment, acetate,
combines with
coenzyme A to
form acetyl CoA
Oxidation of Pyruvate Simplified
c. Citric Acid Cycle

Also known as Krebs cycle, tricarboxylic acid cycle, oxidation
of acetyl-CoA

Breakdown of 2 acetyl-CoA into 4 carbon dioxide

Location: mitochondrial matrix

Aerobic
 8 step process
The Citric acid
(Krebs) cycle
Eight steps
The Citric acid (Krebs) cycle
3 NADH
1 ATP
1 FADH2
12 ATP
of every acetyl -CoA
d. Oxidative phosphorylation





Chemiosmosis
Electron transport chain (ETC)
Location: mitochondria’s inner membrane
Aerobic
In conjunction with the Krebs cycle produces
32-34 ATP
Energy obtained from Glucose
1 Glycolysis
EACH
2ATP
2NADH
TOTAL
2ATP
6ATP
2 Pyruvate oxidation
1 NADH
6ATP
2 Citric acid cycle
and oxidative
phosphorilation
3 NADH
1 ATP
1 FADH2
18ATP
2ATP
4ATP
Total = 38ATP
Maximum energy produced by every
molecule of glucose is 36-38 ATP
NAD+ = 2.5-3.3 ATP
FAD = 1.5-2ATP
ATPs, a comparison
Substrate-level
Oxidative phosphorylation
anaerobic
2 ATP
0 ATP
2 ATP
4 ATP
aerobic
glycolysis
oxidation of pyruvate
Citric acid cycle
Total
6ATP
6 ATP
22 ATP
34 ATP
ATPs

Total (gross) ATPs = 38

- 2 ATPs



One ATP is used as energy in glycolysis to shuttle 2 NADH
into mitochondrial matrix
One ATP is used as energy to actively pump pyruvate into
the mitochondria
Net ATPs = 36
Kcal per mole of glucose
in cellular respiration

36 ATP x -7.3kcal = -263 Kcal

in bomb calorimeter
in cellular respiration

= -686 Kcal (100%)
= -263 Kcal (38%)
FYI







McDonald’s Big Mac (215g): 492kcal +
serving (78g) of fries: 207kcal= ~700 kcal
KFC 1 Chicken Drumstick (67g): 195kcal
Quaker oats (45g): 166kcal
Haagen Dazs Ice Cream (50g): 159kcal
Snickers (64½g) : 323kcal
Peanuts (50g): 311kcal
can of Coke (330ml): 139kcal
Calorie Burning for an Average Person
(67.5 kg or 150 lb of weight)








Bicycling (slow)
Bicycling (fast)
Dancing (slow)
Dancing (fast)
Running
Swimming
Walking (3 mph)
Walking (4 mph)
170 (Kcal/h)
514
202
599
865
535
158
231
Catabolism

Carbohydrates, fats,
and proteins can all
be catabolized through
the same pathways.
Anabolism

Not all food molecules are destined to be oxidized as
fuel for making ATP

Food molecules provide raw materials for biosynthesis

Cells need raw materials for growth and repair
 Some are obtained directly from food
 Others are made from intermediates in glycolysis and
the Krebs cycle

Biosynthesis consumes ATP
Fermentation

Anaerobic process

ATP-producing catabolic pathway

dozens of fermentation types exist

fermentation types of eukaryotes:


alcoholic fermentation
lactic acid fermentation
Alcoholic Fermentation

pyruvate is converted
to ethanol in two steps



1- pyruvate is converted
to acetaldehyde by the
removal of CO2.
2 - acetaldehyde is reduced
by NADH to ethanol.
Alcoholic fermentation


Bacteria
yeast (used in brewing
winemaking and baking)
Alcoholic Fermentation
glucose C6
2ADP + 2Pi
2 NAD +
pyruvate C3
CO2
acetaldehyde C2
NADH
NAD +
ethanol C2
2ATP
2NADH
pyruvate C3
CO2
acetaldehyde C2
NADH
NAD +
ethanol C2
Alcoholic Fermentation, ATP

Net = 2 ATP
2ATP x -7.3 Kcal = -14.6 Kcal

One Mole of Glucose




in bomb calorimeter
in cellular respiration
in fermentation
= -686 Kcal (100%)
= -263 Kcal (38%)
= -14.6 Kcal (2%)
Lactic Acid Fermentation


pyruvate is reduced directly by NADH to form lactate
(ionized form of lactic acid).
Lactic acid fermentation is done by


some fungi and bacteria is
used to make cheese and
yogurt.
Muscle cells to generate ATP
when O2 is scarce

lactate is converted back to
pyruvate in the liver
Lactic Acid Fermentation
glucose C6
2ADP + 2Pi
2ATP
2 NAD +
2NADH
pyruvate C3
pyruvate C3
NADH
NAD +
lactic acid C3
NADH
NAD +
lactic acid C3
Lactic Acid Fermentation, ATP


Net = 2 ATP
2ATP x -7.3 Kcal = -14.6 Kcal
1 mole glucose
in bomb calorimeter
in cellular respiration
in fermentation
= -686 Kcal (100%)
= -263 Kcal (38%)
= -14.6 Kcal (2%)
Facultative Anaerobes

Some organisms (facultative anaerobes), including yeast
and many bacteria, can survive using either fermentation or
respiration.

For facultative anaerobes,
pyruvate is a fork in the
metabolic road that leads
to two alternative routes.

At a cellular level, human
muscle cells can behave
as facultative anaerobes,
but nerve cells cannot.
White or Dark?

Fast or slow fibers





Fast (white) fiber
White meat
Break down glucose thru fermentation (anaerobically)
Fibers (cells) thicker, fewer mitochondria, less myoglobin (pale)
In sprinters (60% fast)





Slow (dark) fiber
Dark meat
Break down glucose thru cell respiration (aerobically)
Fibers (cells) filled with mitochondria and myoglobin (red)
in marathon runners (80% slow)
ACTIVITY




How many ATPs are formed during aerobic
respiration?
How many times more efficient is aerobic
compared to anaerobic respiration?
Where does the Lactic Acid fermentation occur?
give examples of organisms that show anaerobic
respiration.
answers




How many ATPs are formed during aerobic
respiration? 36- 38
How many times more efficient is aerobic
compared to anaerobic respiration? 9x
Where does the Lactic Acid fermentation occur?
muscles
give examples of organisms that show anaerobic
respiration. Some bacteria, yeast.
ACTIVITY: Fill in the blanks
Mitochondrion
Cytosol
2
1
A
3
B
C
D
G
4
E&F
The End