Cellular Energy pt.2

1. Energy & The Cell
Glycolysis, Cellular Respiration &
Fermentation

2. Energy
•All life requires energy
•Therefore cells require energy
–for growth, active transport, synthesis of
carbohydrates, lipids, & proteins
•The source of energy for cells is the energy
stored in chemical bonds of organic molecules
–these molecules = food molecules, especially
carbohydrates (also lipids)
–most common is glucose

3. Recycling Energy

4. ATP
•Cells store energy in the chemical
bonds of sugar, but cannot use it
directly
•To use this energy, the cell must
transfer the energy in sugar molecules
to ATP
•ATP = adenosine triphosphate

5. Structure of ATP
•The base, adenine
•The sugar, ribose
•Ribose is bound to a
chain of 3 phosphate
molecules connected
by high energy
bonds

6. Phosphorylation forms ATP

7. Releasing Energy from ATP
•If the cell needs energy it breaks the
last phosphate bond, releasing energy
ATP « ADP + P + energy
•Almost all energy requiring processes in
cells use ATP as the energy source

9. Fermentation
•So, where does ATP come from?
•Fermentation = breakdown of glucose,
yielding ATP, without O
2

•The first living organisms were single cells
that existed without O
2
–Anaerobic
–Lack the enzymes needed to break down energy
molecules with O
2
•Many types of bacteria and other single
celled organisms still use anaerobic
processes to convert energy

10. Types of Fermentation
•2 kinds:
•Alcoholic fermentation:
–occurs in micro-organisms such as yeast
•Lactic acid fermentation:
–occurs in bacteria and animal cells

11. Fermentation in the Cytosol
•Fermentation occurs
in the cytosol
•It produces lactic
acid or alcohol
•Fermentation begins
with the process of
glycolysis, which is
also part of aerobic
respiration.

12. Glycolysis
•Occurs in the cytoplasm of the cell
•One molecule of glucose is split into two
molecules of a three carbon compound
called pyruvic acid
•2 molecules of ATP provide the energy to
split the glucose molecule
•When glucose splits, it releases enough
energy to form 4 molecules of ATP from
ADP + P
•Therefore 2 molecules of ATP are gained

13. Energy of Glycolysis

14. The Role of NAD in Glycolysis
•During the conversion of glucose to
pyruvic acid, hydrogen is released
•This hydrogen is picked up by a
coenzyme, nicotinamide adenine
dinucleotide (NAD)
•NAD is a hydrogen acceptor
•When it accepts hydrogen, becomes
NADH
2

15. Summary of Glycolysis - Investment

16. Summary of Glycolysis - Payoff

17. Energy of Fermentation
•As a result of fermentation, each
molecule of glucose yields 2 molecules of
ATP
•These ATP molecules come from
glycolysis
–Fermentation produces no ATP beyond
glycolysis
•It removes pyruvic acid, and recycles
NAD, which allows glycolysis to continue,
producing ATP

18. Alcoholic Fermentation
•Pyruvic acid from glycolysis combines with H
from NADH
2
to produce ethyl alcohol
• 2CH
3
COCOOH + 2NADH
2
® 2CH
3
CH
2
OH + 2CO
2
+ 2NAD
–CO
2
is a waste product

19. Alcoholic Fermentation Pathway

20. Lactic Acid Fermentation
•Pyruvic acid combines with H from NADH
2
to
produce lactic acid:
2CH
3
COCOOH + 2NADH
2
® 2CH
3
CHOHCOOH + 2NAD
•Unlike alcoholic fermentation, no CO
2
is given off
•Occurs in human cells when there is not enough O
2

available for aerobic respiration

21. Lactic Acid Fermentation Pathway

22. Uses of Lactic Acid Fermentation
•During strenuous exercise glycolysis occurs at a
high rate
•Pyruvic acid is produced rapidly
•Muscle cells may not receive enough O
2
to process
pyruvic acid through aerobic respiration
•Therefore muscles produce lactic acid which
permits glycolysis to continue to supply ATP to
your muscles
•When lactic acid builds up, your muscles ache
•O
2
you take in from heavy breathing helps convert
lactic acid back to pyruvic acid

23. Cellular Respiration
•Most cells produce ATP by breaking the
energy containing bonds of glucose in the
presence of oxygen
•Production of ATP this way = Respiration
•Uses O
2
to break sugars down to CO
2
& H
2
O
–Not the same as breathing
–provides O
2
, but otherwise quite different
•This process occurs in the many mitochondria
of each cell

24. The Process of Cellular Respiration
•C
6
H
12
O
6
+ 6 O
2
® 6 CO
2
+ 6 H
2
O + energy
(sugar) (ATP)
•Two stages of Cellular Respiration:
–Anaerobic
•without oxygen
–Aerobic
•with oxygen

25. Cellular Respiration Overview

26. Anaerobic Stage
•The anaerobic stage of cellular respiration is
glycolysis, the same pathway used in fermentation
•This part of cellular respiration occurs in the
cytoplasm
•Recall the energy budget for glycolysis:
–One molecule of glucose is split into two molecules of a
three carbon compound called pyruvic acid
–2 molecules of ATP provide the energy to split the
glucose molecule
–When glucose splits, it releases enough energy to form
4 molecules of ATP from ADP + P
–Therefore 2 molecules of ATP are gained

27. Energy of Glycolysis

28. Aerobic Stage
•After glycolysis, the chemical bonds of pyruvic
acid are broken down in a series of chemical
reactions
•These occur in the mitochondria and require O
2
•The aerobic stage has two parts:
–The Citric Acid Cycle
–The Electron Transport Chain

29. Pyruvate Forms Acetyl CoA

30. The Citric Acid Cycle
•Steps to break down pyruvic acid:
•In the presence of O
2
, pyruvic acid breaks down to
acetic acid and CO
2

–CO
2
is released as waste
•Acetic acid combines with coenzyme A ® acetyl
CoA
–This step also forms NADH
2
from NAD
•Acetyl CoA enters the citric acid cycle and
combines with a 4 carbon compound to produce
citric acid
•As the cycle continues, citric acid is broken down in
a series of steps, back to the original 4 carbon
compound

31. Energy from the Citric Acid Cycle
•For each molecule of
acetyl CoA that enters
the cycle, 8 atoms of H
are released.
•These hydrogen atoms
are trapped by NAD,
forming NADH
2
.
•Therefore, each turn of
the cycle yields 4 NADH
2

33. The Electron Transport Chain
•NADH
2
releases the hydrogen atoms trapped
during glycolysis & the citric acid cycle
–Therefore NADH
2
becomes NAD again
•Electrons contained in the H atoms pass through
a series of coenzymes which are electron
acceptors.
•Each time an electron moves from one acceptor
to another, an electron is released
•The electron released is used to form molecules
of ATP from ADP + P
•This whole process = electron transport chain

34. Oxygen & The Electron Transport Chain
•The last part of the
chain is the electron
acceptor, oxygen
•Electrons combine
with oxygen &
hydrogen to form
H
2
O, which is
released as a
byproduct

35. Chemiosmosis
•The process of formation of ATP during the ETS of
aerobic respiration as the result of a pH gradient
across the membrane of the cristae in the
mitochondria = chemiosmosis
•Steps:
–H
+
ions from the matrix are pumped into the space
between the cristae and the outer membrane.
–A H
+
gradient develops between the inside and outside of
the cristae
–This pH differential creates free energy
–H
+
pass back across the membrane through F1
–O
2 is the final H
+
/ electron acceptor producing H
2O

36. Picturing Chemiosmosis

37. Cellular Respiration Summary
•Thus for every molecule of glucose that is broken
down by glycolysis and respiration, 38 molecules of
ATP are formed
–Used 2 ATP to begin the process ® Therefore 36 ATP gained