Transcript Energy in A Cell

Cellular Respiration
Oxidation–Reduction Reactions
 Electrons in the outer energy orbit have more energy than
any other electrons in the atom. These valence electrons
are called high energy electrons.(Those electrons closer to
the nucleus have lower energy)
 During chemical reactions, when the electrons in the outer
orbit are striped away, some energy is released.
 The atom that has lost an electron has been OXIDIZED(lost
a negative charge)
 The atom that gains the electron is REDUCED(Gained a
negative charge)
 These reactions are called oxidation reduction reactions.
The electrons that are lost or gained are high energy
electrons.
 Example: if one atom is oxidized or loses an electron,
that atom becomes partially charged(an ion)
_
Atom X(oxidized)----------- Ion X+ +e
The electron is picked up by another positive ion and
becomes an atom
_
Ion Y + + e -------------Atom Y
 Oxidation –reduction reactions occur in the cell during
cellular respiration. High energy electrons move from
one compound to another. In the cell, these electrons
can’t move on their own- they need a carrier.
 A proton(+) can join with one electron and become a
hydrogen atom. So we write the movement of these
high energy electrons as H atoms. A high energy
electron is contained in an H atom
Other Energy Storing Compounds
 NADH- nicotine adenine dinucleotide
 FADH- flavin adenine dinucleotide
 Both of these high energy storing compounds pick up
energy electrons that have been lost from atoms that
have been oxidized.
NAD+
NADH
FAD+
FADH
Low energy state
High energy state
Oxidized
Reduced
Lost high energy electrons Gained high energy in the
in form of H atoms
form of H atoms
 NADH and FADH are called H acceptors because during a
chemical reaction, like cellular respiration they pick up H
atoms that contain high energy electrons
 Molecules of this compound when written with an H,
contain a high energy electron and are considered high
energy storing compounds similar to ATP.
 Cell can use these compounds as a source of energy.
 When written as ADP+ or NAD+- they have lost their H or
high energy electron.
Cellular Respiration
 Occurs in the mitochondria
 Break down glucose to make ATP-enough energy is
produced to change ADP back to ATP.
 3 stages
1.Glycolysis
2.Citric Acid Cycle (Krebs)
3.Electron Transport Chain
Glycolysis-glucose breaking
 Does not require oxygen(anaerobic)
 Takes place in cytoplasm of cell
 Glucose
2 PGAL
2 Pyruvic Acid
(6C)
phosphoglyceraldehyde
2 (3C’s)
PGAL is oxidized and NAD+ is reduced to NADH
Need 2 ATP to start reaction
Make 4 ATP during glycolysis
Net ATP Production- 2 ATP
Citric Acid Cycle(Krebs)
 No oxygen needed but will only
continue if oxygen is present.
 Produces 2ATP and 2CO2
 Takes place in mitochondria-in matrix
 Total ATP so far- 4 ATP ( -2+4+2)
 Pyruvic acid cannot enter the cycle
 Must be broken down into acetic acid with
the help of an enzyme: Coenzyme A (CoA)
 CoA is actually the vitamin niacin
 Acetic acid enters CAC as acetyl CoA
 Acetyl Co A changed to citric acid
 Citric Acid becomes oxidized and
produces : NADH,FADH,CO2, and 2ATPs
FADH and NADH are the H acceptors. They
are important in the next step.
Electron transport chain
 Occurs in the cristae (folds) of the inner mitochondrial
membrane
 There are many enzymes located in that membrane.
 Requires oxygen
 Oxygen is “final electron acceptor”
 Produces 32 ATP +H2O
 Final ATP Count
make 38-2needed to start Glycolysis
36 ATP TOTAL
 The high energy compounds FADH2 and NADH pass
their electrons from enzyme to enzyme along the
chain. Energy is lost as the electrons travel down the
chain. This energy is used to bond phosphate groups
to ADP.
ETC Steps
1. As FADH2 and NADH arrive at the beginning of
the transport chain, these molecules drop off
their high energy electrons (remember they’re
H atoms.
2. The H atom splits apart into a proton and an
electron.
3. The electron begins its journey down the
enzyme chain.
4. The H+ ion (proton) passes through the membrane
to the other side. Once it passes through the
membrane it cannot come back through. This causes
protons to build up a concentration of positive
charges on the backside of the membrane. The front
side of the membrane where the electrons are
traveling, has a negative charge. This difference in
charge on the membrane is called a charge
differential and is a source of potential energy. The
H+ flows back through at ATP Synthase due to
diffusion. This fuels the production of ATP.
5. As electrons go from enzyme to enzyme, energy is
lost. This energy along with the potential energy
from the charge differential is used to bond 32
phosphate groups to 32 ADP molecules to
regenerate 32 ATP molecules at ATP synthase
Enzyme
6. At the end of the transport chain the electrons are reunited
with the H+ ions to reform a hydrogen atom. Two H atoms
then meet up with oxygen - the final electron acceptor – and
form water. Oxygen is absolutely necessary for this to work.
We breathe
oxygen for this reason.
 From l molecule of glucose the following molecules of ATP are
produced:
glycolysis = 2 ATP(-2+4)
CAC/Kreb’s
= 2 ATP
ETC
= 32 ATP
Grand Total = 36 molecules of ATP
What happens if no oxygen
 FERMENTATION-anaerobic respiration
The first part of fermentation, glycolysis, is just like cellular
respiration,because it’s anaerobic.
But the second part of fermentation is different since no
oxygen is available.
 Pyruvic acid does not go into the Kreb’s Cycle or the ETC and
no ATP is not produced. Instead, pyruvic acid produces
other products depending on the type of cell in which the
fermentation occurs.
ANIMAL CELLS

 Lactic acid fermentation occurs when oxygen is not available.
This happens during vigorous exercise when the lungs cannot
bring enough oxygen to body cells. Glycolysis takes place in
muscle cells but pyruvic acid is oxidized to form lactic acid rather
than going on to the CAC and the ETC to form ATP.
 The build up of lactic acid causes muscle cramping. When
oxygen does become available, for example when the exercising
stops, the cells switch back to aerobic respiration. The lactic acid
that was produced is transported to the liver where it’s
converted back to glucose.
Other Cells
 In unicellular cells such as yeasts, the same
process occurs but instead of lactic acid being
produced from the oxidation of pyruvic acid,
alcohol and carbon dioxide are formed. This
production of ethyl alcohol is used in beer
brewing and the making of wine.
 When more carbon dioxide is produced the
yeasts are used in the baking industry.
Comparing photosynthesis and
cellular respiration
Photosynthesis
6CO2 + 6H2O
Cellular Respiration
C6H12O6 +6O2
C6H12O6 +6O2
CO2 used
CO2 produced
O2 produced
O2 used
Glucose produced
Glucose used
Energy stored
Energy used
Light needed
No light needed
Chloroplast
mitochondria
6CO2 + 6H2O