Transcript Cellular Respirationx

Cellular Respiration
Releasing Stored Energy
Harvesting Chemical Energy
 Autotrophs like plants and cyanobacteria
use photosynthesis to change the sun’s light
energy into chemical energy contained in
the bonds within glucose molecules.
 Both autotrophs and heterotrophs then use
this energy-rich molecule to supply the
energy they need to power their cellular
activities like growth, movement, or
reproduction.
 When glucose or other large molecules are
broken down into smaller molecules, the
energy from the broken chemical bonds is
used to make ATP from ADP and
phosphate.
 ATP is the main energy currency of living
things.
 The complex many-step procedure used by
living things to make ATP from the
breakdown of large molecules such as
glucose is called cellular respiration.
 Cellular respiration can be divided into
several smaller biochemical pathways:
glycolysis
fermentation
aerobic respiration
 Glycolysis evolved very early in the
Earth’s history. There was no free
oxygen in the atmosphere, so the first
organisms (bacteria) all used glycolysis
to produce ATP.
 It took more than one billion years for
bacteria to evolve the process of
photosynthesis.
 Glycolysis provides enough energy for
many current unicellular organisms that
have limited energy needs.
 Larger organisms have greater energy
needs and use aerobic respiration to meet
those needs.
Glycolysis

 A biochemical pathway
is a series of chemical
Glucose
C C C C C C
reactions where the
2 ATP
products of one reaction
become the reactants of
the next reaction.
2 ADP

P- C C C C C C -P 6-C Compound
 Glycolysis is a
biochemical pathway.
In glycolysis, one
molecule of glucose is
split in half to produce P- C C C

C C C -P 2 PGAL
two molecules of
2 NAD+
pyruvic acid (pyruvate)
and two molecules of
2 NADH + 2H+
ATP.
 Glycolysis happens in P- C C C -P P- C C C -P
2 molecules of a 3-C compound
the cell’s cytoplasm. All
4 ADP
living things can

perform glycolysis.
4 ATP
 Glycolysis has 10
C C C
C C C
chemical reactions, but
2 molecules of pyruvic acid
can be summarized in
(pyruvate)
four steps.
Step 1 – Two phosphate
groups are added to the
glucose molecule from 2
ATPs, making a 6-C
compound that can be split.
Step 2 – The 6-C
compound is split into two
3-C molecules of PGAL
(phosphoglyceraldehyde).
Step 3 – The two PGAL
molecules are oxidized and
receive another phosphate
group. The oxidation of
PGAL accompanies the
reduction of NAD+ to
NADH.
Step 4 – the phosphate
groups are removed,
producing 2 pyruvic acid
molecules and 4 ATP, for a
net gain of 2 ATP.
Lactic Acid Fermentation
 In the absence of oxygen, some cells
convert pyruvic acid into other
compounds using one of several other
biochemical pathways.
 These new steps do not make any more
ATP. They are still necessary because
glycolysis in the absence of oxygen will
use up a cell’s supply of NAD+.
 If all of the cell’s NAD+ is gone,
glycolysis will stop and the cell can no
longer make ATP by splitting glucose.
 The combination of glycolysis and
these other NAD+ regenerating steps are
called fermentation.
 There are two main types of
fermentation: lactic acid fermentation
and alcoholic fermentation.
 In lactic acid fermentation, pyruvic acid
is rearranged to form another 3-C
molecule, lactic acid.
 As this occurs, NADH + H+ are
converted back into NAD+, so glycolysis
can continue.
 Lactic acid fermentation by bacteria
makes yogurt or cheese.
 Lactic acid fermentation also happens in
animal muscle tissue during strenuous
exercise, and can result in muscle
cramps.
C
C
C
C
Glucose
C C
2 NAD+
Glycolysis
2 NADH + 2H+
C
C C
C C C
2 molecules of pyruvic acid
(pyruvate)
2 NADH + 2H+
2 NAD+
C
C C
C C
2 molecules of lactic acid
(lactate)
C
Lactic Acid
Fermentation
Alcoholic Fermentation
 Some plant cells, bacteria, and the
unicellular fungus known as yeast use a
biochemical pathway to regenerate NAD+
known as alcoholic fermentation.
 In this pathway, pyruvic acid is converted
into a 2-C compound called ethyl alcohol
(ethanol), and carbon dioxide.
 Like in lactic acid fermentation, these
steps turn NADH and H+ back into
NAD+, thus allowing glycolysis to
continue.
 Alcoholic fermentation is important
economically. It is used in the production
of beers and wines.
 As the yeast ferment the sugars present in
the mix, the ethanol content rises until it
reaches a concentration high enough to
kill the yeast. This is about 12%. The
CO2 is released during fermentation. To
make champagne, the CO2 is retained.
 Bread also depends on alcoholic
fermentation. The bubbles of CO2
produced cause the bread to rise. The
alcohol evaporates during baking,
producing the wonderful smell of baking
bread.
C
C
C
C
C
C
Glucose
2 NAD+
Glycolysis
2 NADH + 2H+
C
C C
C C C
2 molecules of pyruvic acid
(pyruvate)
Alcoholic
Fermentation
2 NADH + 2H+
2 NAD+
C
C
C C
C
C
2 molecules of ethyl alcohol
(ethanol) and 2 CO2
 Glycolysis is not an efficient way to make
ATP. Its efficiency is only about 3.5%
Aerobic Respiration
and Mitochondria
 Aerobic respiration has two major stages:
the Krebs cycle and the electron transport
chain.
 In the presence of O2, in the reactions of the
Krebs cycle, glucose is completely oxidized
into CO2 and H2O.
 As the glucose is oxidized, NAD+ is
reduced to NADH and H+.
 In the presence of oxygen, the electron
transport chain can operate. NADH is fed
into the transport chain and produces large
amounts of ATP as well as regenerating
NAD+.
 Although the Krebs cycle produces a small
amount of ATP, most of the ATP produced
during aerobic respiration is produced by
the electron transport chain.
 In prokaryotes, the reactions of the Krebs
cycle and the electron transport chain occur
in the cell’s cytosol.
 In eukaryotes, these reactions, happen within
mitochondria.
 The pyruvic acid made during glycolysis
diffuses through the double membrane and
into the mitochondrial matrix. The
mitochondrial matrix contains the enzymes
needed for the Krebs cycle.
 When pyruvic acid enters the mitochondrial
matrix, it reacts with a molecule called
coenzyme A to form acetyl coenzyme A
(acetyl CoA) and a molecule of CO2. One
molecule of NAD+ is reduced to NADH and
H+. Acetyl CoA can enter the Krebs cycle.
Aerobic Respiration The Krebs Cycle
 Step 1 - Acetyl CoA bonds
with a 4-C molecule
(oxaloacetic acid) to form a
 The Krebs
6-C molecule (citric acid),
cycle is a
CoA
releasing coenzyme A.
Citric Acid
biochemical
 Step 2 - Citric acid is
C C
C C C C C C
pathway that
oxidized, releasing CO2, an
Acetyl CoA
+ forming
breaks the
H
atom
to
NAD
CO
2
C
remaining
NADH, and a 5-C
compound.
bonds in acetyl
+
NAD
C C C C
CoA, forming
 Step 3 – The 5-C
Oxaloacetic acid
NADH +
compound becomes a 4-C
CO2, H atoms,
H+
compound, forming CO2,
and ATP.
NADH + H+
5-C compound
NADH, and ATP
 In eukaryotic
+
NAD
C C C C C
 Step 4 – The 4-C
cells, the Krebs
compound changes to a
4-C compound
cycle takes
different 4-C compound,
ADP
C C C C
place inside the
releasing an H atom to
C CO2
mitochondrial
ATP
FAD, which forms FADH2.
NAD+
matrix.
FADH2
 Step 5 – The 4-C
NADH +
 The Krebs
compound changes back
H+
FAD
into oxaloacetic acid and
Cycle has 5
C C C C
forming another NADH.
main steps:
4-C compound
Aerobic Respiration – Electron
Transport Chain
 The electron transport chain is the
second part of aerobic respiration.
 In eukaryotic cells, the molecules
needed for this are embedded in the
inner mitochondrial membrane.
 In prokaryotes, the molecules for the
electron transport chain are
embedded in the cell membrane.
 The purpose of the electron transport
chain is to make ATP from ADP.
This happens when NADH and
FADH2 are converted back into
NAD+ and FAD.
 The electrons in the H atoms of
NADH and FADH2 are high energy
electrons.
 As these electrons are passed along the
electron transport chain they lose some
of their excess energy.
 This energy is used to pump the
protons of the H atoms from the
mitochondrial matrix to the other side
of the inner membrane, building up a
concentration gradient.
 As protons pass back through ATP
synthase molecules located in the
membrane, ATP is made from ADP.
 This process can only continue if the
last molecule in the electron transport
chain can get rid of its excess electrons.
It does so by passing them off to
oxygen atoms. This is why O2 is
needed for aerobic respiration.
The Electron Transport Chain
Cytosol
Intermembrane Space
H+
2e-
eee-
NADH
eATP
synthase
ADP
NAD+
FADH2
FAD
ATP
Mitochondrial Matrix
O2 + 4e- + 4H+  2H2O
Cellular Respiration - Energy
Output
Glucose
Glycolysis
2 NADH
2 ATP
6 ATP from
electron transport
chain (ETC)
Pyruvic Acid
2 NADH
6 ATP from ETC
Acetyl CoA
2 ATP produced
directly
Krebs cycle
6 NADH
18 ATP from ETC
2 FADH2
4 ATP from ETC
 Aerobic respiration is a more efficient way to produce ATP
than glycolysis, with an efficiency rate of about 66%.
38 ATP