Transcript cellrespdiagrams

Energy Flow and Chemical
Recycling in Ecosystems
The chemical elements of life are
recycled but energy is not – it flows
into an ecosystem as light and
leaves as heat
Electrons “fall” from organic molecules
to oxygen during cellular respiration
• C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
Oxidation of C6H12O6 coupled to the reduction of O2.
Controlled release of energy to form ATP.
The remainder of the energy is released as heat.
This process is called oxidative phosphorylation.
Overview of Cellular Respiration
Glucose
glycolysis
→ 2 ATP
2 Pyruvate
Overview of Cellular Respiration
The first step is called glycolysis. It occurs in the cytosol.
During glycolysis, a glucose molecule (6 carbons) is converted
to two pyruvate molecules (3 carbons each).
It does not require oxygen (it is anaerobic).
A total of 2 ATP are gained as a result of these reactions.
The Glycolytic Pathway
Summary of Glycolysis
glucose (C6)
2 ATP
4 ATP produced
2 ADP
2C3
2 ADP
- 2 ATP consumed
2 NAD+
2 ATP net
2 NADH
2 ATP
2 NADH are also
produced
2 ADP
2 ATP
2 pyruvate (C3)
Efficiency of Glycolysis
• Compare the kilocalories of glucose with the
kilocalories in the ATP that is made.
• The 2 ATP molecules made during glycolysis
account for only 2% of the energy in glucose
• Where does the rest go?
• It’s still in pyruvic acid
• This small amount of energy is enough for
bacteria, but more complex organisms need
more of glucose’s energy.
Fermentation
• If there is no oxygen some cells can convert
pyruvic acid into other compounds and get
more NAD+
• No ATP is made, but the NAD+ can keep
glycolysis going to make a little ATP
• 2 kinds of fermentation: Lactic acid
fermentation and Alcoholic Fermentation
Anaerobic
Aerobic
Evolutionary Significance of
Glycolysis
• Glycolysis is the most widespread pathway, so it
probably evolved early.
• The first prokaryotes evolved over 3.5 billion years
ago, before there was much O2 in the atmosphere.
• Glycolysis occurs in the cytosol and does not require
membrane-bound organelles.
• Eukaryotic cells with organelles probably evolved
about 2 billion years after prokaryotic cells.
A transport protein built into the membrane
facilitates the movement of pyruvate into
the mitochondrion
Overview of Cellular Respiration
The Krebs Cycle
• The conversion of
pyruvate to acetyl CoA
and the Krebs cycle
produce large quantities
of electron carriers.
The inner mitochondrial membrane couples
electron transport to ATP synthesis
Proton-motive force
Oxidative phosphorylation
• A protein complex, ATP synthase,
in the cristae actually makes ATP
from ADP and Pi.
• ATP used the energy of
an existing proton gradient to
power ATP synthesis.
– This proton gradient
develops between the
intermembrane space
and the matrix.
Feedback mechanisms
control cellular respiration
How are food molecules other than
glucose oxidized to ATP?
RESPIRATION
PROTEINS
CYTOPLASM
GLYCOLOSIS
HAPPENS HERE!
CARBO’S
(SUGARS)
FATS
(LIPIDS)
AMINO
ACIDS
GLUCOSE
C6H12O6
GLYCOLOSIS
IN CYTOPLASM
NO OXYGEN!
ATP TOTALS
GLYCOLOSIS=2
PYRUVIC
ACID
RESPIRATION=34
BOTH=36!
MAKES
2 ATPS
ACETYL-CoA
CO2 IS
RELEASED
O2 ENTERS
HERE
MITOCHONDRIA
RESPIRATION HAPPENS IN
THIS ORGANELLE!
KREBS CYCLE
AND
ELECTRON
TANSPORT
MAKES
34 ATPS