slide 10 Flashcards
The citric acid cycle completes
the energy-yielding
oxidation of organic molecules (breakdown of
pyruvate) when oxygen is present
The citric acid cycle takes place in
the mitochondria
The citric acid cycle has 8 steps
each catalyzed by
a specific enzyme.
Before the citric acid cycle can begin pyruvate must first
bind to coenzyme A and become acetyl coenzyme A
acetyl CoA
The citric acid cycle produces
NADH from NAD+
and a related molecule FADH2
from FAD+.
NADH from NAD+
and a related molecule FADH2
from FAD+.
Both molecules are used in cellular respiration to
transport high energy electrons between reactions.
Citric Acid Cycle
Loss of 2 carbon per cycle (4 per glucose) – conversion to CO2 3 NADH made per cycle (6 per glucose) 1 FADH2 made per cycle (2 per glucose) 1 ATP made per cycle (2 per glucose) CoA regenerated
Oxidative phosphorylation has two components:
the
electron transport chain and chemiosmosis
Following glycolysis and the citric acid cycle, NADH and
FADH2 account for most of the energy extracted from food
These two electron carriers donate electrons to the electron
transport chain, which allows ATP synthesis via
chemiosmosis.
Oxidative phosphorylation
is a series of redox reactions
across the inner membrane of the mitochondria.
The electron transport chain is
comprised
of multiprotein
complexes spanning the inner
mitochodrial membrane
ELECTRON TRANSPORT CHAIN
The carriers alternate reduced
and oxidized states as they
accept and donate electrons
Electrons drop in free energy as
they go down the chain and are
finally passed to O2
, forming H2O.
The electron transport chain produces no ATP directly
At certain steps along the electron transport chain electron
transfer causes protein complexes to pump H+
from the
mitochondrial matrix to the intermembrane space.
ELECTRON TRANSPORT CHAIN
The resulting H+ gradient
– Stores energy
– Is referred to as a proton-motive force
– Drives chemiosmosis
Chemiosmosis
ATP synthase is the enzyme
that makes ATP
ATP synthase uses the H+
gradient
established by the
electron transport chain to
drive ATP synthesis
During respiration, most energy flows in this sequence:
- Glucose
- NADH, FADH2
- electron transport chain
- proton gradient
- ATP
ATP synthesis has a high efficiency among reactions.
About 40% of the energy in a glucose molecule is
transferred to ATP during cellular respiration, making
approximately 32 ATP.
The remainder of energy is lost as heat
Alternatives to Oxidative
Phosphorylation
fermentation
Fermentation
enables some cells to produce ATP without
the use of oxygen or an electron transport chain
Fermentation is an extension of glycolysis
in which ATP
is produced only by substrate-level phosphorylation.
Alcohol fermentation (pyruvate converted to ethanol)
lactic acid fermentation (pyruvate converted to lactate) are
two examples
Catabolic pathways
– Funnel electrons from many kinds of organic molecules into cellular respiration – Molecules other than glucose can feed into cellular respiration
Cellular respiration is a
pathway controlled by
negative feedback.
If ATP concentration drops,
respiration speeds up
Cellular respiration taps
energy that was stored in
food
by photosynthesis
