Download Chapter 26: Cellular Respiration and Carbohydrate Metabolism

INTRODUCTION
Chapter 26
(pp. 1025-1033)
Cellular Respiration and ATP Generation
Mechanisms of ATP Generation
• Phosphorylation is
– bond attaching 3rd phosphate group
contains stored energy
• Mechanisms of phosphorylation
– within animals
• cellular respiration
– in chlorophyll-containing plants or bacteria
• photosynthesis
• The food we eat is our only source of energy
for performing biological work.
• There are three major uses for the nutrients
we ingest:
– energy for active processes (ATP)
– synthesized into structural or functional
molecules (e.g., proteins, nucleic acids)
– converted to fat or glycogen for later use as
energy
Fate of Glucose
• All molecules have energy stored in the
bonds between their atoms.
• Glucose is the body’s preferred source of
energy for synthesizing ATP.
• The fate of absorbed glucose depends on
the energy needs of body cells.
• If the cells require immediate energy,
glucose is oxidized by the cells to produce
ATP.
• Excess glucose can be stored as glycogen or
fat.
Overview of Cellular Respiration
• In cytoplasm (1)
• In mitochondria (2, 3 &
4)
Cellular Respiration
• glucose + O2 produces H2O + CO2 + energy
• 4 steps are involved:
(1) glycolysis
(2) formation of acetyl CoA (transitional step to Krebs cycle)
(3) Krebs cycle (= TCA or citric acid cycle)
(4) electron transport chain
Glycolysis
• Glycolysis refers to the
breakdown of the sixcarbon molecule,
glucose, into two threecarbon molecules of
pyruvic acid.
– 10 step process
occurring in cell cytosol
– use two ATP molecules,
but produce four, a net
gain of two
Glycolysis & Fate
of Pyruvic Acid
Aerobic Pathway
– Pyruvic acid is
converted to
acetylCoA, which
enters the Kreb’s
Cycle
Anaerobic Pathway
(when O2 is scarce)
– pyruvic acid is
reduced to lactic acid
– lactic acid rapidly
diffuses out of cell to
blood and to liver
cells
Formation of
Acetyl Coenzyme A
• Pyruvic acid enters the
mitochondria
• 3-carbon pyruvic acid
converted to a 2-carbon
acetyl group plus CO2
• Acetyl group is attached
to Coenzyme A to form
Acetyl coenzyme A,
which enter Krebs cycle
– coenzyme A is derived
from pantothenic acid
(vitamin B5)
Krebs Cycle
Krebs Cycle
• The Krebs cycle is also
called the citric acid
cycle, or the
tricarboxylic acid
(TCA) cycle. It is a
series of biochemical
reactions that occur in
the matrix of
mitochondria
Krebs Cycle
• The large amount of chemical potential
energy stored in intermediate substances
derived from pyruvic acid is released step by
step.
• For every two molecules of acetyl CoA that
enter the Krebs cycle, 6 NADH, 6 H+, 2
FADH2 and two molecules of ATP are
produced.
• The energy originally in glucose and then
pyruvic acid is primarily in the reduced
coenzymes NADH and FADH2.
Electron Transport Chain
• The electron transport chain involves a sequence of
electron carrier molecules on the inner
mitochondrial membrane.
• As electrons are passed through the chain, there is
a stepwise release of energy from the electrons for
the generation of ATP.
• In aerobic cellular respiration, the last electron
receptor of the chain is molecular oxygen (O2).
• The process involves a series of oxidationreduction reactions in which the energy in NADH
and FADH2 is liberated and transferred to ATP.
Summary of Aerobic Cellular Respiration
• The complete oxidation of glucose can be
represented as follows:
C6H12O6 + 6O2 => 6CO2 + 6H2O + 36 or 38 ATP
• During aerobic respiration, 36 or 38 ATPs can be
generated from one molecule of glucose.
– Two of those ATPs come from glycolysis.
– Two come from the Krebs cycle.
– The rest of the ATPs are generated in the electron
transport chain.
Electron Transport Chain
• Pumping of
hydrogen is linked
to the movement of
electrons along the
electron transport
chain
• H+ ions are
pumped from
matrix into space
between inner &
outer membrane
• As the high
concentration of H+
rushes through the
ATP synthase, ATP
is generated