Download Lecture 14: Powerpoint

Biology 102
Cellular respiration
Lecture Outline
1. Glucose metabolism: Overview
2. Glycolysis: The first step in
capturing energy in glucose
3. Cellular respiration: How
additional energy is generated from
glucose
 Kreb’s cycle
 Electron transport system
1. Glucose metabolism: Overview
Why focus on
glucose?
– All cells do it!
– Relatively simple
– Most other compounds
enter the glucose
metabolism pathway
when being broken
down
– Pathways go both ways
Example: fat from sugar
1. Glucose metabolism: Overview
The formula! (You know this!)
The major reactions
– Glycolysis
No oxygen needed
Generates 2 net ATP and 2 NADH per glucose molecule
3-C molecule, pyruvate, formed that enters other
reactions depending upon presence/absence of O2
– Cellular respiration
requires O2
Includes two parts
– Kreb’s cycle
– Electron transport
Location of different reactions
Glycolysis: cytoplasm
of cell
Kreb’s cycle: matrix
of mitochondrion
Electron transport:
inner membrane of
mitochondrion
2. Glycolysis
Two steps
– Activation (This gets the reaction over that
activation energy hump! 2 ATP used.)
– Energy harvest (4 ATP and 2 NADH produced)
Electrons and protons (H+) also “harvested”!
NET result: 2 ATP, 2 NADH and 2
pyruvate molecules (3-carbon chain)
per glucose molecule
It is actually a bit
more complicated,
but you don’t need to
memorize these
details…
SIDE NOTE: G3P is the same highenergy 3-carbon compound that
directly builds the glucose molecule
in the Calvin-Benson cycle!
What happens to the pyruvate
formed during glycolysis?
A. Used in fermentation (if oxygen absent)



Lactic acid (lactate) formed OR
Alcohol (ethanol) formed
In both cases, electrons and H+ from NADH are given to
the pyruvate so NAD+ can be “recycled” and continue to
carry out its function in glycolysis
What happens to the pyruvate
formed during glycolysis?
B. Used in cellular respiration (if
oxygen present)
– Oxygen is the final acceptor for the
electrons and H+ stripped from the
glucose!
– Water is formed!
Think back to photosynthesis, where water
was the source for electrons and H+, and
O2 was formed!
3. Cellular respiration
The net result:
– LOTS of ATP generated (34-36 ATP)
– CO2 is formed as C-C bonds are broken
Organic back to inorganic
– Water is formed when oxygen serves as
an electron (and H+) acceptor
Remember how it serves as a donor for
these things in photosynthesis?
Focus: Kreb’s cycle
Transition from Glycolysis
– Pyruvate transported to mitochondrial matrix
– One CO2 breaks off
NADH formed
2-C molecule (acetyl Co A) enters..
Kreb’s cycle
– Small amount of ATP generated
– C-C bonds are broken, releasing 2 CO2
– Electrons and H+ to NAD+ and FAD to form NADH and FADH2.
Remember that electrons carry their energy with them.
Focus: Electron transport/
chemiosmosis
NADH and FADH2 carry the electrons,
H+ (and associated energy) to an
electron transport system on the inner
membrane of the mitochondria
Electron transport from high to low
energy carriers is coupled to the
synthesis of ATP
– Creates and utilizes H+ gradients to do this.
Oxygen serves as the final electron
and H+ acceptor, so that water is
formed
Membrane proteins involved in
electron transport
ATP synthesizing enzyme
– H+ ion channel is key part…
Electron transport system
– Series of specific proteins imbedded in membrane
Electron transport
Electrons from NADH and FADH2 deposit electrons to the
system
Electrons move from high to low energy compounds
The energy released is used to transport H+ ions from the
matrix to the intermembrane compartment
Formation of ATP
The H+ gradient drives the production of
ATP
Summary:
Energy harvested from glucose