Chapter 1 Notes

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Transcript Chapter 1 Notes

Chapter 9 notes
Cellular Respiration:
Harvesting Chemical
Concept 9.1
Metabolic pathways that release energy
are called catabolic pathways
- fermentation and cellular respiration
Fermentation: partial degradation of
sugars that occurs w/out the help of O2
Cellular respiration: O2 is consumed as
a reactant along w/ the sugar
- more efficient
Concept 9.1
Cellular respiration occurs in the
Organic + O2  Carbon + H2O + Energy
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
1 glucose = -686 kcals
Concept 9.1
ATP is the central molecule responsible
for energy used by the cell
The cell uses enzymes to transfer
phosphate groups from ATP to other
compounds (making them
ATP  ADP + phosphate
Concept 9.1
Redox reactions release energy when
electrons move closer to electronegative
- the relocation of electrons releases the
energy stored in food molecules, and this
energy is used to synthesize ATP
Concept 9.1
There is a transfer of one or more e- from
one reactant to another; the electron
transfers are called oxidation-reduction
reactions or redox rxns.
- the loss of e- from one substance is
called oxidation
- the addition of e- to another
substance is called reduction
Concept 9.1
Concept 9.1
Electrons “fall” from organic molecules to
oxygen during cellular respiration
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
- by oxidizing glucose, cellular respiration
takes energy out of storage and makes it
available for ATP synthesis
- carbohydrates and fats are reservoirs of
electrons associated w/ hydrogen
Concept 9.1
The “fall” of electrons during respiration is
stepwise, via NAD+ and an electron transport
Glucose is broken down over a series of steps
that are each catalyzed by a specific enzyme
Hydrogen atoms are stripped from the glucose
and usually passed to NAD+.
- NAD+ is reduced in the rxn.
Concept 9.1
NAD+ is transformed to NADH
- NADH will later be tapped to make
ATP as the electrons continue their fall
from NADH to oxygen
Respiration uses an electron transport
chain to break the fall of electrons to
oxygen into several energy-releasing
steps instead of one explosive rxn.
Concept 9.1
Concept 9.1
Electrons removed from food are shuttled
by NADH to the “top” end of the chain.
At the “bottom”, oxygen captures the
electrons along with H+ ions to form
Food NADH  ETC  oxygen
Concept 9.1
Respiration consists of three stages:
- glycolysis, the Krebs cycle, electron
transport chain (ETC)
Glycolysis breaks down 1 glucose into 2
molecules of pyruvate
- occurs in the cytosol
Krebs cycle breaks down pyruvate into CO2
- occurs in the mitochondrial matrix
Concept 9.1
ETC accepts electrons from the breakdown
products of the first 2 stages
- the energy released at each step of the
chain is used to make ATP (oxidative
phosphorylation); through redox rxns.
oxidative phosphorylation accounts for 90%
of generated ATP
Concept 9.1
Concept 9.1
Concept 9.1
Concept 9.1
Substrate-level phosphorylation:
direct transfer of a phosphate to ADP
by an enzyme
Each molecule of glucose is degraded into
carbon dioxide, water and 38 molecules
of ATP
Concept 9.1
Concept 9.2
Glycolysis means “splitting of sugar”
- the 10 steps of glycolysis are broken
down into two phases: energy
investment and energy payoff
- glucose (6C) 2 pyruvate (3C)
Energy investment phase: the cell spends
2 ATP to phosphorylate the fuel
Concept 9.2
Energy payoff phase: 4 ATP are
produced by substrate-level
phosphorylation; 2 NAD+ are reduced
to 2 NADH by the oxidation of food
Net energy yield: 2 ATP and 2 NADH
Concept 9.3
If O2 is present, energy stored in NADH
can be converted to ATP
Upon entering the mitochondrion, each
pyruvate is first converted to a molecule
of acetyl CoA (2C)
- another NAD+ is reduced to NADH
Concept 9.3
Concept 9.3
Acetyl CoA will enter the Krebs cycle for
further oxidation
Krebs cycle
- 8 steps, each catalyzed by a specific
- Acetyl CoA (2C) enters, 2 CO2 (1C)
leave, 3 NAD+  3 NADH, 1 FAD  1
FADH2, 1 ADP  1 ATP
Concept 9.3
Concept 9.4
Cristae: inner membrane folding of the
- increases surface area for more ETC’s
Electrons removed from food during
gycolysis/Krebs are transferred by
NADH to the first molecule of the ETC
Concept 9.4
Concept 9.4
Most of the electron carriers in the ETC
are proteins called cytochromes (cyt).
The process goes downhill with oxygen
being the final e- acceptor
- for every 2 NADH, 1 O2 molecule is
reduced into 2 molecules of water
Concept 9.4
FADH2 adds its e- at a lower energy level
than NADH on the ETC.
- FADH2 = 2 ATP
ETC makes no ATP directly. It moves efrom food to oxygen breaking the
energy drop to manageable amounts.
Concept 9.4
Inside the inner membrane are enzymes
called ATP synthase.
- makes ATP from ADP and a phosphate
ATP synthase uses energy from the ion
gradient to synthesize ATP.
- proton gradient
Concept 9.4
Concept 9.4
The ETC is an energy converter that uses
the exergonic flow of e- to pump H+
ions across the membrane
- from the matrix to the inner
membrane space.
ATP synthases are the only place that are
freely permeable to H+
Concept 9.4
H+ gradient across a membrane couples
the redox rxns. of the ETC to ATP
- chemiosmosis: connection between
the chemical rxn. Makes ATP and
transport across a membrane
Concept 9.4
H+ ions are pumped by members of the
ETC. The resulting gradient is called a
proton-motive force: the gradient
has the capacity to do work
Concept 9.4
Concept 9.4
Chemiosmosis is also found in the
- ATP is generated during
- light drives both e- flow down the ETC
and H+ gradient formation
Concept 9.4
Energy flow during respiration:
Glucose NADH and FADH ETC
proton-motive force  ATP
38 ATP formed; 4 from substrate
phosphorylation, 34 from oxidative
Concept 9.4
Concept 9.5
During glycolysis, glucose is oxidized into
2 molecules of pyruvate
- oxidizing agent is NAD+, not oxygen
If no oxygen is present, electrons are
transferred from NADH to pyruvate
Concept 9.5
Alcohol fermentation: pyruvate 
- CO2 is released to recycle NAD+
- 2 step process to regenerate NAD+
Concept 9.5
Concept 9.5
Lactic acid fermentation: pyruvate 
lactic acid
- human cells make ATP by (LAF) when
oxygen is scarce
- lactate is carried away by blood to the
liver; lactate is converted back to
pyruvate by liver cells
Concept 9.5
Concept 9.5
w/out oxygen, the energy still stored in
pyruvate is unavailable to cells
Facultative anaerobes: yeasts and
bacteria that can make enough ATP to
survive using either fermentation or
Concept 9.5
Ancient prokaryotes probably used
anaerobic fermentation before oxygen
was present in the atmosphere
Also, glycolysis does not require
mitochondria to occur
Concept 9.6
Fats, proteins, and complex carbs can all
be used to make ATP
Fats can be broken into monomers
- glycerol can be converted and can
enter glycolysis
- fatty acids can be converted into
acetyl CoA
Concept 9.6
Concept 9.6
Proteins must be broken down to amino
- various amino acids can be converted
as intermediates of glycolysis and the
Krebs cycle
Concept 9.6
Carbohydrates can be hydrolyzed to form
glucose monomers to enter into
Metabolism works on supply and
Concept 9.6
Carbs and fats can be converted to fats
through intermediates of glycolysis and
the Krebs cycle
We will store fat even if we have a fat
free diet
Concept 9.6
Cellular respiration is controlled by
feedback mechanisms
Feedback inhibition: end products inhibit
the enzymes that catalyze the early
steps of the process
Phosphofructokinase (enzyme for step 3
of glycolysis) is the pacemaker