Transcript Ch. 4, 5: Cellular Respiration and Photosynthesis

Chapter 4
Cellular
Respiration
Anne Van & Cindy Wong
Cellular Respiration Overview
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equation: C6H12 + 6O2  6CO2 + 6H2O + energy
the means by which cells extract energy stored in
food + transfer that energy to molecules of ATP
this energy is instantly available for every cellular
activity (ex. muscle contraction, moving cilia)
2 types of cellular respiration: anaerobic (O2 not
present) and aerobic (O2 present)
leads to glycolysis, then alcoholic fermentation or
lactic acid fermentation (if O2 not present)
leads to glycolysis, then Citric Acid Cycle, ETC,
oxidative phosphorylation (if O2 present)
ATP (Adenosine Triphosphate)
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consists of adenosine
(nucleotide of adenine +
ribose) and 3 phosphates
unstable molecule as 3
phosphate groups are
negatively charged/repel
when 1 phosphate group is
removed from ATP by
hydrolysis - results in more
stable molecule ADP
(adenosine diphosphate)
provides energy for all cell
activity by transferring
phosphates from ATP to
another molecule
Glycolysis
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10 step process – breaks down 1 molecule of
glucose into 2-3 molecules of pyruvate/pyruvic
acid, releases 4 molecules of ATP
occurs in the cytoplasm + produces ATP without
using oxygen
ATP produced by substrate level phosphorylation –
direct enzymatic transfer of phosphate to ATP
enzyme that catalyzes 3rd step,
phosphofructokinase (PFK) is an allosteric enzyme
– inhibits glycolysis when cell contains enough ATP
and doesn’t need any more
Anaerobic Respiration: Fermentation
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an anaerobic catabolic process that consists of
glycolysis + alcohol or lactic acid fermentation
originated millions of years ago when there was no
free O2 in earth’s atmosphere
sole means by which anaerobic bacteria like
botulinum release energy for food
2 types of anaerobes: faculative – can tolerate the
presence of O2 and obligate – cannot live in an
environment that has O2
can generate ATP during anaerobic respiration as
long as there’s adequate supply of NAD+ to accept
electrons
glycolysis would shut down if nothing converted
NADH back to NAD+
Lactic Acid
Fermentation
Alcohol
Fermentation
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process by which certain
cells convert pyruvate
from glycolysis into ethyl
alcohol and CO2 in the
absence of O2
NADH gets oxidized back
to NAD+
bread depends
on yeast to
ferment and
produce CO2
– bread rises
beer, wine,
liquor industries
too
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pyruvate from glycolysis
is reduced to form lactic
acid or lactate
NADH gets oxidized
back to NAD+
dairy industry uses this
process to make
cheese, yogurt
human skeletal muscles
when blood can’t
supply adequate O2 to
muscles during
strenuous exercise
Aerobic Respiration
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highly efficient process, produces a lot of ATP when O2 is present
consists of an anaerobic phase (glycolysis) + an aerobic phase (2
parts - citric acid cycle, oxidative phosphorylation)
Citric Acid Cycle
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mitochondria, requires
pyruvate
 completes the oxidation of
glucose into O2
 turns twice for each
glucose molecule that
enters glycolysis
 generates 1 ATP/turn by
substrate level
phosphorylation – most of
the chemical energy is
transferred to NAD+, FAD
Structure of
Mitochondrion
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enclosed by double
membrane, outer
membrane is smooth and
inner (cristae membrane)
is folded – divides into the
outer compartment and
the matrix
Citric acid cycle happens
in matrix
Electron transport chain
happens in cristae
membrane
NAD+ and FAD
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are required for normal
cell respiration
carry protons/electrons
from glycolysis and citric
acid cycle to ETC
Aerobic Respiration: The
Electron Transport Chain
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ETC is a proton pump in mitochondria that couples 2
reactions – exergonic and endergonic
uses energy released from exergonic flow of electrons
to pump protons against a proton gradient
makes no ATP directly but sets the stage for ATP
production during chemiosmosis
carries electrons delivered by NAD, FAD from glycolysis
+ citric acid cycle to O2 (final electron acceptor)
highly electronegative O2 acts to pull electrons through
the ETC
Oxidative Phosphorylation and
Chemiosmosis
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how most energy is produced during cellular respiration
is the phosphorylation of ADP into ATP by oxidation of
the carrier molecules, NADH and FADH2
powered by redox reactions of the ETC and protons are
pumped from matrix to outer compartment by the ETC
protons cannot diffuse through the cristae membrane –
they can only flow down the gradient into matrix
through ATP synthase channels
this is chemiosmosis – the key to ATP production – as
protons flow through the channels, they generate
energy to phosphorylate ADP into ATP
Overview of Cellular Respiration
Chapter 5
Photosynthesis
Anne Van & Cindy Wong
Photosynthesis Overview
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process by which light energy is converted to
chemical bond energy and carbon is fixed into
organic compounds
equation: 6CO2 + 12H2O  C6H12O6 + 6H2O + 6O2
2 main processes – light dependent (uses light
energy to directly produce ATP) and light
independent reactions (consists of the Calvin
Cycle which produces sugar)
Photosynthetic Pigments
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absorb light energy and use it to provide energy to
carry out photosynthesis
2 major pigments in plants: chlorophylls and carotenoids
chlorophyll a, chlorophyll b – green and absorb
wavelengths of light in red, blue, violet range
carotenoids – are yellow, orange, and red; absorb light
in the blue, green, and violet range
also xanthophyll and phycobilins
antenna pigments – capture wavelengths other than
those captured by chlorophyll a (examples:
carotenoids, chlorophyll b, phycobilins)
The Chloroplast
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contains photosynthetic
pigments, along with
enzymes, that carry out
photosynthesis
grana - light dependent
reactions
stroma – light
independent reactions
grana has layers of
membranes – thylakoids
(site of photosystems I, II)
enclosed by double
membrane
Photosystems (PS)
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2 photosystems – I, II
light harvesting complexes in thylakoid
membranes of chloroplasts – few hundred in each
thylakoid
each consists of a reaction center that has
chlorophyll a and a region of several hundred
antenna pigment molecules
named in order of their discovery not in order they
work - PS II operates first, then PS I
PS I absorbs light best in 700 nm range, PS II
absorbs light best in 680 nm range
Light-Dependent Reactions:
Light Reactions
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light is absorbed by the
photosystems in the
thylakoid membranes
electrons flow through
electron transport
chains
2 possible routes of
electron flow:
noncyclic flow and
cyclic
photophosphorylation
Noncyclic
Photophosphorylation
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electrons enter two electron transport chains, ATP and NADPH
are formed
process begins in PS II – energy is absorbed, electrons are
captured by primary electron acceptor
photolysis - water gets split into two electrons, two protons (H+),
and one O2 atom; and O2 molecule gets released
ETC – electrons pass along an ETC that ultimately leads to PS I;
flow of electrons is exergonic and provides energy to produce
ATP
chemiosmosis – ATP is formed as protons released from water
are diffused down the gradient from the thylakoid space
NADP – becomes reduced to form NADPH
PS I – similar to PS II, but this electron transport chain contains
ferrodoxin and ends with production of NADPH, not ATP
Cyclic Photophosphorylation
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sole purpose is to produce ATP, not NADPH, and also
no oxygen is released
when chloroplast run low on ATP periodically, cyclic
photophosphorylation is carried out to replenish ATP
levels
cyclic electron flow takes photoexcited electrons on
a short circuit pathway
travel from PS II electron transport chain to PS I, to a
primary electron acceptor, then back to
cytochrome complex in electron transport chain of
PS II
The Calvin
Cycle
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cyclic process that produces
3-carbon sugar, PGAL
(phosphoglyceraldehyde)
carbon enters the stomates of
a leaf in the form of CO2 and
becomes fixed/incorporated
into PGAL
carbon fixation is the process
that occurs during the cycle
Calvin Cycle is a reduction
reaction since carbon gains
hydrogen
uses the products of the light
reactions – ATP and NADPH
only occurs in the light
Overview of Photosynthesis
C-4 Photosynthesis
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modification for dry environments
C-4 plants show modified
anatomy + biological pathways
that enable them to minimize
excess water loss and sugar
production
these plants thrive in hot/sunny
places
examples: corn, sugar cane,
crabgrass
CAM Plants
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CAM plants carry out a form of photosynthesis called
crassulacean acid metabolism – another adaptation to dry
environments
stomates are closed during the day and open at night
mesophyll cells store CO2 in organic compounds they synthesize
at night
Example Questions
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