Download Respiration - UniMAP Portal

EQUATION FOR
RESPIRATION
CARBON
DIOXIDE
GLUCOSE
C6H12O6 + 6O2
OXYGEN
ATP
6CO2 + 6H2O + ENERGY
WATER
Recap : The Importance of Photosynthesis
• The energy entering chloroplasts as sunlight gets stored as
chemical energy in organic compounds
• Sugar made in the chloroplasts supplies chemical energy &
carbon skeletons to synthesize the organic molecules of cells
• Plants store excess sugar as starch in structures such as
roots, tubers, seeds, & fruits
• In addition to food production, photosynthesis produces the
O2 in our atmosphere
The Light-dependent Reactions
• The Light-dependent reactions convert
solar energy to chemical energy
– Chlorophyll and other molecules of the
thylakoids capture sunlight energy
– Sunlight energy is converted to the energy
carrier molecules ATP and NADPH
– ATP and NADPH used to fuel the reactions of
the Calvin cycle (light independent or dark
reactions)
– Oxygen gas is released as a by-product
The Light-independent Reactions
• The Light-independent reactions (Calvin
cycle) makes sugar from carbon dioxide
– ATP generated by the light reactions provides the
energy for sugar synthesis
– The NADPH produced by the light reactions provides
the electrons for the reduction of carbon dioxide to
glucose
– ATP and NADPH generated in light reactions used to
fuel the reactions which take CO2 and break it apart,
then reassemble the carbons into glucose.
– Called carbon fixation: taking carbon from an
inorganic molecule (atmospheric CO2) and making an
organic molecule out of it (glucose)
Light-dependent Reactions
• Overview: light energy is absorbed by
chlorophyll molecules - this light energy
excites electrons and boosts them to
higher energy levels. They are trapped by
electron acceptor molecules that are
poised at the start of a neighboring
transport system. The electrons “fall” to a
lower energy state, releasing energy that
is harnessed to make ATP
Two types of photosystems
cooperate in the light reactions
Water-splitting
photosystem
NADPH-producing
photosystem
Cellular Respiration Overview
• Transformation of chemical energy in food
into chemical energy cells can use: ATP
• These reactions proceed the same way in
plants and animals. Process is called
cellular respiration
• Overall Reaction:
– C6H12O6 + 6O2 → 6CO2 + 6H2O
What are the main stages
of glucose metabolism?
• Glycolysis
• Cellular respiration
Cellular Respiration
• Breakdown of glucose begins in the
cytoplasm: the liquid matrix inside the
cell
• At this point life diverges into two forms
and two pathways
– Anaerobic cellular respiration (e.g.
fermentation)
– Aerobic cellular respiration
Cellular Respiration Reactions
• Glycolysis
– Series of reactions which break the 6-carbon
glucose molecule down into two 3-carbon
molecules called pyruvate
– Process is an ancient one - all organisms
from simple bacteria to humans perform it
the same way
– Yields 2 ATP molecules for every one
glucose molecule broken down
– Yields 2 NADH per glucose molecule
Anaerobic Cellular Respiration
• Some organisms thrive in environments with
little or no oxygen
– Marshes, bogs, gut of animals, sewage treatment
ponds
• No oxygen used = ‘an’aerobic (anaerobic)
• Results in no more ATP, final steps in these
pathways serve ONLY to regenerate NAD+ so it
can return to pick up more electrons and
hydrogens in glycolysis.
• End products such as ethanol and CO2 (single
cell fungi (yeast) in beer/bread) or lactic acid
(muscle cells)
energy produced
by
each stage of
glucose
breakdown
Energy Tally
• 36 ATP for aerobic vs. 2 ATP for anaerobic
– Glycolysis
2 ATP
– Kreb’s
2 ATP
– Electron Transport
32 ATP
36 ATP
• Anaerobic organisms can’t be too energetic but
are important for global recycling of carbon
It's not that
easy being
green… but it
is essential for
life on earth!
Water, CO2, and the C4 Pathway
– When Stomata Are Closed to Conserve
Water, Wasteful Photorespiration Occurs
– C4 Plants Reduce Photorespiration by Means
of a Two-Stage Carbon-Fixation Process
– C3 and C4 and Plants Are Each Adapted to
Different Environmental Conditions
C4 Plants Reduce
Photorespiration
• “C4 plants” have chloroplasts in bundle
sheath cells as well as mesophyll cells
– Bundle sheath cells surround vascular
bundles deep within mesophyll
– C3 plants lack bundle sheath cell
chloroplasts
C4 Plants Reduce
Photorespiration
• C4 plants utilize the C4 pathway
– Two-stage carbon fixation pathway
The C4 Pathway
1. Outer mesophyll cells contain
phosphoenolpyruvate (PEP) instead of
RuBP
2. Carbon dioxide-specific enzyme links
CO2 with PEP (unaffected by high O2)
3. 4 carbon molecule then shuttled from
mesophyll to bundle sheath cells...
The C4 Pathway
4. CO2 released in bundle sheath cells,
building up high CO2 concentration
5. CO2 in bundle sheath cells fixed by
standard C3 pathway
6. 3 carbon shuttle molecule returns to
mesophyll cells
Environmental Conditions
• C4 pathway uses up more energy than C3
pathway
• C4 plants thrive when light is abundant but
water is scarce (deserts and hot climates)
– C4 plant examples: corn, sugarcane,
sorghum, crabgrass, some thistles
Environmental Conditions
• C3 plants thrive where water is abundant
or if light levels are low (cool, wet, and
cloudy climates)
– C3 plant examples: most trees, wheat,
oats, rice, Kentucky bluegrass
C3 and C4
plants
(structural)
CAM Plants
• Some plants, including succulents, use
crassulacean acid metabolism (CAM) to
fix carbon
• CAM plants open their stomata at night,
incorporating CO2 into organic acids
– Stomata close during the day, & CO2 is released
from organic acids & used in the Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 10-20
Sugarcane
Pineapple
C4
CAM
CO2
Mesophyll
cell
Organic acid
Bundlesheath
cell
CO2
1 CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
Calvin
Cycle
CO2
2 Organic acids
release CO2 to
Calvin cycle
Night
Day
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
Summary
• Light Dependent Reaction
– Light + chlorophyll --> ATP + NADPH + (O2 as
waste)
• Light Independent Reaction (Calvin Cycle)
– CO2 + ATP + NADPH --> glucose
What happens to the glucose
produced by photosynthesis?
Sucrose
CH2OH
O
H
O
HOCH2
H
H
H
OH
H
O
H
HO
CH2OH
HO
H
OH
Glucose
subunit
HO
H
Fructose
subunit
Starch
CH2OH
O H
H
O
CH2OH
H
OH
H
H
OH
Glucose
subunit
O H
H
O
CH2OH
H
OH
H
H
OH
Glucose
subunit
O H
H
O
H
OH
H
H
OH
Glucose
subunit
O
Up to 1000
or more
monomers