Transcript Photosynthesis – Chapter 6

Enzymes, Metabolism, & Cellular
Respiration
Photosynthesis & Global Warming
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Photosynthesis - Capturing the
Energy in Light
All Organisms Use Energy to Carry
Out the Functions of Life
• Plants are the primary producers
• The use direct sunlight for energy through a
process called photosynthesis
• Autotrophic vs. Heterotrophic
• What is the difference?
Photosynthesis - Involves a complex
set of chemical reactions that form a
biochemical pathway.
Why are plants green?
• Chlorophyll
– Two types:
• Chlorophylla and Chlorophyllb
Accessory pigments
• Carotenoids
• Xanthophylls
– Pigments seen in FALL!!!
The Balance Sheet for
Photosynthesis
• Light Reaction
– Produces stored energy
in the form of ATP and
NADPH from light
energy.
• Calvin Cycle
– Produces organic
compounds, using the
energy stored in ATP
and NADPH during the
light reactions.
The Simplest Chemical Equation for Photosynthesis:
CO2 + H2O + light energy -> (CH2O) + O2
The Balanced Chemical Equation for Photosynthesis:
6CO2 + 6H2O+ light energy -> C6H12O6 + 6O2
Alternative Pathways
• C3 plants fix carbon exclusively through the
Calvin Cycle, because the three carbon PGA is
formed.
• Plants that do not produce the three carbon PGA
live in hot or dry climates and utilize alternative
pathways.
– C4 pathway enables plants to fix into four carbon
compounds. Examples include: corn, sugar cane, and
crabgrass.
– Cactuses, pineapples, and certain other plants that live
in hot, dry climates fix carbon through the CAM
pathway.
Summing it up…
• A plant’s environment can effect its rate of
photosynthesis.
• Light intensity can also be a factor.
• As well as, CO2 levels and temperature.
Photosynthesis
Cellular
Respiration
Cellular Respiration
Cellular Respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O +
energy (ATP)
How are Photosynthesis and Cellular
Respiration Related?
Photosynthesis
–
–
–
–
–
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Uses Light Energy
Uses Carbon Dioxide
Uses Water
Makes Glucose
Makes Oxygen
Happens in the Chloroplasts
6CO2 + 6H2O + light energy
-> C6H12O6 + 6O2
Cellular Respiration
–
–
–
–
–
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Makes Energy (ATP)
Makes Carbon Dioxide
Makes Water
Uses Glucose
Uses Oxygen
Happens in the
Mitochondria
C6H12O6 + 6O2 -> 6CO2 +
6H2O + energy (ATP)
Cellular Respiration
• The food (glucose) is
broken down into CO2
and H2O, and energy
(ATP) is released.
• C6H12O6 + 6O2 -> 6CO2
+ 6H2O + energy (ATP)
• Cellular respiration
takes place in the
mitochondria.
© The Virtual Cell
Textbook
1st Step in Cellular Respiration –
Glycolysis
• Breakdown or splitting of glucose (6 carbons) into two 3carbon molecules called pyruvic acid
• Does not need oxygen in any of its chemical reactions
• Serves as the first step in a variety of anaerobic and aerobic
reactions
• Happens in the cytoplasm of cells
• FYI: The one metabolic pathway found in all living
organisms
• Net yield of two ATP molecules for every molecule of
glucose that is converted into pyruvic acid
Molecular Pictures
2 molecules of
Pyruvic Acid
Glucose
Images taken from:
http://biology.clc.uc.edu/courses/bio104/ce
2 ATP molecules
Fermentation
• Pyruvic acid molecules are turned into some
“waste” product
• Occurs in anaerobic situations
• Two of the most common types of
fermentation are:
– lactic acid and alcoholic fermentation
Lactic Acid Fermentation
• Done by some fungi, some bacteria like the Lactobacillus
acidophilus in yogurt, and sometimes by our muscles.
• The 3-carbon pyruvic acid molecules are turned into lactic
acid
• This process is used in making cheese and yogurt.
• Once our muscles form lactic acid, they can’t do anything
else with it, so until it is gradually washed away by the
blood stream and carried to the liver (which is able to get
rid of it) until it is converted back to pyruvic acid when
oxygen becomes available
Alcoholic Fermentation
• Done by yeast and some kinds of bacteria.
• The “waste” products of this process are
ethanol and carbon dioxide (CO2).
• This process is used in making bread, beer,
and wine.
Fermentation – Two Major Types
•
•
•
•
Lactic Acid Fermentation
Muscles produce lactic
acid
Causes muscles to become
tired
Occurs after exercise
Why does this happen?
– Your muscle cells can’t get
the oxygen they need to
produce ATP by cellular
respiration.
Alcoholic Fermentation
• Yeast cells produce
carbon dioxide and
alcohol
• Example: carbon dioxide
causes bubbles to form in
bread
• Why does this happen?
– Yeast cells eat sugar and
expel carbon dioxide, which
causes bubbles to form in
bread.
Anaerobic Pathways as the oldest
known way of producing ATP???
• Glycolysis is probably the oldest known way of producing
ATP. There is evidence that the process of glycolysis
predates the existence of O2 in the Earth’s atmosphere and
organelles in cells:
– Glycolysis does not need oxygen as part of any of its chemical
reactions. It serves as a first step in a variety of both aerobic and
anaerobic energy-harvesting reactions.
– Glycolysis happens in the cytoplasm of cells, not in some
specialized organelle.
– Glycolysis is the one metabolic pathway found in all living
organisms.
– Total Efficiency of Glycolysis 3.5%
2nd Step of Cellular Respiration –
Krebs Cycle
• In prokaryotes, the reactions of the Krebs Cycle
take place in the cytosol of the cell.
• In eukaryotes, the reactions take place in the
mitochondrial matrix
• The pyruvic acid produced in glycolyis diffuses
across the double membrane of the mitochondria
into the mitochondrial matrix where it reacts with
a molecule called coenzyme A to form acetyl
CoA, which then enters the Krebs Cycle
• In short…the Krebs Cycle breaks down acetyl
CoA, produces CO2, hydrogen atoms, and ATP
Krebs Cycle Cont…
• Recall that…in glycolysis one glucose molecule
produced two pyruvic acid molecules, which can
then form two molecules of acetyl CoA.
• Thus…one glucose molecule causes two turns of
the Krebs Cycle.
• The two turns produce:
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–
–
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Six molecules of NADH -> electron transport chain
Two molecules of FADH2 -> electron transport chain
Two molecules of ATP -> can be used as energy
Four CO2 molecules -> released by the organism
3rd Step in Cellular Respiration –
The Electron Transport Chain
• The concentration gradient drives the synthesis
of ATP by chemiosmosis, the same process
that generates ATP in photosynthesis!!!
• ATP is produced when NADH and FADH2
release hydrogen atoms
• By combining with both electrons and protons
(H+), oxygen forms water!!!
Here is the formula: O2 + 4e- + 4H+ -> 2H2O
How many ATP molecules are made
in aerobic respiration?
• 38 ATP per one glucose molecule!!!
WOW!!!
• FYI: the actual number of ATP molecules
generated through aerobic respiration varies
from cell to cell. Most produce 36 ATP
molecules per glucose molecule.
How efficient is aerobic respiration?
• 66% compared to 3.5% of glycolysis.
• This means that aerobic respiration is 20
times more efficient than anaerobic!!!
• It is even more efficient than a car engine
which is only 25%!!!
Summing Up Cellular Respiration…
• Cellular respiration provides the ATP that all cells
need to support the activities of life.
• Cells also need specific organic compounds (sugars
and starches) from which to build macromolecules,
which not always come from the food we eat.
• That is why Glycolysis and the Krebs Cycle are used
by cells to make the compounds that are missing in
food.
C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)
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