Transcript Photosynthesis and Cellular Respiration

Photosynthesis and
Cellular Respiration
Photosynthesis
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Method of converting sun energy into chemical
energy usable by cells
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Autotrophs: self feeders, organisms capable of
making their own food
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Photosynthesis takes place in specialized
structures inside plant cells called chloroplasts
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Light absorbing pigment molecules (e.g. chlorophyll)
Oxidation and Reduction
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Oxidation means that a reactant lose electrons
Reduction means that a reactant gains
electrons
Overall Reaction
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6CO2 + 6 H2O → C6H12O6 + 6O2
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Carbohydrate made is glucose
Water is split, resulting in the release of electrons
and O2 as a byproduct
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Light-Dependent Reactions
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Overview:
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Light energy is absorbed by electrons in the
chlorophyll and boosts them to higher energy levels.
Electrons are “grabbed” by other molecules (electron
acceptors)
The electrons “fall” to a lower energy state as they
move from molecule to molecule, releasing energy
that is harnessed to make ATP
Energy Shuttling
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ATP: cellular energy molecule with 3 phosphate
groups bonded to it
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When the third phosphate group is removed, lots of
energy is released!
Other nucleotide based molecules move
electrons and protons around within the cell
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NADP+, NADPH
NAD+, NADP
FAD, FADH2
Light-dependent Reactions
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Photosystem: light capturing unit, contains
chlorophyll, the light capturing pigment
Electron Transport Chain: sequence of
electron carrier molecules that shuttle electrons;
energy released is used to make ATP
Light reactions yield ATP and NADPH used to
fuel the reactions of the Calvin Cycle
Step-by-Step…
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Light energy excites electrons in Photosystem II and water molecules
are split to provide additional electrons
The excited electrons move along a sequence of electron carrier
molecules in the thylakoid called the Electron Transport Chain (ETC)
As they move, they lose energy which is used to move protons (H+)
into the thylakoid. This proton gradients lets ATP be made from ADP
Electrons enter Photosystem I and are excited by more light energy
The excited electrons move along another ETC
This ETC moves the electrons close to the stroma where they
combine with a proton and NADP+ to form NADPH
Electrons from Photosystem II replace the ones used in Photosystem
I. Water molecules are split to provide replacement electrons for
Photosystem II.
Calvin Cycle
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ATP and NADPH generated in light reactions are
used to fuel the Calvin Cycle, reactions which
take CO2 and break it apart, then reassemble the
carbons into glucose.
Carbon Fixation occurs
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Taking carbon from an inorganic molecule
(atmospheric CO2) and making an organic molecule
out of it (glucose)
Step-By-Step…
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CO2 diffuses into the stroma and combines each CO2 molecule with
a five-carbon molecule (RuBP)
The new six-carbon molecule is unstable and splits into two threecarbon molecules (3-PGA)
Each three-carbon molecule is coverted into another three-carbon
molecule (G3P). First, it receives a phosphate from ATP. Then it
receives a proton from NADPH and releases a phosphate.
One of the new three-carbon compounds leaves the cycle to make
glucose.
The remain three-carbon compounds are converted back into five
carbon molecules (RuBP) through the addition of phosphates from
ATP
Harvesting Chemical Energy
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Plants and animals both use products of
photosynthesis (glucose) for metabolic fuel
Heterotrophs: must take in energy from outside
sources, cannot make their own e.g. animals
When we take in glucose (or other carbs),
proteins, and fats-these foods don’t come to
us the way our cells can use them
Cellular Respiration Overview
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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:
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C6H12O6 + 6O2 → 6CO2 + 6H2O
Cellular Respiration Overview
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Breakdown of glucose begins in the cytoplasm
At this point life diverges into two forms and two
pathways
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Anaerobic cellular respiration (aka fermentation)
Aerobic cellular respiration
Cellular Respiration Reactions
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Glycolysis
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Series of reactions which break the 6-carbon glucose
molecule down into two 3-carbon molecules called
pyruvate using ATP
Process is ancient -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
Step-By-Step…
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2 ATP molecules attach to two phosphates to a glucose
molecule, making a new six carbon compound
The six-carbon compound is split into two three-carbon
compounds (G3P)
The two three-carbon compounds are oxidized and receive a
phosphate and make a new three-carbon compound
NAD+ is reduced to NADH
The phosphate groups are removed, producing two molecules
of pyruvic acid and 4 ATP are made
Anaerobic Cellular Respiration
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Some organisms thrive in environments with little
or no oxygen
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No oxygen used = 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
Lactic Acid Production
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After glycolysis, a hydrogen atom is transferred
from NADH (oxidizing to NAD+) and a free
proton is added to pyruvic acid to form lactic acid
NAD+ is used in glycolysis
Fermentation can be used to produce cheese,
yogurt, sour cream and more
Alcoholic Fermentation
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After glycolysis, a CO2 molecule is removed from
pyruvic acid, leaving a two-carbon compound
Two hydrogen atoms, from NADH and a proton,
are added to the two-carbon compound to form
ethyl alcohol
Alcoholic fermentation by yeast cells is the basis
of the wine and beer industry
Bread also rises due to CO2 production
Aerobic Cellular Respiration
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Oxygen required = aerobic
2 more sets of reactions which occur in a
specialized structure within the cell called the
mitochondria
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1. Kreb’s Cycle
2. Electron Transport Chain
Kreb’s Cycle
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Completes the breakdown of glucose
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Takes the pyruvate (3-carbons) and breaks it down
The carbon and oxygen atoms end up in CO2 and H2O
Hydrogens and electrons are stripped and loaded onto
NAD+ and FAD to produce NADH and FADH2
Production of only 2 more ATP but loads up
the coenzymes with H+ and electrons which
move to the 3rd stage
Step-By-Step
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A two-carbon compound (acetyl CoA) combines with a four-carbon
compound (oxaloacetic acid) to make a six-carbon compound (citric
acid)
Citric acid releases a CO2 molecule and a hydrogen atom to form a
five-carbon compound
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The five-carbon compound releases a CO2 molecule and a hydrogen
atom to form a four-carbon compound. NAD+ becomes NADH
The four-carbon compound releases a hydrogen atom to form
another four-carbon compound
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The hydrogen atom is transferred to NAD+ to make NADH
This hydrogen atom reduces FAD to FADH2
The four-carbon compound releases another hydrogen atom to
regenerate oxaloacetic acid and reduces NAD+ to NADH
Krebs Cycle Outcome
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One glucose molecule is completely broken
down after two turns of the Krebs Cycle
Two turns produce four CO2 molecules, two ATP
molecules and hydrogen molecules used to
make six NADH and two FADH2
CO2 diffuses as waste
ATP is used for energy
Add in the four NADH from glycolysis and
conversion to pyruvic acid, and we’re ready for
the next step!
Electron Transport Chain
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Electron carriers loaded with electrons and
protons from the Kreb’s cycle move to this chainlike a series of steps (staircase).
As electrons drop down stairs, energy released
to form a total of 32 ATP
Oxygen waits at bottom of staircase, picks up
electrons and protons and in doing so becomes
water
Step-By-Step
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Electrons in the hydrogen atoms from NADH and FADH2
are at a high energy
NADH and FADH2 give up electrons to the ETC
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NADH donates them at the beginning
FADH2 donates them midway
The electrons move down the chain, loosing energy
The energy creates a proton gradient and an electrical
gradient from the positive charge
ATP is generated from the gradients from ADP and
phosphate
Oxygen is the final acceptor of electrons that have
passed down the chain. The protons, electrons, and
oxygen combine to form water.
Energy Tally
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36 ATP for aerobic vs. 2 ATP for anaerobic
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Glycolysis
2 ATP
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Kreb’s
2 ATP
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Electron Transport
32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but
are important for global recycling of carbon