Download How Cells Obtain Energy Cell Respiration

How Cells Obtain Energy
Cell Respiration & Photosynthesis
How Cells Obtain Energy
Overview
Energy
Metabolism
Aerobic Cell Respiration
Anaerobic Cell Respiration
Photosynthesis
How Cells Obtain Energy
Energy
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Bioenergetics
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Flow of energy through
living systems
Sun if our “local” source
of energy
Living organisms are
“open” systems; energy
flows in and then out of
living things
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How Cells Obtain Energy
Energy
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Thermodynamics
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The study of energy
transfer involving
physical matter
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First & Second Laws
of Thermodynamics
must be followed in all
living systems
How Cells Obtain Energy
Energy
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Thermodynamics
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First Law of Thermodynamics
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The amount of energy in the
universe is constant
Energy is neither created nor
destroyed
Transferred from place to place
Energy may exist in different
forms
–
Heat, light, chemical, etc
How Cells Obtain Energy
Energy
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Thermodynamics
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Second Law of
Thermodynamics
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Energy will always be
lost as heat in energy
transfers
How Cells Obtain Energy
Energy
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Thermodynamics
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Potential vs Kinetic Energy
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Potential-stored energy
Kinetic-energy to do work
Potential Energy
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Often stored as
chemical bonds in
organic molecules in
the cell
How Cells Obtain Energy
Metabolism
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The sum total of all chemical reactions in a cell
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Metabolic pathways
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Series of chemical changes to molecules
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Catabolic: energy releasing reactions (exergonic & spontaneous)
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Anabolic: energy requiring reactions (endogonic & nonspontaneous)
How Cells Obtain Energy
Metabolism
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Free Energy & Activation Energy
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Free Energy: Net energy released in catabolic reactions
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Activation Energy: Small amount of energy needed to allow ALL
chemical reactions to occur
How Cells Obtain Energy
Metabolism
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Role of Enzymes
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Proteins (tertiary)
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Control the rate of chemical
reactions by reducing the
activation energy needed for
a chemical reaction to occur
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Active site
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Enzyme-substrate complex
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Allosteric site
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Control of enzymes
How Cells Obtain Energy
Metabolism
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Role of Enzymes
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Proteins (tertiary)
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Control the rate of chemical
reactions by reducing the
activation energy needed for a
chemical reaction to occur
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Active site
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Allosteric site
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Activation
Inhibition
Control of Enzymes
How Cells Obtain Energy
Metabolism
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Role of Enzymes
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Proteins (tertiary)
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Control the rate of chemical reactions by reducing the activation energy needed for a chemical reaction to occur
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Active site
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Allosteric site
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Control of Enzymes
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Feedback Inhibition
How Cells Obtain Energy
Aerobic Cell Respiration
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Sum total of all the catabolic
(exergonic) reactions that occur
in a cell
Free energy released is stored
as chemical energy
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ATP (adenosine triphosphate)
3 Steps
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Glycolysis
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Citric Acid Cycle (Kreb’s Cycle)
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Oxidative Phosphorylation
(Electron Transport Chain)
ATP
How Cells Obtain Energy
Aerobic Cell Respiration
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Glycolysis
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Glucose broken down
to pyruvic acid
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ATP formed
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NADH (an electron
carrier) formed
How Cells Obtain Energy
Aerobic Cell Respiration
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Glycolysis
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Pyruvic acid is next converted to acetyl CoA
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Necessary in order for pyruvic acid to enter the Citric Acid Cycle
How Cells Obtain Energy
Aerobic Cell Respiration
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Citric Acid Cycle
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Acetyl CoA broken down to carbon dioxide (CO 2)
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ATP formed
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NADH formed
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FADH2 (another electron carrier) formed
How Cells Obtain Energy
Aerobic Cell Respiration
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Oxidative Phosphorylation
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Occurs in the electron transport
chain of molecules in the
mitochondria of eukaryotic cells
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Occurs in the cell membrane of
prokaryotic cells like bacteria
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NADH & FADH2 transfer
electrons via hydrogen atoms
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Electron chain molecules keep
electrons and discard protons
(H+) of the hydrogen atom
How Cells Obtain Energy
Aerobic Cell Respiration
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Oxidative Phosphorylation
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As electrons are transferred
through the chain oxygen (O2)
eventually received the electrons
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O2 is the final electron acceptor
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ATP Synthase (enzyme) pumps H+
back across the membrane
(chemiosmosis)
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3 ATP are formed by ATP Synthase
for every H+ pumped back in
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Oxygen combines with H+ to form
water (H20)
How Cells Obtain Energy
Aerobic Cell Respiration
Glucose + O2 + ATP + NAD+ + ADP + P
Carbon dioxide (CO2) + Water (H2O) + 38 ATP
How Cells Obtain Energy
Aerobic Cell Respiration
Can other organic molecules yield energy for the
cell?
Yes, and the same metabolic pathway is used
How Cells Obtain Energy
Anaerobic Cell Respiration
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Occurs when cells lack O2 or can’t utilize O2
O2 was the final electron acceptor in aerobic cell
respiration
Lack of O2 or the inability to use O 2 forces some
cells to either create their own final electron
acceptor (endogenous electron acceptor) or use a
compound acquired from outside the cell
(exogenous electron acceptor)
How Cells Obtain Energy
Anaerobic Cell Respiration
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Fermentation
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Endogenous electron acceptors are formed
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Lactic acid
Ethyl alcohol (ethanol)
How Cells Obtain Energy
Anaerobic Cell Respiration
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Lactic Acid Fermentation
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Common in animals and
some bacteria
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Glycolysis with one
additional chemical step
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Insures that NAD+ is
regenerated
Yield only 2 ATP/glucose
molecule metabolized
How Cells Obtain Energy
Anaerobic Cell Respiration
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Ethanol Fermentation
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Common in animals and
some bacteria
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Glycolysis with two
additional chemical steps
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Insures that NAD+ is
regenerated
Yield only 2 ATP/glucose
molecule metabolized
Glycolysis
How Cells Obtain Energy
Anaerobic Cell Respiration
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Exogenous electron
acceptors are formed
Common in some species of
bacteria
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sulfates (SO4-)form hydrogen
sulfide (H2S, “rotten egg gas”)
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nitrates (NO3-) form nitrites
(NO2-)
Very important to life on Earth!
How Cells Obtain Energy
Photosynthesis
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Process of transferring light energy into
stored chemical energy by converting
carbon dioxide and water into complex
carbohydrates like glucose
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Oxygen is a by-product
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Photoautotrophs
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Plants
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Algae
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Some bacteria
Essential for life on earth as the energy
in carbohydrates of photoautotrophs is
passed on to all organisms in the food
chain
How Cells Obtain Energy
Photosynthesis in Plants
Leaf Structure
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Upper Epidermis
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Mesophyll
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Cells containing chloroplasts
Chloroplasts-pigmented organelles
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Inner & Outer Membrane
Thylakoids (middle layer of folded
membranes)
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Contain chlorophyll pigments
Granum-stack of thalakoids
Stroma-space between grana
Lower Epidermis
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Stoma-openings for O2 & CO2
How Cells Obtain Energy
Photosynthesis in Plants
Light & Chlorophyll
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Light
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Form of electromagnetic radiation (energy)
Chlorophylls (pigment molecules)
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Absorb light energy and emit electrons as a
result
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Absorption spectum
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Chlorophyll a
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Present in all plants
Absorbs blue and red light, not green
Chlorophyll b
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Frequency of visible light capable of being absorbed by a
chlorophyll molecule
Absorbs blue and red-orange light
Carotenoids
How Cells Obtain Energy
Photosynthesis in
Plants
2 Steps
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Light-dependent
reactions
Calvin Cycle
How Cells Obtain Energy
Photosynthesis in Plants
Light-dependent reactions
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Begin in a group of chlorophylls and
proteins called a photosystem II found
in the thylakoids
Light energy is transferred to electrons
in chlorophyll
Electrons are lost from chlorophyll and
are passed along a series of
cytochrome molecules called an
electron transport chain
H2O breaks down to donate electrons
lost from chlorophyll so chlorophyll can
respond to more light energy
How Cells Obtain Energy
Photosynthesis in Plants
Light-dependent reactions
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Energy from the moving
electrons allows membrane
pumps to move H+ from the
stroma to the thylakoid space
The build up of H+ in the
thylakoid space prompts ATP
synthase to pump the H+
back into the stroma and at
the same time produce ATP
How Cells Obtain Energy
Photosynthesis in Plants
Light-dependent reactions
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As the electrons passes through the
electron transport chain it eventually is
donated to a chlorophyll molecule in
another photosystem, photosystem I
More light energy excites these electrons
in the pigments of photosystem I causing
them to move through another set of
molecules and eventually be donated to
NADP+ (an electron carrier) along with a
H+ to form NADPH
The end result: light energy is transferred
and stored as chemical energy in the ATP
and NADPH molecules
How Cells Obtain Energy
Photosynthesis in Plants
Calvin Cycle Reactions
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Occur in the stroma of the
chloroplasts
CO2 which enters from the
stoma of the leaf is
synthesized into sugars
using the energy from ATP
& NADPH generated in the
light-dependent reactions
How Cells Obtain Energy
Photosynthesis in Plants
Calvin Cycle Reactions
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Stage 1- Carbon Fixation
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Inorganic CO2 molecules
are bonded to ribulose
biphosphate (RuBP) to
form a 6- carbon organic
molecule which breaks
down into 2 3-carbon
organic compounds
How Cells Obtain Energy
Photosynthesis in Plants
Calvin Cycle Reactions
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Stage 2- Reduction
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The 2 3-carbon organic
molecules are reduced
(electrons added to them)
using ATP & NADPH
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The resulting ADP &
NADP+ return to the lightdependent reaction to be
reused
How Cells Obtain Energy
Photosynthesis in Plants
Calvin Cycle Reactions
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Stage 3- Regeneration
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The 2 3-carbon organic molecules are
reduced using ATP & NADPH (electrons
added to them) to G3P
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The resulting ADP & NADP+ return to the
light-dependent reaction to be reused
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After 3 turns of the Calvin Cycle some of the
G3P bonds together to form glucose and the
remaining G3P molecules are used to
regenerate RuBP for succeeding turns of the
Calvin Cycle
The end result of photosynthesis is that light
energy is converted to stored energy
(potential energy) in the form of glucose
How Cells Obtain Energy
Photosynthesis in Bacteria
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A bacterial cell has infolded
regions of the plasma
membrane that function like
thylakoids
Although these are not
contained in an organelle,
such as a chloroplast, all of
the necessary components
are present to carry out
photosynthesis