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Chapter 10
Cell Energy- ATP
Photosynthesis and Cellular
Respiration
Cool “Fires” Attract Mates and
Meals
• Fireflies use light, instead
of chemical signals, to
send signals to potential
mates
• Females can also use
light flashes to attract
males of other firefly
species — as meals, not
mates
• The light comes from
a set of chemical
reactions, the
luciferin-luciferase
system
• Fireflies make light
energy from chemical
energy
• Life is dependent on
energy conversions
ENERGY AND THE CELL
• Living cells are compartmentalized by
membranes
• Membranes are sites where chemical reactions
can occur in an orderly manner
• Living cells process energy by means of enzymecontrolled chemical reactions
Energy is the capacity to perform
work
• Energy is defined as the capacity to do
work
• All organisms require energy to stay
alive
• Energy makes change possible
Chemical reactions either store or
release energy
• Cells carry out thousands of chemical reactions
– The sum of these reactions constitutes cellular
metabolism
ATP shuttles chemical energy
within the cell
• In cellular respiration, some energy is stored in
ATP molecules
• ATP powers nearly all forms of cellular work
• ATP molecules are the key to energy coupling
• When the bond joining a phosphate group to the
rest of an ATP molecule is broken by hydrolysis,
the reaction supplies energy for cellular work
Phosphate
groups
Adenine
Hydrolysis
Energy
Ribose
Adenosine triphosphate
Adenosine diphosphate
(ADP)
Potential energy of molecules
• How ATP powers cellular work
Reactants
Protein
Products
Work
Hydrolysis
Energy from
exergonic
reactions
Dehydration synthesis
• The ATP cycle
Energy for
endergonic
reactions
Life in the Sun
• Light is central to the life of a plant
• Photosynthesis is the most important chemical
process on Earth
– It provides food for
virtually all organisms
• Plant cells convert light
into chemical signals
that affect a plant’s
life cycle
• Light can influence the architecture of a plant
– Plants that get adequate light are often bushy, with
deep green leaves
– Without enough light, plants
become tall and spindly with
small pale leaves
• Too much sunlight can
damage a plant
– Chloroplasts and carotenoids
help to prevent such damage
AN OVERVIEW OF
PHOTOSYNTHESIS
• Photosynthesis is the process by which
autotrophic organisms use light energy to make
sugar and oxygen gas from carbon dioxide and
water
Carbon
dioxide
Water
Glucose
PHOTOSYNTHESIS
Oxygen
gas
Autotrophs are the producers of the
biosphere
• Plants, some protists, and some bacteria are
photosynthetic autotrophs
– They are the ultimate producers of food consumed by
virtually all organisms
On land, plants such as oak trees and cacti are the
predominant producers
In aquatic environments, algae and photosynthetic
bacteria are the main food producers
Photosynthesis occurs in chloroplasts
• In most plants, photosynthesis occurs primarily
in the leaves, in the chloroplasts
• A chloroplast contains:
– stroma, a fluid
– grana, stacks of thylakoids
• The thylakoids contain chlorophyll
– Chlorophyll is the green pigment that captures light
for photosynthesis
• The location and structure of chloroplasts
Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Grana
Stroma
Inner
membrane
Stroma
Thylakoid
Thylakoid
compartment
Plants produce O2 gas by splitting
water
• The O2 liberated by photosynthesis is made from
the oxygen in water
Overview: Photosynthesis occurs in
two stages linked by ATP and
NADPH
• The complete process of photosynthesis consists
of two linked sets of reactions:
– the light reactions and the Calvin cycle
• The light reactions convert light energy to
chemical energy and produce O2
• The Calvin cycle assembles sugar molecules
from CO2 using the energy-carrying products of
the light reactions
• An overview of photosynthesis
H2O
CO2
Chloroplast
Light
NADP+
ADP
+ P
LIGHT
REACTIONS
(in grana)
CALVIN
CYCLE
(in stroma)
ATP
NADPH
O2
Sugar
THE LIGHT REACTIONS:
CONVERTING SOLAR ENERGY
TO CHEMICAL ENERGY
• Certain wavelengths of visible light drive the
light reactions of photosynthesis
Gamma
rays
X-rays
UV
Infrared
Visible light
Wavelength (nm)
Microwaves
Radio
waves
Light
Chloroplast
Absorbed
light
Transmitted
light
Reflected
light
Photosystems capture solar power
• Each of the many light-harvesting photosystems
consists of:
– an “antenna” of chlorophyll and other pigment
molecules that absorb light
– a primary electron acceptor that receives excited
electrons from the reaction-center chlorophyll
Primary
electron acceptor
PHOTOSYSTEM
Photon
Reaction center
Pigment
molecules
of antenna
• Fluorescence of isolated chlorophyll in solution
Heat
Photon
Photon
(fluorescence)
Chlorophyll
molecule
• Excitation of
chlorophyll in
a chloroplast
Primary
electron acceptor
Other
compounds
Photon
Chlorophyll
molecule
In the light reactions, electron
transport chains generate ATP,
NADPH, and O2
• Two connected photosystems collect photons of
light and transfer the energy to chlorophyll
electrons
• The excited electrons are passed from the
primary electron acceptor to electron transport
chains
– Their energy ends up in ATP and NADPH
• Photosystem II regains electrons by splitting
water, leaving O2 gas as a by-product
Primary
electron acceptor
Primary
electron acceptor
Photons
Energy for
synthesis of
PHOTOSYSTEM I
PHOTOSYSTEM II
by chemiosmosis
• The production of ATP by chemiosmosis in
photosynthesis
Thylakoid
compartment
(high H+)
Light
Light
Thylakoid
membrane
Antenna
molecules
Stroma
(low H+)
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
THE CALVIN CYCLE:
CONVERTING CO2 TO SUGARS
ATP and NADPH power sugar
synthesis in the Calvin cycle
• The Calvin cycle occurs
in the chloroplast’s
stroma
CALVIN
CYCLE
– This is where carbon
fixation takes place and
sugar is manufactured
OUTPUT:
• Details of the
Calvin cycle
3
INPUT:
Step 1 Carbon
fixation.
CO2
In a reaction catalyzed by
rubisco, 3 molecules of CO2
are fixed.
1
3 P
P
6
P
RuBP
Step 2 Energy
consumption and redox.
3-PGA
6
3 ADP
3
ATP
CALVIN
CYCLE
4
Step 3 Release of one
molecule of G3P.
ATP
6 ADP + P
2
6 NADPH
6 NADP+
5
P
6
G3P
P
G3P
3
Step 4 Regeneration
of RuBP.
OUTPUT:
1
P
G3P
Glucose
and other
compounds
PHOTOSYNTHESIS REVIEWED
AND EXTENDED
Review: Photosynthesis uses light
energy to make food molecules
Chloroplast
• A summary
of the
chemical
processes of
photosynthesis
Light
Photosystem II
Electron
transport
chains
Photosystem I
CALVIN
CYCLE
Stroma
Cellular
respiration
Cellulose
Starch
LIGHT REACTIONS
CALVIN CYCLE
Other
organic
compounds
• Many plants make more sugar than they need
– The excess is stored in roots, tuber, and fruits
– These are a major source of food for animals
STAGES OF CELLULAR
RESPIRATION AND
FERMENTATION
Overview: Respiration occurs in three
main stages
• Cellular respiration oxidizes sugar and produces
ATP in three main stages
– Glycolysis occurs in the cytoplasm
– The Krebs cycle and the electron transport chain
occur in the mitochondria
• An overview of cellular respiration
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Cytoplasmic
fluid
Pyruvic
acid
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
Glycolysis harvests chemical energy
by oxidizing glucose to pyruvic
acid
Glucose
Pyruvic
acid
The Krebs cycle completes the
oxidation of organic fuel
Acetyl CoA
• The Krebs cycle
is a series of
reactions in
which enzymes
strip away
electrons and H+
from each acetyl
group
KREBS
CYCLE
2
CO2
2 carbons enter cycle
Oxaloacetic
acid
1
Citric acid
CO2 leaves cycle
5
KREBS
CYCLE
2
Malic
acid
4
Alpha-ketoglutaric acid
3
CO2 leaves cycle
Succinic
acid
Step 1
Acetyl CoA stokes
the furnace
Steps 2 and 3
NADH, ATP, and CO2 are generated
during redox reactions.
Steps 4 and 5
Redox reactions generate FADH2
and NADH.
• Chemiosmosis in the mitochondrion
Protein
complex
Intermembrane
space
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
Connection:Certain Poisons can interrupt the
“chain”
Rotenone
Cyanide,
carbon monoxide
ELECTRON TRANSPORT CHAIN
Oligomycin
ATP SYNTHASE
For each glucose molecule that enters
cellular respiration, chemiosmosis
produces up to 38 ATP molecules
Cytoplasmic
fluid
Mitochondrion
Electron shuttle
across
membranes
GLYCOLYSIS
2
Glucose
Pyruvic
acid
by substrate-level
phosphorylation
2
Acetyl
CoA
used for shuttling electrons
from NADH made in glycolysis
Maximum per glucose:
KREBS
CYCLE
by substrate-level
phosphorylation
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
by chemiosmotic
phosphorylation
Fermentation is an anaerobic
alternative to aerobic respiration
• Under anaerobic conditions, many kinds of cells
can use glycolysis alone to produce small
amounts of ATP
– But a cell must have a way of replenishing NAD+
• In alcoholic fermentation, pyruvic acid is
converted to CO2 and ethanol
– This recycles NAD+ to keep glycolysis working
released
GLYCOLYSIS
Glucose
2 Pyruvic
acid
2 Ethanol
• In lactic acid fermentation, pyruvic acid is
converted to lactic acid
– As in alcoholic fermentation, NAD+ is recycled
• Lactic acid fermentation is used to make cheese
and yogurt
GLYCOLYSIS
Glucose
2 Pyruvic
acid
2 Lactic acid
Food molecules provide raw
materials for biosynthesis
• In addition to energy, cells need raw materials
for growth and repair
– Some are obtained directly from food
– Others are made from intermediates in glycolysis
and the Krebs cycle
• Biosynthesis consumes ATP
• Biosynthesis of macromolecules from
intermediates in cellular respiration
ATP needed to
drive biosynthesis
KREBS
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvic
acid
G3P
Glucose
Amino
groups
Amino acids
Fatty acids Glycerol
Sugars
Proteins
Fats
Polyscaccharides
Cells, tissues, organisms
The fuel for respiration ultimately
comes from photosynthesis
• All organisms have the
ability to harvest energy
from organic molecules
– Plants, but not animals,
can also make these
molecules from inorganic
sources by the process of
photosynthesis