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Chapter 10
Cell Energy- ATP
Photosynthesis and Cellular Respiration
• 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
Cool “Fires” Attract Mates and Meals
• 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
• 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 enzyme-controlled chemical reactions
ENERGY AND THE CELL
• Energy is defined as the capacity to do work
• All organisms require energy to stay alive
• Energy makes change possible
Energy is the capacity to perform work
• Cells carry out thousands of chemical reactions
– The sum of these reactions constitutes cellular metabolism
Chemical reactions either store or release energy
• 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
ATP shuttles chemical energy within the cell
• 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
Phosphategroups
Adenine
Ribose
Adenosine triphosphate
Hydrolysis
Adenosine diphosphate(ADP)
Energy
• How ATP powers cellular work
Reactants
Po
ten
tia
l en
erg
y o
f m
ole
cule
s
Products
Protein Work
• The ATP cycle
Energy from exergonic reactions
Deh
yd
rati
on
syn
thes
is
Hyd
roly
sis
Energy for endergonic reactions
• 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
Life in the Sun
• 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
• Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbondioxide
Water Glucose Oxygengas
PHOTOSYNTHESIS
• Plants, some protists, and some bacteria are photosynthetic autotrophs – They are the ultimate producers of food consumed by
virtually all organisms
Autotrophs are the producers of the biosphere
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
• 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
Photosynthesis occurs in chloroplasts
• The location and structure of chloroplasts
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outermembrane
Innermembrane
ThylakoidcompartmentThylakoidStroma
Granum
StromaGrana
• The O2 liberated by photosynthesis is made from the oxygen in water
Plants produce O2 gas by splitting water
• 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
Overview: Photosynthesis occurs in two stages linked by ATP and
NADPH
• An overview of photosynthesis
Light
Chloroplast
LIGHTREACTIONS
(in grana)
CALVINCYCLE
(in stroma)
Electrons
H2O
O2
CO2
NADP+
ADP+ P
Sugar
ATP
NADPH
• Certain wavelengths of visible light drive the light reactions of photosynthesis
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY
TO CHEMICAL ENERGY
Gammarays
X-rays UV Infrared Micro-waves
Radiowaves
Visible light
Wavelength (nm)
Light
Chloroplast
Reflectedlight
Absorbedlight
Transmittedlight
• 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
Photosystems capture solar power
Primaryelectron acceptor
Photon
Reaction center
PHOTOSYSTEM
Pigmentmoleculesof antenna
• Fluorescence of isolated chlorophyll in solution
Heat
Photon(fluorescence)Photon
Chlorophyllmolecule
• Excitation of chlorophyll in a chloroplast
Primaryelectron acceptor
Othercompounds
Chlorophyllmolecule
Photon
• 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
In the light reactions, electron transport chains generate ATP,
NADPH, and O2
• Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product
Primaryelectron acceptor
Primaryelectron acceptor
Electron transport chain
Electron transport
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy forsynthesis of
by chemiosmosis
• The production of ATP by chemiosmosis in photosynthesis
Thylakoidcompartment(high H+)
Thylakoidmembrane
Stroma(low H+)
Light
Antennamolecules
Light
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
• The Calvin cycle occurs in the chloroplast’s stroma – This is where carbon
fixation takes place and sugar is manufactured
ATP and NADPH power sugar synthesis in the Calvin cycle
THE CALVIN CYCLE: CONVERTING CO2 TO SUGARS
OUTPUT:
CALVINCYCLE
• Details of the Calvin cycle INPUT:
Step Carbon
fixation.
In a reaction catalyzed by rubisco, 3 molecules of CO2 are fixed.
11
Step Energy
consumption and redox.
2
3 P P P6
6
2
ATP
6 ADP + P
6 NADPH
6 NADP+
6 P
G3P
Step Release of one
molecule of G3P.
3
CALVINCYCLE
3
OUTPUT: 1 PGlucoseand other compounds
G3P
Step Regeneration
of RuBP.
4
G3P
4
3 ADP
3 ATP
3CO2
5 P
RuBP 3-PGA
• A summary of the chemical processes of photo-synthesis
Review: Photosynthesis uses light energy to make food molecules
PHOTOSYNTHESIS REVIEWED AND EXTENDED
Light
Chloroplast
Photosystem IIElectron transport
chains Photosystem I
CALVIN CYCLE Stroma
Electrons
LIGHT REACTIONS CALVIN CYCLE
Cellular respiration
Cellulose
Starch
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
• 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
Overview: Respiration occurs in three main stages
STAGES OF CELLULAR RESPIRATION AND
FERMENTATION
• An overview of cellular respiration
High-energy electrons carried by NADH
GLYCOLYSIS
Glucose Pyruvicacid
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
MitochondrionCytoplasmic
fluid
Glycolysis harvests chemical energy by oxidizing glucose to pyruvic
acid
Glucose Pyruvicacid
• The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group
The Krebs cycle completes the oxidation of organic fuel
Acetyl CoA
KREBSCYCLE
2CO2
Oxaloaceticacid
Step Acetyl CoA stokesthe furnace
1
2 carbons enter cycle
Citric acid
Steps and NADH, ATP, and CO2 are generatedduring redox reactions.
2 3
CO2 leaves cycle
Alpha-ketoglutaric acid
CO2 leaves cycle
Succinicacid
KREBSCYCLE
Steps and Redox reactions generate FADH2
and NADH.
4 5
Malicacid
1
2
3
4
5
• Chemiosmosis in the mitochondrion
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Proteincomplex
Electroncarrier
Electronflow
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
Rotenone Cyanide,carbon monoxide
Oligomycin
ELECTRON TRANSPORT CHAIN ATP SYNTHASE
Connection:Certain Poisons can interrupt the “chain”
For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules
KREBSCYCLE
Electron shuttleacrossmembranes
Cytoplasmic fluid
GLYCOLYSIS
Glucose2
Pyruvicacid
2AcetylCoA
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
by substrate-levelphosphorylation
used for shuttling electronsfrom NADH made in glycolysis
by substrate-levelphosphorylation
by chemiosmoticphosphorylation
Maximum per glucose:
• 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+
Fermentation is an anaerobic alternative to aerobic respiration
• In alcoholic fermentation, pyruvic acid is converted to CO2 and ethanol
– This recycles NAD+ to keep glycolysis working
GLYCOLYSIS
2 Pyruvicacid
released
2 EthanolGlucose
• 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
2 Pyruvicacid
2 Lactic acidGlucose
• 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
Food molecules provide raw materials for biosynthesis
• Biosynthesis of macromolecules from intermediates in cellular respiration
ATP needed todrive biosynthesis
PolyscaccharidesFatsProteins
KREBSCYCLE
AcetylCoA
Pyruvicacid G3P Glucose
GLUCOSE SYNTHESIS
Aminogroups
Amino acids Fatty acids Glycerol Sugars
Cells, tissues, organisms
• 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
The fuel for respiration ultimately comes from photosynthesis
