Chapter 10 Cell Energy- ATP Photosynthesis and Cellular Respiration

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