Chapter 9

Energy in a CellEnergy in a Cell

• Cells need energy, its essential to lifeCells need energy, its essential to life

• Our body has a source of energy Our body has a source of energy available to usavailable to us

• The energy is stored in the chemical The energy is stored in the chemical bonds of ATPbonds of ATP

9.1 ATP in a molecule

• ATP = adenosine triphosphateATP = adenosine triphosphate– Adenosine moleculeAdenosine molecule– Three phosphatesThree phosphates

• ATP is a small compound that is a ATP is a small compound that is a quick source of energyquick source of energy

• Binds to specific sites on a cellBinds to specific sites on a cell

• When phosphate bond broken, When phosphate bond broken, energy is released – cell uses this energy is released – cell uses this energyenergy

ADPAdenosine Diphosphate

• Formed when a phosphate is cleaved Formed when a phosphate is cleaved from ATPfrom ATP– Releases energyReleases energy

• ADP can reform ATP which creates ADP can reform ATP which creates a renewable cycle of ATP formation a renewable cycle of ATP formation and breakdownand breakdown

• This cycle continues as long as there This cycle continues as long as there are phosphate molecules availableare phosphate molecules available

What do you think would happen if What do you think would happen if there were no more phosphate there were no more phosphate

molecules available?molecules available?

• ATP binds to a moleculeATP binds to a molecule• Phosphate group is cleaved off and Phosphate group is cleaved off and

ADP leavesADP leaves– Phosphate group gives the cell its Phosphate group gives the cell its

energyenergy• Another ADP molecule binds to the Another ADP molecule binds to the

phosphate molecule and the process phosphate molecule and the process starts overstarts over

• Cells use the energy for many Cells use the energy for many purposespurposes– Physical activityPhysical activity–Making new enzymes to carry out Making new enzymes to carry out

chemical reactionschemical reactions– Build membranes and cell organellesBuild membranes and cell organelles–Maintain homeostasisMaintain homeostasis– Dispose of waste substancesDispose of waste substances

9.2 Photosynthesis:Trapping the Sun’s Energy

• Photosynthesis Photosynthesis • 6CO6CO22 + 6H + 6H22O O C C66HH1212OO6 6 + 6O+ 6O22

– Converts light energy into chemical Converts light energy into chemical energyenergy– two phases two phases • Light-dependent + light-independent Light-dependent + light-independent

– Builds carbohydrates that store energyBuilds carbohydrates that store energy– Produces ATPProduces ATP– Occurs in membranes of thylakoid discs Occurs in membranes of thylakoid discs

• Thylakoid discs Thylakoid discs – Located in chloroplastsLocated in chloroplasts– contain pigments that absorb light = contain pigments that absorb light =

chlorophyllchlorophyll

Light-dependent Reactions• First phase of photosynthesisFirst phase of photosynthesis

• Sunlight hits plants and they absorb Sunlight hits plants and they absorb energyenergy

• Transfer energy to electrons on the Transfer energy to electrons on the Electron Transport ChainElectron Transport Chain

• Electron Transport Chain is a series Electron Transport Chain is a series of proteins embedded in thylakoid of proteins embedded in thylakoid membranemembrane

• In the ETC, Energy is passed from In the ETC, Energy is passed from protein to proteinprotein to protein

• Each transfer a little bit of energy is Each transfer a little bit of energy is releasedreleased

• This energy is used to form ATP This energy is used to form ATP from ADPfrom ADP

• The ETC also splits a water molecule The ETC also splits a water molecule and hydrogen ions, Hand hydrogen ions, H++, bind with an , bind with an NADPNADP++ molecule forming NADPH molecule forming NADPH

• NADPH is used to form NADPH is used to form carbohydrates in light-independent carbohydrates in light-independent reactionsreactions

Light-independent Reactions

• Calvin CycleCalvin Cycle– Takes place in the stroma of the Takes place in the stroma of the

chloroplastchloroplast– 5 steps – page 2355 steps – page 235– Each step adds a COEach step adds a CO22 molecule molecule – Takes 6 cycles to form a sugaTakes 6 cycles to form a sugarr

9.3 Getting energy to make ATP

Cellular Respiration

• 3 stages3 stages–GlycolysisGlycolysis–Citric acid cycleCitric acid cycle–Electron transport chainElectron transport chain

Glycolysis

• Anaerobic – no oxygenAnaerobic – no oxygen• Occurs in the cytoplasmOccurs in the cytoplasm• Break down glucose into pyruvic Break down glucose into pyruvic

acidacid• ATP – 2 used, 4 produced; net gain ATP – 2 used, 4 produced; net gain

of 2 moleculesof 2 molecules

• Pyruvic acid molecules move to Pyruvic acid molecules move to mitochondria, loses a molecule of mitochondria, loses a molecule of COCO22 and combines with and combines with coenzyme A to form acetyl-CoAcoenzyme A to form acetyl-CoA

The Citric Acid Cycle

• Glucose is broken downGlucose is broken down• One ATP molecule formedOne ATP molecule formed• Charged electrons are carried via Charged electrons are carried via

NADH & FADHNADH & FADH22 to the electron to the electron transport chain in the mitochondriatransport chain in the mitochondria

The Electron Transport Chain

• Energized electrons passed from Energized electrons passed from protein to proteinprotein to protein

• Mitochondria inner membrane Mitochondria inner membrane becomes positive charged, due to becomes positive charged, due to high concentration of Hhigh concentration of H++ ions ions

• Mitochondria outside membrane Mitochondria outside membrane becomes negatively charged due to becomes negatively charged due to electrons on the outsideelectrons on the outside

• A concentration gradient occurs: A concentration gradient occurs: electrical & chemicalelectrical & chemical

• Electrical = charge differenceElectrical = charge difference• Chemical = concentration differenceChemical = concentration difference

• Inner membrane of mitochondria Inner membrane of mitochondria forms ATPforms ATP

• Final electron acceptor is OxygenFinal electron acceptor is Oxygen

• 32 ATP molecules formed32 ATP molecules formed

• 35 ATP produced overall35 ATP produced overall

• Glycolysis Glycolysis – 2 ATP2 ATP

• Citric Acid CycleCitric Acid Cycle– 1 ATP1 ATP

• Electron Transport ChainElectron Transport Chain– 32 ATP32 ATP

Fermentation

Lactic Acid Fermentation

• 2 molecules of pyruvic acid use 2 molecules of pyruvic acid use NADH to form 2 molecules of lactic NADH to form 2 molecules of lactic acidacid

• 2 molecules ATP produced2 molecules ATP produced• Muscle fatigue = lactic acid build-upMuscle fatigue = lactic acid build-up

Alcoholic Fermentation

• Yeast cells produce COYeast cells produce CO22 and ethyl and ethyl alcoholalcohol

• Bread – yeast cells produce carbon Bread – yeast cells produce carbon dioxide that forms bubbles in dough, dioxide that forms bubbles in dough, heat kills COheat kills CO22 & bubbles in dough & bubbles in dough lighten breadlighten bread

Photosynthesis vs. Cellular Respiration• Food accumulated• CO2 taken in• Energy stored in

glucose• Occurs only in light• Occurs only in

presence of chlorophyll

• Food broken down• CO2 given off• Energy released

from glucose• Occurs day &

night• Occurs in all living

cells

The EndThe End