Introduction – all Introduction – all forms of life depend forms of life depend directly or indirectly directly or indirectly on light energy on light energy captured during captured during photosynthesis – photosynthesis – glucose molecules glucose molecules are broken down are broken down back into carbon back into carbon dioxide and water dioxide and water (molecules the (molecules the plant started with) plant started with)

Cellular RespirationCellular Respiration

ATP – Adenosine ATP – Adenosine triphosphatetriphosphate

most common energy carrier in cellsmost common energy carrier in cells nucleotide composed of adenine, the nucleotide composed of adenine, the

sugar ribose, and three phosphate sugar ribose, and three phosphate groupsgroups

synthesized from adenosine diphosphate synthesized from adenosine diphosphate (ADP) and inorganic phosphate – process (ADP) and inorganic phosphate – process is called phosphorylationis called phosphorylation

during glucose breakdown, energy is during glucose breakdown, energy is release and stored in bonds of ATP release and stored in bonds of ATP

Summary of complete glucose Summary of complete glucose metabolism:metabolism:

Photosynthesis:Photosynthesis:

6CO6CO22 + 6H + 6H22O + sunlight energy O + sunlight energy C C66HH1212OO66 + 6O + 6O22

Complete glucose metabolism:Complete glucose metabolism:

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22O + chemical and heat O + chemical and heat

energiesenergies

GlycolysisGlycolysis first stage of aerobic respirationfirst stage of aerobic respiration does not require Odoes not require O22 ( (anaerobic) anaerobic) and proceeds in and proceeds in

exactly the same way under both aerobic (with exactly the same way under both aerobic (with oxygen) and anaerobic (without oxygen) oxygen) and anaerobic (without oxygen) conditionsconditions

Splits apart a single glucose molecule (6 carbon) Splits apart a single glucose molecule (6 carbon) into two molecules of into two molecules of pyruvatepyruvate (3 carbon) (3 carbon)

under anaerobic conditions, pyruvate converted under anaerobic conditions, pyruvate converted by fermentation to lactic acid or ethanolby fermentation to lactic acid or ethanol

occurs in cytoplasmoccurs in cytoplasm pyruvate may enter mitochondria if oxygen pyruvate may enter mitochondria if oxygen

available – breaks pyruvate down completely to available – breaks pyruvate down completely to COCO22 and water generating an additional 34 to 36 and water generating an additional 34 to 36 ATP – aerobic respirationATP – aerobic respiration

each step (reaction) is catalyzed by an enzymeeach step (reaction) is catalyzed by an enzyme

products are 2 molecules of ATP products are 2 molecules of ATP and 2 molecules of NADHand 2 molecules of NADH

– nicotinamide adenine dinucleotide – an nicotinamide adenine dinucleotide – an electron carrier that transports energy electron carrier that transports energy in form of energetic electrons - in form of energetic electrons - CoenzymeCoenzyme

– electrons are held in high-energy outer electrons are held in high-energy outer electron shells – NADelectron shells – NAD++ NADH NADH

– donates the electrons and their energy donates the electrons and their energy to other moleculesto other molecules

– hydrogen ions are often picked up hydrogen ions are often picked up simultaneously simultaneously

formed through oxidation/reduction formed through oxidation/reduction reactions – involves two reactions – involves two complementary reactionscomplementary reactions

– oxidation – liberates energy from the oxidation – liberates energy from the oxidation substance; results from the oxidation substance; results from the removal of one more electrons, alone removal of one more electrons, alone or with Hor with H++

– reduction – stores energy in a reduced reduction – stores energy in a reduced compound; reduction results from compound; reduction results from addition of one or more electrons, addition of one or more electrons, alone or with Halone or with H++

Glycolysis consists of two major sets of Glycolysis consists of two major sets of reactions:reactions:

Step 1 - Step 1 - glucose activationglucose activation– 2 ATP are used to convert stable 2 ATP are used to convert stable

glucose into highly unstable fructose glucose into highly unstable fructose bisphosphate (6 C)bisphosphate (6 C)

Step 2 – Step 2 – Energy harvestEnergy harvest fructose bisphosphate splits into two 3 C molecules fructose bisphosphate splits into two 3 C molecules

of glyceraldehyde 3-phosphate (G3P or PGAL)of glyceraldehyde 3-phosphate (G3P or PGAL) each G3P molecule goes through series of reactions each G3P molecule goes through series of reactions

that convert it into pyruvate (pyruvic acid)that convert it into pyruvate (pyruvic acid) 2 ATPs are made per G3P for a total of 4 – however, 2 ATPs are made per G3P for a total of 4 – however,

net gain is only 2 ATPsnet gain is only 2 ATPs During these reactions, 2 high energy electrons and During these reactions, 2 high energy electrons and

a Ha H++ are added to NAD are added to NAD++ to form “energized” carrier to form “energized” carrier NADH – 2 NADH are made (one from each G3P) NADH – 2 NADH are made (one from each G3P)

FermentationFermentation In the absence of oxygen, pyruvate acts as In the absence of oxygen, pyruvate acts as

electron acceptor from NADH producing electron acceptor from NADH producing ethanol or lactic acid – this process is ethanol or lactic acid – this process is called called fermentationfermentation

NADH production is not used as method to NADH production is not used as method to capture energy – used to get rid of capture energy – used to get rid of hydrogen ions and electrons made when hydrogen ions and electrons made when glucose is broken downglucose is broken down

NADNAD++ is regenerated by pyruvate acting as is regenerated by pyruvate acting as final electron acceptor - pyruvate may be final electron acceptor - pyruvate may be converted to lactic acid (converted to lactic acid (lactic acid lactic acid fermentationfermentation – occurs in human muscles – occurs in human muscles during strenuous exercise) or ethanol and during strenuous exercise) or ethanol and COCO22 ( (alcoholic fermentationalcoholic fermentation) )

Aerobic RespirationAerobic Respiration In presence of oxygen, oxygen is the In presence of oxygen, oxygen is the

electron acceptor (in the electron electron acceptor (in the electron transport system) allowing pyruvate to transport system) allowing pyruvate to be fully broken down (back into CObe fully broken down (back into CO22 and and water) to make even more ATPwater) to make even more ATP

Aerobic Cellular Respiration – series of Aerobic Cellular Respiration – series of reactions, occurring under aerobic reactions, occurring under aerobic conditions, in which large amounts of conditions, in which large amounts of ATP are produced – pyruvate is broken ATP are produced – pyruvate is broken down into carbon dioxide and water – down into carbon dioxide and water – oxygen serves as final electron acceptor oxygen serves as final electron acceptor – each step catalyzed by enzymes – each step catalyzed by enzymes

Aerobic RespirationAerobic Respiration occurs in the mitochondriaoccurs in the mitochondria

– double membrane – inner folds are called double membrane – inner folds are called cristaecristae– inner compartment contains fluid inner compartment contains fluid matrixmatrix– intermembrane compartmentintermembrane compartment separates the two membranes separates the two membranes – Mitochondria have their own DNA (circular chromosome) Mitochondria have their own DNA (circular chromosome)

and ribosomes (70s – smaller than eukaryotic ribosomes)and ribosomes (70s – smaller than eukaryotic ribosomes)

Aerobic RespirationAerobic Respiration Step 1 – GlycolysisStep 1 – Glycolysis Step 2 – Step 2 – Oxidative DecarboxylationOxidative Decarboxylation

– two molecules of pyruvate produced two molecules of pyruvate produced by glycolysis are transported across by glycolysis are transported across both mitochondrial membranes into both mitochondrial membranes into matrix matrix

– each pyruvate is split into COeach pyruvate is split into CO22 and a 2 and a 2 C acetyl group which immediately C acetyl group which immediately attaches to coenzyme A to form acetyl attaches to coenzyme A to form acetyl CoA – during this reaction NADH is CoA – during this reaction NADH is produced produced

Step 3 – Krebs Cycle (Citric Acid Step 3 – Krebs Cycle (Citric Acid Cycle)Cycle) the acetyl CoA enter Krebs cycle by briefly the acetyl CoA enter Krebs cycle by briefly

combining with oxaloacetate to form citrate – combining with oxaloacetate to form citrate – coenzyme A is released to be reusedcoenzyme A is released to be reused

Kreb’s cycle rearranges citrate to regenerate Kreb’s cycle rearranges citrate to regenerate oxaloacetate giving off 2 COoxaloacetate giving off 2 CO22, 1 ATP and four , 1 ATP and four electron carriers (1 FADHelectron carriers (1 FADH22 and 3 NADH) per and 3 NADH) per pyruvate molecule (x2 per glucose molecule)pyruvate molecule (x2 per glucose molecule)

Electron Transport System (Oxidative Electron Transport System (Oxidative Phosphorylation)Phosphorylation)

energetic electrons from NADH and FADHenergetic electrons from NADH and FADH22 are used to generate more ATP (3 ATP are are used to generate more ATP (3 ATP are generated per NADH and 2 ATP per FADHgenerated per NADH and 2 ATP per FADH22))

located in inner mitochondrial membranelocated in inner mitochondrial membrane electrons move from molecule to molecule electrons move from molecule to molecule

along transport system – energy released along transport system – energy released by electrons is used to pump hydrogen by electrons is used to pump hydrogen ions from the matrix across the inner ions from the matrix across the inner membrane into the intermembrane membrane into the intermembrane compartment (used for chemiosmosis)compartment (used for chemiosmosis)

at the end of the ETS, oxygen and at the end of the ETS, oxygen and hydrogen ions accept the electrons to form hydrogen ions accept the electrons to form water – clears out transport system for water – clears out transport system for more electrons to run through more electrons to run through

Chemiosmosis Chemiosmosis hydrogen ions pumped across the inner hydrogen ions pumped across the inner

membrane generate a large Hmembrane generate a large H++ concentration concentration gradient (high concentration in gradient (high concentration in intermembrane compartment and low intermembrane compartment and low concentration in matrix)concentration in matrix)

inner membrane is impermeable to hydrogen inner membrane is impermeable to hydrogen ions except at protein channels that are part ions except at protein channels that are part of ATP-synthesizing enzymes (ATP synthase) of ATP-synthesizing enzymes (ATP synthase) - whole thing is called the F- whole thing is called the F11 complex complex

during chemiosmosis, hydrogen ions move during chemiosmosis, hydrogen ions move down the concentration gradient from down the concentration gradient from intermembrane compartment to matrix by intermembrane compartment to matrix by means of the Fmeans of the F11 complex complex

the flow of hydrogen ions provides energy to the flow of hydrogen ions provides energy to synthesize 32 – 34 ATPs from ADP synthesize 32 – 34 ATPs from ADP

Coupled Reactions Coupled Reactions

Many steps involved in respiration Many steps involved in respiration are coupled - reactions in which are coupled - reactions in which exergonic reactions drive exergonic reactions drive endergonic reactionsendergonic reactions

Some reactions occur together Some reactions occur together with two reactions sharing a with two reactions sharing a common intermediate molecule common intermediate molecule

Metabolism of Fats and Metabolism of Fats and Proteins Proteins

cells can extract energy from fats and proteinscells can extract energy from fats and proteins breakdown of fat and proteins creates products that breakdown of fat and proteins creates products that

can be fed into the enzyme pathways of respirationcan be fed into the enzyme pathways of respiration FatsFats

– starts with hydrolysis into glycerol and fatty acidsstarts with hydrolysis into glycerol and fatty acids– glycerol is converted into G3P and enters glycerol is converted into G3P and enters

pathwaypathway– fatty acids are converted into acetyl-CoA and fatty acids are converted into acetyl-CoA and

enter pathwayenter pathway ProteinsProteins

– amino acids are broken down in a number of amino acids are broken down in a number of waysways

the amino group is first removed (deamination)the amino group is first removed (deamination) some amino acids are converted into pyruvic some amino acids are converted into pyruvic

acid, some into acetyl-CoA, and some into acid, some into acetyl-CoA, and some into other compounds in the Krebs cycle other compounds in the Krebs cycle

Body Temperature and Body Temperature and MetabolismMetabolism cellular respiration captures energy in the bonds cellular respiration captures energy in the bonds

of ATP however, much of the energy is lost as of ATP however, much of the energy is lost as heat (approx 60% of energy available is lost)heat (approx 60% of energy available is lost)

the majority of animals and plants quickly lose the majority of animals and plants quickly lose this thermal energy to the environment – referred this thermal energy to the environment – referred to as to as poikilothermicpoikilothermic (“of variable heat”) or (“of variable heat”) or ectothermicectothermic (“externally heated”) (“externally heated”)

body heat comes from external sources, body body heat comes from external sources, body temp fluctuates with environmental temptemp fluctuates with environmental temp

metabolic rate (organism’s rate of oxygen metabolic rate (organism’s rate of oxygen consumption or release of COconsumption or release of CO22) increases with ) increases with temp (enzymes more active at higher temps)temp (enzymes more active at higher temps)

ectotherms are more active with higher temps ectotherms are more active with higher temps and sluggish with lower tempsand sluggish with lower temps

many have behavioral adaptations to assist with many have behavioral adaptations to assist with temp control (basking) temp control (basking)

Mammals and birds (and some other Mammals and birds (and some other organisms) make use of heat organisms) make use of heat produced during metabolism – have produced during metabolism – have evolved mechanisms to conserve heat evolved mechanisms to conserve heat (insulation with fat, hair, feathers)(insulation with fat, hair, feathers)

endothermicendothermic (“internally heated”) – (“internally heated”) – have fairly high body temps (higher have fairly high body temps (higher than environment)than environment)

tend to maintain fairly constant body tend to maintain fairly constant body temp – temp – homeothermichomeothermic even when even when environmental temp fluctuatesenvironmental temp fluctuates

metabolic rate stays fairly constantmetabolic rate stays fairly constant

metabolic rate is inversely related to metabolic rate is inversely related to body size in both endo and body size in both endo and ectothermsectotherms

endothermic, smaller animals have a endothermic, smaller animals have a higher surface area-to- volume ratio higher surface area-to- volume ratio and therefore a larger relative heat and therefore a larger relative heat loss to the environmentloss to the environment

must have faster metabolism to must have faster metabolism to replace heat – have to consume replace heat – have to consume relatively large amounts of food relatively large amounts of food

metabolic rate is higher in smaller metabolic rate is higher in smaller ectotherms too but has never been ectotherms too but has never been fully explained as to whyfully explained as to why