Cellular Respiration

Energy Flow• photosynthesis

– carried out by plants

• uses energy from sunlight

• converts it into glucose & oxygen

• used in cellular respiration

• oxygen is consumed • glucose is broken down

into CO2 & H2O

Respiration• means breathing

• cellular respiration

– exchange of gases

• O2 from the environment is used and & CO2 is released & removed by blood

Cellular Respiration• provides ATP for cellular work

• called oxidation

• oxidizes food molecules, like glucose, to CO2 & water

• 6C6H12O2 + 6O2 6CO2 + 6H2O + ATP

• energy is trapped in ATP

Cellular Respiration-Oxidation• electrons are transferred from sugar to

O2 making H2O• do not see electron transfer in equation• see changes in H ions• glucose molecule loses hydrogen

atoms as it is converted to CO2 • O2 gains hydrogen atoms to form water• O2 is an electron grabber

– pulls harder than other atoms to get electrons

• these hydrogen movements represent electron transfers

• each hydrogen atom consists of one electron and one proton

• electrons move along with hydrogens from glucose to O2

• it is as if they are falling• energy is released in the process• process is possible only because of O2

• if you stop breathingno ATP would be madeall processes stopdeath

6C6H12O2 + 6O2 6CO2 + 6H2O + ATP

Complete Oxidation of Glucose• C6H12O6 + 6O2 6CO2 + 6H2O

• for one thing to be oxidized-another must be reduced

• oxidation & reduction reactions occur together

• redox reactions

Oxidation/Reduction Reactions• Oxidation

– H+ atoms are removed from compounds

• Oxidized things lose electrons• electron lostoxidized-loses

energy• Reduction

– H+ atoms are added to compounds

• gain electronreduced-gains energy

• food fuels are oxidized-lose energy transferred to other moleculesATP

• coenzymes act as hydrogen or electron acceptors– reduced each time substrate

is oxidized

CoEnzymes• needed in oxidation reactions• NAD+-niacin-nicotinamide adenine dinucleotide• FAD-flavin adenine dinucleotide-riboflavin

Glucose Oxidation Steps• Glycolysis

– occurs in cytosol– does not require oxygen– also called anaerobic

• Kreb’s Cycle– occurs in mitochondria

– require O2

– aerobic

• Electron Transport Chain– occurs in mitochondria

– require O2

– aerobic

Glycolysis• first step in complete oxidation of

glucose• takes place in cytosol• begins when enzyme

phosphorylates glucose– adds PO4 group to glucose

Glu6PO4• traps glucose

– most cells do not have enzyme to reverse reaction & lack transport system for phosphorylated sugars

– ensures glucose is trapped• Glu6PO4isomerizedFru6P+

ATP fructose-1,6-bisphosphate-Fru 1,6diP

• reaction uses 2 ATPs• Energy Investment Phase

Glycolysis• Glyceraldehyde-3-P

dehydrogenase catalyzes NAD+ dependent oxidation of glyceraldehyde 3P2 pyruvates

Glycolysis• removed H+

–picked up by NAD+NADH + H+

• Glucose + 2NAD + 2ADP + pi2 pyruvic acids + 2NADH + 2 ATP

Glycolysis

Pyruvate• important branch point in

glucose metabolism• fate depends on oxygen

availability• not enough oxygen

– NAD+ is regenerated by converting pyruvatelactic acid

• anaerobic fermentation• O2 available• pyruvic acid enters

aerobic pathways of Krebs cycle

• aerobic respiration

Anaerobic Fermentation• not enough oxygen• NAD+ regenerated by converting

pyruvatelactic acid• limited by buildup of lactic acid

– produces acid/base problems– degrades athletic

performances– impairs muscle cell

contractions & produces physical discomfort

• used for short bursts of high level activity lasting several minutes

• cannot supply ATP for long, endurance activities

Alcohol Fermentation• yeast without

oxygen

• provides ATP

• by product-ethanol

• regenerates NAD+

Aerobic Respiration• pyruvic acid enters

mitochondria• once inside converted

acetyl CoA• during conversion• hydrogen atoms of pyruvate

are removed by coenzymes• pyruvate is decarboxylated

(carbons removed) released as CO2diffuses out of cells into bloodexpelled by lungs

• pyruvic acid + NAD + + coenzyme A CO2 + NADH + Acetyl CoA

Acetyl CoA• major branch

point in metabolism

• 2 carbons can be converted into fatty acids, amino acids or energy

Krebs Cycle• Acetyl CoA enters Krebs Cycle

– also tricarboxylic acid cycle or Citric Acid Cycle

• during cycle hydrogen atoms are removed from organic moleculestransferred to coenzymes

• cycle begins & ends with same substrate: oxaloacetate (OAA)

• acetyl CoA condenses with oxaloacetate- 4 carbon compoundcitrate-6 carbon compound

• cycle continues around through 8 successive step

• during steps atoms of citric acid are rearranged producing different intermediates called keto acids

• eventually turns into OAA

Krebs Cycle• complete revolution per acetyl

CoA includes 2 decarboxylations & 4 oxidations

• Yields– 2 CO2

– reducing equivalents-3 NADH & 1 FADH2

• further oxidized in electron transport chain

– 1 GTP-ATP equivalent

Since two pyruvates are obtained from oxidation of glucose amounts need to be doubled for complete oxidation results

Electron Transport Chain• transfers pairs of electrons

from entering substrate to final electron acceptor-oxygen

• electrons are led through series of oxidation-reduction reactions before combining with O2 atoms

• reactions takes place on inner mitochondrial membrane

• only permeable to water, oxygen & CO2

Electron Transport Chain• members of chain• FMN-flavin mononucleotide• Fe-S centers• copper ions• coenzyme Q• cytochromes

– Sequence- b,c, a & a3

Oxidative Phosphorylation/Electron Transport Chain System

• responsible for 90% of ATP used by cells

• basis-2H + O22 H20• releases great deal of energy all at

once• cells cannot handle so much energy

at one time• reactions occur in series of steps • Oxidation reactions

– remove H+ atoms & lose energy (H+)• Oxidized things lose electrons• compounds that gain electrons

reduced-gain energy• enzymes cannot accept H atoms• Coenzymes needed to accept

hydrogens • when coenzyme accepts hydrogen

atoms coenzyme reduced & gains energy

Oxidative Phosphorylation• Step 1: coenzyme strips pair of hydrogen

atoms from substrate• FADH2 is reduced

– FAD accepted 2 hydrogens & 2 electrons in TCA cycle

– NADH accepted 2 electrons• bound one as hydrogen atom

• Step 2: NADH & FADH2 deliver hydrogen atoms to coenzymes in inner mitochondrion membrane

– one of 2 paths can be taken depending on donor

• Step 3: conenzyme Q accepts hydrogen atoms from FADH2passes electrons to cytochromes

– hydrogen atoms released as hydrogen ions-H+

• Step 4: electrons passed along energy lost at each step as passed from cytochrome to cytochrome

– released as hydrogens• Step 5: oxygen atom accepts electron

creating oxygen ion O- which has strong affinity for H+combinesH2O

– does not produce ATP directly– creates conditions needed for ATP production

Chemiosmosis• ETC creates conditions needed for ATP

production by creating concentration gradient across inner mitochondrial membrane

• as energy is released-as electrons are transferred drives H ion pumps that move H across membrane into space between 2 membranes

• pumps create large concentration gradients for H

• H ions cannot diffuse into matrix because not lipid soluble

• channels allow H ions to enter matrix• Chemiosmosis

– energy released during oxidation of fuels=chemi

– pumping H ions across membranes of mitochondria into inter membrane space =osmo

– creates steep diffusion gradient for Hs across membrane

• when hydrogens flow across membrane, through membrane channel proteinATP synthase attaches PO4 to ADP ATP

ATP synthase

Oxidative Phosphorylation• for each pair of

electrons removed by NAD from substrate in TCA cycle6 hydrogen ions are pumped across inner membrane of mitrochondria makes 3 ATP

• FAD4 hydrogens pumped across2 ATP

Energy Yield • aerobic metabolism generates

more ATP per mole of glucose oxidized than anaerobic metabolism

• Glycolysis– net 2 ATPs

• Krebs Cycle– 2 ATP– 8 NADH + H+ X 3=24 ATP– 2 FADH2 X 2=4 ATP

• 2 moles pyruvate2 NADH + H+-glycolysis 2 X 2 = 4 ATP

• Total 36 ATP

Metabolism Overview