CELL RESPIRATION

REACTIONS

OXIDATION OXIDATION

• Addition of oxygen Addition of oxygen atomsatoms

• Removal of hydrogen Removal of hydrogen atomsatoms

• Loss of electrons from Loss of electrons from a substancea substance

REDUCTIONREDUCTION

• Removal of oxygen Removal of oxygen atomsatoms

• Addition of hydrogen Addition of hydrogen atomsatoms

• Addition of electrons Addition of electrons to a substanceto a substance

RESPIRATIONRESPIRATIONGLUCOSE GLUCOSE FATTY ACIDSFATTY ACIDSAMINO ACIDSAMINO ACIDS

OXIDATIONOXIDATION

GLYCOLYSISGLYCOLYSIS•IF THE RESPIRATORY SUBSTRATE IS GLUCOSE THEN THE FIRST STAGE OF CELLULAR RESPIRATION IS GLYCOLYSIS

•THIS PATHWAY OCCURS IN THE CYTOPLASM

•LESS AMOUNT OF ENERGY IS PRODUCED

•PARTIAL OXIDATION OF GLUCOSE OCCURS, AND DOES NOT REQUIRE DOES NOT REQUIRE OXYGENOXYGEN

•IT OCCURS IN BOTH AEROBIC AND ANAEROBIC RESPI RATION.

•IT OCCURS IN BOTH PROKARYOTES & EUKARYOTES

STEPS INVOLVED IN GLYCOLSISSTEPS INVOLVED IN GLYCOLSISSTEP I PHOSPHORYLATIONSTEP I PHOSPHORYLATION

• 2PO2PO44 groups are added to a groups are added to a GLUCOSEGLUCOSE molecule to form molecule to form HEXOSE BIPHOSPHATEHEXOSE BIPHOSPHATE. .

• 2ATP2ATP molecules provide the molecules provide the POPO44

• Energy level of the hexose formed is raised by phosphorylation and this makes the subsequent reactions possibleEnergy level of the hexose formed is raised by phosphorylation and this makes the subsequent reactions possible

GLUCOSE GLUCOSE HEXOSE HEXOSE

BIPHOSPHATE BIPHOSPHATE

2 ATP2 ATP 2 ADP2 ADP

STEP II: LYSISSTEP II: LYSIS

• EachEach HEXOSE BIPHOSPHATE HEXOSE BIPHOSPHATE splits to form splits to form 2 2 molecules ofmolecules of TRIOSE PHOSPHATE . TRIOSE PHOSPHATE .

HEXOSE HEXOSE BIPHOSPHATE BIPHOSPHATE

2 molecules 2 molecules TRIOSE TRIOSE

PHOSPHATE PHOSPHATE

STEP III: OXIDATION of Triose phosphateSTEP III: OXIDATION of Triose phosphate

2 molecules of 2 molecules of TRIOSE TRIOSE

PHOSPHATE PHOSPHATE

3 CARBON 3 CARBON COMPOUND COMPOUND

carrying carrying 2PO2PO44

groups eachgroups each

2 NAD2 NAD++ 2 NADH + H2 NADH + H++

STEP IV: ATP formationSTEP IV: ATP formation

Two Two 3 3 CARBON CARBON

COMPOUND COMPOUND formedformed

2 PYRUVATE 2 PYRUVATE MOLECULESMOLECULES

4 ADP4 ADP 4 ATP4 ATP

Enzymes remove the 2 phosphate groups and provide them to ADP for ATP formation

STEP IV: ATP formationSTEP IV: ATP formation

STEPS INVOLVED IN GLYCOLSISSTEPS INVOLVED IN GLYCOLSIS

STEP III: OXIDATION of Triose phosphateSTEP III: OXIDATION of Triose phosphate

STEP II: LYSISSTEP II: LYSIS

STEP I: PHOSPHORYLATIONSTEP I: PHOSPHORYLATION

glucoseglucose

Hexose Hexose biphosphate (6c)biphosphate (6c)

2 triose phosphate 2 triose phosphate (3c) molecules(3c) molecules

2 pyruvate 2 pyruvate moleculesmolecules

2 ATP2 ATP

2 ADP2 ADP

2 INTERMEDIATE 2 INTERMEDIATE (3c) molecules(3c) molecules

4 ADP4 ADP

4 ATP4 ATP

2 NAD2 NAD++ 2 NADH + H2 NADH + H++

• The fate of Pyruvate is decided by the is decided by the availability of oxygen.availability of oxygen.

• This step occurs only if oxygen is not not available or is in short supply; ie . ANAEROBIC RESPIRATION

Each molecule of Each molecule of PYRUVATEPYRUVATE

Ethanol (2 C) Ethanol (2 C) COMPOUND COMPOUND

COCO22In plantsIn plants

In animalsIn animals

In animalsIn animals

LINK REACTION LINK REACTION

LINK REACTION

• Pyruvate passes from the cytosol to the inner passes from the cytosol to the inner mitochondrial matrix mitochondrial matrix by active transport

• This step occurs only if oxygen is available; ie . AEROBIC RESPIRATION

Each molecule Each molecule of of PYRUVATEPYRUVATE

2 CARBON 2 CARBON COMPOUND COMPOUND ACETYL CoAACETYL CoA

NADNAD++ NADH + HNADH + H++

COCO22 CoACoA

• DeCarboxylationDeCarboxylation and Oxidation Oxidation occur simultaneously hence the step is called Oxidative Oxidative decarboxylationdecarboxylation

• Pyruvate + CoA forms Acetyl CoAAcetyl CoA• CoA CoA comprises of [ adenine + ribose sugar + Pantothenic acid]comprises of [ adenine + ribose sugar + Pantothenic acid]

• CoA is a carrier for Acetyl group into the Krebs cycle.

NADNAD++ NADH + HNADH + H++

COCO22 CoACoA CoACoA

Link reaction Link reaction summarysummary

• The energy stored in NADH is used to generate The energy stored in NADH is used to generate a proton gradient across the inner membrane.a proton gradient across the inner membrane.

• The energy of the proton gradient is used to The energy of the proton gradient is used to make ATP (phosphorylate).make ATP (phosphorylate).

• Glucose on oxidation during glycolysis and Glucose on oxidation during glycolysis and Krebs cycle , the Co-enzymes NAD and FAD are Krebs cycle , the Co-enzymes NAD and FAD are reduced to reduced to NADH + H NADH + H++ & FADH + H & FADH + H++

Oxidation phosphorylationOxidation phosphorylation

• In the mitochondrial matrix electrons from In the mitochondrial matrix electrons from NADH are transferred to Co Q by NADH NADH are transferred to Co Q by NADH DEHYDROGENASE; energy is releasedDEHYDROGENASE; energy is released

• As a result the H+ ions ( protons) are As a result the H+ ions ( protons) are transferred to the inter membrane space.transferred to the inter membrane space.

• Co Q carries the electrons to cytochrome bc1 Co Q carries the electrons to cytochrome bc1 complex ; energy is releasedcomplex ; energy is released

• Electrons are carried forward from cytochrome Electrons are carried forward from cytochrome bc1 complex to cytochrome c ; energy is bc1 complex to cytochrome c ; energy is releasedreleased

• As a result the more and more H+ ions As a result the more and more H+ ions ( protons) are transferred to the inter ( protons) are transferred to the inter membrane space.membrane space.

• In the mitochondrial matrix electrons from In the mitochondrial matrix electrons from FADH are transferred to Co Q; energy is FADH are transferred to Co Q; energy is releasedreleased

• As a result the H+ ions ( protons) are As a result the H+ ions ( protons) are transferred to the inter membrane space.transferred to the inter membrane space.

• Co Q carries the electrons to cytochrome bc1 Co Q carries the electrons to cytochrome bc1 complex ; energy is releasedcomplex ; energy is released

• Electrons are carried forward from Cytochrome Electrons are carried forward from Cytochrome C to Cytochrome c oxidase; energy is releasedC to Cytochrome c oxidase; energy is released

• As a result the more and more H+ ions As a result the more and more H+ ions ( protons) are transferred to the inter ( protons) are transferred to the inter membrane space.membrane space.

Cytochrome c oxidase ultimately transfers Cytochrome c oxidase ultimately transfers electrons to Oxygen (terminal e acceptor) and electrons to Oxygen (terminal e acceptor) and water is formed as an end product. water is formed as an end product.

• Transfer of protons to the inter membrane Transfer of protons to the inter membrane space develops a proton motive force across the space develops a proton motive force across the membrane.membrane.

• Inner membrane is impermeable to protons so Inner membrane is impermeable to protons so protons can pass through into the matrix is only protons can pass through into the matrix is only through the ATP Synthase enzyme.through the ATP Synthase enzyme.

Energy derived from the movement of Energy derived from the movement of these protons back into the inner matrix these protons back into the inner matrix

is used to synthesize ATP from ADP is used to synthesize ATP from ADP This is oxidative phosphorylation.This is oxidative phosphorylation.

Respiration chemiosmosisRespiration chemiosmosis• Involves an electron transport chain in the membrane s of the

cristae• Energy is released when electrons are exchanged from 1 carrier

to another• Released energy is used to actively pump hydrogen ions into the

inter-membrane space• Hydrogen ions come from the matrix• H ions diffuse back into the matrix through the channels of ATP

synthase• ATP synthase catalyses the oxidative phosphorylation of ADP to

ATP

PHOTOSYNTHESISPHOTOSYNTHESIS 6CO2 + 12 H2O C6H12O6 + 6 H2O + 6 O2.• Draw and label the chloroplast as seen under the electron microscope• State that photosynthesis contains light dependent and light independent reactions.• Explain light dependent reactions.

Structure of ChloroplastStructure of Chloroplast• Chloroplast contains a double layered membrane• Like mitochondria it contains its own DNA (plasmid) and 70s

ribosomes.• Stroma- matrix similar to the cytosol of the cell ; it contains

enzymes and chemicals necessary for dark reaction , some lipid molecules and starch granules.

• Grana- contains stacked thylakoids – flat membranous sacs containing chlorophyll pigment in units called photosystems

• Membranes of the grana contain electron carriers and hold the pigment enzymes & provide a large surface area for light dependent reactions to occur.

The overall processThe overall process• The reactions on establishing bonds for the formation of

organic molecules.• 6CO2 + 12 H2O C6H12O6 + 6 H2O + 6 O2

• Photosynthesis is an anabolic process• Ocuurs in 2 steps LIGHT DEPENDENT STAGE LIGHT DEPENDENT STAGE ( occurs in the

GRANA) and LIGHT INDEPENDENT STAGELIGHT INDEPENDENT STAGE ( occurs in the STROMA)

The Light dependent reactions:The Light dependent reactions:• Light supplies energy for these reactions to occur• Pigments are arranged on the thylakoid membranes in a

PHOTOSYSTEM (chlorophyll a , accessory pigments and protein matrix and the reaction centre (chlorophyll a , primary electron acceptor and protein matrix)

• Photosystem 1 is effective at 700 nm • Photosystem II is effective at 680 nm.• They work together to bring about non cyclic electron

transfer.

The Light dependent reactions:The Light dependent reactions:• Light strikes the Photosystem II causing it to transfer e to

primary electron acceptor at the reaction centre.• Excited e travel down the ETC electron transport chain

(plastoquinone to cytochrome complex), electron loses energy at each exchange.

• Electrons are replaced by splitting water molecules, to produce elctrons, H+ and Oxygen atoms, this is photolysis of water.

• Electrons obtained are supplied 1 by 1 to the reaction centre.• Chemiosmosis occurs , H+ are pumped into the thylakoid

membrane

The Light dependent reactions:The Light dependent reactions:• The outflow of the H+ into the stroma via the ATP synthase

enzyme causes Phosphorylation --- ATP generation from ADP and PO4 –called NON CYCLIC PHOSPHORYLATION.

• Light strikes the Photosystem I causing it to transfer e to primary electron acceptor at the reaction centre.

• Excited e travel down the ETC electron transport chain (INVOLVING FERREDOXIN & NADP reductase which provides 2 electrons to NADP+ & reduces it to NADPH)

• NADPH & ATP are the final products of light reaction• oxygen which is a waste product is excreted .

Photosynthesis chemiosmosisPhotosynthesis chemiosmosis• Involves an electron transport chain in the membrane s of the

thylakoids• Energy is released when electrons are exchanged from 1 carrier

to another• Released energy is used to actively pump hydrogen ions into the

thylakoid space• Hydrogen ions come from the stroma• H ions diffuse back into the stroma through the channels of ATP

synthase• ATP synthase catalyses the oxidative phosphorylation of ADP to

ATP

Cyclic photophosphorylationCyclic photophosphorylation

• It requires photosystem Iphotosystem I, but not photosystem II. photosystem II. • Light-dependent electron transport occurs in the

thylakoid membranes, where electrons follow a cyclic pathway, returning to the photosystem I reaction center.

• The energy of this electron transport results in a H+ gradient formation, the energy source for ATP synthesis. ATP is formed from ADP and Pi, but NADP+ is not reduced.

LIGHT INDEPENDENT REACTIONSLIGHT INDEPENDENT REACTIONS• Occurs in the stroma• It involves Calvins cycle• Ribulose biphosphate (RuBP) (5c), binds to an incoming CO2 ---

Carbon fixing catalyzed by enzyme RuBP carboxylase,( rubisco) , thus forming an unstable 6C compound.

• It breaks down into 2 (3c) compounds – glycerate-3-phosphate.• glycerate-3-phosphate are acted upon by ATP & NADPH from the

light reactions to form 2 more compounds called TRIOSE PHOSPHATE (3c), this is reduction division.

• TP may go in 2 directions , some leave the cycle to become sugar phosphates that become CELLULOSE/STARCH; while most continue in the cycle to form RuBP.

• In order to regain RuBP from TP , the cycle uses ATP.