Topics 5-6

• Aerobic respiration is a combustion reaction

• It’s a series of coupled REDOX reactions

• Transfers some of the released energy (ATP, NADH,H2O)

• Non-polar covalent bonds in the reactants are broken

• Polar covalent bonds in the products are formed

• Bonding between carbon atoms in glucose move farther away from the C nuclei in CO2 glucose is oxidized

• Bonding between oxygen atoms in O2 have moved closer to the O nuclei in H2O

Electron carrier coenzymes

• Bio redox reactions generate reduction potential (the potential to reduce something else) that is stored in electron carriers

• We can think of reduced electron carriers as energy transport molecules that move e- from 1 reaction to another

• Green part is the only step that requires oxygen

Glycolysis

• Partial oxidation of glucose

• 10 connected redox reactions

• Each step requires an enzymes

• Occurs in the cytosol

• Glucose (6c) chopped in half is 2 pyruvate (3c)

• Gonna consume 2 ATP to release 2 ADP+Pi

• 2NAD+turns into 2NADH

• 4 ADP turns into 4 ATP

• Net 2 ATP/glucose

• Still has lots of Ep

• An enzyme catalyzes the transfer of PO4 from a phosphorylated substrate to ADP to generate ATP and an unphosphorylated product

• Glycolysis is partial glucose oxidation

• Not much ATP has been made; a lot of Ep is in the pyruvate

• The cell needs to remove pyruvate; must remove final product to keep glycolysis going

• We need to restore NAD+; better to oxidize NADH than to generate new NAD+

• Fermentation is the anaerobic reduction of pyruvate 

• Following glycolysis there is a branch, depends on oxygen; +O2=oxidize pyruvate, -O2=reduce pyruvate

• Pyruvate is reduced in fermentation

• Wants to remove pyruvate so glycolysis can continue, then it can oxidize NADH

• Big difference bt lactate and alcoholic fermentation is a decarboxylation reaction

• Fermentation allows glycolysis to continue without oxygen

• Cytosol is outside mitochondrion

• 2 bilayers (outer membrane, inter membrane space, inner membran

• Full lipid bilayers

• Matrix is inside both membranes

Cytosol [pyruvate] increase

Om        uses transport protein to cross into IMS

IMS       [pyruvate] low

IM          uses another transport protein

Matrix    [pyruvate] increase

Relative to intermembrane space

How might the cell accomplish this? (topic 4)

• Most forgotten step (pyruvate oxidation) bridge reaction

• Pyruvate converts to Acetyl-CoA

• Enzymes involved carry out a decarboxyl reaction

• NAD+ reduced to NADH

• Add coenzyme A 

Citric Acid (krebs) cycle

• Finishes the oxidation of glucose

• 8 connected (5 coupled) reactions

• Oxidize acetyl to CO2

• Each step has a unique enzyme

• Acetyl-CoA (2C) oxaloacetate (4C)  citrate (6C)

• First reactants is also final products

• Release 2 carboxyl groups, 3NADH, FADH2, ATP

• By substrate-level P

• Not just for glucose

• Amino acids, Nucleic acids, Lipids, Other monosaccharides

Protein complexes of the ETC

• 4 complexes

• Associated with IM

• 3 are integral 1 is peripheral (complex 2 is on the matrix side)

• The ETC moves e- through many redox reactions

• Electron flow is a redox reaction

• Complex 1 uses high E electrons 

• O2 is the final electron acceptor and all the energy from the electrons has been used up

• Moves Hydrogen from the matrix into IMS

• Protons form an electrochemical gradient across the inner membrane

• pH=5 IMS pH=7 Matrix

Complexes 1 and 2

• NADH is in the matrix donates e- (reduces) complex 1

• H+ are pumped from matrix into the IMS by complex 1

• FADH2 in matrix donates e-  to complex  2

• Ubiquinone (UQ) is a hydrophobic electron taxi

• Taxis e- from C1 to complex 3 

• Taxis e- from C2 to complex 3

• When reduced, UQ takes H+ from the matrix and releases the H+ in the IMS when oxidized at C3

Complex 3, Cytochrome c and complex 4 

• the e- from UQ flow through C3 to cytochrome c (cytc)

• Cytc is a hydrophilic electron taxi (exist on inner membrane side) that moves e- to C4

• E- flow through c4 and c 4 pump H+ from matrix to the IMS

• C4 reduces O2 to H2O consumes H+ from the matrix

• [H+] is lower in the matrix when they are moved across the membrane or used th reduce O2

• The H+ electrochemical gradient is called Proton Motive Force

• Proton Motive Force is used for chemiosmosis

• Using the Ep of PMF to power ATP synthase 

• As H+ move through ATP synthase, the energy released is used to make ATP

• Oxidative phosphorylation is the whole thing together

• ATP synthase

• F0 The channel part! Allows H+ to move to the matrix

• F1 The catalyst! Adds pi to ADP to make ATP

• Exergonic and spontaneous has free energy of -5 kJ/mol

ATP yields

• Total ATP made in aerobic respiration is about 32 ATP, can be as high as 38 ATP

• Chemiosmosis makes a lot of ATP

• Why? The model studied, PMF is used for other things, NADH and FADH2 are used for other things

Metabolic Integration

• If you dont need ATP glucose can be stored as a polymer, animals use glycogen (medium storage) plants use starch

• Triglycerides can be generated for even longer term storage

• These processes can be reverse

• Organisms need carbons for macromolecules

• Amino acids, nucleic acids and lipids

• Acetyl groups can polymerize into fatty acids = triglycerides 

Aerobic Respiration- prokaryotes

• Do not have membrane bound organelles (No mitochondria)

• All metabolism occurs in the cytosol

Anaerobic respiration and chemolithotrophy

• Oxygen is not a final electron acceptor

Phototrophic

• Polar covalent bond in the reactants are broken

• Non polar covalent bonds in the products are formed

• Bonding electrons between the carbon and oxygen in carbon dioxide have moved closer to the C atoms which become reduces

• Bonding electrons between the oxygen and hydrogen in H2O have moved farther away from the O atoms which become oxidized

Chloroplast

• Tripe membrane organelle

• Outer membrane, IMS, inner membrane

• Stroma and thylakoid membrane inside inner membrane 

• Notice the massive amount of surface area

• Thylakoid space (lumen)

Photosynthetic Processes

• Light reactions are dependent on light

• Calvin cycle (light independent reactions)

The electromagnetic spectrum

• Numbers of wavelength are associated with frequency

• Light is a particle-photon

• Every photon has an associated wavelength

• Short wavelengths have lots of energy

• Photons can be reflected, transmitted, or absorbed

• Photons absorbed by electrons which gain energy associated with the photon

Pigment

• Molecules efficient in absorbing photons

• Their chemical structure allows their valence electrons to absorb photons

• Pigments absorb photons of specific wavelength

• The wavelength must match the energy needed to raise the electron to a higher energy level

• If it is not exact…nothing will happen

• Blue e- raise 2 shells lots energy

• Red e- raise 1 shell low energy

• Green cant be absorbed

• Electron drops to ground state and energy is released

• Transfer the energy

• Lose an energized e-

Photosynthetic Pigments

Carbon Fixation

• The step where CO2 is added to RuBP molecule

Photosystem 2

-

Photosystem 1

• Produces NADPH

• Notice energy from light exciting P700

• P700* reduces a primary electron acceptor which passes e- to ferredoxin

• Ferredoxin is hydrophilic e- taxi that reduces NADP+ reductase

• NADP+ reductase will reduce NADP+ TO NADPH which forms in stroma

• P700+ replaces e- from plastocyanin

The force is strong

• H+ released in thylakoid lumen when H2O is oxidized

• Protons moved from stroma to lumen by PQ

• H+ “used” in stroma to reduce NADP+ to NADPH

• pH of stroma = 8 pH of lumen = 5

Photophosphorylation

• Using solar energy to generate PMF to power ATP synthase 

• ATP is generated on the stroma side of the membrane

• It takes a lot of energy to oxidize water and reduce NADP+

• Takes 2 photosystems 

• P680* is high energy but not enough to reduce NADP+

• By the time they reach P700, they use almost all the energy

• But P700 has a higher energy state than P680 so it allows us to reduce NADP+

Calvin Cycle

• Occurs in the stroma

• Uses all the ATP+NADPH formed in light dependant reaction

• RuBP→3-PGA

• Carboxylation adds CO2 to RuBP to form 3-PGA

• Reduction of 3-PGA→G3P 

• Nadph goes in and nadp+ comes out

• Atp becomes adp

• Regeneration of RuBP from G3P

• Occasionally G3P leaves

CYCLIC ELECTRON TRANSPORT

• Calvin cycle requires more ATP than NADPH

• Ferredoxin will reduce to PQ

• Energy will be used for PMF

G3P is the product of Photosynthesis

• G3P formed in the calvin cycle is converted to glucose:

G3P(3C)+G3P(3C) → glucose(6C)

• Used in glycolysis to fuel aerobic respiration

• Linked into polymers of starch (storage) or cellulose(cell walls)

• Used to generate amino acids nucleotides and lipids

Oxygenic Photosynthesis(prokaryotes)

• All metabolism occurs in the cytosol and on the cell membrane

• They have PS2,PS1 and calvin cycle

• Responsible for making the earth aerobic

Anoxygenic Photosynthesis

• Only known to occur in prokaryotes

• Only use cyclic electron flow

• Doesn’t split water

• Does not split O2

Look at the similarities and differences between photosynthesis and cellular respiration