Ch 9 cellular respiration

the sun, directly, or indirectly via plants photosynthesis

energy cells need to do work comes from…

cell res and photosynthesis cycle

photosynthesis produces O₂ and C₆H₁₂O₆ which is used in cell respiration, which has byproducts of CO₂ abd H₂O used by plants in photosynthesis

one way flow of energy

sun → plants → animals

→ energy lost as heat

• chemicals are recycled, energy is not

cellular respiration

process by which cells breakdown organic complex molecules into simpler ones with less energy in the presence of oxygen producing energy extracted from these molecules, harnessed and used to make ATP in a series of redox reactions or lost as heat

• exergonic reaction

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (used to make ATP)

• electrons passed to successively lower energy levels in a series of enzymatically controlled reactions: energy is released slowly so that more can be used/captured - conservation of energy

• → 12 stages/reactions within from start to finish

redox reactions

chemical reactions where there is a partial or complete loss/gain of electrons

→ oxidation and reduction

• electrons in a polar covalent bond have less chemical energy than those in a nonpolar covalent bond→ partial or complete loss

oxidation

partial or complete loss of electrons

reduction

partial or complete gain of electrons

electron carriers

used in cell res to transport the high energy electrons removed from organic molecules (food)

• coenzymes: NAD+, FAD+

dehydrogenases

enzymes that remove high energy electrons and hydrogens from organic molecules and transfer them to NAD+ and FAD+

electron transport chain

high energy electrons carried by the coenzymes are passed between electron carriers to lower and lower energy states (higher e-neg conditions) in a series of redox reactions and finally to oxygen

• as the electrons are passed down, the energy is slowly released and used to make ATP

glycolysis

first stage of cell res

• “glucose” “splitting”

• in cytoplasm

• occurs in presence or absence of oxygen

• glucose (C6) is broken down into 2 pyruvate (C3) molecules

• energy investment phase + energy yielding phase

in: glucose, NAD+, ATP, ADP

out: 2 pyruvates, 2 ATP, 2 NADH

starting molecules of glycolysis

glucose, NAD+, ADP, ATP

molecules produced in glycolysis

2 pyruvate, 2 ATP, 2 NADH

energy investment phase

1st phase of glycolysis

activates glucose molecules by using 2 ATP and transfers the phosphates using enzymes kinases

→ glucose (C6) becomes 2 pyruvate (C3) molecules

energy yielding phase

2nd phase of glycolysis

synthesizes the 2 pryuvate molecules by substrate level phosphorylation to produce 4 ATP (for a new gain of 2 ATP) and 2 NADH

• high energy electrons produced from breaking the bonds of the glucose molecule into pyruvates are carried to the electron transport chain via NADH

• a phosphate group is then removed from the pyruvates and added to an ADP to make ATP, 1 per pyruvate, 2 per glucose

substrate level phosphorylation

transfers a phosphate group from a pyruvate of glucose and attaches it to ADP, synthesizing ATP

transition reaction

2nd step of cell res

• only occursin presence of oxygen (aerobic)

• no ATP is made

• pyruvate continues process of being broken down for cellular res

  • transported into mitochondrial matrix by facilitated diffusion

  • carboxyl group is broken off and released as CO₂, the bond break becomes energy and molecules

  • high energy electrons from break are carried via NADH to the electron transport chain (final step)

  • converts what’s left of pyruvate (acetate) to Acetyl-CoA (adds coenzyme A) → 2 per glucose

in: 2 pyruvates, NAD+, coenzyme A

out: Acetyl CoA, NADH, CO₂

starting molecules in transition reaction

pyruvate/pyruvic acid

NAD+

coenzyme A

molecules produced in transition reaction

acetyl CoA (2/glucose), NADH, CO₂

Krebs cycle

3rd step of cell res

• completes breakdown of glucose in mitochondrial matrix, extracts most energy from glucose derivatives (Acetyl CoAs)

• aka citric acid cycle

• 2x cycles (1 per Acetyl CoA, 2 per glucose molecule)

• 8 reactions per cycle

• most energy still stored in electron carriers, lot’s of e- produced here (lots of reactions that release high energy electrons)

• 2 ATP produced

in: Acetyl CoA, NAD+, FAD+, ADP

out: NADH, FADH, ATP, CO₂

starting molecules in the Krebs cycle

2 acetyl CoAs, ADP, NAD+

molecules produced in the Krebs cycle

electron carriers NADH and FADH₂, CO₂, and 2 ATP

electron transport chain

4th step of cell res

• + chemiosmosis = oxidative phosphorylation

• makes most ATP

• coenzymes donate high energy electrons to chain of proteins along inner mitochondrial membrane

• electrons cascade down a series of electron carriers in redox reactions (electrons lose energy as they move through with each step)

• oxygen is the final electron acceptor - binds with H+ to make water → released

• energy released as protons (H ions) in inter membrane space → ATP by oxidatative phosphorylation and chemiosmosis

in: NADH, FADH₂ carrying high-energy electrons, ADP, O₂

out: high energy electrons, H₂O, H+ ions

chemiosmosis

second part of oxidative phosphorylation

• energy released by falling electrons is used to create a proton gradient of H+

• protons are pumped through proteins out of the matric into the intermembrane space creating a pH difference

• gradient has potential energy, unbalanced sides of the membrane creates pressure (proton motive force)

• H+ are released and diffuse back into the matrix through protein pump ATP synthase, embedded in inner mitochondrial membrane, right next to ETC

• ATP synthase uses the energy released as the gradient decreases through the pump to make ATP from ADP and phosphates

in: high energy electrons that produce a H+ proton gradient, ADP

out: ATP, heat

→ yields about 36-38 ATP molecules/glucose, rest is lost as heat

starting molecules of ETC

NADH + FADH₂ carrying high energy e, ADP, oxygen

molecules produced by ETC/chemiosmosis

32-34 ATP molecules, H₂O, NAD+, FAD+

efficiency of cellular respiration

• 36 or 38 ATP is only 40% of total energy in glucose molecule

• rest of energy is lost as heat

after ATP is made in the mitochondria

it is transported out of the matrix and is free to move throughout the cell

→ drive a multitude of reactions that cells need to stay alive and do their job

→ ADP produced from reactions will diffuse into the matrix and the whole process begins again

fermentation

process of converting the high energy electrons into lactic acid or alcohol that occurs if oxygen is not present for the NADH to be used in the electron transport chain

• anaerobic conditions = no oxygen

• regenerates the NAD+ and glycolysis can continue → 2 ATP, 2% efficiency

• → lactic acid build up in muscle is toxic → cramps when working out! b/c used up all the O₂s in cells

• ex:

  • lactic acid gives flavor to cheese, yogurt, sour cream

  • CO₂ released from yeast makes bread rise

  • ethyl alcohol released by yeast makes beer/wine

aerobic respiration

oxygen is present for NADH to carry electrons to ETC and successfully complete cell respiration (oxygen is needed to catch electrons and releases water)

anaerobic respiration

oxygen is not present for cell respiration (the ETC) to function properly and maximize the glucose’s energy → fermentation → production of lactic acid or alcohol instead

cell res is not just for glucose

• breakdown products of other macromolecules (proteins and lipids) can feed into pathway at many different points

• intermedieates in the pathway of respiration can be taken out of the process and used as building blocks for macromolecules

• this process of cellular respiration is connected to the metabolism of other macromolecules in the grand scheme of cellular metabolism

effects of toxins on ETC

• some pesticides block electron transport at first ETC protein carrier

• cyaniade and carbon monoxide block ETC protein in complex IV

• fungal antibiotic oligomycin blocks passage of protons through ATP synthase

• “uncouplers” cause mitocondrial memebrane to leak: diintrophenol used for weight loss drug in 1940s until death stopped its usage