Cellular Respiration Overview: ATP Production and Energy Transfer

1. Chapter 4Cellular Respiration Anne Van & Cindy Wong

2. Cellular Respiration Overview • equation: C6H12+ 6O2 6CO2 + 6H2O + energy • the means by which cells extract energy stored in food + transfer that energy to molecules of ATP • this energy is instantly available for every cellular activity (ex. muscle contraction, moving cilia) • 2 types of cellular respiration: anaerobic (O2 not present) and aerobic (O2 present) • leads to glycolysis, then alcoholic fermentation or lactic acid fermentation (if O2 not present) • leads to glycolysis, then Citric Acid Cycle, ETC, oxidative phosphorylation (if O2 present)

3. ATP (Adenosine Triphosphate) • consists of adenosine (nucleotide of adenine + ribose) and 3 phosphates • unstable molecule as 3 phosphate groups are negatively charged/repel • when 1 phosphate group is removed from ATP by hydrolysis - results in more stable molecule ADP (adenosine diphosphate) • provides energy for all cell activity by transferring phosphates from ATP to another molecule

4. Glycolysis • 10 step process – breaks down 1 molecule of glucose into 2-3 molecules of pyruvate/pyruvic acid, releases 4 molecules of ATP • occurs in the cytoplasm + produces ATP without using oxygen • ATP produced by substrate level phosphorylation – direct enzymatic transfer of phosphate to ATP • enzyme that catalyzes 3rd step, phosphofructokinase (PFK) is an allosteric enzyme – inhibits glycolysis when cell contains enough ATP and doesn’t need any more

5. Anaerobic Respiration: Fermentation • an anaerobic catabolic process that consists of glycolysis + alcohol or lactic acid fermentation • originated millions of years ago when there was no free O2 in earth’s atmosphere • sole means by which anaerobic bacteria like botulinum release energy for food • 2 types of anaerobes: faculative – can tolerate the presence of O2 and obligate – cannot live in an environment that has O2 • can generate ATP during anaerobic respiration as long as there’s adequate supply of NAD+ to accept electrons • glycolysis would shut down if nothing converted NADH back to NAD+

6. Lactic Acid Fermentation Alcohol Fermentation • process by which certain cells convert pyruvate from glycolysis into ethyl alcohol and CO2 in the absence of O2 • NADH gets oxidized back to NAD+ • bread depends on yeast to ferment and produce CO2 – bread rises • beer, wine, liquor industries too • pyruvate from glycolysis is reduced to form lactic acid or lactate • NADH gets oxidized back to NAD+ • dairy industry uses this process to make cheese, yogurt • human skeletal muscles when blood can’t supply adequate O2 to muscles during strenuous exercise

7. Aerobic Respiration • highly efficient process, produces a lot of ATP when O2 is present • consists of an anaerobic phase (glycolysis) + an aerobic phase (2 parts - citric acid cycle, oxidative phosphorylation) Citric Acid Cycle • takes place in the matrix of mitochondria, requires pyruvate • completes the oxidation of glucose into O2 • turns twice for each glucose molecule that enters glycolysis • generates 1 ATP/turn by substrate level phosphorylation – most of the chemical energy is transferred to NAD+, FAD

8. Structure of Mitochondrion NAD+ and FAD are required for normal cell respiration carry protons/electrons from glycolysis and citric acid cycle to ETC • enclosed by double membrane, outer membrane is smooth and inner (cristae membrane) is folded – divides into the outer compartment and the matrix • Citric acid cycle happens in matrix • Electron transport chain happens in cristae membrane

9. Aerobic Respiration: The Electron Transport Chain • ETC is a proton pump in mitochondria that couples 2 reactions – exergonic and endergonic • uses energy released from exergonic flow of electrons to pump protons against a proton gradient • makes no ATP directly but sets the stage for ATP production during chemiosmosis • carries electrons delivered by NAD, FAD from glycolysis + citric acid cycle to O2 (final electron acceptor) • highly electronegative O2 acts to pull electrons through the ETC

10. Oxidative Phosphorylation and Chemiosmosis • how most energy is produced during cellular respiration • is the phosphorylation of ADP into ATP by oxidation of the carrier molecules, NADH and FADH2 • powered by redox reactions of the ETC and protons are pumped from matrix to outer compartment by the ETC • protons cannot diffuse through the cristae membrane – they can only flow down the gradient into matrix through ATP synthase channels • this is chemiosmosis – the key to ATP production – as protons flow through the channels, they generate energy to phosphorylate ADP into ATP

11. Overview of Cellular Respiration

12. Chapter 5Photosynthesis Anne Van & Cindy Wong

13. Photosynthesis Overview • process by which light energy is converted to chemical bond energy and carbon is fixed into organic compounds • equation: 6CO2 + 12H2O  C6H12O6 + 6H2O + 6O2 • 2 main processes – light dependent (uses light energy to directly produce ATP) and light independent reactions (consists of the Calvin Cycle which produces sugar)

14. Photosynthetic Pigments • absorb light energy and use it to provide energy to carry out photosynthesis • 2 major pigments in plants: chlorophylls and carotenoids • chlorophyll a, chlorophyll b – green and absorb wavelengths of light in red, blue, violet range • carotenoids – are yellow, orange, and red; absorb light in the blue, green, and violet range • also xanthophyll and phycobilins • antenna pigments – capture wavelengths other than those captured by chlorophyll a (examples: carotenoids, chlorophyll b, phycobilins)

15. The Chloroplast • contains photosynthetic pigments, along with enzymes, that carry out photosynthesis • grana - light dependent reactions • stroma – light independent reactions • grana has layers of membranes – thylakoids (site of photosystems I, II) • enclosed by double membrane

16. Photosystems (PS) • 2 photosystems – I, II • light harvesting complexes in thylakoid membranes of chloroplasts – few hundred in each thylakoid • each consists of a reaction center that has chlorophyll a and a region of several hundred antenna pigment molecules • named in order of their discovery not in order they work - PS II operates first, then PS I • PS I absorbs light best in 700 nm range, PS II absorbs light best in 680 nm range

17. Light-Dependent Reactions: Light Reactions • light is absorbed by the photosystems in the thylakoid membranes • electrons flow through electron transport chains • 2 possible routes of electron flow: noncyclic flow and cyclic photophosphorylation

18. Noncyclic Photophosphorylation • electrons enter two electron transport chains, ATP and NADPH are formed • process begins in PS II – energy is absorbed, electrons are captured by primary electron acceptor • photolysis - water gets split into two electrons, two protons (H+), and one O2 atom; and O2 molecule gets released • ETC – electrons pass along an ETC that ultimately leads to PS I; flow of electrons is exergonic and provides energy to produce ATP • chemiosmosis – ATP is formed as protons released from water are diffused down the gradient from the thylakoid space • NADP – becomes reduced to form NADPH • PS I – similar to PS II, but this electron transport chain contains ferrodoxin and ends with production of NADPH, not ATP

19. Cyclic Photophosphorylation • sole purpose is to produce ATP, not NADPH, and also no oxygen is released • when chloroplast run low on ATP periodically, cyclic photophosphorylation is carried out to replenish ATP levels • cyclic electron flow takes photoexcited electrons on a short circuit pathway • travel from PS II electron transport chain to PS I, to a primary electron acceptor, then back to cytochrome complex in electron transport chain of PS II

20. The Calvin Cycle • cyclic process that produces 3-carbon sugar, PGAL (phosphoglyceraldehyde) • carbon enters the stomates of a leaf in the form of CO2 and becomes fixed/incorporated into PGAL • carbon fixation is the process that occurs during the cycle • Calvin Cycle is a reduction reaction since carbon gains hydrogen • uses the products of the light reactions – ATP and NADPH • only occurs in the light

21. Overview of Photosynthesis

22. C-4 Photosynthesis • modification for dry environments • C-4 plants show modified anatomy + biological pathways that enable them to minimize excess water loss and sugar production • these plants thrive in hot/sunny places • examples: corn, sugar cane, crabgrass CAM Plants • CAM plants carry out a form of photosynthesis called crassulacean acid metabolism – another adaptation to dry environments • stomates are closed during the day and open at night • mesophyll cells store CO2 in organic compounds they synthesize at night

23. Example Questions

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