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Chapter 4 Cellular Respiration Anne Van & Cindy Wong.

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1 Chapter 4 Cellular Respiration Anne Van & Cindy Wong

2 Cellular Respiration Overview  equation: C 6 H 12 + 6O 2  6CO 2 + 6H 2 O + 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 (O 2 not present) and aerobic (O 2 present)  leads to glycolysis, then alcoholic fermentation or lactic acid fermentation (if O 2 not present)  leads to glycolysis, then Citric Acid Cycle, ETC, oxidative phosphorylation (if O 2 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 3 rd 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 O 2 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 O 2 and obligate – cannot live in an environment that has O 2  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 Alcohol Fermentation  process by which certain cells convert pyruvate from glycolysis into ethyl alcohol and CO 2 in the absence of O 2  NADH gets oxidized back to NAD +  bread depends on yeast to ferment and produce CO 2 – 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 O 2 to muscles during strenuous exercise Lactic Acid Fermentation

7 Aerobic Respiration  highly efficient process, produces a lot of ATP when O 2 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 O 2  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  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 NAD + and FAD  are required for normal cell respiration  carry protons/electrons from glycolysis and citric acid cycle to ETC

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 O 2 (final electron acceptor)  highly electronegative O 2 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 FADH 2  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 5 Photosynthesis 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: 6CO 2 + 12H 2 O  C 6 H 12 O 6 + 6H 2 O + 6O 2  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 O 2 atom; and O 2 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 CO 2 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 CO 2 in organic compounds they synthesize at night

23 Example Questions

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