Chapter 4 Cellular Respiration Anne Van & Cindy Wong

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)

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

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

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+

Lactic Acid Fermentation Alcohol Fermentation Lactic Acid 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

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

Structure of Mitochondrion NAD+ and FAD 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 are required for normal cell respiration carry protons/electrons from glycolysis and citric acid cycle to ETC

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

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

Overview of Cellular Respiration

Chapter 5 Photosynthesis Anne Van & Cindy Wong

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)

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)

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

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

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

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

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

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

Overview of Photosynthesis

C-4 Photosynthesis CAM Plants 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

Example Questions

Thanks for Watching!