Exam Critical Concepts Chapters 9 & 10 Cellular Energy

 Transforms energy stored in a carbon molecule to ATP  Redox reaction (oxidation-reduction): transfer of electrons  The transfer of electrons releases energy stored in organic molecules  Respiration: Occurs in the mitochondria

 Aerobic: requiring oxygen  Anaerobic: oxygen not required  Carbohydrates, fats, and proteins are all consumed as fuel  Cellular respiration equation: C 6 H 12 O O 2  6 CO H 2 O + Energy (ATP + heat)

 Redox reactions: chemical reactions that transfer electrons between reactants ◦ Two types: 1. Oxidation: substance loses electrons ◦ is oxidized 2. Reduction: substance gains electrons ◦ is reduced (the amount of positive charge is reduced)  Coenzyme: electrons from organic compounds are usually first transferred to NAD +

 NAD + and F AD ++ : oxidizing agents during cellular respiration ◦ Electron acceptors  NADH: the reduced form of NAD+ ◦ stored energy that is tapped to synthesize ATP ◦ passes the electrons to the electron transport chain  Electron transport chain: passes electrons in a series of steps instead of one explosive reaction ◦ O 2 pulls electrons down the chain in an energy- yielding tumble  The energy yielded is used to regenerate ATP

 Cellular respiration: ◦ the fuel (such as glucose) is oxidized ◦ O 2 is reduced: becomes oxidized becomes reduced

 Steps in cellular respiration: 1.Glycolysis: breaks down glucose into two molecules of pyruvate 2.Citric acid cycle: completes breakdown of glucose 3.Oxidative phosphorylation: accounts for most of the ATP synthesis

1. Glycolysis: “splitting of sugar” breaks down glucose into two molecules of pyruvate  Occurs in the cytoplasm Inputs Glycolysis Outputs 2 2 ATP NADH 2 Glucose Pyruvate

2. Citric acid cycle ( AKA : Krebs cycle )  Presence of O 2 : pyruvate enters the mitochondrion  Completes the energy-yielding oxidation of glucose  Takes place within the mitochondrial matrix  The cycle oxidizes organic fuel derived from pyruvate, generating: ◦ 1 ATP, 3 NADH, and 1 FADH 2 per turn  The NADH and FADH 2 produced relay electrons extracted from food to the electron transport chain

3. Oxidative phosphorylation:  Generates most of the ATP ◦ Powered by redox reactions  Accounts for almost 90% of the ATP generated by cellular respiration  Occur in the cristae of the mitochondrion  The carriers ( NAD + and FAD ++ ) alternate between reduced and oxidized states as they accept and donate electrons  Electrons drop in free energy as they go down the chain and are finally passed to O 2, forming H 2 O

 Oxidative phosphorylation: ◦ Electrons are transferred from NADH or FADH 2 to the electron transport chain ◦ Electrons are passed through a number of proteins including cytochromes to O 2 ◦ The electron transport chain generates no ATP ◦ The chain’s function is to break the large free- energy drop from food to O 2 into smaller steps that release energy in manageable amounts ◦ Electron transfer in the electron transport chain causes proteins to pump H + from the mitochondrial matrix to the intermembrane space

 Oxidative phosphorylation: ◦ H + then moves back across the membrane, passing through channels in ATP synthase ◦ ATP synthase uses the exergonic flow of H + to drive phosphorylation of ATP ◦ Chemiosmosis: the use of energy in a H + gradient to drive cellular work ◦ energy stored in a H + gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis ◦ The H + gradient is referred to as a proton-motive force, emphasizing its capacity to do work

 Fermentation: absence of O 2 ◦ glycolysis couples with fermentation or anaerobic respiration to produce ATP  Uses an electron transport chain with an electron acceptor other than O 2, for example sulfate  Fermentation uses phosphorylation instead of an electron transport chain to generate ATP  Two common types 1.Alcohol fermentation 2.Lactic acid fermentation

 Fermentation: Pyruvate is converted to ethanol in two steps, with the first releasing CO 2  1. Alcohol fermentation by yeast is used in brewing, winemaking, and baking  2. Lactic Acid Fermentation: Pyruvate is reduced to NADH ◦ lactate as an end product with no release of CO 2 ◦ some fungi and bacteria is used to make cheese and yogurt ◦ Human muscle to generate ATP when O 2 is scarce

 Fermentation vs. Aerobic respiration: ◦ Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate ◦ Different final electron acceptors:  An organic molecule such as pyruvate or acetaldehyde in fermentation  Cellular respiration produces 38 ATP per glucose molecule  Fermentation produces 2 ATP per glucose molecule

 Obligate anaerobes: carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2  Facultative anaerobes: can survive using either fermentation or cellular ◦ Yeast and many bacteria are meaning that they respiration  Facultative anaerobe: pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

Glucose Glycolysis Pyruvate CYTOSOL No O 2 present: Fermentation O 2 present: Aerobic cellular respiration MITOCHONDRION Acetyl CoA Ethanol or lactate Citric acid cycle  Pathways of Pyruvate: ◦ O 2 : cellular respiration ◦ Without O 2 : fermentation

 Photosynthesis: occurs in plants, algae, certain other autotrophic protists. ◦ feed themselves and most of the living world  Chloroplasts are the major locations of photosynthesis  Chlorophyll the green pigment within chloroplasts  Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast  Stomata: opening allowing CO 2 to enter and O 2 exits the leaf

 Photosynthesis equation: 6 CO H 2 O  C 6 H 12 O O H 2 O  Chloroplasts split H 2 O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules  Redox : H 2 O is oxidized and CO 2 is reduced  Photosynthesis occurs in two steps: 1.Light reaction 2.Calvin cycle

The light reaction (the photo part):  Split H 2 O and Releases O 2  In the thylakoids of chloroplast  Reduce NADP + to NADPH : electron carrier to power next step (dark reaction)  Photophosphorylation: Generate ATP from ADP  Photosystems: light energy absorbed here ◦ Two types: 1.Photosystem II 2.Photosystem I

 Photons: light particle captured by pigments  Absorption spectrum: light absorbed by pigments  Action spectrum: light energy “used” by pigments  Pigments: Substances that absorb light ◦ Chlorophyll a : main photosynthetic pigment ◦ Chlorophyll b: accessory pigments broaden the spectrum used for photosynthesis ◦ Carotenoids: accessory pigment absorbing excessive light that would damage chlorophyll

Calvin cycle (the synthesis part)  Also called dark reaction  Occurs in the stroma  Forms sugar from CO 2, using ATP and NADPH  Carbon fixation: incorporating CO 2 into organic molecules ◦ Makes bigger molecules (glucose) from smaller (carbon dioxide)  Like the citric acid cycle in cellular respiration regenerates its starting material after molecules entering and leaving the cycle

The Light and Dark Reactions