AP Bio Exam Review: Cell Energy (Respiration & Photosynthesis)

Catabolic pathways release energy by breaking down complex molecules into simpler compounds C6H12O6 +6O2 6H2O + 6CO2 +E Anabolic pathways consume energy to build complex molecules from simpler ones 6H20+6CO2 + E C6H12O6 +6O2

A cell does three main kinds of work: Mechanical Transport Chemical Concept 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work: Mechanical Transport Chemical To do work, cells manage energy resources by energy coupling, the use of an exergonic (energy releasing) process to drive an endergonic (energy absorbing) one

Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction An enzyme is a catalytic protein Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction

Substrate Specificity of Enzymes The reactant that an enzyme acts on is called the enzyme’s substrate The enzyme binds to its substrate, forming an enzyme-substrate complex The active site is the region on the enzyme where the substrate binds

Cofactors Enzyme Inhibitors Cofactors are nonprotein enzyme helpers such as minerals Coenzymes are organic cofactors such as vitamins Enzyme Inhibitors

Allosteric Regulation a protein’s function at one site is affected by binding of a regulatory molecule at another site Allosteric regulation may either inhibit or stimulate an enzyme’s activity

Feedback Inhibition In feedback inhibition, the end product of a metabolic pathway shuts down the pathway

Energy Harvest Energy is released as electrons “fall” from organic molecules to O2 Broken down into steps: Food  NADH  ETC  O2 Coenzyme NAD+ = electron acceptor NAD+ picks up 2e- and 2H+  NADH (stores E) NADH carries electrons to the electron transport chain (ETC) ETC: transfers e- to O2 to make H2O ; releases energy

Cellular Respiration

Mitochondrion Structure Citric Acid Cycle (matrix) ETC (inner membrane)

Glycolysis Without O2 O2 present Fermentation Respiration Occurs in plants and animals Occurs in cytosol Keep glycolysis going No oxygen needed Creates alcohol [+ CO2] or lactic acid Release E from breakdown of food with O2 Occurs in mitochondria O2 required (final electron acceptor) Produces CO2, H2O and up to 38 ATP (NADH, FADH2)

PURPOSE = NAD+ recycled for glycolysis Types of Fermentation Alcohol fermentation Lactic acid fermentation Pyruvate  Ethanol + CO2 Ex. bacteria, yeast Used in brewing, winemaking, baking Pyruvate  Lactate Ex. fungi, bacteria, human muscle cells Used to make cheese, yogurt, acetone, methanol Note: Lactate build-up does NOT causes muscle fatigue and pain (old idea) PURPOSE = NAD+ recycled for glycolysis

Various sources of fuel Carbohydrates, fats and proteins can ALL be used as fuel for cellular respiration Monomers enter glycolysis or citric acid cycle at different points

ENERGY glycolysis Respiration Krebs cycle fermentation ethanol + CO2 aerobic (with O2) anaerobic (without O2) glycolysis (cytosol) Respiration (mitochondria) substrate-level phosphorylation Krebs cycle (citric acid cycle) fermentation electron transport chain Oxidative Phosphorylation ethanol + CO2 (yeast, some bacteria) lactic acid (animals) chemiosmosis

Sites of Photosynthesis Leaf cross section Vein Mesophyll Stomata CO2 O2 Mesophyll cell Chloroplast 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid Granum Stroma 1 µm mesophyll: chloroplasts mainly found in these cells of leaf stomata: pores in leaf (CO2 enter/O2 exits) chlorophyll: green pigment in thylakoid membranes of chloroplasts

Photosynthesis = Light Reactions + Calvin Cycle

Light Reactions

Both respiration and photosynthesis use chemiosmosis to generate ATP

Calvin Cycle = produce 3C sugar (G3P)

Photorespiration: low carbon-fixation when stomata closed in hot, dry climate CAM C fixation & Calvin together C fixation & Calvin in different cells C fixation & Calvin at different TIMES Rubisco (normally fixes CO2) PEP carboxylase fixes CO2 Organic acid Mesophyll cells Mesophyll: fix CO2 Bundle Sheath: Calvin Cycle Night: fix CO2 in 4C acids Day: Calvin Cycle Ex. rice, wheat, soybeans Ex. sugarcane, grass Ex. cacti, pineapple, succulent

Comparison RESPIRATION PHOTOSYNTHESIS Plants + Animals Needs O2 and food Produces CO2, H2O and ATP, NADH Occurs in mitochondria membrane & matrix Oxidative phosphorylation Proton gradient across membrane Plants Needs CO2, H2O, sunlight Produces glucose, O2 and ATP, NADPH Occurs in chloroplast thylakoid membrane & stroma Photorespiration Proton gradient across membrane