Chapter 6 Cellular Energetics AP Biology Exam Review

Chapter 6: Cellular Energetics AP Biology Exam Review

• Catabolic pathways release energy by breaking down complex molecules into simpler compounds • C 6 H 12 O 6 +6 O 2 6 H 2 O + 6 CO 2 +E • Anabolic pathways consume energy to build complex molecules from simpler ones • 6 H 20+6 CO 2 + E C 6 H 12 O 6 +6 O 2

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 enzymesubstrate complex • The active site is the region on the enzyme where the substrate binds

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 O 2 • Broken down into steps: Food NADH ETC O 2 – Coenzyme NAD+ = electron acceptor – NAD+ picks up 2 e- and 2 H+ NADH (stores E) – NADH carries electrons to the electron transport chain (ETC) – ETC: transfers e- to O 2 to make H 2 O ; releases energy

Cellular Respiration

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

Without O 2 Glycolysis Fermentation • • • Occurs in plants and animals Occurs in cytosol Keep glycolysis going No oxygen needed Creates alcohol [+ CO 2] or lactic acid O 2 present Respiration • Release E from breakdown of food with O 2 • Occurs in mitochondria • O 2 required (final electron acceptor) • Produces CO 2, H 2 O and up to 38 ATP (NADH, FADH 2)

Types of Fermentation Alcohol fermentation Lactic acid fermentation • Pyruvate Ethanol + CO 2 • 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 aerobic (with O 2) glycolysis anaerobic (without O 2) (cytosol) Respiration (mitochondria) Krebs cycle (citric acid cycle) electron transport chain chemiosmosis substrate-level phosphorylation fermentation Oxidative Phosphorylation ethanol + CO 2 (yeast, some bacteria) lactic acid (animals)

Leaf cross section Sites of Photosynthesis Vein Mesophyll • mesophyll: chloroplasts mainly found in these cells of leaf • stomata: pores in leaf (CO 2 enter/O 2 exits) • chlorophyll: green pigment in thylakoid membranes of chloroplasts Stomata Chloroplast CO 2 Mesophyll cell 5 µm Thylakoid Stroma Granum space Outer membrane Intermembrane space Inner membrane 1 µm

Photosynthesis = Light Reactions + Calvin Cycle “photo” “synthesis”

Light Reactions

Both respiration and photosynthesis use chemiosmosis to generate ATP

Calvin Cycle = produce 3 C sugar (G 3 P)

Photorespiration: low carbon-fixation when stomata closed in hot, dry climate C 3 C 4 CAM C fixation & Calvin in C fixation & Calvin at together different cells different TIMES Rubisco PEP carboxylase Organic acid (normally fixes CO 2) fixes CO 2 Mesophyll cells Mesophyll: fix CO 2 Bundle Sheath: Calvin Cycle Night: fix CO 2 in 4 C acids Day: Calvin Cycle Ex. rice, wheat, soybeans Ex. sugarcane, grass Ex. cacti, pineapple, succulent

Comparison RESPIRATION • Plants + Animals • Needs O 2 and food • Produces CO 2, H 2 O and ATP, NADH • Occurs in mitochondria membrane & matrix • Oxidative phosphorylation • Proton gradient across membrane PHOTOSYNTHESIS • Plants • Needs CO 2, H 2 O, sunlight • Produces glucose, O 2 and ATP, NADPH • Occurs in chloroplast thylakoid membrane & stroma • Photorespiration • Proton gradient across membrane