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

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

CofactorsCofactors are nonprotein enzyme helpers such as

mineralsCoenzymes 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)

Citric Acid Cycle(matrix)

ETC(inner membrane)

ETC(inner membrane)

Glycolysis

Fermentation• Occurs in plants and

animals• Occurs in cytosol• Keep glycolysis going• No oxygen needed• Creates alcohol [+ CO2] or

lactic acid

Respiration• 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)

O2 presentWithout O2

Types of Fermentation

Alcohol fermentation

• Pyruvate Ethanol + CO2

• Ex. bacteria, yeast• Used in brewing,

winemaking, baking

Lactic acid fermentation

• 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

Respiration(mitochondria)

Respiration(mitochondria)

Krebs cycle(citric acid cycle)Krebs cycle(citric acid cycle)

ENERGY

glycolysis(cytosol)

glycolysis(cytosol)

fermentationfermentation

ethanol + CO2(yeast, some bacteria)

ethanol + CO2(yeast, some bacteria)

anaerobic (without O2)

aerobic (with O2)

lactic acid(animals)

lactic acid(animals)

electron transport

chain

electron transport

chain

chemiosmosischemiosmosis

Oxidative Phosphorylation

Leaf cross sectionVein

Mesophyll

Stomata CO2 O2

Mesophyll cellChloroplast

5 µm

Outermembrane

Intermembranespace

Innermembrane

Thylakoidspace

Thylakoid

GranumStroma

1 µm

Sites of Photosynthesis

• 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“photo” “synthesis”

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

C3 C4 CAMC fixation & Calvin

togetherC fixation & Calvin in

different cellsC fixation & Calvin at different TIMES

Rubisco(normally fixes CO2)

PEP carboxylase fixes CO2

Organic acid

Mesophyll cellsMesophyll: 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