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AP Bio Exam Review:Cell Energy
(Respiration & Photosynthesis)
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• 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
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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
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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
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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
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CofactorsCofactors are nonprotein enzyme helpers such as
mineralsCoenzymes are organic cofactors such as vitamins
Enzyme Inhibitors
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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
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Feedback Inhibition
• In feedback inhibition, the end product of a metabolic pathway shuts down the pathway
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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
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Cellular Respiration
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Mitochondrion Structure
Citric Acid Cycle(matrix)
Citric Acid Cycle(matrix)
ETC(inner membrane)
ETC(inner membrane)
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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
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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
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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
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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
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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
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Photosynthesis = Light Reactions + Calvin Cycle“photo” “synthesis”
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Light Reactions
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Both respiration and photosynthesis use chemiosmosis to generate ATP
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Calvin Cycle = produce 3C sugar (G3P)
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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
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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