Chapter 4Cellular Respiration

Anne Van & Cindy Wong

Cellular Respiration Overview equation: C6H12 + 6O2 6CO2 + 6H2O +

energy the means by which cells extract energy stored in

food + transfer that energy to molecules of ATP this energy is instantly available for every cellular

activity (ex. muscle contraction, moving cilia) 2 types of cellular respiration: anaerobic (O2 not

present) and aerobic (O2 present) leads to glycolysis, then alcoholic fermentation or

lactic acid fermentation (if O2 not present) leads to glycolysis, then Citric Acid Cycle, ETC,

oxidative phosphorylation (if O2 present)

ATP (Adenosine Triphosphate) consists of adenosine

(nucleotide of adenine + ribose) and 3 phosphates

unstable molecule as 3 phosphate groups are negatively charged/repel

when 1 phosphate group is removed from ATP by hydrolysis - results in more stable molecule ADP (adenosine diphosphate)

provides energy for all cell activity by transferring phosphates from ATP to another molecule

Glycolysis 10 step process – breaks down 1 molecule of

glucose into 2-3 molecules of pyruvate/pyruvic acid, releases 4 molecules of ATP

occurs in the cytoplasm + produces ATP without using oxygen

ATP produced by substrate level phosphorylation – direct enzymatic transfer of phosphate to ATP

enzyme that catalyzes 3rd step, phosphofructokinase (PFK) is an allosteric enzyme – inhibits glycolysis when cell contains enough ATP and doesn’t need any more

Anaerobic Respiration: Fermentation an anaerobic catabolic process that consists of

glycolysis + alcohol or lactic acid fermentation originated millions of years ago when there was no free

O2 in earth’s atmosphere sole means by which anaerobic bacteria like botulinum

release energy for food 2 types of anaerobes: faculative – can tolerate the

presence of O2 and obligate – cannot live in an environment that has O2

can generate ATP during anaerobic respiration as long as there’s adequate supply of NAD+ to accept electrons

glycolysis would shut down if nothing converted NADH back to NAD+

Alcohol Fermentation

process by which certain cells convert pyruvate from glycolysis into ethyl alcohol and CO2 in the absence of O2

NADH gets oxidized back to NAD+

bread depends on yeast to ferment and produce CO2 – bread rises beer, wine, liquor industries too

pyruvate from glycolysis is reduced to form lactic acid or lactate

NADH gets oxidized back to NAD+

dairy industry uses this process to make cheese, yogurt

human skeletal muscles when blood can’t supply adequate O2 to muscles during strenuous exercise

Lactic Acid Fermentation

Aerobic Respiration highly efficient process, produces a lot of ATP when O2 is present consists of an anaerobic phase (glycolysis) + an aerobic phase (2

parts - citric acid cycle, oxidative phosphorylation)

Citric Acid Cycle takes place in the matrix of

mitochondria, requires pyruvate

completes the oxidation of glucose into O2

turns twice for each glucose molecule that enters glycolysis

generates 1 ATP/turn by substrate level phosphorylation – most of the chemical energy is transferred to NAD+, FAD

Structure of Mitochondrion

enclosed by double membrane, outer membrane is smooth and inner (cristae membrane) is folded – divides into the outer compartment and the matrix

Citric acid cycle happens in matrix

Electron transport chain happens in cristae membrane

NAD+ and FAD are required for normal

cell respiration carry protons/electrons

from glycolysis and citric acid cycle to ETC

Aerobic Respiration: The Electron Transport Chain

ETC is a proton pump in mitochondria that couples 2 reactions – exergonic and endergonic

uses energy released from exergonic flow of electrons to pump protons against a proton gradient

makes no ATP directly but sets the stage for ATP production during chemiosmosis

carries electrons delivered by NAD, FAD from glycolysis + citric acid cycle to O2 (final electron acceptor)

highly electronegative O2 acts to pull electrons through the ETC

Oxidative Phosphorylation and Chemiosmosis

how most energy is produced during cellular respiration is the phosphorylation of ADP into ATP by oxidation of the

carrier molecules, NADH and FADH2 powered by redox reactions of the ETC and protons are

pumped from matrix to outer compartment by the ETC protons cannot diffuse through the cristae membrane –

they can only flow down the gradient into matrix through ATP synthase channels

this is chemiosmosis – the key to ATP production – as protons flow through the channels, they generate energy to phosphorylate ADP into ATP

Overview of Cellular Respiration

Chapter 5Photosynthesis Anne Van & Cindy Wong

Photosynthesis Overview process by which light energy is converted to

chemical bond energy and carbon is fixed into organic compounds

equation: 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 2 main processes – light dependent (uses light

energy to directly produce ATP) and light independent reactions (consists of the Calvin Cycle which produces sugar)

Photosynthetic Pigments absorb light energy and use it to provide energy to

carry out photosynthesis 2 major pigments in plants: chlorophylls and

carotenoids chlorophyll a, chlorophyll b – green and absorb

wavelengths of light in red, blue, violet range carotenoids – are yellow, orange, and red; absorb

light in the blue, green, and violet range also xanthophyll and phycobilins antenna pigments – capture wavelengths other

than those captured by chlorophyll a (examples: carotenoids, chlorophyll b, phycobilins)

The Chloroplast contains photosynthetic

pigments, along with enzymes, that carry out photosynthesis

grana - light dependent reactions

stroma – light independent reactions

grana has layers of membranes – thylakoids (site of photosystems I, II)

enclosed by double membrane

Photosystems (PS) 2 photosystems – I, II light harvesting complexes in thylakoid

membranes of chloroplasts – few hundred in each thylakoid

each consists of a reaction center that has chlorophyll a and a region of several hundred antenna pigment molecules

named in order of their discovery not in order they work - PS II operates first, then PS I

PS I absorbs light best in 700 nm range, PS II absorbs light best in 680 nm range

Light-Dependent Reactions: Light Reactions

light is absorbed by the photosystems in the thylakoid membranes

electrons flow through electron transport chains

2 possible routes of electron flow: noncyclic flow and cyclic photophosphorylation

Noncyclic Photophosphorylation electrons enter two electron transport chains, ATP and NADPH

are formed process begins in PS II – energy is absorbed, electrons are

captured by primary electron acceptor photolysis - water gets split into two electrons, two protons

(H+), and one O2 atom; and O2 molecule gets released ETC – electrons pass along an ETC that ultimately leads to PS I;

flow of electrons is exergonic and provides energy to produce ATP

chemiosmosis – ATP is formed as protons released from water are diffused down the gradient from the thylakoid space

NADP – becomes reduced to form NADPH PS I – similar to PS II, but this electron transport chain contains

ferrodoxin and ends with production of NADPH, not ATP

Cyclic Photophosphorylation sole purpose is to produce ATP, not NADPH, and

also no oxygen is released when chloroplast run low on ATP periodically, cyclic

photophosphorylation is carried out to replenish ATP levels

cyclic electron flow takes photoexcited electrons on a short circuit pathway

travel from PS II electron transport chain to PS I, to a primary electron acceptor, then back to cytochrome complex in electron transport chain of PS II

The Calvin Cycle

cyclic process that produces 3-carbon sugar, PGAL (phosphoglyceraldehyde)

carbon enters the stomates of a leaf in the form of CO2 and becomes fixed/incorporated into PGAL

carbon fixation is the process that occurs during the cycle

Calvin Cycle is a reduction reaction since carbon gains hydrogen

uses the products of the light reactions – ATP and NADPH

only occurs in the light

Overview of Photosynthesis

C-4 Photosynthesis modification for dry environments C-4 plants show modified

anatomy + biological pathways that enable them to minimize excess water loss and sugar production

these plants thrive in hot/sunny places

examples: corn, sugar cane, crabgrass

CAM Plants CAM plants carry out a form of photosynthesis called

crassulacean acid metabolism – another adaptation to dry environments

stomates are closed during the day and open at night mesophyll cells store CO2 in organic compounds they

synthesize at night

Example Questions

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