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Chapter 7: Energy and Metabolism Biological Work

o Energy: capacity to do work Express energy in kilojoules (units of work) Express energy in kilocalories (units of heat energy; thermal energy going from high temp. to low temp.) 1 kcal = 4.184 kJ

o Kinetic energy: energy of motiono Potential energy: capacity to do work as a result of position or stateo Chemical energy: potential energy stored in chemical bondso Mechanical energy: performs work by moving matter

The Laws of Thermodynamicso Thermodynamics: study of energy and its transformationso Closed system: does not exchange energy with its surroundings

o Open system: exchanges energy with its surroundings (ie: biological systems)o First law of thermodynamics: energy cannot be created or destroyed

Organisms must capture energy from the environment and transform it to a form that can be used for biological worko Second law of thermodynamics: when energy is converted from one form to another, some is converted into heat that disperses

into surroundingso Heat: kinetic energy of randomly moving particles

Total amount of energy that is available to do workis decreasing over timeo Entropy (S): measure of disorganized energy (unusable energy)

Total entropy always increases over time Energy and Metabolism

o Metabolism: sum of all the chemical activities taking place in an organism Anabolism: various pathway sin which complex molecules are synthesized from simpler substances Catabolism: pathways in which larger molecules are broken down into smaller ones

o Bond energy: energy required to break that bondo Enthalpy (H): total potential energy of the system (total energy of a system)o Free energy (G): amount of energy available to do work under the conditions of a biochemical reaction (usable energy)

H=G+TS [enthalpy = free energy + absolute temperature of system (K) * entropy]

As entropy increases, amount of free energy decreases: G=H-TS As temperature increases, increase in entropy

o Exergonic reaction: releases energy and is spontaneous or a downhill reaction from high to low G (G i>Gf) so G is (-)

Free energy decreases during an exergonic reaction. Free energy increases during an endergonic reaction

o Endergonic reaction: gain of free energy (Gireaction is endergonic reaction thus G is (+), is not spontaneous, does not take place w/o energy source Reactant>product is exergonic reaction thus G is (-), is spontaneous

ATP, the Energy Currency of the Cello Adenosine triphosphate (ATP): holds readily available energy for very short periods; cells energy source like cash

Nucleotide consisting of: adenine (nitrogen-containing organic base), ribose (5 C sugar), 3 phosphate (PO 4) groupso ATP donates energy through transfer of phosphate group

Adenosine diphosphate (ADP): left when terminal phosphate is removed from ATP

Inorganic phosphate (Pi): if phosphate group is not transferred to another molecule

Exergonic reaction with a large -G Phosphorylation reaction: phosphate group is transferred to some other compound

o Adding phosphate group to AMP creates ADP and adding phosphate to ADP creates ATP

o ATP is link between exergonic reaction which is component of catabolic pathwayso ATP is link between endergonic reaction which is component of anabolic pathways

o Cell maintains ration of ATP to ADP far from equilibrium point, typically 10 ATP per ADP Makes hydrolysis reaction more strongly exergonic and more able to drive endergonic reactions to which it is coupled

Energy Transfer in Redox Reactionso Redox reaction: every oxidation reaction is accompanied by reduction reaction (OIL RIG)

Oxidation reaction: substance loses electrons Reduction reaction: substance gains electrons Substance that becomes oxidized gives up energy as it releases electrons Substance that becomes reduced receives energy as it gains electrons Redox reactions usually involve transfer of hydrogen atom rather than just an electron

o When an electron is removed from organic compound, takes some energy stored in chemical bond that it was a part of. Thatelectron along with its energy is transferred to an acceptor molecule

o Electron progressively loses free energy as it is transferred from one acceptor to another

o Nicotinamide adenine dinucleotide (NAD+): frequently encountered acceptor molecules; when reduced it temporarily stores large

amounts of free energy

NADH is produced when NAD+ + H2 thus NAD+ is oxidized and NADH is reduced


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o Nicotinamide adenine dinucleotide phosphate (NADP+): hydrogen acceptor that is chemically similar to NAD+ but has extra PO4

NADPH: reduced form of NADP+; not involved in ATP synthesis; used to provide energy for certain reactionso Flavin adenine dinucleotide (FAD): nucleotide that accepts hydrogen atoms and their electrons

FADH2: reduced form of FAD

o Cytochromes: proteins that contain iron; iron component accepts e - from H atoms and then transfers e- to other compound

o NAD+, NADP+, FAD, cytochromes are electron transfer agents

Exists in reduced state which has more free energy or oxidized state which has less free energy Enzymes

o Enzymes: biological catalysts that increase the speed of chemical reactions without being consumed by the reaction

Catalase: highest catalytic rate; protects cells by destroying hydrogen peroxide (H2O2)

o Energy of activation (EA) or activation energy: energy required to break existing bonds and begin reactiono Enzyme lowers activation energy thus allowing the reaction to proceed faster

Enzyme has no effect on overall free-energy changeo Substrate: substance on which enzyme forms unstable intermediate complex witho Active site: region to which the substrate binds, to form enzyme-substrate complex (ES complex)

Grooves or cavities in enzyme formed by amino acid side chains; located close to surfaceo Induced fit: change in shape of enzyme from binding of substrate to enzymeo Shape of substrate changes slightly which distorts its chemical bonds facilitating breakage of old bonds and formation of new on

thus substrate is now a product which diffuses away from enzyme and enzyme is free to catalyze other reactionso Enzymes are specific in bonding to a certain shape or to a certain chemical bondo Cofactors of enzyme: separately two have no catalytic activity but together it allows the enzyme to function

Apoenzyme: protein component of enzyme Cofactor: chemical component that is either inorganic or organic

o Coenzyme: organic, nonpolypeptide compound that binds to apoenzyme and serves as cofactor; transfers e -

o Coenzyme A: involved in transfer of groups derived from organic acids

o Enzymes work best under certain optimal conditions: temperature, pH, ion concentration; any deviation from optimal conditionadversely affects enzyme activity

Temperature: 35C-40C; as T increases, molecular collisions inc.; high T denatures enzymes so unable to metabolize pH: 6 8; when very acidic or basic, most enzymes become inactive and irreversibly denatured

o Metabolic pathway: series of chemical reactions in which product of one reaction becomes substrate of next reactiono If pH and T are kept constant, concentration of substrate or enzyme affects rate of reaction

If excess of substrate present, enzyme concentration is rate-limiting factor; initial rate is proportional to enzyme conc. If enzyme conc. kept constant, rate of enzymatic reaction is proportional to substrate conc. Substrate conc. is rate limiting factor at lower concentrations, rate of reaction is proportional to substrate conc. At higher substrate conc. enzyme molecules are saturated with substrate (substrate bound to all available active sites of

enzyme molecules); increasing substrate conc. does not increase net reaction rateo Feedback inhibition: formation of product inhibits an earlier reaction in sequence

o Enzymatic control: in inactive form, active sites misshaped; factors influencing are pH, conc. of ions, addition of PO4 to AAo Allosteric site: receptor site other than active site; when substrate binds, active site changes, modifying enzymes activityo

Allosteric regulators: substances that affect enzyme activity by binding to allosteric sites; some keep enzyme inactiveo Reversible inhibition: when inhibitor forms weak chemical bonds with enzyme

Competitive inhibition: inhibitor competes with normal substrate for binding to active site Fits into active site temporarily, thus not allowing actual substrate to bind Increasing substrate concentration reverses competitive inhibition

Noncompetitive inhibition: inhibitor binds to allosteric site Inactivates enzyme by altering shape so active site cannot bind with substrate

Irreversible inhibition: inhibitor permanently inactivates or destroys an enzyme when the inhibitor combines with one ofenzymes functional groups, either at active site or allosteric site

Chapter 8: How Cells Make ATP: Energy-Releasing Pathways Redox Reactions

o Aerobic respiration: form of cellular respiration requiring molecular oxygen (O2)

Nutrients are catabolized to CO2 and H2O Used to obtain energy from glucose

Glucose becomes oxidized and oxygen becomes reduced

C 6H12O6 + 6 O2 + 6 H2O ( 6 CO2 + 12 H2O + energy (in chemical bonds of ATP) [oxidation and reduction] The Four Stages of Aerobic Respiration

o Glycolysis (takes place in cytosol) Six carbon glucose molecule is converted to two three carbon molecules of pyruvate C6H12O6 + 2 ATP + 2 ADP + 2 Pi + 2 NAD+ ( 2 pyruvate + 4 ATP + 2 NADH + H2O

o Formation of acetyl coenzyme A (takes place in mitochondria) Each pyruvate enters a mitochondrion and is oxidized to a two-carbon group (acetate) that combines with coenzyme A, form

acetyl conenzyme A

NADPH is produced, CO2 is released as waste product

2 pyruvate + 2 coenzyme A + 2 NAD+ 2 acetyl CoA + 2 CO2 + 2 NADHo The citric acid cycle (takes place in mitochondria)

Acetate group of acetyl coenzyme A combines with four carbon molecule (oxaloacetate) to form six carbon molecule (citrate

Citrate is recycled to oxaloacetate and CO2 is released as waste product. Energy captured as ATP and reduced NADH and

FADH2


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2 acetyl CoA + 6 NAD+ + 2 FAD + 2 ADP + 2 Pi + 2 H2O 4 CO2 + 6 NADH + 2 FADH2 + 2 ATP + 2 CoAo Electron transport and chemiosmosis (takes place in mitochondria)

Electrons removed from glucose during preceding stages are transferred from NADH and FADH2 to chain of electron acceptocompounds

As electrons are passed from one electron acceptor to another, some of energy is used to transport hydrogen ions across innmitochondrial membrane forming proton gradient

In process known as chemiosmosis, energy of proton gradient used to produce ATP

NADH + 3 ADP + 3 P i + O2 NAD+ + 3 ATP + H2OFADH2 + 2 ADP + 2 Pi + O2 FAD+ + 2 ATP + H2O

o Types of reactions involved in aerobic respirations are:

Dehydrogenations: two hydrogen atoms are removed from substrate and transferred to NAD+ or FAD

Decarboxylations: part of carboxyl group (COOH) is removed from substrate as molecule of CO2 Preparation reactions: molecules undergo rearrangements and other changes that can undergo further dehydrogenation or

decarboxylationso Glycolysis: sugar splitting; sugar glucose is metabolized

Does not require oxygen and proceeds under aerobic or anaerobic conditions Some energy is captured, net yield of two ATP and two NADH molecules

Take place in cytosol where ADP, NAD+, Pi float freely and used as necessary Endergonic reaction requiring ATP is phase 1

Energy investment phase: broken down in 2 phosphorlyation reactions: PO4 is transferred from ATP to sugar Resulting sugar (fructose-1,6-biphosphate) is less stable and is broken enzymatically into two three carbon molecules:

dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (G3P)o Dihydroxyacetone phosphate is enzymatically converted to G2P so products are 2 G3P : 1 glucose

o Glucose + 2 ATP 2 G3P + 2 ADP

Exergonic reaction yielding ATP and NADH is phase 2 Energy capture phase: G3P converted to pyruvate

G3P oxidized by removal of 2 electrons, immediately combining with NAD+ (hydrogen carrier molecule)

o NAD+ (oxidized) + 2 H (from G3P) NADH (reduced) + H+

Substrate-level phosphorylation: ATP forms when PO4 is transferred to ADP from phosphorylated intermediate In EIP, two molecules of ATP consumed but in ECP four molecules of ATP produced; glycolysis yields net energy profit of two

ATPs per glucose

2 G3P + 2 NAD+ + 4 ADP 2 pyruvate + 2 NADH + 4 ATPo Acetyl coenzyme A (acetyl CoA): pyruvate molecules formed in glycolysis enter mitochondria, converting into this

Occur in cyosol of aerobic prokaryotes Oxidative decarboxylation: pyruvate undergoes this process

Carboxyl is removed as carbon dioxide, which diffuses out of cell

Remaining two carbon fragment becomes oxidized and NAD+ accepts electrons removed during oxidation Oxidized two carbon fragment, an acetyl group, becomes attached to coenzyme A, yielding acetyl

2 pyruvate + 2 NAD+ + 2 CoA 2 acetyl CoA + 2 NADH + 2 CO2o Four NADH molecules formed: 2 during glycolysis, 2 during formation of acetyl CoA from pyruvateo Citric acid cycle (tricarboxylic acid (TCA) cycle or Krebs cycle): takes place in mitochondria

Acetyl CoA transfers two carbon acetyl group to four carbon acceptor compound oxaloacetate forming citrate (six carboncompound) Oxaloacetate + acetyl CoA ( citrate + CoA

Citrate loses first then second carboxyl group as CO2 One ATP formed per acetyl group by substrate-level phosphorylation; energy is transferred as NAD+ forming NADH For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced Electrons are transferred to electron acceptor FAD, forming FADH2 Two molecules of CO2 and about eight H are removed, forming three NADH and one FADH2 Four carbon oxaloacetate has been regenerated and cycle continues

o Because two acetyl CoA are produced from each glucose, two cycles required per glucose; after two turns, original glucose has lall its carbons

o Citric acid cycle yields four CO2, six NADH, two FADH2, and two ATPs per glucose moleculeo Four molecules of ATP formed: two during glycolysis and two during citric acid cycleo Oxidative phosphorylation: electrons passed along series of exergonic redox reactions, energy is used for ATP (endergonic),

because ATP synthesis is coupled to redox reactions in electron transport chaino Electron transport chain: high energy electrons of hydrogen atoms are shuttled from one acceptor to another

Series of electron carriers embedded in inner mitochondrial membrane of eukaryotes and in plasma membrane of aerobicprokaryotes

Each acceptor molecule becomes reduced as it accepts electrons and oxidized as it gives it up Electrons start with high energy content and lose some along the way Complex I: NADH-ubiquinone oxidoreductase; accepts electrons from NADH produced in glycolysis, formation of acetyl CoA,

and citric acid cycle

Complex II: succinate-ubiqunone oxidoreuctase; accepts electrons from FADH2 produced in citric acid cycle Complex III: ubiquinone-cytochrome c oxidoreductase; product from I and II (reduced ubiquinone) is substrate; accepts

electrons from reduced ubiquinone and passes to cytochrome c Complex IV: cytochrome c oxidase; ccepts electrons from cytochrome c and uses electrons to reduce O and form water


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If no oxygen available to accept, then last cytochrome retains its electrons; each acceptor molecule in chain retains itselectrons (remains in reduced state), and entire chain is blocked all the way back to NADH

No additional ATP produced by electron transport chaino Chemiosmosis allows exergonic redox reactions to drive endergonic reaction in which ATP is produced by phosphorylating ADP

whereas in photosynthesis, ATP is produced by a comparable processo ATPs: 2 from glycolysis, 2 from citric acid cycle, 32 34 from electron transport and chemiosmosis = 36 38 ATPs

mostly through oxidative phosphorylation (electron transport chain and chemiosmosis)o Mitochondrial shuttle system

In liver, kidney, heart: transfers electrons from NADH through inner mitochondrial membrane to NAD+ to ETC In skeletal muscle, brain: accepted by ubiquinone

o Rate of aerobic respiration regulated by how much ADP and phosphate are available Energy Yield of Nutrients Other Than Glucose

o

Deamination: amino acids metabolized by amino group being first removedo -oxidation: fatty acids are converted to acetyl CoA in the mitochondrial matrix then enters CAC

Anaerobic Respiration and Fermentationo Anaerobic respiration: does not use oxygen as final electron acceptor

Electrons transferred from glucose to NADH then down ETC that is coupled to ATP synthesis by chemiosmosis but inorganicsubstance replaces O as terminal electron acceptor; end product is CO2, Pi, ATP

Nitrogen cycle: C6H12O6 + 12 KNO3 6 CO2 + 6 H2O + 12 KNO2 + energy (in chemical bonds of ATP) Fermentation: anaerobic pathway that does not involve ETC; only two ATPs are formed per glucose

o Facultative anaerobes: carry out aerobic respiration when oxygen is availableo Alcohol fermentation: carry out anaerobic respiration when oxygen is unavailable

Decarboxylate pyruvate, release CO2 and form two carbon compound acetaldehyde

C6H12O6 2 CO2 + 2 ethyl alcohol + energy (2 ATP)o Lactate fermentation: NADH transfer H to pyruvate reducing it to lactate

C6H12O6 2 lactate + energy (2 ATP)Chapter 9: Photosynthesis: Capturing Energy

Lighto Wavelength: distance from one wave peak to next

Violet has shortest wavelength and red has longesto Photons: small particles or packets of energy composing light

Energy of photon is inversely proportional to wavelength Short wavelength has more energy per photon than long wavelength light

o When molecule absorbs photon of light energy, two things may happen Atom may return to ground state (condition in which all electrons are in normal lowest energy levels) Energy at ground state dissipates as heat or emission of light (fluorescence) Or energized electron may leave atom and be accepted by electron acceptor molecule which becomes reduced

Chloroplastso Chlorophyll is confined to chloroplastso Chloroplasts are mainly in mesophyll (layer with many air spaces and high concentration of water vapor)o Interior of leaf exchanges gases with outside through stomata (microscopic pores)o Enclosed by outer and inner membraneso Inner membrane encloses stroma (fluid-filled region containing most of enzymes required to produce carbohydrate mol.o Thylakoids: suspended in stroma, forms interconnected set of flat, disclike sacs

Thylakoid lumen: fluid-filled interior space enclosed by thylakoid membrane Grana: stacks of thylakoid sacs

o Chlorophyll: main pigment of photosynthesis, absorbs light primarily in blue and red regions of visible spectrum Contains complex ring structure porphyrin ring (joined smaller rings composed of C and N; absorbs light energy) Or contains long hydrocarbon side chain that makes molecule nonpolar and anchors chlorophyll in membrane All chlorophyll molecules in thylakoid membrane are associated with specific chlorophyll-binding proteins

Chlorophyll a: pigment initiates light-dependent reactions of photosynthesis; contains methyl group (CH3) Chlorophyll b: accessory pigment that also participates in photosynthesis; contains carbonyl group (CHO) Carotenoids: yellow and orange accessory photosynthetic pigment absorbing different wavelengths of light

o Absorption spectrum: plot of absorption of light of different wavelengthso Action spectrum: graph of relative effectives of different wavelengths of light; rate v. wavelengtho

Chlorophyll in chloroplasts is responsible for photosynthesis Overview of Photsynthesis

o Cell uses light energy captured by chlorophyll to power synthesis of carbohydrates

6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6 H2Oo Reactions of photosynthesis divided into two phases:

Light-dependent reaction: photo part of photosynthesis in thylakoids Begin as chlorophyll captures light causing electrons to move to higher energy state then transferred to acceptor molec

and replace by electron from water then water splits and O is released Some energy used to phosphorylate ADP forming ATP

Coenzyme NADP+ is reduced forming NADPH Carbon fixation reaction: synthesis part of photosynthesis in stroma

ATP and NADPH from light-dependent reaction are used to transfer chemical energy

Carbon fixation: fix C from CO2 to existing skeletons of organic molecules; no direct requirement for light The Light-Dependent Reactions

o 12 H2O + 12 NADP+ + 18 ADP + 18 Pi 6 O2 + 12 NADPH + 18 ATP


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o Antenna complexes: arrangement of chlorophyll, accessory pigments, and pigment binding proteins into light gathering units inthylakoid Absorbs light and transfers to reaction center (consists of chlorophyll molecules and proteins)

o Light then converted to chemical energy in reaction centers by a series of electron transfer reactionso Two types of photosynthetic units

Photosystem I: consists of pair of chlorophyll a molecules with absorption peak at 700 nm and referred to as P700 Photosystem II: made up of pair of chlorophyll a molecules with absorption peak of 680 nm and referred to as P680

o When pigment molecule absorbs light energy, energy Is passed from one pigment to another with antenna complex until it reacreaction center. When reaches P700 or P680, electron is raised to higher energy level

o Noncyclic electron transport: in photosynthesis, linear flow of electrons, produced by photolysis of water, through photosystems

and II; results in formation of ATP (by chemiosmosis) NADPH, and O2

Pigment in antenna complex associated with photosystem I absorbs photon of light; energy is transferred from one pigment

molecule to another until reaches reaction center, where it excites an electron in a molecule of P700. Energized electron istransferred to primary electron acceptor then electron goes through electron transport chain until passed to ferredoxin (ironcontaining protein). Ferredoxin transfers electron to NADP+ in presence of enzyme ferredoxin-NADP+ reductase. When NADPaccepts two electrons, they unite with H+, thus reduced form is NADPH which is released into stroma. P700 becomes positivcharged when giving up electron to primary electron acceptor; missing electron is replaced by one donated by photosystem

Photosystem II is activated when pigment molecule in antenna complex absorbs photon of light energy. Energy is transferreto reaction center, where it causes electron in P680 to move to higher energy level. Energized electron is accepted by primaelectron acceptor and then passes along electron transport chain until donated to P700

Electron donated in ETC replaced by photolysis (light splitting) of water

P680 molecule giving up energized electron to primary electron acceptor is positively charged (P680+). P680+ is oxidizinagent pulling away O from water. Water broken into 2 electrons, 2 protons, 2 O. Each electron donated to P680 + whichthen loses positive charge; proteins are released into thylakoid lymen

Light splits water indirectly by causing P680 to become oxidized. NET provides continuous supply of replacements for energized electrons that were given up by P700

o Cyclic electron transport: only photosystem I is involved; simple light-dependent reaction

Energized electrons that originate from P700 at reaction center eventually return to P700o Photophosphorylation: synthesis of ATP is coupled to transport of electrons that have been energized by protons of light

o ATP synthase: thylakoid membrane is impermeable to H+ except through certain channels formed by enzyme

The Carbon Fixation Reactions

o Energy of ATP and NADPH is used in formation of organic molecules from CO2

o 12 NADPH + 18 ATP + 6 CO2 C6H12O6 + 12 NADP+ + 18 ADP + 18 P i + 6 H2Oo Occurs in stroma through Calvin Cycle in three phases:

CO2 uptake: single reaction in which molecule of CO2 reacts with ribulose biphosphate (RuBP; phosphorylated 5 C) Catalyzed by ribulose biphosphate carboxylase / oxygenase or rubisco Product is unstable, 6 C intermediate which immediately breaks down into 2 phosphoglycerate (PGA) with 3 C each

C that was originally part of CO2 is now part of carbon skeleton, carbon is fixed

Calvin cycle also known as C3 pathway because product of intial carbon fixation reaction is 3 C; plans is C 3 plants Carbon reduction: energy and reducing power from ATP and NADPH are used to convert PGA to G3P

Reaction of two G3P molecules is exergonic and leads to formation of glucose or fructose RuBP regeneration: series of 10 reactions

30 carbons are rearranged into six molecules of ribulose phosphate each of which becomes phosphorylated by ATP toproduce RuBP, five carbon compound with which cycle started

o Inputs required are six molecules of CO2, phosphates transferred from ATP, and electrons from NADPH

o Outputs are six carbons from CO2 are accounted for by harvest of hexose molecule; remaining G3P are used to synthesize RuBP

molecules with which more CO2 molecules may combine

o Photorespiration: occurs in presence of light, requires oxygen, produces CO2 and H2O but does not produce ATP and reduces

photosynthetic efficiency because it removes some of intermediates used in Calvin Cycle

o C4 plants first fix CO2 into four carbon compound, oxaloacetate; step precedes Calvin Cycleo CAM plants initially fix carbon at night through formation of oxaloacetate; step precedes Calvin Cycle

o C4 pathway: CO2 is fixed through formation of oxaloacetate occurs before C3 pathway in different cells

Bundle sheath cells: encircle veins of leaf Pathway occurs in mesophyll cells whereas Calvin Cycle occurs in bundle sheath cells Has phosphoenolpyruvate (PEP) carboxylase enzyme that has an extremely high affinity thus binding effectively

Previous step formed oxaloacetate which is converted to malate which then passes onto chloroplasts within bundle sheath cwhere different enzyme catalyzes decarboxylation of malate to yield pyruvate and CO2

CO2 then combines with RuBP to go through Calvin Cycle. Pyruvate formed returns to mesophyll cello Crassulacean acid metabolism (CAM) pathway: plants living in dry conditions have a special carbon fixation pathway

Open stomata at night, admitting CO2, while minimizing water loss

Use enzyme PEP carboxylase to fix CO2 forming oxaloacetate which is converted to malate and stored in cell vacuoles

During day, stomata are closed and gas exchange cannot occur between plant and atmosphere, CO2 is removed from malatby decarboxylation reaction

Now CO2 is available within leaf tissue to be fixed into sugar by Calvin Cycle

o Important differences between CAM and C4 are:

C4 and C3 occur in different location within leaf of C4 plant


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CAM and C3 pathways occur at different times within same cell of CAM plant

C4 promotes rapid growth, CAM is successful adaptation to dry conditions (can survive in desert) Metabolic Diversity

o Photoautotrophs: land plants, algae, and certain prokaryotes Phototrophs: use light energy to make ATP and NADPH which temporarily hold chemical energy but are unstable and canno

stockpiled in cell

Autotrophs: chemical energy of ATP and NADPH then drives carbon fixation, anabolic pathway in which stable organicmolecules are synthesized from CO2 and water

o Chemoheterotrophs: animals, fungi, and most bacteria Chemotrophs: obtain energy from chemicals, typically redox reactions Heterotrophs: cannot fix carbon, use organic molecules produced by other organisms as building blocks from which they

synthesize the carbon compounds they needo Photoheterotrophs: able to use light energy but unable to carry out C fixation and must obtain C from organic compoundso Chemoautotrophs: obtain energy from oxidation of reduced inorganic molecules

Photosynthesis in Plants and in the Environmento By fixing carbon, photoautotrophs are ultimate source of all organic molecules used as energy and carbon sources

o Photolysis of water by photosystem II releases O2 that all aerobic organisms require for aerobic respiration

Chapter 10: Chromosomes, Mitosis, and Meiosis Eukaryotic Chromosomes

o Chromosomes: major carriers of genetic information in eukaryotes which lie within nucleus Chromatin: material consisting of DNA and associated proteins; makes up chromosomes

o Genome: numerous amount of genes in an organismo Histones: facilitates chromosome packaging; positive charge because high proportion of amino acids with basic side chains

Associates with DNA which has negative charge because of phosphate groups to form nucleosomes Nucleosome: beadlike structure with 146 base pairs of DNA wrapped around a disc-shaped core of 8 histone molecules Scaffolding proteins: nonhistone proteins that help maintain chromosome structure

o Condensin: group of proteins required for chromosome compaction; binds to DNA and wraps it into coiled loops that are compacinto a mitotic or meiotic chromosome

The Cell Cycle and Mitosiso Cell cycle: the stages through which a cell passes from one cell division to the nexto The cell cycle consists of two main phases, interphase and M phase.

M phase involves two main processes, mitosis and cytokinesis. Mitosis, a process involving the nucleus, ensures that each nreceives the same number and types of chromosomes as were present in the original nucleus. Cytokinesis, which generallybegins before mitosis is complete, is the division of the cell cytoplasm to form two cells.

Interphase: the time when no cell division is occurring. G1 phase growth and normal metabolism take place. Typically the longest phase. S phase DNA replicates and histone proteins are synthesized so that the cell can make duplicate copies of its

chromosomes. G2 phase increased protein synthesis

o Mitosis, the nuclear division that produces two nuclei containing chromosomes identical to the parental nucleus. Prophase: Chromosome compaction, when the long chromatin fibers begin a coiling process that makes them shorter and

thicker. The chromatin can then be distributed to the daughter cells with less likelihood of tangling. After compactin, the

chromatin is referred to as chromosomes. It is now apparent that each chromosome was duplicated and consists of a pair ofsister chromatids, which contain identical, double-stranded DNA sequences. Each chromatid includes a constricted regioncalled the centromere. Sister chromatids are physically linked by a ring-shaped protein complex called cohesin. Cohesionsextend along the length of the sister chromatid arms and are particularly concentrated at the centromere. Kinetochore, amultiprotein complex to which microtubules can bind. Animal cells have a pair of centrioles in the middle of each microtubuorganizing center. microtubules radiate from each pole forming the mitotic spindle, a structure that separates the duplicatechromosomes during anaphase.

Metaphase: all the cells chromosomes align at the cells metaphase plane. Each chromatid is completely condensed andappears thick and distinct.

Anaphase: sister chromatids separate. Once chromatids are no longer attached to their duplicates, each chromatid is called chromosome. The now-separated chromosomes move to opposite poles, using the spindle mircrotubules as tracks.

Telophase: chromosomes decondense by partially uncoiling. A new nuclear envelope forms around each set of chromosomeSpindle microtubules disappear and the nucleoli reorganize.

Cytokinesis, the division of the cytoplasm to yield two daughter cells. In animal cells, an actomyosin contractile ring attachethe PM encircles the cell and contracts, producing a cleavage furrow that gradually deepens and eventually separates the

cytoplasm into two daughter cells, each with a complete nucleus. In plant cells, cytokinesis occurs by forming a cell plate asline of vesicles originating in the Golgi complex. The vesicles contain materials to construct both a primary cell wall for eachdaughter cell and a middle lamella that cements the primary cell walls together.

o Prokaryotes reproduce asexually, generally by binary fission, a process in which one cell divides into two offspring cells. Sexual Reproduction and Meiosis

o Asexual reproduction a single parent splits to produce two or more individuals.o In Sexual reproduction two haploid sex cells or gametes fuse to form a single diploid zygote.o A diploid cell has a characteristic number of chromosome pairs per cell. The members of each pair, called homologous

chromosomes, are similar in length, shape and other features and carry genes affecting the same kinds of attributes of theorganism. A haploid cell contains only one member of each homologous pair.

o A diploid cell undergoing meiosis completes two successive cell divisions, yielding four haploid cells. Sexual life cycles in eukaryorequire meiosis, which makes it possible for each gamete to contain only half the number of chromosomes in the parent cell.

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