Lecture Notes for Chapter 7 - 10

Chapter 7 Outline

Energy & Metabolism
1. Matter & Energy
A. Terms:
Matter is anything that has mass and takes up space.
Energy is the capacity to do work, which is any change in the state or motion of matter.
E=mc2 - Matter and energy are interchangable
B. Types of energy
Potential energy is the capacity to do work as a result of position or state.
Kinetic energy is the energy of motion.
Chemical energy is a type of potential energy - stored in chemical bonds, important to organisms.

2. Laws of Thermodynamics
A. The first law of thermodynamics:
Energy cannot be created or destroyed, although it can be transferred or converted from one form to another, including conversions between matter and energy.
Organisms cannot create energy–must capture it from the surroundings.
B. The second law of thermodynamics:
When energy is converted from one form to another, some usable energy–that is, energy available to do work–is converted into heat that disperses into the surroundings.
Heat is the kinetic energy of randomly moving particles.
Unlike heat energy, which flows from an object with a higher temperature to one of lower temperature, this random motion cannot do work.
Total energy is not decreasing, but total usable energy is decreasing
Entropy (S) - a measure of the less-usable energy which is disordered or random
Usable energy has low entropy
Disorganized energy, such as heat, has high entropy
Organisms maintain high level of organization (low entropy) by importing low entropy energy sources

3. Energy & Metabolism
A. Terms
Metabolism - the sum of all the chemical activities taking place in an aroganism
Anabolism - various pathways that make more complex chemicals from simpler chemicals

Amino acids to dipeptids to proteins
Monosaccharides to polysaccharides to starch
Overall energy requirements - increasing order
3. Catabolism - various pathways that break down more complex chemicals
into simpler ones
Proteins to amino acids
Starch to monosaccharides (glucose)
Overall energy release - decreasing order
4. Enthalpy (H)
Total potential energy of the system
Bond Energy - energy required to break that bond
Total bond energy is equivalent to enthalpy (H)
5. Free energy/Gibbs free energy (G)
Amount of energy available to do work under the conditions of a biochemical reaction
Only kind of energy that can do cell work
Aspect of thermodynamics of greatest interest to biologists
6. G = H - TS or Free energy = Enthalpy (total potential energy) - T (absolute temperature in Kelvins) * S (entropy)
If entropy 0, free energy (G) = total potential energy (H)
As entropy increases, free energy decreases
As temperature increases, entropy increases
Measured in terms of change between initial state before a reaction and end state after a reaction
ΔG = ΔH -TΔS
B. Exergonic reactions
Releases energy
Spontaneous or ‘downhill’ reaction - from higher to lower free energy
ΔG (free energy) is a negative number
Spontaneous does not equal instantaneous - some happen very slowly
Some require activation energy to get started
Diffusion is a exergonic reaction
C. Endergonic reactions
Consumes energy/energy requiring
An ‘uphill’ reaction - from lower to higher free energy
Gain of free energy or ΔG (free energy) is a positive number
Does not happen in isolation - energy must be supplied by the surroundings
D. Free-energy changes depend on the concentrations of reactants and products
In biochemistry, little intrinsic free-energy difference between reactants and products
A W B
Dynamic equilibrium - rate of reverse reaction equals the rate of forward reaction
Increase initial concentration of A, force reaction to the right
Decrease the concentration of B as made, force reaction to the right
Visa versa
Cell reactions virtually never at equilibrium
E. ATP
Energy currency of the cell
Holds readily available energy for very short periods of time
Links exergonic and endergonic reactions (Fig 7-6)
Hydrolysis of ATP to ADP is exergonic - high energy because has a large -ΔG number
Phosphorylation reactions - example of glucose to sucrose (page 158)
Cannot be stored for very long

F. NAD+
Redox reactions - oxidation (lose of electrons) and reductions (gain of electrons) happens simultaneously
Happen in a series in the cells
Transfer of an electron is a transfer of energy
Not easy to remove an electron from a covalent compound - easier to transfer hydrogen (electron & proton)
Electron (either alone or part of hydrogen) transfers its energy (part of energy of chemical bond coming from) to acceptor
Loses energy with each transfer
NAD+ (nicotinamide adenine dinucleotide) - one of most frequently encountered acceptor molecules
Basic reaction (page 159)
Energy transferred to NADH (reduced form) from X when H is removed
Energy transferred to new X when NADH transfers H and is oxidized to NAD+
Specific reactions (Chapter 8)
9. Other electron acceptors:
NADP+ (nicotinamide adenine dinucleotide phosphate) - not involved in ATP synthesis, more in photosynthesis
FAD (flavin adenine dinucleotide)
Cytochromes - proteins that contain iron, which accepts the electron (more in Chapter 8)

3. Enzymes
A. Enzyme is a biological/organic catalyst - increases the speed of a chemical reaction without being consumed by the reaction.
All reactions have a required energy of activation (EA) or activation enery
- energy required to break the existing bonds
Molecules with relatively high kinetic energy are likely to react to form product - Flash point
Even an strongly exergonic reaction may be prevented from proceeding by the activation energy required to begin
Enzymes lower the activation energy of a reaction - speed up reaction rates
Doesn’t change free energy - can promote only a reaction that would proceed without it
Reactants and product reach equilibrium, no catalyst can cause a reaction to proceed in a thermodynamically unfavorable direction or can influence the final concentrations
B. How acts as a catalyst
Forms an unstable enzyme-substrate complex
Product releases when enzyme-substrate breaks up
Enzyme free to form another enzyme-substrate complex
Enzyme contains one or more active sites - regions to which the substrate binds to form ES complex
Grooves or cavities formed by amino acid side chains, usually close to the surface
Induced fit
Shape of enzyme not exactly complementary to the substrate
Binding of substrate induces a change in the shape of the enzyme and the substrate
Bonds in substrate may be distorted
Proximity and orientation of the reactants and strains in chemical bonds facilitate breakage of old bonds and formation of new ones
C. Enzymes are specific
Because shape of the active site is closely related to the shape of substrate, most enzymes are highly specific
Some catalyze reactions with only one substrate
Urease - decomposes urea to ammonia and carbon diooxide - no other substrate
Sucrase splits only sucrose
3. Few others catalyze reactions with a certain type of bond
Lipase - splits ester linkages connecting the glycerol and fatty acids of a wide variety of fats
D. CofactorsSome enzymes are only proteins
Others have two components: a protein called an apoenzyme and an additional chemical component called a cofactor
Apoenzyme and cofactor must be combined to function
Cofactor may be organic or inorganic
Inorganic can be trace metals, such as iron, copper, zinc, manganese

Organic are nonpolypeptides, usually carrier molecules for electron transfer, such as NADH, NADPH, and FADH2
ATP functions as a cofactor in phosphorylation reactions
Coenzyme A - transfers groups derived from organic acids - will discuss more in next chapter
Vitamins - cofactors or parts of cofactors the organism can’t manufacture by self
E. Optimal conditions
1. Each enzyme has an optimal temperature
Temperature too low - enzymatic reaction takes place slowly or not at all
Temperature too high - enzyme bonds responsible for secondary, tertiary and quaternary structures are broken; protein denatures; enzyme permanently inactivated as new shape is formed
Heat kills for this reason
Some organisms operate outside 35 - 40C human optimal range
Enzymes from organisms feeding on whale carcasses - cold water detergents
Enzymes from organisms living in hot pools, such as in Yellowstone - hot applications, such as PCR enzymes
2. Each enzyme has an optimal pH
Most enzymes are active over a narrow pH range, have optimal pH in which the reaction proceeds fastest
pH affects ionization of the amino acid side chains, etc.
Buffers minimize change in pH, help maintain optimal pH
Lysosome enzymes have optimal pH at lower pH than that of cell
Pepsin - protein splitter secreted by stomach - optimal pH of 2
Trypsin - protein splitter secreted by pancreas - optimal pH found in slightly basic environment of small intestine.
F. Regulation of enzymes
1. Cell can regulate pH, temperature, and enzyme and substrate concentration
2. Feedback inhibition
In a series of reactions, the end product may inhibit the first enzyme in the series
3. Reversible inhibition
Most enzyme can be inhibited by chemical agents
Reversible inhibition occurs when an inhibitor forms weak chemical bonds with the enzyme
Competitive inhibition - competes with the normal substrate for binding to the active site of the enzyme (Fig 7-17, page 167)
Noncompetitive inhibition - inhibitor binds with the enzyme at a site other than the active site

4. Allosteric sites and allosteric regulators - form of noncompetitive inhibition
Some enzymes have a site other than the active site, called an allosteric site
Substrate binds to allosteric site, changes the shape of the active site, affects enzyme activity
Allosteric activators - result in an enzyme with a functional active site
Allosteric inhibitors - result in an enzyme with a nonfunctional active site
Cell signaling examples - IP3 binds to calcium channels (Fig 6-9, page 144) to activate, cyclic AMP-dependant protein kinase (Fig 7-16, page 166) is inhibited by an allosteric inhibitor until inhibitor is removed (inhibited) by cAMP
5. Irreversible inhibition
An inhibitor permanently inactivates or destroys an enzyme when inhibitor combines with one of the enzyme’s functional groups, either at the active site or elsewhere
Many poisons are examples of irreversible inhibition - cyanide irreversibly inhibits action of cytochrome oxidase (Chapter 8) in mitochondria
Some drugs are irreversible inhibitors - penicillin irreversibly inhibits bacterial enzyme transpeptidase - establishes linkages in cell wall, cell wall ‘leaks’
Humans don’t produce cell walls, usually not affected by penicillin (except allergies)
Bacteria have fought back by producing penicillinase


Chapter 8 Outline

1. Stages of cellular respiration, terminating in aerobic respiration
A. Need to know’s
Table 8-1, page 173
Fig 8-2, page 173
Fig 8-4, pages 176 - 177
Fig 8-5, page 178
Fig 8-7, page 180
Fig 8-10, page 186
Table 8-2, page 187
Reactants & products
Enzymes
B. Overall significance or ‘purpose’ of cellular respiration
1. Cellular respiration - the name for some of the catabolic processes that convert the energy in the chemical bonds of nutrients to chemical energy stored in ATP
2. Cellular respiration may be aerobic or anaerobic.
3. Aerobic respiration requires oxygen.
4. Anaerobic pathways do not require oxygen
a. Anaerobic respiration
b. Fermentation
2. Aerobic respiration - four stages
A. Glycolysis
Fig 8-4, pages 176 - 177
B. Formation of acetyl coenzyme A
Fig 8-5, page 178
C. Citric acid cycle/Krebs Cycle
Fig 8-7, page 180
D. Electron transport & chemiosmosis
Fig 8-10, page 186
E. Two types of phosporylation:
1. Substrate-level phosphorylation: when a phosphate group is transferred to ADP from a phophorylated intermediate. Takes place during gycolysis in the cytosol and in the Krebs cycle in mitochondria.
2. Oxidative phosphorylation: production of ATP using energy derived from the transfer of electrons in the electron transport system - occurs only by chemiosmosis. Occurs in the matrix of mitochondria.
3. Anaerobic respiration
A. Table 8-2, page 187
B. Nitrate (NO3 -) or sulfate (SO4 2-) are the terminal electron acceptors instead of oxygen
C. Nitrogen cycle:
C6H12O6 + KNO3 6CO2 + 6H2O + 12 KNO2 + energy (in bonds of ATP)
potassium nitrate potassium nitrite
4. Fermentation
A. Fig 8-13, page 187


Chapter 9 Outline

1. Physical properties of light
A. Wavelength
1. Visible light represents a very small portion of a vast, continuous range of radiation called the electromagnetic spectrum.
2. All radiation in the electromagnetic spectrum travel in waves.
3. A wavelength is the distance between one wave peak and the next.
4. Fig. 9-1
a. Gamma rays have the shortest wavelength (fractions of nm) and TV and radio waves have the longest (measured in kilometers).
b. Visible spectrum or visible light is from 380 - 760 nm.
B. Photons
1. Light has both wave and particle properties.
2. Particles of light are called photons.
3. Photons have more energy when they have shorter wavelengths.
4. Photosynthesis uses the energy found in visible light.
2. Photosynthesis - General
A. Photosynthesis
1. Biological process that captures light energy and transforms it into the chemical energy of organic molecules (e.g. carbohydrates), which are manufactured from carbon dioxide and water.
2. Important to a plant because it generates energy and organic building blocks.
a. Plant uses energy to form ATP and NAPH.
b. Because ATP and NADPH are unstable, they are converted into more stable energy-storing molecules, such as glucose.
c. Glucose may then be stored as a part of sucrose, starch, etc.
d. ATP also fuels anabolic reactions that produce carbohydrates, proteins, fats, etc, that become part of the plant’s structure.
3. Important to other organisms because other organisms use energy-storing molecules and organic chemicals generated by plants.
a. Plants are autotrophs (photoautotrophs) because the chemical energy of ATP and NADPH then drives carbon fixation, the anabolic pathway in which stable organic molecules are synthesized from CO2 and water.
b. Chemoheterotrophs
1. Most animals, fungi, and most bacteria.
2. Chemotrophs because they obtain energy from chemicals.
3. Heterotrophs because they cannon fix carbon – use organic molecules produced by other organisms as the building blocks from which they synthesize the carbon compounds they need.
4. Photoheterotrophs - nonsulfur purple bacteria can use light energy but unable to carry out carbon-fixation and so need organic molecules from other organisms.
5. Chemoautotrophs - use oxidation of high energy, reduced compounds to obtain energy for carbon fixation.
B. Leaf structure
1. Mesophyll - a layer in the leaf with many air spaces and a very high concentration of water vapor.
2. Chloroplasts mainly found in cells of the mesophyll.
3. Interior of the leaf exchanges gasses with the outside through microscopic pores called stomata.
C. Chloroplast structure
1. Enclosed by outer and inner membranes.
2. Inner membrane encloses a fluid-filled region called the stroma - contains most of the enzymes for carbohydrate synthesis.
3. Suspended in the stroma is a third system of membranes that forms an interconnected set of flat, disclike sacs called thylakoids.
4. Thylakoid membrane encloses a fluid-filled interior space called the thylakoid lumen.
5. Thylakoids can be arranged in stacks called grana.
3. Light-dependent reactions
A. Take place in thylakoids of the choroplast
B. Noncyclic electron transport (Fig. 9-11 on page 199)
1. Explain photosystems I & II
a. Pigments - substances that absorb visible light.
1. Chlorophyll
The main pigment of photosynthesis.
Absorbs light mainly in the blue (422 - 492 nm) and red (647 - 760 nm).
Comes in two main forms, a and b.
Chlorophyll a initiates the light-dependant reactions of photosynthesis.
Chlorophyll b is an accessory pigment that helps absorb light.
2. Carotenoids
Yellow and orange pigments.
Absorb light in wavelengths other than those absorbed by chlorophyll.
Pass energy onto chlorophyll a.
b. Antenna complexes - chlorophyll a and b and accessory pigment molecules are organized with pigment-binding proteins in the thylakoid membrane into units called antenna complexes.
c. Each antenna complex absorbs light energy and transfers it to the reaction center.
1. P700 - Photosystem I reaction center consists of a pair of chlorophyll a molecules with an absorption peak at 700 nm.
2. P680 - Photosystem II reaction center consists of a pair of chlorophyll a molecules with an absorption peak at 680 nm.
2. Absorption of the light energy
a. Structure of chlorophyll
A long side chain that anchors the molecule in the membrane of the thylakoid.
Porphyrin ring made up of joined smaller rings (composed of carbon and nitrogen atoms) and an atom of magnesium in the center of the ring
b. Chlorophyll in the reaction center absorbs light energy passed to it from the antenna complex.
c. Light energy causes excitation of an electron in the magnesium atom (Mg).
d. Excited electron has more energy than it had before.
e. Energy can be released in two ways:
As light if the electron drops back to its original orbit.
It can be removed to an electron transport chain.
In chlorophyll, excited electron is removed to an electron transport chain.
2. Go over flow of electrons through photosystems I and II.
3. Go over products produced (look in other books - does Fig. 9-11 have a mistake in showing ATP synthesis? - does - ATP only generated by ATP synthase by chemiosmosis)
C. Cyclic electron transport (modify Fig 9-11)
1. Go over flow of electrons through photosystem I and reduction of NADPH to restore a electron to P700.
2. Some energy is used to pump H+ ions into the thylakoid lumen.
3. Energy from H+ gradient used to produce ATP.
4. No NADPH (required for carbon fixation) produced, no H2O split, and O2 is not generated.
5. Possible reasons for cyclic electron transport:
a. Occurs when too little NADP+ to accept electrons from ferredoxin.
b May help maintain the optimal ration of ATP to NADPH required for carbon fixation.
c May provide extra ATP for ATP-requiring processes in chloroplasts.
D. ATP synthesis (Fig 9-13 on page 201)
a. Explain how proton gradient is established across the thyakoid membrane.
b. Go over ATP synthesis by ATP synthase using the proton gradient (chemiosmosis).
4. Carbon fixation reactions/The Calvin cycle
A. Take place in the stoma of the chloroplast
B. Most plant use the Calvin cycle to fix carbon
1. Also known as the C3 pathway because the product of the initial carbon fixation reaction is a three-carbon compound, phosphoglycerate (PGA).
2. Plants that initially fix carbon in this way are called C3 plants.
C. The Calvin cycle (Fig 9-14 on page 203)
1. Summarize the three phases (CO2 uptake, Carbon reduction phase, and RuBP regeneration phase).
2. Indicate the roles of ATP and NADPH in this process.
5. Other carbon fixation pathways
A. Photorespiration
1. During hot temperatures, C3 plants balance need for CO2 with need to conserve water.
2. On hot dry days, leaves close stomata to conserve water.
3. Photosynthesis rapidly uses up the CO2 remaining the leaf - O2 accumulates in the chloroplasts.
4. CO2 and O2 compete for the active site of rubisco, which can act as either a carboxylase or an oxygenase - reaction can go either way.
5. Some intermediates are degraded to CO2 and H2O
a. Does not produce ATP
b. Removes intermediates from Calvin cycle
c. Reduces the photosynthetic efficiency
6. Called photorespiration because
a. It occurs in the presence of light
b. Requires oxygen
c. Produces CO2 and H2O (byproducts of aerobic respiration).
7. Many plants that live in hot, dry environments have adaptions that facilitate carbon fixation.
B. C4 pathway
1. C4 pathway efficiently fixes CO2 at low concentrations.
a. Called C4 because the product of the initial carbon fixation reaction is a four carbon compound, oxaloacetate (remember from Citric acid cycle).
b. C4 cycle used in conjunction with C3/Calvin cycle - separates the initial carbon fixation step from the rest of the Calvin cycle.
c. Plants that use the C4 cycle are called C4 plants.
2. Fig. 9-15 on page 205 - location of various cycles in C3 vs C4 plants.
3. Fig. 9-16 on page 206 to show interaction of the C3 and C4 pathways.
4. Because C4 pathway captures CO2 and provides it to the bundle sheath cells so efficiently, CO2 concentration within the bundle sheath cells is about 10 - 60 times as great as its concentration in the mesophyll cells of plants having only the C3 pathway - photorespiration is negligible.
C. CAM pathway
1. Plants living in very dry, or xeric (desert) conditions have special adaptions.
2. One is a carbon fixation pathway called the crassulacean acid metabolism (CAM) pathway.
a. Name comes from the stonecrop plant family (Crassulaceae).
b. Pathway evolved independently in other plant families.
3. Unlike most plants, open stomata at night.
a. Admit CO2.
b. Prevents water lose.
4. Use the enzyme PEP carboxylase to fix CO2 - forming oxaloacetate.
5. Oxaloacetate converted to malate.
6. Malate is stored in cell vacuoles.
7. During day, when stomata are closed, CO2 is removed from malate by decarboxylation.
8. CO2 is now available for use in the Calvin/C3 cycle.
D. Differences between C4 and CAM pathways.
1. C4 pathway - C3 and C4 pathways occur in different parts of the leaf.
2. CAM pathway - C3 and CAM pathways occur at different times in the leaf (day vs night).
3. Both maintain high levels of CO2 for use in the Calvin cycle to prevent photorespiration while preventing water lose.

Chapter 10 Outline

I. Organization of Eukaryotic Cell DNA (Fig. 10-4 on page 214)
A. DNA double helix - basic structure
1. Draw structure of a few connected nucleotides
2. Draw second, paired strand for double helix
3. In this form for replication and transcription
4. Genes
a. The term ‘gene’ has changed as we have gained understanding.
b. Always centered on being an informational unit.
May contribute to what we can see - eye color, hair color, height (polygenic), etc.
May be involved in regulation - regulator enzyme or regulatory molecule production.
May be involved in enzyme production, which is involved in protein, lipid, carbohydrate production - subunit or whole enzyme.
May be involved in structural protein production - subunit or whole protein.
B. Nucleosomes
1. DNA double helix very long - human sperm contains ~3x109 base pairs - 1 m long. Fits into a nucleus with a diameter of 10um.
2. Reasons for packaging DNA
a. Fit
b. Gene regulation
3. Packaging of DNA
a. Histones
Proteins that have a positive charge - high proportion of amino acids with basic side chains.
DNA has a negative charge because of the phosphate groups.
Histones and DNA associate to form structures called nucleosomes.
b. Nucleosomes
Fundamental unit of each nucleosome - beadlike structure with 146 base pairs of DNA wrapped around a disc-shaped core of eight histone molecules.
Histone molecules consist of two each of four different histone types.
Nucleosomes function like spools, preventing DNA from tangling.
Histones function in gene regulation - turned on or off.
Wrapping of DNA into nucleosomes represents the first level of
chromosome structure.
C. Packed nuclosomes
1. Another, fifth type of histone, histone H1, associates with the linker DNA.
2. Packs adjacent nucleosomes together to form a compacted 30-nm chromatin fiber.
D. Extended chromatin
1. Chromatin fibers form large, coiled loops held together by scaffolding proteins.
E. Chromosomes
1. Coiled loops interact to form the condensed chromatin in chromosomes.
2. Group of proteins called condensin.
Binds to DNA and wraps it into coiled loops that are compacted into a nitotic or meiotic chromosome.
DNA safely packaged for transport, so to speak.
II. Cell Cycle of an Eukaryotic Cell
A. Stages through which a cell passes from one cell division to the next are collectively referred to as the cell cycle.
1. Timing varies widely.
2. Nerve cells - years
3. Actively growing animal and plant cells - 8 - 20 hours.
B. Interphase - Time when no cell division is occurring - most of cell life.
1. G1
a. First gap phase
b. Growth and normal metabolism takes place
c. Typically longest phase
d. Cells that are not dividing usually become arrested in this part of the cell cycle and are said to be in a state called G0
e. Toward the end of G1, synthesis of proteins needed to initiate cells division and DNA sysnthesis
2. S
a. Synthesis phase
b. Chromosome duplication
DNA replication
Histone protein synthesis
3. G2
a. Second gap phase
b. Usually shorter than G1.
c. Synthesis of proteins needed for cell division.
C. M phase - Time when the cell is dividing.
1. Mitosis or Meiosis
a. Nuclear division
b. Insures that the correct number and kind of chromosomes goes to each new nucleus.
2. Cytokinesis
a. Division of the cell cytoplasm between two cells.
III. Mitosis (Fig 10-6, pages 216 - 217)
A. Nuclear division that produces two nuclei containing chromosomes identical to the parental nucleus
B. Interphase
1. Chromosomes are ‘unpacked’ into chromotin.
2. Nucleolus
3. Nuclear envelope
C. Prophase
1. Chromosome compaction - chromatin can be distributed to the daughter cells with less likelihood of tangling.
a. Sister chromatids - contain identical, double-stranded DNA sequences.
b. Each chromatid contains a constricted region called the centromere where sister chromatids are associated
c. Sister chromatids are physically linked by a ring-shaped protein complex called cohesion.
2. Kinetochore - multiprotein complex attached to centromere to which microtubles can bind.
3. Mitotic spindle develops
a. Structure that separates the duplicated chromosomes during anaphase.
b. Made up of microtubules, motor proteins, and controlled by variety of signaling molecules.
c. Microtubule-organizing center
Found in both plant and animal cells at the poles of the dividing cell
Animal cells have a pair of centrioles in the middle of each microtubule-organizing center
Centrioles surrounded by fibrils that make up the pericentriolar material
Late in propase, microtubules radiate from the pericentriolar material - called asters
Two asters migrate to two poles of the mitotic spindle
D. Prometaphase
1. Begins when nuclear envelope breaks up - sequestered for later use.
2. Nucleolus shrinks and usually disappears
3. Mitotic spindle completely assembled.
4. Duplicate chromosomes are scattered through out the nuclear region.
5. Spindle microtubules grow and shrink as they move towardd the center of the cell in a ‘search and capture’ process.
a. Microtubule comes near a kinetochore it is ‘captured’ by the kinetochore - kinetochore microtubles.
b. Move toward cell’s equator.
c. Sister chromatids kinetochore becomes attached to spindle from other pole.
6. Cohesins dissociate from sister chromatid arms but remain in the vicinity fo the centromere.
E. Metaphase
1. All cell’s chromosomes align at the cell’s midplane or metaphase plate.
2. Microtubules not connected to kinetochores are called polar microtubules or non-kinetochore microtubules - extend from each pole and overlap at equatorial region.
3. Kinetochore microtubules - extend from each pole to a kinetochore.
4. Each chromatid is completely condensed and easy to see - cells generally checked for karyotype (chromosome make up) at this stage if chromosome abnormalities are suspected.
5. Remaining cohesions dissociate from centromere.
F. Anaphase
1. Sister chromatids separate - now called chromosomes.
2. Chromosomes move to separate poles, using the microtubules as tracks.
Kinetochore lead way, arms trailing.
Micortubules depolymerize to shorten.
Polar microtubules slide against each other where they overlap at the poles, lengthening the spindle and pushing the poles apart.
3. Anaphase ends when all chromosomes reach poles.
G. Telophase
1. Arrival of the chromosomes at the poles.
2. Return of interphase nuclear conditions:
a. Chromosomes decondense by partially uncoiling.
b. New nuclear envelope forms around each set of chromosomes.
c. Spindle microtubules disappear.
d. Nucleoli reorganize.
IV. Cytokinesis
A. Division of cytoplasm to yeild two daughter cells.
1. Usually overlaps mitosis, beginning during telophase.
B. Animals & fungi
1. Actomyosin contractile ring attached to the plasma membrane encircles the cell in the equatorial region, at right angles to the spindle.
2. Contractile ring is an association between actin and myosin filaments.
3. Ring contracts, producing an cleavage furrow that gradually deepens and eventually separates the cytoplasm into two daughter cells.
B. Plants
1. Formation of a cell plate in the equatorial region.
2. Begins as a line of vesicles originating in the Golgi complex.
a. Contain materials to contruct both a primary cell wall and a middle lamella that cements the primary cell walls together.
b. Vesicles fuse to form plasma membrane of each daughter cell.
V. Meiosis (Fig. 10-13, pages 226 - 227)
A. Diploid vs Haploid
1. Diploid - two sets of each chromosome, one set from each parent.
a. Somatic cells - body cells.
b. Homologous chromosomes - carry information about the same trait - redundant system.
2. Haploid - one of each chromosome
a. Gamete formation for sexual reproduction.
b. Gametes fuse to form a zygote - return to diploid.
B. Meiosis I
1. Prophase I
a. Each duplicated chromosome (duplicated in interphase) consists of two chromatids, linked by cohsisn.
b. Synapsis
While chromatids are still elongated and thin, homologous chromosomes come to lie lengthwise side by side - synapsis (fastening together).
Results in two homologous pairs - association of four chromatids called a tetrad.
One homologous pair is called the maternal homologue, the other the paternal homologue.
Synaptonemal complex - proteinous structure holds homologous chromosomes together.
Crossing-over - enzymes break and rejoin DNA molecules, allowing paired homologous chromosomes to exchange genetic material.
Crossing-over results in genetic recombination.
c. Spindle forms.
d. Centrioles move to each pole.
e. Nuclear envelope disappears.
f. Centromeres and kinetochores of the homologous chromosomes become separated from one another - held together only where crossing-over had occurred
Called chiasmata.
Cohesions hold homologous chromosomes together after synaptonemal complex has disassembled.
2. Metaphase I
a. Tetrads align as midplate.
b. In contrast to mitosis, both sister kinetochores of one duplicated chromosome are attached to same pole.
3. Anaphase I
a. Paired homologous chromosomes separate and move toward opposite poles.
b. Each cell receives a random combination of maternal and paternal chromosomes, but only one member of each homologous pair is present at each pole.
c. Sister chromatids remain united at their centromers, unlike in mitosis.
4. Telophase I
a. Chromatids generally decondense somewhat, nuclear envelope may reform, and cytokinesis may take place.
b. Each nucleus contains the haploid number of chromosomes, but each chromsome is a duplicated chromosome (pair of chromatids).
c. A short interphase-like stage usually follows called interkinesis.
C. Meiosis II
1. Prophase II
a. Because chromosomes remain partially condensed, prophase II is brief.
b. Similar to mitotic prophase.
2. Metaphase II
a. Chromosomes line up on the midplanes of the cells.
b. Groups of two vs tetrads of metaphase I.
c. Not always obvious in living cells.
3. Anaphase II
a. Move to opposite poles, just as they would in mitotic anaphase.
b. Each former chromatid now called a chromosome, like in mitosis.
4. Telophase II
a. One representative for each homologous pair at each pole - each is an unduplicated (single) chromosome.
b. Nuclear envelopes reform.
c. Chromosomes gradually elongate to form chromatin fibers.
d. Cytokinesis occurs.
5. Genetic variation
a. DNA segments are exchanged between maternal and paternal homologues during cross-over.
b. Maternal and paternal chromosomes of homologous pairs separate independently - shuffled.
VI. Differences Between Mitosis & Meiosis
A. Nuclear divisions:
1. Mitosis is a single nuclear division in which sister chromatids separate from each other.
2. Meiosis - diploid cell undergoes two successive nuclear divisions (meiosis I & II)
B. Genetic composition and number of the daughter cells
1. Mitosis results in two identical cells.
2. Meiosis ends with four genetically different, haploid daughter cells.
a. Meiosis - synapsis to form tetrads (prophase I) which cross-over.
b. Meiosis I - homologous chromosomes separate.
c. Meiosis II - sister chromosomes separate.
VII. Reproduction
A. Asexual
1. Cloning of the cell.
2. Less genetic variation
3. Those that are genetically fit multiply.
B. Sexual
1. Genetic variation - offspring are different from both parents.
2. Those that are genetically fit may not have genetically fit offspring.
3. Possibility for more genetically fit offspring to arrise.
C. Variations in the Cycles (Fig. 10-17, page 230)