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Exam 2 Study Guide
Chapter 6 – Metabolism
6
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○ Metabolism: ​all the chemical reactions that take place inside cells, including
anabolism and catabolism
○ The breakdown of glucose: C6H12O6+6O2→6CO2+6H2O+energy
○ The synthesis of glucose: 6CO2+6H2O+energy→C6H12O6+6O2
○ During the chemical reaction of photosynthesis, energy is provided in the form of
ATP
...

○ Photosynthesis:
■ Light energy is initially transformed to chemical energy that is temporarily
stored in the energy carrier molecules ATP and NADPH
...

○ *Energy is stored long-term in the bonds of glucose and used short-term to
perform work from an ATP molecule
...

○ Two types:
1
...

○ Example: synthesizing sugar from CO2; DNA replication
● Demand energy provided by ATP and other high energy molecules
like NADH and NADPH
2
...
2 | Potential, Kinetic, Free, and Activation Energy
● Types of Energy:
○ Energy: the ability to do work
○ Kinetic Energy: energy associated with objects in motion
■ Examples: speeding bullet, walking person, rapid movement of
molecules in air, electromagnetic radiation
○ Potential Energy: type of energy that has the potential to do work; stored
energy; location and structure
■ Examples: energy of water held behind a dam, person about to
skydive out of an airplane; potential energy stored in bonds; food
■ Chemical energy: type of potential energy that exists within
chemical bombs when those bonds are broken
● Free Energy:
○ Free energy: Gibbs free energy is the usable energy, or energy that is
available to do work; a measurement of free energy is used to quantitate
energy transfers
○ Second law of thermodynamics: all energy transfers involve the loss of
some amount of energy in an unusable form such as heat, resulting in
entropy
○ ∆G (​delta G): a change in free energy
■ ΔG=ΔH−TΔS
● To calculat​e ∆G, subtract the amount of energy lost to
entropy (denoted as ∆S) from the total energy change in the
system
...

■ Expressed as an amount of energy per mole
of the reaction product (kilojoules, kJ/mol)
○ Endergonic Reactions and Exergonic Reactions:
■ Exergonic Reactions: reactions that have a negative ∆G and
consequently release free energy; ‘exiting the system’
● If energy is released during a chemical reaction, then the
resulting value ∆G will be a negative number; ∆G <0
○ Negative ∆G means that the products of the reaction
have less free energy that the reactants, because
they gave off some free energy during the reaction
● Referred to as spontaneous reactions, because they can
occur without the addition of energy into the system
● Example: catabolic process of breaking down sugar into
simpler molecules; rust
■ Endergonic Reactions: reactions that have a positive ∆G and
requires an input of energy

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●

The products have more free energy than the reactants; can
be thought of as energy-storing molecules
● Non-spontaneous: will not take place on its own without
the addition of free energy
● Example: anabolic processes of building complex molecules
of sugar
■ Chemical Equilibrium:
● the reactants within a closed system will undergo chemical
reactions will in both directions until a state of equilibrium
is reached;
● State of Equilibrium: one of the lowest possible free and
and a state of maximal entropy
○ A cel would die because there would be insufficient
free energy left to perform work
● Energy must be put into the system to push the reactants
and products away from a state of equilibrium; reactants or
products added, removed, or changed
● Activation Energy:
○ Activation Energy(EA​): the small amount of energy input necessary for all
​
chemical reactions to occur; aka free energy of activation; always positive
■ The higher the activation energy, the slower the chemical reaction
will be
■ Example: contort a molecule to make carbon bonds break to
release energy
○ Transition State: high energy, unstable state (an intermediate between the
substrate and the product) occurring during a chemical reaction; don’t last
long
○ Heat Energy: the total bond energy of reactants or products in a chemical
reaction; typically the source of activation energy needed to push reactions
forward
■ Speeds up the motion of molecules, increasing the frequency and
force with which they collide
■ Moves atoms and bonds within the molecule slightly, helping them
reach the transition state
○ Catalysis: in order for important cellular reactions to occur at appreciable
rates, their activation energies must be lowered
6
...

● The Second Law of Thermodynamics:
○ The Second Law of Thermodynamics: in every energy transfer, some
amount of energy is lost in a form that is unusable form, such as heat
energy, resulting in a more disordered system
...
High entropy means
high disorder and low energy
...
[less dense aka gas =
highest entropy]
6
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■ ATP is hydrolyzed into ADP: ​ATP+H2O→ADP+Pi+free energy
■ Reversible and requires free energy:​ ADP+Pi+free energy→ATP+H2O

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The calculated ∆G for the hydrolysis of one mole of ATP into ADP and Pi is −7
...
5 kJ/mol)
...

○ Energy Coupling: how the energy released by ATP hyrolysis is used to perform
work inside the cell
■ Cells couple the exergonic reaction of ATP hydrolysis with endergonic
reactions, allowing them to proceed
...
5 | Enzymes
● Enzyme Active Site and Substrate Specificity:
○ Catalyst: a substance that helps a chemical reaction occur
○ Enzymes: the special molecules that catalyze biochemical reactions
■ Almost all enzymes are proteins, made up of chains of amino acids, and
they perform the critical task of lowering the activation energies of
chemical reactions inside the cell
...

■ Enzymes lower the activation energy of the reaction but do not change the
free energy (∆G) of the reaction
...

○ Active Site: the location within the enzyme where the substrate binds
■ Unique combination of amino acid residues (aka side chains or R groups)
● Each residue is characterized by different properties: large or
small, weakly acidic or basic, hydrophilic or hydrophobic,
positively or negatively charged, or neutral
...

■ Subject to influences by the local environment
...

○

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●

pH: Active site amino acid residues have their own acidic or basic
properties that are optimal for catalysis
...

● Denature: a process that changes the natural properties of a
substance
...

As the enzyme and substrate come together, their interaction causes a mild
shift in the enzyme’s structure that confirms an ideal binding arrangement
between the enzyme and the transition state of the substrate
...

● Both enzyme and substrate undergo dynamic conformational
changes upon binding
...

■ Enzyme-Substrate Complex: when an enzyme binds its substrate; lowers
the activation energy of the reaction and promotes its rapid progression
● Enzymes promote chemical reactions (2 ways)
○ That involve more than one substrate by bringing the
substrates together in an optimal orientation
○ Creating an optimal environment within the active site for
the reaction to occur; emerge from a particular
arrangement of amino acid residues
■ Enzymatic Action: The enzyme-substrate complex can lower the activation
energy by…
● Contorting substrate molecules in such a way as to facilitate
bond-breaking, helping to reach the transition state
...
The amino acid
residues can provide certain ions or chemical groups that actually
form covalent bonds with substrate molecules as a necessary step
of the reaction process
...

● When an allosteric inhibitor binds to an enzyme, all active sites on
the protein subunits are changed slightly such that they bind their
substrates with less efficiency
■ Allosteric Activators: bind to locations on an enzyme away from the active
site, including a conformational change that increases the affinity of the
enzyme’s active(s) for its substrate(s)
...
Enzymes required only
for certain cellular processes can be housed separately along with their
substrates, allowing for more efficient chemical reactions
...
The cell responds to the abundance of specific
products by slowing down production during anabolic or catabolic
reactions
...


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Chapter 7 – Cellular Respiration
7
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Rather, the electron is
shifted to a second compound, reducing the second compound
...

○ Reduction Reaction: The addition of this electron to another compound
○ Redox Reactions: Chemical reaction that consists of the coupling of an oxidation
reaction and a reduction reaction
○ Electron Carriers:
■ Electron Shuttles: They bind and carry high-energy electrons between
compounds in pathways
...

● RH is a reducing agent, and NAD+ is reduced to NADH
...

● NAD+ is an oxidizing agent, and RH is oxidized to R
...
The energy is used to do
work by the cell, usually by the released phosphate binding to another
molecule, activating it
...

■ The addition of a phosphate group to a molecule requires energy
...
This repulsion
makes the ADP and ATP molecules inherently unstable
...

● Water is regenerated when a third phosphate is added to the ADP
molecule, reforming ATP
...

○ Phosphorylation:
■ Enzymes may bind to several substrates that react with each other on the
enzyme, forming an intermediate complex
● Intermediate complex: a temporary structure that allows one of the
substrates (such as ATP) and reactants to more readily react with
each other; in reactions involving ATP, ATP is one of the substrates
and ADP is a product
...


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○

Substrate Phosphorylation:
■ Substrate-Level Phosphorylation: production of ATP from ADP using the
excess energy from a chemical reaction and a phosphate group from a
reactant; direct method of phosphorylation; the gamma (third) phosphate
of ATP is attached to a protein
○ Oxidative Phosphorylation:
■ Chemiosmosis: a process of ATP production in cellular metabolism, used to
generate 90 percent of the ATP made during glucose catabolism
(breakdown) and is also the method used in the light reaction of
photosynthesis to harness the energy of sunlight; takes place in the
mitochondria within a eukaryotic cell or the plasma membrane of a
prokaryotic cell
■ Oxidative Phosphorylation: the production of ATP using the process of
chemiosmosis and oxygen
7
...
Hexokinase phosphorylates (donates high energy phosphate groups) glucose
using ATP as the source of the phosphate, producing glucose-6-phosphate, a more
reactive form of glucose
...
It can no longer

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leave the cell because the negatively-charged phosphate will not allow it to cross
the hydrophobic interior of the plasma membrane
...
An isomerase converts glucose-6-phosphate into one of its isomers,
fructose-6-phosphate
...

3
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If it is active when the
concentration of ADP is high; it is less active when ADP levels are low and the
concentration of ATP is high
...
(ATP is the end product of glucose catabolism)
● A second ATP molecule donates a high-energy phosphate to
fructose-6-phosphate, producing fructose-1, 6-biphosphate
...
The newly added high-energy phosphates further destabilize fructose-1,
6-biphosphate
...
An isomerase transforms the dihydoxyacetone-phosphate into its isomer,
glyceraldehyde-3-phosphate
...
At this point in the pathways, there is a net investment of energy from
two ATP molecules in the breakdown of one glucose molecule
...
Oxidizes the sugar (glyceraldehyde-3-phosphate--PHOSPHOGLYCERALDEHYDE
aka PGAL), extracting high energy electrons, which are picked up by the electron
carrier NAD+, producing NADH
...
Note that the second
phosphate group does not require another ATP molecule
...
Thus
NADH must be continuously oxidized (remove an electron) back into
NAD+ in order to keep this system going
...
If oxygen is available in the
system, the NADH will be oxidized readily, though indirectly, and the
high-energy electrons from the hydrogen released in this process will be
used to produce ATP
...
In the seventh step, catalyzed by phosphoglycerate kinase (an enzyme named for
the reverse reaction), 1,3-biphosphoglycerate donates a high energy phosphate to
ADP, forming one molecule of ATP (substrate level phosphorylation)
...

8
...

● The enzyme catalyzing this step is a mutase (isomerase)
...
Dehydration Reaction:Enolase catalyzes the ninth step
...

10
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Many
enzymes in enzymatic pathways are named for these reverse reactions, since the
enzyme can catalyze both forward and reverse reactions (these may have been
described initially by the reverse reaction that takes place in vitro, under
non-physiological conditions)
...
3 | Oxidation of Pyruvate and the Citric Acid Cycle
● Breakdown of Pyruvate: in mitochondria
○ acetyl CoA: combination of an acetyl group derived from pyruvic acid and
coenzyme A, which is made from pantothenic acid (a B-group vitamin)
■ Pyruvate will be transformed into an acetyl group that will be picked up
and activated by a carrier compound called coenzyme A (CoA)
■ CoA made from vitamin B5
■ Major function: to deliver the acetyl group derived from pyruvate to the
next stage of the pathway in glucose catabolism
○ 3 Step Process:

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●

1
...
The result of this step is a
two-carbon hydroxyethyl group bound to the enzyme (pyruvate
dehydrogenase)
...

a
...

2
...
The high energy
electron from NADH will be used later to generate ATP
...
The enzyme-bound acetyl group is transferred to CoA, producing a
molecule of acetyl CoA
...

○ Steps in the Citric Acid Cycle:
1
...
Condensation Step: combining the two-carbon acetyl group with a
four-carbon oxaloacetate molecule to form a six-carbon molecule of
ctirate
...
CoA is bound to a sulfhydryl group (-SH) and diffuses away to
eventually combine with another acetyl group
...
Rate of this reaction controlled by negative feedback and the
amount of ATP available
...
If ATP is in short supply, the rate increases
...
Citrate loses one water molecule and gains another as citrate is converted
into its isomer, isocitrate
...
Isocitrate is oxidized (loses an electron), producing a five-carbon molecule,
α-ketoglutarate, together with a molecule of CO2 and two electrons,

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which reduce (gain an electron) NAD+ to NADH
...

4
...
Α-ketoglutarate is the product
of step three, and a succinyl group is the product of step four
...
The enzyme that catalyzes step four is regulated by
feedback inhibition of ATP, succinyl CoA, and NADH
...
A phosphate group is substituted for coenzyme A, and a high-energy bond
is formed
...

a
...

i
...
Example: heart and skeletal tissue
ii
...
Example: Liver
b
...

Example: protein synthesis
6
...
Two hydrogen
atoms are transferred to FAD, producing FADH2
...
Unlike NADH, this carrier remains attached to the enzyme and
transfers the electrons to the electron transport chain directly
...

7
...
The last step in the
citric acid cycle regenerates oxaloacetate by oxidizing malate
...

Products of the Citric Acid Cycle:
○ Two carbon atoms come into the citric acid cycle from each acetyl group,
representing four out of the six carbons of one glucose molecule
...

■ The two acetyl carbon atoms will eventually be released on later turns of
the cycle; thus all six carbon atoms from the original glucose molecule are
incorporated into carbon dioxide
...

These carriers will connect with the last portion of aerobic respiration to produce
ATP molecules
...

Amphibolic: both catabolic and anabolic; several intermediate compounds in the
citric acid cycle can be used in synthesizing non-essential amino acids
7
...
This causes hydrogen ions to
accumulate within the matrix space through ATP synthase
...

○ Electron Transport: a series of redox reaction that resemble a relay race or bucket
brigade in that electrons are passed rapidly from one component to the next, to
the endpoint of the chain where the electrons reduce molecular oxygen, producing
water
...
This complex,
labeled I, is composed of flavin mononucleotide (FMN) and an iron-sulfur
(Fe-S)-containing protein
...

● Prosthetic Group: a non-protein molecule required for the activity
of a protein; are organic or inorganic, non-peptide molecules bound
to a protein that facilitate its function; prosthetic groups include
coenzymes, which are the prosthetic group of enzymes
● NADH dehydrogenase: a very large protein, containing 45 amino
acid chains
...

○ Q and Complex II:
■ Directly receives FADH2, which does not pass through complex I
...

■ Q receives the electrons derived from NADH from complex I and the
electrons derived from FADH2 from complex II, including succinate
dehydrogenase
...


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●

●

Since these electrons bypass and thus do not energize the proton
pump in the first complex, fewer ATP molecules are made from the
FADH2 electrons
...

○ Complex III:
■ Cytochrome Oxidoreductase: composed of cytochrome b, another Fe-S
protein, Reiske center (2Fe-2S center), and cytochrome c proteins
● Cytochrome proteins have a prosthetic group of heme
○ Heme similar to the heme in hemoglobin, but it carries
electrons, not oxygen
...

○ The heme molecules in the cytochromes have slightly
different characteristics due to the effects of the different
proteins binding them, giving slightly different
characteristics to each complex
...

○ Complex IV:
■ Composed of cytochrome proteins c, a, and a3
...


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○

The uneven distribution of H+ ions across the membrane establishes both
concentration and electrical gradients (thus, an electrochemical gradient), owing
to the hydrogen ions’ positive charge and their aggression on one side of the
membrane
...

○ Many ions cannot diffuse through the nonpolar regions of phospholipid
membranes without the aid of ion channels
■ Hydrogen ions in the matrix can only pass through it by an integral
membrane protein called ATP synthase
...

● The turning of parts of this molecular machine facilitates the
addition of phosphate to ADP, forming ATP, using the potential
energy of the hydrogen ion gradient
...
These atoms were
originally part of a glucose molecule
...

■ The extra electrons on the oxygen attract hydrogen ions (protons) from
the surrounding medium, and water is formed
...

7
...
The loss of carbon dioxide reduces the size of the
molecule by one carbon (leaving only two carbones left), making
acetaldehyde
...

○ Other types of fermentation:
■ Facultatively Anaerobic: many prokaryotes can switch between aerobic
respiration and fermentation, depending on the availability of oxygen
...

7
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■ Made and stored in both liver and muscle
■ Glycogen will be hydrolyzed into glucose monomer (G-1-P) if blood sugar
levels drop
...
Glycogen is
broken down into G-1-P and converted in both muscle and liver cells, and
this product enter the glycolytic pathways
...

○ Fructose: one of the three dietary monosaccharides, along with glucose and
galactose (which is part of the milk sugar, disaccharide lactose), which are
absorbed directly into the bloodstream during digestion
...

■ The carbon skeletons (each amino acid must have its amino group
removed prior to entry) of certain amino acids derived in proteins can feed
into the TCA
■ In mammals, the liver synthesizes urea from two ammonia molecules and
a carbon dioxide molecule
● Urea is the waste product from the nitrogen originating in amino
acids
● Connections of Lipid and Glucose Metabolisms:
○ The lipids that are connected to the glucose pathways are cholesterol and
triglycerides
■ Cholesterol: a lipid that contributes to cell membrane flexibility and is a
precursor of steroid hormones
● Synthesis starts with acetyl groups and proceeds in only one
direction (irreversible)
■ Triglycerides: a form of long-term energy storage in animals
● Made of a glycerol and three fatty acids
● Can be both made and broken down through parts of the glucose
catabolism pathways
...

○ Beta-Oxidation: catabolizing fatty acids in the matrix of the
mitochondria and converts their fatty acid chains into two
carbon units of acetyl groups
7
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Glut4 allows glucose to enter the cell
...


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■

●

Reactions that are catalyzed by only one enzyme can go to equilibrium,
stalling the reaction
...

■ The enzyme catalyzing the first committed reaction of the pathway is
controlled by attachment of a molecule to an allosteric site on the protein
...

○ This alterations of the protein’s (the enzyme’s) structure
either increases or decreases its affinity for its substrate,
with the effect of increasing or decreasing the rate of the
reaction
...

○ Effective as long as the chemical affecting it is attached to
the enzyme
...

Control of Catabolic Pathways
○ Glycolysis Regulation:
■ Hexokinase: first step; catalyzes the phosphorylation of glucose, which
helps to prepare the compound for cleavage in a later step
...

■ When hexokinase is inhibited, glucose diffuses out of the cell and does not
become a substrate for the respiration pathways in that tissue
...

● Phosphofructokinase: the main enzyme controlled in glycolysis
...

■ An increase in citrate concentration can occur
because of a blockage in the citric acid cycle
■ Pyruvate Kinase: the last step in glycolysis
● The pyruvate produced can proceed to be catabolized or converted
into the amino acid alanine
...


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○

○

The enzyme’s activity is increased when fructose-1,6-bisphosphate
(intermediate in the first half of glycolysis) levels increase
...

○ Dephosphorylation by a phosphatase reactivates it
● Pyruvate kinase also regulated by ATP (a negative allosteric effect)
■ Pyruvate Dehydrogenase:
● If more energy is needed, more pyruvate will be converted into
acetyl CoA through the action of pyruvate dehydrogenase
...

● Regulated by phosphorylation: a kinase phosphorylates it to form
an inactive enzyme, and a phosphatase reactivates it
...

Citric Acid Cycle:
■ Controlled through the enzymes that catalyze the reactions that make the
first two molecules of NADH (isotrate dehydrogenase and α-ketoglutarate
dehydrogenase)
● When ATP and NADH levels adequate, the rates of these reactions
decrease
○ When more ATP is needed, as reflected in rising ADP levels,
the rate increases
...

ETC:
■ Specific enzymes of the electron transport chain are unaffected by
feedback inhibition, but the rate of electron transport through the pathway
is affected by the levels of ADP and ATP
...

● Decreased ATP usage by a cell is indicated by a lower concentration
of ADP, and now, ATP begins to build up in the cell
...
1 | Cell Division
● Genomic DNA:
○ Cell Cycle: an orderly sequence of events that describes the stages of a cell’s life
from the division of a single parent cell to the production of two new daughter
cells
■ Highly regulated
○ Genome: a cell’s DNA, packaged as a double-stranded DNA molecule
■ Prokaryotes: genome composed of a single, double stranded DNA molecule
in the form of a loop or circle
● Plasmids: smaller loops of DNA found in some prokaryotes that are
not essential for normal growth
● Nucleoid: the region in the cell containing the genetic material
■ Eukaryotes: genome consists of several double stranded linear DNA
molecules
● Example: Humans cells have 46 chromosomes; two matched sets of
autosomes and a pair of sex chromosomes
○ Diploid: cell, nucleus, or organism containing two set of
chromosomes (2n)
■ n: the letter n is used to represent a single set of
chromosomes
■ Gametes: haploid reproductive cell or sex cell (sperm, pollen grain, or egg)
● Haploid: cell, nucleus, or organism containing one set of
chromosomes (n)
○ Homologous Chromosomes: matched pairs of chromosomes in a diploid organism

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■

Homologous chromosomes are the same length and have specific
nucleotide segments called genes in exactly the same location, or locus
...

● Locus: position of a gene on a chromosome
● Eukaryotic Chromosomal Structure and Compaction:
○ Compaction of DNA: all 46 chromosomes laid out end to end is 2m; diameter only
2nm
○ First Level of Compaction: A DNA molecule in this form is about seven times
shorter than the double helix without the histones, and the beads are about 10nm
in diameter, in contrast with the 2-nm diameter of a DNA double helix
■ Histone Proteins: one of several similar, highly conserved, low molecular
weight, basic proteins found in the chromatin of all eukaryotic cells;
associates with DNA to form nucleosomes
● Chromatin: DNA histone complex
○ Nucleosomes: subunit of chromatin composed of a short
length of DNA wrapped around a core of histone proteins
...
2 | The Cell Cycle
● The Cell Cycle: an ordered series of events involving cell growth and cell division that
produces two new daughter cells
● Interphase: period of the cell cycle leading up to mitosis; includes G1, S, and G2 phases
(the interim period between two consecutive cell divisions)
○ G1 Phase (First Gap):
■ Little changes visible microscopically

24

■

●

Cell accumulates the building blocks of chromosomal DNA and the
associated proteins as well as accumulating sufficient energy reserves to
complete the task of replicating each chromosome in the nucleus
○ S Phase (Synthesis of DNA):
■ DNA replication proceeds through the mechanisms that result in the
formation of identical pairs of DNA molecules--sister chromatids--that are
firmly attached to the centromere
■ Centrosome is duplicated, give rise to the mitotic spindle
● Mitotic Spindle: the apparatus that orchestrates the movement of
chromosomes during mitosis
● Centrioles: rod-like structure constructed of microtubules at the
center of each animal cell centrosome; help organize cell division
○ G2 Phase (Second Gap):
■ The cell replenishes its energy stores and synthesizes proteins necessary
for chromosome manipulation
...

○ Cell Plate: structure formed during plant cell cytokinesis by
Golgi vesicles, forming a temporary (phragmoplast) and
fusing at the metaphase plate; ultimately leads to the
formation of cell walls that separate the two daughter cells
○ G0​ Phase: distinct from the G1 phase of interphase; a cell in G0 is not preparing to
​
divide
■ Quiescent: refers to a cell that is performing normal cell functions and has
not initiated preparations for cell division
10
...

■ P53: cell cycle regulatory protein that regulates cell
growth and monitors DNA damage; it halts the
progression of the cell cycle in cases of DNA damage
and may induce apoptosis
● Apoptosis: cell suicide to prevent the
duplication of damaged chromosomes
■ P21: cell cycle regulatory protein that inhibits the
cell cycle; its levels are controlled by p53
● Binds and inhibits the activity if the
Cdk/cyclin complex when p53 levels are
high
For the cell to move past each of the checkpoints, all
positive regulators must be turned on and all negative
regulators must be turned off
...
4 | Cancer and the Cell Cycle
● Cancer:
○ Comprises many different disease caused by a common mechanism: uncontrolled
cell growth
○ All cancers start when a gene mutation gives rise to a faulty protein that plays a
key role in cell reproduction
○ Tumor: “-oma”; results from uncontrolled growth of the mutated cells and
outpaces the growth of normal cells in the area
● Proto-oncogenes:
○ Proto-oncogenes: genes that code for the positive cell cycle regulators
○ Oncogenes: mutated version of a normal gene involved in the positive regulation
of the cell cycle; cause a cell to become cancerous
○ In most instances, the alteration of the DNA sequence will result in a less
functional (or non-functional) protein; damage is minimal
...
A
cell that carries a mutated form of a negative regulator might not be able to halt
the cell cycle if there is a problem
...
5 | Prokaryotic Cell Division
● Binary (Prokaryotic) Fission: prokaryotic cell division process
● Five steps:
○ Replication of the circular prokaryotic chromosome begins at the origin of
replication and continues in both directions at once
■ Origin: (also, ORI) region of the prokaryotic chromosome where
replication begins (origin of replication)
○ Cell begins to elongate
...

■ FtsZ: tubulin-like protein component of the prokaryotic cytoskeleton that
is important in prokaryotic cytokinesis (Filamenting
temperature-sensitive mutant Z); a ring composed of repeating units of a
protein called FtsZ directs the partition between the nucleoids
○ The duplicated chromosomes separate and continue to move away from each
other toward opposite ends of the cell
...

○ The FtsZ ring directs the formation of a septum that divides the cell
...

○ After the septum is complete, the cell pinches in two, forming two daughter cells
...

■ Septum: structure formed in a bacterial cell as a precursor to the
separation of the cell into two daughter cells

29

Chapter 11 – Meiosis and Sexual Reproduction
11
...

■ Homologous chromosomes bind firmly together along their length,
forming a tetrad
...

● Chiasmata: the structure that forms at the crossover points after
genetic material is exchanged
○ There must be at least one chiasma per chromosome for
proper separation of homologous chromosomes during
meiosis I
○ Tetrads: two duplicated homologous (four chromatids)
bound together by chiasmata during prophase I
■ Crossing over occurs at the chiasmata
...

Prometaphase I:
■ Homologous chromosomes are attached to spindle microtubules at the
fused kinetochore shared by sister chromatids
■ Chromosomes continue to condense,
■ The nuclear envelope completely disappears
Metaphase I:
■ Homologous chromosomes randomly assemble at the metaphase plate,
where they have been maneuvered into place by the microtubules
...

■ The sister chromatids are still attached to the centromere
...

■ A nuclear envelope forms around each nucleus and the cytoplasm is
divided by a cleavage furrow
...

● Each cell contains one duplicated copy of each homologous
chromosome pair
...


31

■ A new spindle begins to form
...

○ Prometaphase II:
■ The nuclear envelope disappears
...

○ Metaphase II:
■ Sister chromatids line up at the metaphase plate
...

■ Non-kinetochore microtubules lengthen the cell
...

■ Nuclear envelopes surround the four nuclei
...

● Comparing Meiosis and Mitosis:
■ Mitotic divisions are single nuclear division that produce daughter nuclei
that are genetically identical and have the same number of chromosome
sets as the original cell
...

■ The main differences between the processes occur in the first division of
meiosis, in which homologous chromosomes are paired and exchange
non-sister chromatid segments
...
2 | Sexual Reproduction
● Life Cycles of Sexually Reproducing Organisms:
○ Life Cycles: the sequence of events in the development of an organism and the
production of cells that produce offspring
...

■ The zygote immediately undergoes meiosis to form four haploid cells
called spores

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