Biology 243 Condensed Lecture Notes

8/2/2019 Biology 243 Condensed Lecture Notes

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Biology 243 Summary Notes


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Themes 1 and 2

Evolution: A Brief History

- Jean-Baptiste Lamarcko Believed that species changed over timeo Lamarckism Acquired traits can be inherited

- Thomas Malthuso Principle of Populations human population can increase faster than food

supply, and therefore this leads to competition and survival of the fittest

- Alfred Russell Wallaceo Cam up with theory of natural selection independently of Darwin

- Charles Darwino Voyage of the Beagle

Described and collected plant and animal specimens and foundinteresting patterns regarding distribution of species

o The Origin of Species Provides evidence for the evolution of species Idea of descent with modification Describes natural selection as the mechanism for evolutionary change

o The Galapagos Islands Endemics Animals live there that are found nowhere else on earth Limited gene flow between islands and mainland

- Darwins 4 Postulates for Evolution via Natural Selectiono Individuals VARYo More offspring are produced than can survive and/or reproduceo Survival and reproduction is not randomo Some variation is passed to offspring (Heritable)

- Evolutiono A change in the frequency of an alleleo Evolution can occur quickly enough to observe within a matter of seasonso Evolutionary change can be very small scale


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Theme 3

Topic 1 DNA as an Information Molecule

Genotype

- Entire DNA sequence (genome) that is inherited from parents to progeny and containsall the biological information needed to build and maintain a living organism

- The full set of genes inherited by an organism- Turning on genes produces RNA and proteins

Phenotype: body plan, behaviour, metabolism, & much more

- Proteins determine phenotype, as proteins ultimately control every reaction in the cello Enzymes, structural proteins, signalling proteins, etc.

Establishing DNA as the Hereditary Molecule

- Griffith Transformation Principleo The conversion of a cells hereditary makeup by the uptake of DNA from another

cell

o Injected mice with the bacteria to understand how infection takes place- Avery et al. Identifying the Chemical Nature of the Transformation Principle

o Determined whether it was DNA, RNA, orprotein that allowed for transformation

principle to take place

o Found that DNA was the transformationmolecule

- Hershey and ChaseThe Blender Experimento Determined that the nature of genetic material

in the bacteriophages was DNA, not proteins

o Tagged bacteriophage DNA and proteins withradioactive isotopes

32P and

35S respectively


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C1

OH

H

C2

H

OH

C3H

OH

4C

HOCH2

H

5O

C1

OH

H

C2

H

H

C3H

OH

4C

HOCH2

H

5O

Ribose (RNA) 2-Deoxyribose(DNA)

Topic 2 Structure of DNA

Components of DNA

- DNA consists of equal parts ofo Pentose Sugar (Ribose for RNA, Deoxyribose for DNA)o Phosphateo Nitrogenous Bases

- Pentose Sugarso Carbon atoms are labeled for orientationo Absence of the 2 hydroxyl group in deoxyribose increases mechanical flexibility

in DNA compared to RNA

- Deoxynucleotides (dNTPs) are the building blocks of DNA- They form by the removal of water

Purines Pyrimidine

Guanine Cytosine

Uracil ThymineAdenine


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Polynucleotides

- The polymerization of nucleotide monomers- Covalent bonds form phosphodiester back

bone

- Polynucleotide has directionality and polarity- Type of nucleic acid depends on sugar (DNA =

deoxyribose, RNA = ribose) present

- Upstream = towards 5 PO43- end- Downstream = towards 3 OH- end- Synthesized in 5 to 3 direction

Chargaffs Rule

- States % purines = % pyrimidinesFranklins X-Ray Diffraction

- Revealed the structure of DNA- Significant patterns in arrangement of atoms

viewed in repeating intervals

- It was discovered that DNA was cylindrical,and ultimately helical

Watson and Crick

- Created a scale model of DNA- Two sugar-phosphate backbones running

antiparallel to one another

- They discovered the backbone to be hydrophilic, and the bases to be hydrophobic- Purines always paired with pyrimidines complimentary base pairing

o Purine-purine base pairing is too wideo Pyrimidine-pyrimidine base pairing is too narrow

- Hydrogen bonds hold the nucleotides and the two strands together

%A = %T and %C = %G
http://localhost/upload.wikimedia.org/wikipedia/commons/6/67/AT_base_pair_jypx3.pnghttp://localhost/upload.wikimedia.org/wikipedia/commons/2/21/GC_base_pair_jypx3.png


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- Watson and Crick decided that genetic information must be coded in the nucleotidesequences of DNA

Watson and Cricks Model of DNA Replication

- Parental strands act as templates for replication through complimentary base pairing- Parental strands unwind by breaking hydrogen bonds- Semiconservative replication where new double helix contains one parental and one

newly synthesized strand

DNA Organization

- Can be circular or linear- Prokaryotes

o Typically have one chromosome (usually circular)o Also have other small independent circular DNA called plasmids in the cytoplasm

- Eukaryoteso Linear and enclosed in nucleotideso Compacted in DNA to fit in cell nucleuso Chromosomal structure protects DNA from damageo Chromosomes can easily be separated during cell division

Essential Components of Eukaryotic Chromosomes

1) Origin of Replicationo The attraction of multiple proteins to initiate DNA replication

2) Centromereo DNA sequences required for correct segregation of chromosomes after DNA

replication

3) Telomereso DNA sequences located at the ends of the chromosome that attracted proteins

preventing degradation and allow for proper replication of chromosomal ends

Histones

- Positively charged proteins that DNA wind around- Histone H1: Binds DNA to nucleosomes to form

chromatin fibre

- ProkaryotesDO NOT have histones since bacterialchromosomes need not be compacted


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Chromatin

- Heterochromatino Regions of higher DNA compactiono Where transcription is turned offo Found in telomeres and centromereso Barr Body an X chromosome becomes inactive by the block of heterochromatin

- Euchromatino Regions of less DNA compactiono High levels of gene expression

Note: More complex organisms typically have lower gene densityan organisms complexity

is not directly proportional to genome size

Topic 3 DNA Replication

Three Putative Models of DNA Replication

1) Semiconservative Complimentary base pairing allows for parental strands to act as templates for

replication

Parental strands unwind through breaking of H-bonds2) Conservative

After replication, both daughter strands pair up3) Dispersion

Daughter strands will have a mixture of parental and newly-synthesized DNA

1 2 3


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Meselson and Stahl Experiment

- Distinguished between old and new DNA to determine how replication occurred- DNA labelled with isotopes 15N and 14N and isotopes incorporated into DNA molecules

via nitrogenous bases

- Tracking of parental and newly synthesized DNA strands over many generationsanalyzed

- Discovered that semiconservative model was correctDNA Polymerases

- Synthesizes the new strand in the 5-3 direction, with new nucleotides added to thenew strand at the 3 OH end

- Requires an RNA primer to begin synthesis- Contains a single active site that can catalyze four different reactions and requires

optimum confirmation of site for incoming nucleotide to add to correct base pair

DNA Replication in Prokaryotes

1) Initiation Unwinding and separation of the two template DNA strands, forming two

replication forks

2) Elongation Simultaneous synthesis of the two new DNA strands from the template strands

by DNA polymerase

3) Termination When forks meet at opposite side of circular DNA, replication stops and protein

complex of DNA polymerase drops off from DNA


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Replication Forks

- One strand continuously synthesized (leading strand)- Other strand synthesized discontinuously (lagging strand)- The small fragments (Okazaki fragments) are linked

together

DNA Replication Enzymes

- The Replisome is the complex of enzymes that replicateDNA

Enzyme Function

Helicase Unwinds the double helix by breaking hydrogen bondsPrimase Synthesizes RNA primers for DNA polymerase

Single-Strand Binding

Protein

Stabilizes ssDNA before replication by preventing reannealing so

that the strands can serve as template

DNA

Topoisomerase/Gyrase

Removes super coils that form ahead of the replication fork,

relieves torque/tension of mainly circular DNA

DNA Polymerase III Synthesizes DNA by adding nucleotides to the new DNA strand

DNA Polymerase I Removes RNA primer and fills the gaps with DNA

DNA Ligase Joins the ends of DNA segments by forming phosphodiester

bonds

DNA Replication Steps

1) Helicase unwinds the DNA and Primase synthesizes RNA primers


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2) RNA primers used as starting points for addition of nucleotides by DNA Polymerase

3) DNA unwinding, leading strand synthesized continuously, lagging stranddiscontinuously

4) DNA Polymerase I removes RNA primer, replaces with DNA, leaving a nick


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5) DNA Ligase closes the nick

6) DNA continues to unwind and synthesis cycle repeats

Plasmid Replication

- Occurs by the process of rolling circle replication- Fertility plasmids contain genes for conjugation


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DNA Replication in Eukaryotes

- There are multiple origins along chromosomes so DNA replication can be completed intime during S phase

- End Replication Problemo When RNA primer is removed, DNA Polymerase I can elongate 3 end of Okazaki

fragment

o At the very end of chromosome, no such fragment is present on 3 endo Therefore there is additive loss at chromosomal ends after each replicationo Genes can become deleted leading to organismal deatho Telomeres solve this problem

Telomeres

- Genes protected by a buffer of non-coding DNA added to the 3 end of chromosomes byTelomerase

- Telomerase adds additional telomere repeats to the end of the template strand prior toreplication

- Approximately 10000 bp long- Can be worn away after each replication, and when completely gone, cell stops dividing

Proofreading Activities of DNA Polymerases

- 3 exonuclease activity to remove the most recent mismatched nucleotidesPhotoreactivation: repair of UV-Induced DNA Damage

- DNA absorbs photonic energy resulting in fusing of adjacent thymines- Photolyase recognizes this and uses light energy to separate the fused thymines

(photoreactivation)

Topic 4 Central Dogma


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Central Dogma: The universal flow from DNA to protein in order to convert genotype to

phenotype

Gene

- The basic physical and functional unit of heredity- Made up of DNA and act as instruction to make proteins- Genes encode for:

o Coding RNA (mRNA): codes for a protein o Noncoding RNA (tRNA, rRNA, snRNA, microRNA): does not code for a protein

Beadle and Tatum

- Hypothesized that genes encode enzymes that function at each step of a biochemicalpathway needed to make an essential nutrient

- Believed that mutating a gene that coded for an enzyme would interrupt metabolicpathway and the organism would no longer be able to synthesize needed nutrient

- They showed the direct relationship between gene and enzyme

The Genetic Code

- Nonsense/Stop Codonso Three codons that do not specify amino acids

- Redundnacy/Degeneracyo Synonyms for same amino acid

- There are no commas in the genetic code, and therefore there is only one correctreading frame


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Topic 5 Transcription

Transcription in Prokaryotes

1) Initiation RNA Polymerase binds to promoter DNA unwound freeing the template strand (transcription bubble) Ribonucleotides added de novo

2) Elongation RNA Polymerase moves along template DNA unwinding DNA in front, and

reannealing DNA behind

3) Termination Sequences located at the 3 end of the new RNA molecule causes dissociation of

the RNA and RNA polymerase from DNA template

RNA Polymerase

- Binds to promoter region to initiatetranscription

- Does not need a primer- Unwinds and rewinds DNA helix during

RNA synthesis

- The promoter specifies where the RNAPolymerase will begin transcription

Prokaryotic Promoter

- Located immediately upstream (towards 5) of transcriptional start point (+1)- A specialized DNA sequence where transcription determines which gene is turned on or

off

- Promoter strength determines how well the RNA polymerase binds and initiatestranscription


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Pribnow Box - The sequence TATAAT and serves as the location of transcription initiation

Prokaryotic Elongation

- RNA is created in the 5 to 3 direction- Uses the 3 to 5 DNA strand as a template- RNA Polymerase breaks the complimentary base pairs by breaking hydrogen bonds- Behind the enzyme, DNA strands reforms a double helix- Transcription continues until the end of the gene- Another RNA polymerase can start creating another RNA transcript as soon as there is

room at the promoter

Prokaryotic Termination

- The completed RNA molecule is released from template DNA- Double helix of DNA reforms- In prokaryotes, transcription is terminated in two ways:

o Rho-Independent Termination Terminator sequence in mRNA base pairs with itself to form GC hairpin Causes RNA polymerase to stall and dissociate

o Rho-Dependent Termination Terminator sequence in mRNA is recognized and bound to the Rho

helicase which unwinds the RNA from the template DNA and RNA

polymerase

Features of the Prokaryotic Gene

- Operono Cluster of prokaryotic genes

and the DNA sequences

involved in their regulation

- Promotero Transcription initiation

Note: Prokaryotic mRNA is polycistronic

a single mRNA encodes for multiplepeptides usually involved in the same function


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Comparing RNA Transcription and DNA Replication

Transcription in Eukaryotes

- Three types of RNA polymerases I, II, III which make rRNA, mRNA, and tRNA respectively- Several general transcription factors (GTFs) are necessary to recruit RNA polymerase to

the promoter

- mRNA termination mediated by a polyadenylation signal- Eukaryotic mRNA is monocistronicEukaryotic Initiation

- RNA pol I and III non-protein coding genes- RNA pol II protein-coding genes- RNA pol does not recognize promoter- A key element in protein-coding genes = TATA Box- Transcription factors recognize and bind to TATA Box RNA pol II recognizes multi-

protein complex and bind to it

DNA

Promoter

TATABox

Transcription Unit

3 UTR

IntronExon

5 UTR

IntronExon Exon


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- Transcription initiation mediated by binding of DNA-binding proteins to specific regionson gene

- General Transcription Factors bind to promoter and recruit RNA polymerase II forinitiation (basal transcription)

- Activator Transcription Factors bind to promoter proximal regions and enhancerregions to cause

o Enhancerbinding proteins increase transcription rate by stimulating initiationof RNA polymerase

o Enhancers and associated proteins are brought close to the promoter by DNAlooping

TFI

TFIID, A, B, F, E, H

(GTFs) and RNA Pol II


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Chromatin Remodelling During Initiation

- Transcription initiation inhibited by densearrays of nucleosomes

- Access of promoter to RNA polymerase andGTFs requires reorganization of nucleosomes

- Activator proteins displace nucleosomes frompromoter regions

- Activator proteins recruit histoneacetyltransferase that add acetyl groups to

histones loosening DNA binding

mRNA Processing in Eukaryotes

- Precursor-mRNA contains transcribed intronsand exons

- Pre-mRNA undergoes processing in the nucleus to produce mature translatable mRNA- A 5 Cap (modified guanosine triphosphate) added by a capping enzyme following

transcription initiation

o Functions as a binding site during translation- Transcription termination controlled by a polyadenylation signal in the 3 sequence

o Protects mRNA from RNA digesting enzymes

Eukaryotic Transcriptional Termination slide 34 in T3T5

- Termination is linked to polyadenylation- CPSF (Cleavage and Polyadenylation Specificity Factor) cleaves mRNA after

transcription passes the poly-A signal- The poly-A tail is added to the 3 end of mRNA by poly-A polymerase


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mRNA Splicing: pre-mRNA to RNA

- pre-mRNA contains exons and introns (exons being coding segments, introns being non-coding segments)

- Introns are removed from the pre-mRNA and exons spliced together to form maturemRNA

- Splicing is carried out by the spliceosome which is made up of non-coding mRNAs calledsnRNPs or Small Ribonucleoprotein Particles

- After introns are removed, they are degraded and snRNPs are free to be reused

Alternative mRNA Splicing

- Joining different exons can amount todifferent protein diversity

- Several related protein products (isoforms) orthe same mRNA molecule can be formed by

making different combination of mRNAs

- Alternative splicing dramatically increases the number and variety of proteins that canbe encoded by the genome

- The most highly expressed genes had only SHORT INTRONS


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Transcriptional and Posttranscriptional Regulation in Eukaryotes

- 5 cap, 3 polyadenylation tail, splicing, and microRNAs- Half-life of mRNA can vary significantly and depends upon regulation of mRNA after

transcription

- Removal of the poly-A tail or 5 cap results in mRNA degradation by exoribonucleases- MicroRNAs as a regulator:

o Noncoding RNA located within genes are transcribed by RNA polymerase IIo Hairpin miRNA cleaved to 21-23 bp by Dicer Rnaseo Silencing RNAs (siRNAs) are unwound and one of the strands functions as a

template in RISC (RNA induced silencing complex) to guide cleavage of

complimentary mRNA and inhibit translation

Reverse Transcription

- Found in viruses with RNA genomes- Even if viral genome is RNA, a DNA template must be made to produce mRNA

Topic 6 Translation

The Genetic Codes

- Consists of 64 sense codons and the amino acids specified by these codons- Codons are written 5 to 3as they appear in the mRNA- AUG (methionine) an initiation (start) codon- UAA, UAG, UGA = termination codons and do not code for amino acids

o The tRNA does not bind to these codons- Codons are non-overlapping and contain no gaps

Amino Acids

- Contain an amino acid and carboxyl group bonded to a central carbon with ahydrogen and R functional group

- R group determines uniqueness of amino acid- Amino acids joined together by a covalent peptide bond- Polypeptides are chains of amino acids linked by peptide bonds- Nonpolar amino acids (R groups containCH2 or -CH3)- Uncharged polar amino acids (R groups usually containOH)- Charged amino acids (R groups that contain acids/bases that can ionize)- Aromatic amino acids (R groups contain benzene ring)


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The Ribosome

- A complex molecule made of rRNA molecules form a factor for protein synthesis in cells- Composed of two subunits

o Large 50S subunito Small 30S subunit

- Each subunit exists separately in the cytoplasm, but the two join together on the mRNAmolecule

- The ribosomal subunits contain proteins and specialized RNA molecules ribosomalrRNA and transfer RNA (tRNA)

- 3 binding sites (A, P, E)o Aminoacyl (A) site: binds to aminoacyl-tRNAo

Peptidyl (P) site: for the aminoacyl-tRNA carrying the growing polypeptide chaino Exit (E) site


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tRNA Molecules

- tRNAs bring amino acids to the ribosomeo Small RNAs (75-90 nucleotides)o Act as an adaptor between codons and amino acids

- Aminoacyl-tRNA (charging): tRNA + amino acido Aminoacyl-tRNA synthetase adds correct amino acid to the acceptor stem of

correct tRNA- tRNA and the Wobble Effect

o The complete set of 61 codons can be read by FEWER than 61 tRNAso This is because of the pairing properties in the bases of anticodonso Pairing of anticodon with first 2 nucleotides is precise, but the third has more

flexibility

o Third position can wobble


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Phases of Translation

- The beginning of mRNA is not translated during initiation- Untranslated region (UTR) is located between the first nucleotide that is transcribed and

one before the start codon (AUG) region

o Does not affect the sequence of amino acids in a protein

Initiation

- 5 UTR contains the ribosomal binding site- Initiation occurs with the interaction of certain key proteins of 5 cap- Small ribosomal subunit binds to 5 UTR- Methionine charged tRNA binds to the AUG start codon, completing the initiation

complex

- Large ribosomal subunit joins initiation complex- Met-tRNA now occupies P site establishing the reading frame

Elongation

- Elongation factor G - a protein that allows the ribosome to move along mRNA in the 5to 3 direction (translocation)

- The tRNA for second codon can then bind to the A site- tRNA molecule enters E site and is released into cytoplasm to pick up another amino

acid


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Termination

- Termination codons are not recognized by tRNAs- In place of a tRNA, a termination factor binds and facilitates release of mRNA from the

ribosome and causes the separation of the ribosome

Post-translational Modification of Polypeptides

- Eukaryotic proteins inactive when released from ribosome- Post-translational modification is necessary protein biosynthesis- Enzymes may remove amino acids from the amino end of the protein- Methionine is usually taken off during post-translational modification

Topics 7 & 8 Changes in DNA Sequences and Spontaneous MutationsMutation: A change in the physics structure or in the nucleic acid sequence, resulting in an

error in the transmission of genetic information

- Occurs in DNA and RNA- Occurs in somatic or germ line cells- Can result in change to the amino acid sequence resulting in phenotypic variation- Effects can be neutral, deleterious, or beneficial

Types of Mutations

- Somatic:o Occur in any of the body cells except gamete cellso Therefore, these mutations are NOT heritable

- Germ Line:o These types of mutations are of evolutionary significanceo Mutation is the only process that is both necessary for evolution and sufficient

by itself to cause evolution

- Small Scale locus specifico Point mutations (missense, nonsense, silent)o Insertions/deletions (frameshift)

- Large Scale - chromosomalo Gene duplications/deletionso Translocations/inversions


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Point Mutations

- Substitution of a single pair of nucleotide bases with another pair- Substitution of purine for purine or pyrimidine for pyrimidine is 2x as common as a

pyrimidine for purine substitution

- Can have discrete effects on the amino acid sequenceo Missensecodes for different amino acido Nonsensenew codon is a STOP codon causing premature terminationo Silent (Synonymous)no change in amino acid sequence

Insertion/Deletion/Frameshift

- A shift in reading frame, affecting translation of other codons in coding DNA


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Large Scale Mutations Chromosomal Duplication/Deletion

- Entire chromosomes can also change- An individual with an abnormal set of chromosomes is an aneuploid- Aneuploidy occurs mainly through non-disjunction

o ex) Downs Syndrome (trisomy 21)Copy Number Variation (CNV)

- Large regions of the genome that have been deleted or duplicated- Variation accounts for ~12% of human genomic DNA

Spontaneous Mutations (Natural)

- Naturally occurring as a result of errors in DNA replicationo ex) Deamination and depurination of nitrogenous bases

- Slippage Mutationso Causes an increase and decrease in the number of sequenceso Common in repetitive sequences of DNA

- Microsatelliteso Short tandem repeats (STR) of DNAo Mutations can lead to a new number of repeats (due to replication slippage, and

thus new alleles)

- Spontaneous mutation rates vary with organism, and with tissue type in organism


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Induced Mutations

- Mutagenso Induce mutations by replacing a baseo Alters a base causing a mispair with another baseo Damages bases so no pairing is possible

- Base Analogso Mimic bases and incorporates into DNA (can cause mispairing during DNA

replication)

- Chemicals that alter base structure- Damage to bases through UV radiation exposure

Note: Not all types of mutations occur with equal probability and therefore are not truly

random occur randomly with respect to whether their effects are beneficial or deleterious

RNA Mutations

- Very high rates of mutations in RNA viruses- Viral RNA polymerases lack proof-reading ability of DNA polymerases

Mutant Alleles

- Wild Type Alleleo Normal form of the gene found in nature of the standard laboratory strains of a

model organism

- Amorphs/Null Alleleso No gene function, usually entire gene is deleted (recessive mutation)

- Hypomorphso Reduced gene function relative to wild type (recessive mutation in gene that

partially affects gene function)

- Hypermorphso Enhanced gene function relative to wild type (dominant gain-of-function

mutation)


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Topic 9 Inheritance

Cell Division in Prokaryotes

- Binary Fissiono Prokaryotes undergo a cycle of cytoplasmic growth,

DNA replication, and cell division

o Replication begins at orio Replicated origins migrate to ends of poleso Inward growth of plasma membrane and partition

assembly of new cell wall, dividing replicated DNA

producing two daughter cells

o Effective method since only one chromosomeEukaryotic Cell Cycle

Interphase

- Gap 0 (G0) Phaseo A resting phase where the cell has left the cycle and has stopped dividing

- Gap 1 (G1) Phaseo Initial period of cytoplasmic growtho Synthesis of enzymes required for S

phase, mainly those needed for DNA

replication and structural proteins- Synthesis (S) Phase

o Rapid duplication of DNA andchromosomal proteins

- Gap 2 (G2) Phaseo Period of cell growtho End of G2 signifies the end of interphase

- G2/M Checkpointo A DNA damage checkpointo

An arrest of the cell in G2 prior to mitotic entry in response to genotoxic stresssuch as:

UV radiation Oxidative stress DNA intercalating agents


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Mitosis

- Prophaseo Chromatin condenses into chromosomeo Nucleolus disappears RNA synthesis ENDSo Chromosomes bounds together at centromereo Centrosomes nucleate microtubules to form spindle by polymerizing tubulino Molecular motor proteins push centrosomes to create spindle poles

- Prometaphaseo Nuclear membrane breakdowno Spindle microtubules have direct access to chromosomeso Each kinetochore of sister chromatids attached to spindle microtubuleso Chromosomes move to equator of cello Microtubules connect to each chromosome at its kinetochore, a complex of

proteins positioned at the centromere

- Metaphaseo Chromosomes align along cell equatoro Kinetochore microtubules attach the chromosomes to the spindle pole

- Anaphaseo Sister chromatids separate, moving to

opposite poles becoming independent

chromosomes

o Enzymatic breakdown ofcohesin linkedthe sister chromatids together during

prophase

o Chromosomes walk themselves alongstationary microtubules, using motor

proteins in their kinetochores

- Telophaseo Chromosome arrive at poleso Mitotic spindle disassembleso Formation of new nuclear membrane

around each group of chromosomes- Cytokinesis

o Physical process that splits the parent cellinto two identical daughter cells with cytoplasm dividing by furrowing

o Cell membrane pinches in at the cell equator, forming cleavage furrowo Position of furrow dependant on position of astral and interpolar microtubules


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Regulation of the Eukaryotic Cell Cycle

- G1/S Control Pointo Initiation of DNA synthesis

- G2/M Control Pointo Regulation of mitotic entry

- Progression past these points depends upon activation ofCDK(cyclic dependent kinase)bound to its regulatory cyclin subunit prompting cell to proceed into next cell cycle

phase

o CDK allows cycle to proceed past control points, telling cell to proceed to nextstep of cell cycle

- Cyclins are expressed in specific phases of the cell cycle which determines when a CDK isactive

- Cell Size Checkpointo Must attain a certain size at START, and G2/M checkpointso The cells must be twice as big as daughter cells at G2/M checkpoint

When Cell Cycle Regulation Goes Wrong

- Cancero Uncontrolled cell divisiono Altered expression of multiple genes due to mutations

- Oncogeneso Positive regulators (gain of function) in the cell cycle

- Tumor Suppressor Geneso Loss of function at checkpoint geneso Mutation prevents there from being division regulation

START

START

G1

G1

Buddingyeast

Mother cell (larger)

Daughter cell (smaller)

Daughter cell spends a longer time in G1 phase

as it must take more time to grow

These mutated

genes implicate

cancer


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Cell Division Senescence (When cells become very old)

- Infinite division of cells impossibleo Due to damage, defective telomeres, etc.

- Genes affecting cellular again we first found to be tumor supressors- Division arrest followed by either

o Apoptosis (cell suicide)o Senescence (stopping cell division)

Genetic Recombination

- At the level of population, variation is necessary for evolution bynatural selection

- Ultimate source of variation is mutation- Diversity increases through genetic recombination

Genetic Recombination in Bacteria

- F-factor and conjugation bridge necessary for genetic material transfer-

Bacterial conjugation is equivalent of mating as genetic material is exchanged- Bacteria have a conjugative plasmid integrated into genomic DNA called F-factor

o Attempts to transfer entire DNA through the mating bridgeo Since F-factor transfers itself during conjugation, the rest ofgenome is dragged

along with it

Asexual Sexual

- Offspring are clones of parents

- Inheritance of ALL parental genes in

offspring

- Transformation/transductionprovide addition of sources of DNA

for recombination

- Gametic union

- Dependant on meiosis

- Inheritance of alleles from each parent

- Offspring not likely to be likeparent/sibling

Genetic recombination


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- F+ and F- cell differ in alleleso F+ = a+, b+, c+, d+o F- = a-, b-, c-, d-

- Recombination occurs between donor chromosome and recipientschromosome

- Crossover produces a b+ recombinant (F-: a-, b+, c-, d-)Strategic Sex

- Evolution of recombination had to have happened in presence ofasexuals

- Sex is expensiveo Cost of finding a mateo Ecologicalo

Mechanical

Comparing Mitosis and Meiosis

F+ cell F- cell

Mitosis

Meiosis


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Fertilization (aka Syngamy)

- Haploid gametes come together to create a diploid zygotethrough fusion

- Resulting in a zygote with a maternal and paternal cellIntroduction to Meiosis

- Reduction Division (Meiosis I)- Equational Division (Meiosis II)- G1, S, G2 and M still occur- DNA replicated in S phase

o Each chromosome copied (now there is a pair of sisterchromatids refer to diagram)

Meiosis 1

- Prophase 1o Synapsis occurs (homologous chromosomes pair up)o Chromosomes have sequences that act as signals for

pairing and alignment

o Fully paired chromosomes are called tetrads whenthere are four chromatids together

o Holliday Junctions

Important in maintaining genomic integrity (faithful replication) Promotion of crossing over at the junction

o Genetic recombination/crossing over physical exchange mixing alleles of thehomologous chromosomes

Occurs between any two chromatids in tetradstructure

Visualized in structures called chiasmata Cells not forming chiasmata may cause aneuploidy in

gametes

Recombination results in different allele combinations- Prometaphase I

o Nuclear envelope breaks down spindles enter- Metaphase/Anaphase I

o Alignment of tetrads and separation of chromosomes of eachhomologous pair


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- Telophase I and Interkinesiso No synthesis, reassembly of microtubules for 2nd division

Meiosis II

- There is no preceding S phase so meiosis II is not exactly like mitosis o Chromosomal behaviour is however like mitosis

How Germ Cells are Affected by Environment

- Male germ cellso Meiosis occurs after pubertyo Mutation rates are higher in males due to the meiotic rate

- Female germ cellso Meiosis occurs within fetal ovary and all eggs are arrested in meiotic prophase

until maturity

Nondisjunction

- Failure of homologous chromosomes to separate in meiosis I- Failure of sister chromatids to separate in meiosis II- Imbalance of chromosomes (aneuploidy)

o Monosomy Loss of chromosome (2n-1)

o Trisomy Gaining an extra chromosome

Meiosis and Diversity

- Variation increases chance that some offspring in a populationhave favorable combinations of alleles to survive

- Different combinations of maternal/paternal chromosomes duringsegregation

o Randomo Independent Assortment

- Spindle connections are random, not distinguishing betweenmaternal and paternal chromosomes

- Each chromosome carries one recombinant and one non-recombinant chromatid

- Random fertilization occurs between gametes providing multiple combinations ofzygotes too


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Topic 10Mendels Experiments, Genes, and Alleles

3 Hypotheses

1) All plants carry apair of factors (genes) governing inheritance of a character2) A pair of genes consists of different alleles, with one allele dominant over the other3) Alleles that control a character separate as gametes separate

Mendels Principle of Segregation

- Each organism is diploid: has two alleles- Homozygous: two alleles are the same- Heterozygous: two alleles are different- Parental Cross: Cross of true breeding lines (homozygous)- F1 Generation: First Filial Generation- A recessive allele is only expressed if two copies of recessive allele is present

Things to ask Dr. Rogers:

- Is the polyadenylation signal only used during eukaryotic transcription?


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- The difference between something being polycistronic and monocistronic, because thevariation in the introns and exons cause a single mRNA molecule to code for different

types of proteins but in that case is the mRNA still considered monocistronic?

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Documents

Biology 243 Condensed Lecture Notes