BIOB10H3 Study Guide - Midterm Guide: Exon, Hexokinase, Hydrolysis

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5 Dec 2010
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BGY10 t Midterm #2
Lecture #1: Chromosomes, Genes, DNA t Chapter 10
- units of inheritance govern plant characteristics (genes encoded by DNA)
- each plant has 2 copies of gene t alleles = control trait development (homo/hetero-zygous)
- inheritance = allele comes from each parent
- traits can be either dominant or recessive
- gametes = reproductive cells, have only 1 copy of each gene/trait
- each pair of alleles = genotype which produces trait = phenotype t remain together thru life but
can be separates/segregated during reproduction (gamete/meiosis formation)
- PP]}v}(]}(ooo}v[((}Zooo
o Law of SegregationW}Pv]u[îooolPPµ]vP gamete formation t
1 gamete carries 1 allele for each trait
o Law of Independent Assortment: segregation of allele pair for 1 trait has no effect on
segregation of alleles for another trait (segregate independently)
- chromosomes = carry inheritable traits (genes) t each interphase chromosome has 1 double-
stranded DNA molecule w/ many genes
- eukaryotic nuclear chromosomes are linear, prokaryotic chromosomes are circular
- 1880s, Flemming observed concept that material outside nucleus becomes organized into visible
threads (chromosomes) during cell division
- 1903, Sutton used sperm cells (spermatogonium) of grasshopper for homologous chromosomes
o pairing of homologous chromosomes = tetrads/bivalents
o 1st meiotic division separates 2 homologous chromosomes into different cells
o mitosis separates 2 chromosomes into 2 cells
- homologous chromosomes ~ÁlDvo[]vZ]o]ZÇ}Z]WZ}u}}u
physical carriers of genetic factors (and meiosis is a reductive division)
- mutations = spontaneous inheritable changes in genes occur
o can b induced by chemicals that damage DNA
o include substitutions, deletions, insertions, inversions t can lead to change in gene
expression
- altered trait passed thru generations if mutation occurs in germ-line cells = gametes but if in
somatic cells, not inheritable
- mutations result in variation in pops t different pops can become genetically different =
evolutionary role
- mutations (spontaneous or induced) used for genetic studies t comparing wild type to mutants
- 2 different genes on same chr}u}}u}v[oÁÇu]v}PZµ]vPPu
production (not linked)
- crossing over/recombination causes genes on separate homologous chromosomes to shuffle
o result: in maternal and paternal genes inherited on same chromosome, breakdown of
linkage as result of bivalents exchanging genetic material during meiosis
- during meiosis, cross over points occur at recombination nodules t chiasma forms at point
where crossing over has occurred
o single cross over even on one homologous chromosome pair
- recombination frequency at loci (gene position on chromosome) determined by distance
between 2 genes on chromosomes
o greater distance between 2 genes on chromosomes = more likely to cross over
(breakage t genes become unlinked)
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o can be used to map gene positions on chromosomes
- meiosis = reductive process t produced haploid gametes by 2 sequential divisions w/out DNA
replication
o in prophase I, crossing over occurs t genetic diversity
- synaptonemal complex (Sc): chromosome synapsis accompanied by formation of SC t Sc
believed to provide scaffold for chromatids to complete crossing over and is fully formed in
pachytene
o recombination nodule form w/in SC and correspond to crossing over events
o at completion of crossing over, SC breaks down = end of prophase I
o lateral elements bind together chromatin of sister chromatids t protein filaments
connect that 2 lateral elements of SC
- in meiosis I, metaphase I t homologous pairs held together as bivalent by chiasmata: forms after
SC dissolves and cohesions holds chromatids together too
o in anaphase I, cleavage of cohesions allow separation of homologues
o in meiosis II, metaphase II t cohesion at centromere and separation of homologous
chromosomes during meiosis I and separations of chromatids in meiosis II
o in anaphase II t kinetochore formed, cohesion at centromere cleaved and chromatids
move to opposite poles
- DNA = deoxyribonucleic acid, double stranded (2 strands of DNA), w/ double helix and 4
different nucleotides
- nucleosides = just a sugar and a base
- nucleotides = a nucleoside w/ 1, 2, or 3 phosphates t A and G = purines (2 rings, bigger), C and T
= pyrimidines (1 ring, smaller)
- DNA = linear t info in specific order, each strand used as template for DNA replication t is
unbranched, made of monomeric subunits (4 nucleotides = dATP, dCTP, dGTP, dTTP), and
antiparallel = complementary
- strands held together by H bonds t weak individually and easily broken
o long chain of nucleotides = stable b/c of H bonds
o ability to break bonds allow DNA stands to denature and renature (for DNA rep and RNA
syn t transcription)
- ZP(([]vP: A=T, G=C, but A+T does not = G+C
- DNA double stranded molecule in spiral to form pair of right-hand helices (t(}u
o 2 chains comprise of 1 double helix t run in opposite directions
- DNA has sugar/phosphate backbone on outside of molecule w/ base from each strand in center
t 2 bonds between A+T and 3 bonds between G+C
o major/minor grooves of double stranded molecule = site of transcription factor binding
sites
- Watson and Crick bp: structural restriction of base interactions, entire DNA strand
complementary to other strand, and complementarity critical to all nucleic acid interactions
- genome = entire DNA makeup of organism
- eukaryotes: nuclear, extra chromosomal (outside nucleus t e.g. chloroplast, mitochondria)),
mitochondria, chloroplast, plastid
- genetic material used for: storage, DNA template (replication t cell division, inheritable t
daughter cells), gene expression
- supercoiling = DNA molecule twists on itself
o when DNA unwound and not supercoiled, unstable
o ot-form, right handed helix, 10 bases/turn, considered underwound = negative
supercoils
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o positive supercoils = left-handed helix, considered overwound
o relaxed = no supercoils in most of circle t more than 10 bases/turn b/c of nicking
o stressed/positive supercoils = Topoisomerases alter DNA supercoiling for DNA rep and
transcription by nicking 1 strand (Topo I) and allow separation of sister chromatids by
double-stranded break (Topo II) t Topoisomerase used to relax double stranded DNA
when the strands separate (an enzyme)
Lecture #2: DNA t Chapter 10
- double helix so 2 strands can unwind (held together by H bonds t weak and noncovalent) and
separate into 2 individual strands = denaturation
- when DNA dissolved in weak saline solution and slowly warmed to certain tem, strands begin to
separate and few degrees more, strand completely separated t driven apart by electrostatic
repulsion of negative charges on sugar-phosphate backbone
- DNA melting (denaturation) monitored by following increase in absorbance of dissolved DNA
- *nitrogenous bases of nucleic acids absorb UV radiation at absorbance maximum near 260nm*
- single stranded DNA absorbs twice as much light t can use absorbance to monitor de/re-
naturation
- uo]vPuµ¡AuÁZZ](]v}v]Zo(}uo
- ability of complementary single strand to reassociate = reanneal (follows denaturation into
stable double-stranded molecule) critical for molecule process and important bio observation
- nucleic hybridization = complementary strands from different sources mix to form double-
stranded hybrid molecule t base for genome complexity
- 3 steps in renaturation: highly repeated fraction, moderately repeated fraction, nonrepeated
fraction
o highly repeated fraction = clusters in tandem, anneal quickly, need dilute concentrations
to monitor
o moderately repeated fraction = 20-80% of DNA, can code for RNA/proteins
o nonrepeated fraction = single copy, most proteins, multigene families
- simple-sequence DNA composed of tandem repeats of short sequences = short tandem repeats
(STR) from gene duplication
o 1. satellite DNA (5-500bp) in tandem repeats up to 100Kb t found at centromeres and
telomeres
o 2. microsatellite (1-5bp) clustered 50-100bp, scattered in genome, highly variable
(mutations) used to compare pops
o 3. minisatellite (12-100np) up to 3000 repeats (1-5kB) variable (polymorphic), differ in
individuals of pops, criminal and paternity cases (DNA fingerprinting/RFLP) using
Southern blotting/PCR
- DNA hybridization = ability of DNA to reanneal t can be used to map relative location of single
copy of genes
- Southern Blot = nucleic acid hybridization t detect DNA complementary to probe
- DNA = genetic material
o sequence organization in genome can change rapidly from 1 generation to another or
w/in lifetime t include mutations and gene duplications (common form of DNA
duplication)
- gene duplication = duplicates small portion of chromosome, occurs in high frequency, readily
identified by genetic analysis
o gene families from gene duplication of ancestral gene
o candidate process of gene duplication is unequal crossing over
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