Flashcards in Genetic Material Deck (38)
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1
DNA compostion
polymer of nitrogenous bases (purines and pyrimidines) linked together by a backbone of an alternating series of sugars (5 carbon pentose) and phosphate residues
2
nucleotides
consists of a nitrogenous base, a pentose and one or more phosphate group
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nucleoside
a nitrogenous base with a pentose. so it is a nucleotide without and phosphates.
4
DNTP's
deoxynucleoside 5' triphosphates
activated precursor in the synthesis of DNA
5
primary structure of DNA
-linear polymer of deoxyribonucleotides connected 3'-5' phosphodiester linkages.
-polymer consists of a pentose phosphate backbone with N base on each link
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oligonucleotides/primers
small groups 5-50 of nucleotides linked via phosphodiester bonds
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denotations of the 5' and 3' ends
5' = phosphate
3' = hydroxyl
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Watson and Crick Double helix:
directionality
structure
bonding
-right handed
-two polynucleotide chains wound around one another
-antiparallel = 5' end of one strand is paired with the 3' stand of the other
-sugar phosphate backbones are on the outside and the nitrogenous bases faces inward towards their complementary base (hydrophobic)
-helix held together via hydrogen bonds
-stacked 3.4A apart
-10 BP per turn
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Features of the structure of DNA
-can store vast amounts of charge at phys pH
-complimentary structure suggested a mode of replicaion
-structure prevents information loss when dmage occurs
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supercoiling of DNA
can be positively supercoiled or negatively supercoiled
supercoiling confers energy into the molecule which can later be used for seperation of the strands.
Coiling is directly correlated to regulation of gene expression
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topoisomerases
enzymes that catalze change in the supercoiling of DNA
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Topoisomerase 1 and 2:
reaction catalyzed
cancer
catalyze a 3 step reaction to change the conformation of DNA:
1. Cleavage of one (topo1) or both (topo2) strands of DNA
2. passage of DNA around the breaks
3. resealing of the DNA breaks
cancer drugs inhibit these enzymes
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camptothecin
inactivates topo1
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mAMSA
inhibits topo2
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Doxorubicin
indirectly inhibits topo2
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Z DNA
-this is a left handed helix of DNA
-alternating purines and pyrimidines are more likely to adopt this structure
-adopted in response to negative supercoiling
-purpose unclear, may be in recombination/regulation of expression
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DNA Bending
-some sequences are inherently bent
-adenine repeats are prone to bending
-may be a result of protein-DNA interactions
-examples: bending DNA around histones
-may bring distant sequences closer together
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Triplex DNA structure
-polypurine/polypyrimidine tracts can form this (H-DNA)
-biological consequences unknown
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DNA Melting
-results in disruption of the duplex structure and -seperation of the strands.
-narrow range of temps
-varies with ion conc and sequence comp (G and C more stable, has 3 H bonds vs 2 in A-T)
-
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Reannealing
-Hybridization (reassociation) of the 2 strand just below the Tm
-highly specific, must be complimentary
-important in the use of probes
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Functional Genes
-only accounts for 1-2% of the human genome
-range in size from 1-100kb
-genes involved in similar systems are located together (color vision genes are together). have the same "domain"
-families in the same domain reflects that a genes arose from a common ancestral gene
-may have multiple repeating copies of commonly used genes
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lost genes
could be because the gene product is readily attainable in our food supply
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additional gene elements, "junk DNA"
some of it has regulatory roles but much of it is said not to be used
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Pseudogenes
-closely related to functional genes and arose in the same duplication process that give rise to gene families.
-they do not code for normal gene products (deletions, point mutations, insertions, etc.)
25
processed pseudogenes
formed when DNA copies of RNA (reverse transcripts) are inserted back into the genome. large amount of these can sometimes be found
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proviruses
-DNA copies of retroviruses inserted into chromosomes
-all species carry them in their chromosomes
27
repetitive DNA sequences
-can be complex patterns or simple nucleotide repeats
-includes transposable elements, simple sequence repeats, and satellite DNA
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transposable elements:
definition
classes
sequences capable of inserting copies of themselves into new genomic locations.
1. elements that transpose through reinsertion of the products of reverse transcription (proviruses, SINE and LINE, and processed pseudogenes)
2. transpose directly through DNA copies and encode their own transposase (little evidence for this in humans)
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SINE's
-Short Interspersed Repeat Elements
-among the most abundant sequences in the human genome
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