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39 Cards in this Set
- Front
- Back
dna to be accepted as the genetic material needs
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-be present in cell nucleus and in chromosomes
-doubles in cell cycle (s phase) -is twice as abundant in diploid cells -has same pattern of transmission as its genetic information (fertilization) |
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dna chemical composition
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-is a polymer of nucleotides: deoxyribose + phosphate group + nitrogen base (by covalent bonds)
-bases: purines-- adenine and guanine pyrimidines-- cytosine and thymine (by hydrogen bonds) |
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chargaff's rule
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-the abundance of purines = the abundance of pyrimidines
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francis crick and james watson and rosalin franklin
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-Rosalin franklin uses xray for helical dna stands
-strands are anti-parallel. 5-3, 3-5 carbon sugar -Crick and watson suggested that nucleotide bases are on interior of 2 strands with a sugar-phosphate backbone on outside |
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dna functions
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-storage of genetic info-- millions of nucleotides
-precise replication during cell division-- by completing base pairing -susceptibility to mutations-- a change in information -expression of coded information as the phenotype-- nucleotide sequence is transcribed into rna and determines sequence of amino acid in proteins |
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2 steps in dna replication semi conservative
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-double helix is unwound, making 2 template strands available for new base pairing
-new nucleotides form base pairs with template strands and linked together by phosphodiester bonds -template is read in the 3-5 direction -semi conservative because half is of parental in dna |
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origins of replication (ori)
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-where replications begins
-2 strands are separated, opening up replication bubble -proceeds in both direction from each origin, until entire molecule is copied |
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replication fork
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-at end of each replication bubble
-y shaped region where new dna strands are elongating |
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helicases
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-enzymes that untwist double helix at replication fork
-breaks hydrogen bonds |
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single-strand binding protein
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-binds to and stabilizes single-stranded dna until it can be used as a template
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topoisomerase
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-corrects "overwinding" ahead of replication forks by breaking, swiveling, and rejoining dna strands
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dna polymerases
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-enyzmes that catalyzes the elongation of new dna at replication fork
-most polymerases require primer and dna template strand (adding nucleotide) |
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when a single replication fork opens up in one direction, 2 dna strands are
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-antiparallel- the 3 end of one strand is paired with the 5 end of other
-dna replicates in 5-3 direction |
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lagging strand
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-to elongate other new stand, dna polymerase must work in direction away from replication fork
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okazaki fragments
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-lagging strand is synthesized as series of fragments which are joined together by dna ligase
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telomeres
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-repetitive sequences at ends of eukaryotic chromosomes
-prevent chromosomes ends from being joined together by dna repair system |
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telomerase
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-acts as template for telomeric dna sequence
-is lost over time in most cells, but not in continuously dividing cells like bone marrow and gametes |
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cells have 2 major repair mechanisms
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-proofreading-- as dna polymerase adds nucleotides, it has proofreading function and if bases are paired incorrectly, the nucleotide is removed
-mismatch repair-- after replication, other proteins scan for mismatched bases missed in proofreading, and replace them with correct ones |
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mutations
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-changes in nucleotide sequence of dna that are passed on from 1 cell, or organism, to another
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somatic mutations
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-occur in somatic cells, passed on by mitosis but not to sexually produced offspring
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germ line mutations
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-occur in germ line cells that give rise to gametes. a gamete passes a mutation on at fertilization
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mutation are caused in 2 ways:
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-spontaneous mutations-- occur with no outside influence, and are permanent
-induced mutations-- due to an outside agent, a mutagen (ie radiation, cigarettes, or liquor) |
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induced mutation examples
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-chemicals can alter nucleotide bases
-some chemical add other groups to bases (ie. benzopyrene adds group to guanine and prevents pairing) -ionizing radiation, such as x rays, creates free radicals than change bases, break sugar phosphate bonds -uv radiation (from sun or tanning bed) is absorbed by thymine, disrupts dna replication |
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protein synthesis occurs in 2 steps
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-transcription
-translation |
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transcription
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-copies information from dna sequence (a gene) to complimentary rna sequence
-only in nucleus -needs dna template, nucleosides, and enzyme rna polymerase (rna = u-a, c-g) -final product mRNA |
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translation
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-converts rna sequence into amino acid sequence of polypeptide
-in cytosol |
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3 kinds of rna in protein synthesis
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-messenger rna (mRNA)
-ribosomal rna (rRNA) -transfer rna (tRNA) |
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messenger rna
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-in transcription--carries copy of dna sequence to site of protein synthesis at ribosome
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ribosomal rna
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-in translation--catalyzes peptide bonds between amino acids
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transfer rna
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-in translation
-mediates between mRNA and protein--carries amino acids for polypeptide assembly |
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formation of specific rna from a specific dna sequence requires
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-dna template for base pairing
-nucleosides (ATP,GTP,CTP,UTP) -an rna polymerase enzyme |
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transcription occurs in 3 phases
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-initiation
-elongation -termination |
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transcription initiation
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-requires promoter that tell rna polymerase where to start trancription and which strand of dna to transcribe
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elongation transcription
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-make long by adding bases to pre mRNA
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transcription termination
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-removal of intron keep exon
-coding regions |
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coding regions
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-sequences of dna molecule that are expressed as proteins
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introns
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-eukaryotic genes may have noncoding sequences
-intervening regions |
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exons
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-information we need
-coding sequence -expressed regions |
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dna synthesis recipe
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1.dna
2. semi conservative (half from parents) 3.enzymes -3.1-- helicase to untwist dna -3.2-- single strand for binding protein -3.3-- topoisomerase prevents overwinding -3.4-- polymerase adds nucleotides to leading strand and lagging stand (= okaski fragments) ---dna polymerase and ligase (glue) |