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Unformatted text preview: BIO EXAM #2 Structure of DNA o Molecules are polynucleotides Each has purine (A/G) or pyrimidine (C/T), a sugar, and a phosphate Before cell divides, amt of DNA is doubled, Then divided equally between 2 daughter cells o Double helix of two polynucleotide strands Hydrophilic sugar phosphates outside, less hydrophilic nucleotide bases inside Only uniform if purine paired w/ pyrimidine A & T paired w/ 2 hydrogren bonds, C & G with three Replication of DNA o Due to pairing of specific nucleotides, DNA can be unwound Each strand can be used for replication of new complementary strand o DNA polymerase Responsible for replication Complex of several proteins Separates the 2 strands of DNA & unwinds a portion of the molecule Adds complementary nucleotide to the template strand, verifying it as it goes During this proofreading, if mistake is found, its replaced w/ correct nucleotide Example of molecular motor Moves along DNA template Uses deoxyribonucleoside triphosphates as energy to drive the motor and monomer to be polymerized Mutations o Changes in DNA sequence in gene/chromosome o Range from point to large-scale Point Changes that occur in one/several nucleotides of a gene Can be substitutions, deletions, insertions In each case, DNA code is altered, sometimes producing change in phenotype Large-scale Long sequences of DNA or even entire chromosomes are altered o Errors in replication are responsible for low rate of mutation, but there are external causes too Mutagens Physical/chemical agents that interact w/ DNA to cause mutations Include x-rays, UV light, products of metabolism of oxygen (like free radicals), and other chemicals o Most mutations are caught by cells DNA replication machinery Transcription o Transfer of info from DNA into RNA form o RNA transcript is created from DNA template by enzyme RNA polymerase Structure allows to recognize & bind specific region of a gene, the promoter Once bound, unwinds portion of DNA helix, producing RNA copy of template strand (mRNA) o RNA polymerase is molecular motor Uses ribonucleoside triphosphates as energy for motor & monomers for new strand of mRNA When transcribed to end of gene, encounters terminator region & ends transcription o In prokaryotes, occurs in cytoplasm Transcribed mRNA goes to ribosomes o In eukaryotes, occurs in nucleus RNA transcript must be processed before exiting the nucleus towards ribosomes Original RNA transcript is called precursor mRNA (pre-mRNA) Contains regions of non-coding nucleic acid, introns Introns are interspersed with exons o Coding regions Spliceosomes cut out introns & rejoin the introns to form final, edited mRNA Translation o Genetic info in mRNA is interpreted by ribosomes Produce polypeptides according to sequence originally prescribed by DNA o Process of going from mRNA transcript to polypeptide of prescribed sequence...
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- Winter '07