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36 Cards in this Set
- Front
- Back
semiconservative method
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two copies of the original DNA contain one new strand and one original strand
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Meselson experiment
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used heavy and light nitrogen isotopes to discover that DNA replicated and combined using the semiconservative method
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3 steps of replication
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1. initiation
2. elongation 3. termination |
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initiation of replication
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1. at oriC DnaA - replication initiator protein- recruits DnaB (helicase) and DnaC (helicase loader) to unwind DNA bidirectionally
2. replication fork appears at either end of the replication bubble 3. DNA primase and RNA polymerase make primers |
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elongation replication
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synthesizes complementary base pairs to create an exact copy of the template
1. DNA poly III elongates the existing primers in 5' --> 3' 2. lagging strand v leading strand 3. Okazaki fragments are linked together by DNA ligase 4. DNA poly I replaces RNA primer with DNA 5. RNAse H removes RNA primers of Okazaki fragments |
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replisome
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stationary complex that stays stationary relative to the DNA (which is moving); exhibit rotational symmetry; there is one at both forks
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termination replication
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ends replication process by separating DNA molecules; topoisomerase IV; terminus located roughly opposite oriC
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DNA polymerase III
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1. proofreading/self correcting
2. adds bases 5'-->3' 3. elongates new strand 4. can't ADD nucleotides together, only extend chain 5. dehydrates Hbonds between 3' OH group and alpha phosphate |
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topioisomerases
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induce supercoiling of DNA
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type 1 topioisomerases
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remove negative supercoils
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type II topioisomerases
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introduce negative supercoils
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differences between RNA and DNA
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1. sugars: RNA (ribose) DNA (deoxyribose)
2. nitrogenous bases: RNA (uracil) DNA (thymine) 3. structure: RNA (single stranded; short) DNA (double stranded; very long) 4. stability: RNA (unstable) DNA (stable) |
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RNA polymerase (RNAP)
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1. key transcription enzyme
2. synthesizes from DNA template 3. synthesizes RNA from 5'-->3' 4. does not require a primer |
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steps of transcription
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1. initiation
2. elongation 3. termination |
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initiation of transcription
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1. sigma factor binds to core RNAP
2. holoenzyme seeks out promotor region (Pribnow box and consensus region) 3. holoenzyme binds to promotor, forms closed complex 4. mRNA synthesis occurs, sigma factor leaves 5. DNA opens, forming open complex |
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elongation of transcription
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1. mRNA synthesized until reaches termination signal on DNA
2. ribosomes bind to mRNA and begin translation |
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termination of transcription
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1. rho-dependent (site on mRNA attracts termination rho factor)
2. rho-independent (stem-loop structure forms) 3. exit channel (crevice in RNAP where mRNA exits once its snythesized) |
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sigma factor
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transcription initiation factors that recognizes promoter sequences
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translation
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RNA directed synthesis of protein
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translation process
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1. requires many ribosomes
2. occurs simultaneously with transcription and replication 3. ribosomes bind at 5' end; ribosomes will then slide down to 3' end as translation continues |
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genetic code conclusions
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1. redundant
2. a amino acid is specified by 3 bases 3. commaless 4. requires other features to stop/start protein synthesis |
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how many bases needed to specify an amino acid and why?
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1. 3
2. because there will be 64 possible amino acids, compared to just 16 and 4 aa if only 2 and 1 were required respectively 3. there are 20 known amino acids |
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how did they determine that 3 bases specify an amino acid?
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1. conducted commaless test
2. 1 base removed/added = didn't proceed 3. 1 base removed and 1 added = proceeded normally 4. 3 bases added = proceed normally |
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tRNA
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1. transfers aa to polypeptide chain growing at ribosome during translation
2. 3' acceptor end/stem - aa is bound (always have same CCA) 3. anticodon loop - where anticodon is bound |
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anticodon
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3 bases complementary to codons
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initiation translation
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ribosome is assembled onto the RNA transcript
1. 30S ribosome looks for RBS and AUG sequence (start codon) 2. once 30S binds to transcript, 50S binds to 30S forming 70S |
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elongation translation
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polypeptide chain is extended as RNA transcript is read and aa added
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termination translation
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polypeptide synthesis is stoped
1. terminates at stop codon |
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DNA in transcription =
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= RNA translation
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RNA in transcription =
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= protein in translation
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NTPs in transcription =
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= amino acids in translation
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RNAP in transcription =
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= ribosomes in translation
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promoter in transcription =
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= RBS in translation
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start site in transcription =
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= start codon in translation
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termination site in transcription =
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= stop codon in translation
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operon
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group of genes that share one promoter and one terminator transcription regions; not eukaryotes
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