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30 Cards in this Set
- Front
- Back
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what is translation
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protein synthesis from mRNA template
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What is being translated?
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1. Genetic information encoded mRNA translated from 5' --> 3' into a chain of AAs.
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Where does translation occur
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predominantly in the cytoplasm, some in mitochondria and possibly in the nucleus
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What mediates translation
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ribosomes
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Name major types of RNA in the cell and describe the function and/or structural roles of each
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1) rRNA - RNA associated with ribosomes; functional in protein synthesis
2) mRNA- The product of DNA transcription; serves as template for protein synthesis 3) tRNA - small RNA with CV bonded AA that reads the codon message on mRNA and incorporates the AA into the protein being synthesized 4) mitochondrial RNA - RNA produced from mitochondrial DNA 5) small RNAs - 6) primer: short strand of RNA used for initiation of replication in DNA synthesis |
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Compare the structure of RNA to DNA
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RNA are nucleic acids formed by NTs with a ribose sugar connected to a nitrogenous base (adenine, guanine, cytosine and uracil)
DNA - nucleic acid formed by NTs with a deoxy ribose sugar and one of the following nitrogenous bases (adenine, guanine, cytosine and thymine) |
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Discuss the function and types of RNA polymerases
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Prokaryotes:
1 RNA polymerase Eukaryotes: 1. RNA poly. I - transcribes larger rRNA genes; does NOT code for proteins 2. RNA poly. II - transcribes mRNA genes - DOES code for proteins 3. RNA poly. III - transcribes tRNA, 5S rRNA genes and small RNAs. 4. Mitoch. RNA poly. - makes mitoch. RNA from mitoch. DNA. |
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Describe a promoter
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short segment (40-60bps) of DNA that are UPSTREAM from the transcription initiation site where the affinity of the RNA polymerase holoenz. increases
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What are the common subregion sequences of promoters:
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prokary.
-10 TATAAT (Pribnow seq) -35 TTGACA eukary. TATA box sequence |
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Describe the initiation step of transcription
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1. Transcription begins with the recognition of the promoter by RNA poly.
-sigma subunit binds to RNA poly. -sigma subunit recognizes promoter -RNA polymerase binds to DNA 2. Binding of RNA poly. to promoter causes the DNA double helix to unwind in the promoter region (12-15 bps called the transcription bubble) 3. RNA poly. moves along the template strand to the transcription start site ( +1 position) 4. Synth. of RNA begins with entry of the first ribonucleotide (by HB to the DNA template +1 base) and binding to the RNA poly active site, then entry of the 2nd ribonucleotide complementary to the +2 base. -ribonucleoside triphosphates are used to synth. RNA. 5. RNA poly catalyzes the formation of a phosphodiester bond btw the first 2 nucleotides. |
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Describe elongation step of transcription
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1. Ribonucleoside triphosphates are used to extend the RNA chain in the 5' --> 3' direction, making RNA complementary to the DNA template
2. The sigma subunit dissociates after ~10bps have been added, leaving the CORE enz. to continue elongation 3. RNA poly synth RNA with a high degree of accuracy (1 error in 10^4 - 10^5 bases) but cannot correct errors 4. Rxn catalyzed by ribonucletide triphosphates NTP + (NMP)n ------> (NMP)n+1 + PPi 5. phosphodiester bond if formed by nucleophilic attack of the 3' -OH group of the growing RNA chain on the alpha-phosphate of the entering NTP. 6. Requirements for the rxn: 1) Four ribonucleoside triphosphates (ATP, GTP, CTP, UTP) 2) DNA template 3) Mg2+ ion |
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Describe the termination step of transcription
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1) Termination is controlled by specific termination seq on the DNA template
2) Prokary. use two termination methods 1) rho protein termination factor disrupts RNA:DNA hybrid, causing dissociation of the transcript from the DNA template 2) stop signal on DNA template is a specific base seq that causes the RNA transcript to end in a hairpin loop (rho-independent) 3) For eukary, only the stop signal method is employed |
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Do eukaryotes or prokaryotes require more post-transcriptional modifications
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eukaryotes
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Describe post-transcriptional processing required by tRNA primary transcripts
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1) trimming of ends (done by ribonuclease P in prokary.)
2) splicing to remove introns 3) modification of bases (methylation) 4) addition of terminal seq to 3' end (CCA sequence) |
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Describe post-transcriptional processing required by rRNA primary transcripts
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1) trimming to appropriate sizes (5S, 28S rRNAs)
2) modification of bases (methylation) |
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Describe post-transcriptional processing required by mRNA primary transcripts
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1) 5' 7-methylguanine "cap" is added
- protects mRNA from degradation -req'd for export from nucleus to the cytoplasm and association with ribosomes -methyl "caps" on ribose -OHs may also be added 2) Poly-A tails (20-250bps) added to 3' end by a POLYADENYLATE POLYMERASE -also protects mRNA from degradation -promotes export across nuclear membrane into cytoplasm 3) Removal of introns by splicing -removed enzymatically and EXONS spliced together; exons code for proteins -alternative splicing can generate different end products -Transesterification rxns catalyzed by protein enz or ribozymes (catalyic RNA) |
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What is a primary transcript
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newly made RNA which is in an inactive form and requires processing
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Describe RNA-directed RNA synthesis
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Used by RNA viruses (with RNA genome) to make RNA
1) template is RNA 2) catalyzed by RNA replicase 3) 5' --> 3' direction 4) same nucleophilic attack mech. 5) RNA is complementary to RNA template 6) No editing or proofreading by RNA replicase Eukary. do NOT perform RNA-directed RNA synth. |
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what is an enhancer
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Region of DNA that some eukary. activators bind to. Enhancer may be some distance from promoter.
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What is a TATA box
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DNA sequence found in the promoter region
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What is gene expression
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The process by which inheritable information from a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA.
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What is a transcription factor
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proteins needed by eukary. to initiate transcription. They are needed to recognize the TATA box and segments of DNA that are to be transcribed
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How does gene silencing occur
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1) When non-coding seqs of RNA interfere with the expression of specific genes
2) si (small,intervening)RNA is an example. Most come from introns 3) important in the regulation of gene expression |
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T/F
Prokary. use different downstream promoters sequences |
False -
use different upstream promoter sequence. |
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T/F
Sigma subunit of RNA poly. does not dissociate in prokary. |
False -
does not dissociate in eukary. |
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describe the mechanisms of inhibitors of transcription
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1) intercalating into double helical DNA to block transcription
-Actinomycin (Cosmegen) 2) inhibition of RNA synth by binding to the beta subunit of prokary. RNA poly and keeping it bound to the promoter - Rifampin (Rifadin) 3) bind to RNA poly II in eukary. to block formation of mRNA - alpha-Amanatin |
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Describe alpha-Amanatin
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1) cyclic polypeptide TOXIN found in certain mushrooms that binds RNA poly. II in eukary and blocks formation of mRNA
2) No trade name |
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Describe Actinomycin
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1) Trade name - Cosmegen
2) Polypeptide-containing antibiotic from Strephtomyces, that intercalates into double helical DNA to block transcription 3) Effective in BOTH eukary and prokary. 4) Used as chemotherapeutic agent for some cancer types b/c it inhibits the growth of rapidly dividing cells |
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Describe Rifampin
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1) Trade name - Rifadin
2) Used for TB 3) Antibiotic that inhibits the initiation of RNA synthesis by binding to the beta subunit of prokary RNA poly and keeping it bound to the promoter 4) Most effective in prokary, but can also inhibit eukary mitoch polymerase 5) resistant bacterial mutants have an altered poly beta subunit |
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What species of mushrooms is alpha-Amanatin found in
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Amanita phalloides
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