MMG Microbial Genetics: DNA Transfer
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- What is the central Dogma of molecular biology?
- -DNA, RNA, Protein
- What are the informational macromolecules?
- -DNA, RNA, Protein
- How is information in DNA and RNA encoded?
- -by sequence of bases
- How is information in protein is encoded?
- -in sequence of amino acids
- What is a gene?
-
-segment of DNA that encodes a RNA molecule
-mRNA, tRNA, rRNA - What does polycistronic mean?
- -when more than one gene is transcribed into one mRNA of prokaryotes
- What does monocistronic mean?
- -one gene gets one mRNA (can be prokaryotic or eukaryotic)
- What does primary mRNA transcript contain?
- -exons and introns
-
What are exons?
What are introns? -
-protein-coding sequences
-intervening sequences - How are introns removed?
-
-by RNA processing
-RNA must be transported out of nucleus - What are the three stages of Transcription?
-
-initiation
-elongation
-termination - How does transcription occur?
- -in a 5' to 3' direction (concurrent in E. coli)
- What does transcription of E. coli require?
-
-RNA polymerase (one in bacteria)
-multisubunit core enzyme
-sigma factor -
What is a sigma factor used for?
How about multiple sigma factors? -
-specificity of initiation
-transcription of different genes - How does RNA polymerase (RNAP) work in transcription of E. coli?
- -binds promoter sequences 5' to mRNA start site which is determined by Pribnow box and about 35 sequences
- What are the two types of termination of transcription?
-
-self-termination
-protein-dependent terminationd - How does self-termination work?
-
-only RNAP is needed for termination
-no other protein factors are required
-requires stem-loop formation in RNA and about 6 U residues - How does protein-dependent termination work?
-
-Rho protein is needed for termination
-requires DNA sequence righ in C residues
-Rho binds mRNA and unwinds RNA-DNA complex
-unwinding causes RNAP to fall off - What is RNA processing?
- -conversion of a precursor RNA to a mature RNA
- In prokaryotes and eukaryotes, what molecules are made as precusors that are cut to make final mature RNA's?
- -tRNA's and rRNA's
- In eukaryotes, what do mRNA molecules do?
- -made as pre-mRNA precursors; introns are spliced out to make mature mRNA's
- What is capping?
- -addition of methylated guanine residue to 5' end of mRNA
- What is polyadenylation?
- -addition of long stretch of A residues to 3' end of mRNA; occurs during termination
- What is a spliceosome?
-
-multiprotein complex
-splicing creates an exon-exon junction and an intron lariat - What is a ribozyme?
-
-catalytic RNA
-no proteins needed
-found in self-splicing introns - What is a genetic code?
- -information that allows nucleic acid sequences to be translated into amino acid sequences in proteins
- What is a codon?
- -triplet of three bases encoding an amino acid
- What is degeneracy of code?
-
-most amino acids are encoded by more than one codon
-codon usage varies from organism to organism - How does translation occur in protein synthesis?
- -base pairing of codon with anticodon on specific charged tRNA molecule
- What can computer programs pick out in DNA codes?
-
-the ORF's (Open-reading frames)
*doesn't prove they are expressed though - What are open-reading frames?
- -defined by a start codon, then a number of codons, and lastly a stop codon
- What are start codons?
- -methionine (AUG)
- What are some sotp codons?
-
-UAA
-UAG
-UGA - Describe tRNA.
-
-adaptor molecules that contain anticodon that base pairs with codon
-short, single-stranded RNA; 73-93 nucleotides; cloverleaf
-about 60 tRNA's in bacteria (100-110 in mamalian cells)
-each tRNA is specific for an AA that binds to ribose sugar of A residue of CCA acceptor and sequence - What are Aminoacyl-tRNA synthetases?
-
-enzymes that covalently attach amino acids to tRNA
-must recognize tRNA anticodon loop and specific amino acid
-high degree of fidelity required so that wrong amino acid doesn't get incormporated into polypeptides - What are ribosomes?
-
-sites of protein synthsis that contain multiple proteins and ribosomal RNA (rRNA)
-free or on rough ER - What are antibiotics?
- -inhibit initiation (streptomycin) and elongation (puromycin, chloramphenical, clcyoheximide, tetracycline, kanamycin)
-
What are the bacteria-specific antibiotics?
How about eukaryote specific? -
-streptomycin, chloramphenical
-cycloheximide - How does initiation in translation occur in bacteria?
- -16S rRNA base pairs with sequences upstream of start codon
- How do eukaryotes begin initiation in translation?
- -ribosome recognizes 5' cap and starts at first AUG
- What does initiation include for translation?
- -complex of 30S small subunit, mRNA, tRNA, and initiation factors (proteins)
- What are polysomes and what are they for?
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-multiple ribosomes translate the same mRNA; independent events
-increase speed and efficiency
-some nascent proteins fold spontaneously while being synthesized - What are molecular chaperones?
-
-proteins that assist in the folding of polypeptides post-translation or after denaturation
-do NOT become part of protein
-require energy (ATP)