lect 17: DNA to protein II Flashcards
what are the learning objectives of this lecture?
-explain the structure of ribosomal and transfer RNA molecules
-know how to read the genetic code into amino acids and the different mutations that can happen
-describe the role of transfer RNAs in protein synthesis
-outline the translation of genetic information from initiation through termination
what is the table of the principal types of RNAs produced in cells?
what are the types of RNA produced in cells?
what do each RNA polymerase synthesize in eukaryotes?
- RNA polymerase I
-synthesizes larger rRNAs - RNA polymerase II
-synthesizes mRNA and most small nuclear RNAs - RNA polymerase III
-synthesizes small RNAs: tRNAs and small rRNA
what is ribosomal RNA (rRNA)?
ribosomal DNA (rDNA)
-multiple tandem repeats
-gene clusters: nucleolus
nucleoli are the site of biogenesis
-most of nucleolus=nascent ribosomal subunits
what is the structure of eukaryotic ribosomes?
what is the comparison of bacterial and eukaryotic ribosomes?
-differ in exact number and size of rRNA and protein components
-similar in overall structure and function (highly conserved)
what is the synthesis and processing of mammalian rRNA (cleavage)?
3 of 4 human rRNAs derived from single primary transcript- pre-rRNA (45S precursor)
-28S, 18S, 5.8 S
-synthesized by RNA polymerase I
-cleaved via various nucleases
5S
-synthesized by separate RNA precursor outside of nucleolus
-via RNA polymerase III
five “cut” locations
-first cut at sites 1 and 5
-second cut at site 2 or 3
what is the synthesis and processing of mammalian rRNA (nucleotide modifications)?
nucleotide modifications
-methylation
-conversion of uridine to pseudouridine
-modified residues are part of final gene products
preformed by snoRNAs (small nucleolar RNA)
-snoRNAs+proteins
-200 different snoRNAs: one for every site in the pre-rRNA that is modified
positions of modified rRNA ribonucleotides are conserved in evolution
-function is not well understood
what are examples of nucleotide modification?
what is the synthesis and processing of eukaryote transfer RNAs (tRNAs)
what is the flow of encoding genetic information?
what are the properties of the genetic code?
redundant
-most amino acids coded by more than one codon
conservative
-when multiple codons specify same amino acid, the first two bases identical (variable in 3rd spot)
unambiguous
-one codon codes for only one amino acid
universal
-all codons specify same amino acid across species
what are some important codons?
what is the graph of encoding genetic information?
what is the role of tRNAs?
tRNAs decode info (“adaptors”)
-match mRNA codon with amino acids it codes for
-each tRNA is linked to a specific amino acid
-tRNA recognizes a particular codon in the mRNA via region known as the anticodon (complementary base pair in tRNA matches codon)
what is the structure of tRNA?
-complex single stranded RNA structure
-complementary intra-chain base pairing
-“clover lead” structure in 2D
-similar NOT identical L-shaped 3D structure
2 important regions
-anticodon loop (7 NTs)
-AA acceptor arm- 3’ C-C-A sequence
contains modified nucleotides (loops)
-D-arm: interacts with enzyme that adds amino acid to tRNA
-T-arm: interacts with ribosome
what is the wobble hypothesis?
explains why multiple codons can code for a single amino acid
-one tRNA molecule can recognize/bind to more than one codon
-interchangeability of base in 3rd position
-non-watson-crick base pairing
what is tRNA charging?
linking the correct amino acid with tRNA
recognition and attachment of correct amino acid to tRNAs depends on aminoacyl-tRNA synthetases (very unique to each AA it binds)
-covalently link amino acids to tRNA 3’ end
-energy-dependent process
-aminoacyl-tRNA synthetases unique to each amino acid
-proofreading capability
what is initiator tRNA?
newly made proteins all have methionine as first amino acid (N-terminal)
-in bacteria, it is a modified methionine residue= formyl-methionine
-only amino acid that can bind to P site when large ribosomal subunit is not present
-this amino acid is usually removed later on
what is translating genetic information?
protein synthesis (translation)
-similar between prokaryotes and eukaryotes
ribosome subunits assemble like a sandwich on the strand of mRNA
-small subunit (40S in euks): decodes the genetic message
-large subunit (60S in euks): catalyzes peptide bond formation (between newly synthesize chain and incoming amino acids)
like transcription, translation is divided into 3 steps:
1. initiation
2. elongation
3. termination
what is the simplified overview of the initiation of translation in eukaryotes?
what is the first step of initiation of translation in eukaryotes?
what is the second step of the initiation of translation of eukaryotes?
