CH 11: Translation Flashcards
The one gene, one enzyme hypothesis was modified to become the one gene, one polypeptide hypothesis. What did these both mean?
one gene, one enzyme hypothesis - idea each gene encodes a separate enzyme
one gene, one polypeptide hypothesis - each gene encodes a separate polypeptide chain
*the genetic code is mostly universal
Amino acids link together by ? bonds and form proteins. What are the primary, secondary, tertiary structures?
peptide bonds
primary - amino acid seq
secondary - alpha helix beta sheets
tertiary - 3D structure, fold on itself
quaternary - two+ polypeptide chains together
A codon is _____. There are ? possible codons. How many stop and sense codons are there? How many amino acids are there?
three RNA nucleotides that code for specific amino acids
64 total possible codons, 3 stop, 61 sense (code for 20 amino acids)
What does it mean when we say the genetic code is degenerate? What are synonymous codons? What are isoaccepting tRNAs?
degenerate - amino acids are specified by more than one codon
synonymous codons - codons that code for same amino acid
isoaccepting tRNAs - different tRNAs that accept same amino acid but have different anticodons
What is the start codon? What are the 3 main stop codons?
AUG - methionine
UAA, UAG, UGA
What is the wobble hypothesis?
codons can have multiple nucleotide sequences that code for the same codon
tRNAs possess anticodons that are complementary to codons
however, when the codon and anticodon pair together, a bond forms strongly between the first nucleotide and then second, but the third nucleotide is loosely bonded so there is some leeway for the tRNA to bond with more than one codon on an mRNA
Reading frames refer to the way we read nucleotide sequences. Explain why we can read the nucleotide sequence in three different ways?
What is a nonoverlapping code?
each different way of the reading sequence is called a reading frame
there are three potential sets of codons to there are three ways to read the sequence - making proteins with varying amino acid sequences
establish right reading frame using a start codon
nonoverlapping code - a single nucleotide is not included in more than one codon
Translation of an mRNA strand takes place on _____. The _____ reads mRNA and synthesizes a polypeptide chain in the _____ direction. Letter ? represents amino acid end of a protein. Letter ? represents carboxyl end. Amino acids are continuously added to what terminus of the polypeptide chain?
ribosome, ribosome, 5’-3’, N, C, added to C terminus
Protein synthesis is divided into what four stages.
trNA charging - tRNA binds to amino acid
initiation - componenets needed for translation are assembled at ribosome
elongation - amino acids form polypeptide chain
termination - termination codon reached and polypeptide chain released from ribosome
The attachment of tRNA to the appropriate amino acid is called _____. Amino acids add to which side of tRNA?
There are exactly ? different aminoacyl-tRNA synthetases in a cell. One for each amino acid. What are aminoacyl-tRNA synthetases?
tRNA charging, 3’ side of tRNA
20, enzymes that attaches an amino acid to a tRNA, each aminoacyl-tRNA recognizes a specific amino acid
Bacteria Initiation - In bacteria, what does the initiation factor IF-3 do?
Now, the initiator tRNA attached with N-formylmethionine forms what complex?
*Also note, GTP is used in this process.
IF-3 keeps large and small ribosomal subunits from binding together during initiation
fmet-tRNA
Prokaryotic vs Eukaryotic cells in translation
prok - 2 subunits needed to separate to allow access to mRNA molecule, IF-3 keeps subunits apart from each other, initiator tRNA is IF-3, use GTP for translation, Shine-Dalgarno seq
euk - more initiation factors, initiator tRNA is met-tRNA, Kozak sequence
Shine-Dalgarno vs Kozak Sequence
Shine-Dalgarno - consensus seq in bacterial cells that is recognized by the small ribosomal subunit
Kozak - seq in euk cells that facilitates identification of the start codon
- in combination with 5’ cap, accessory proteins, AUG start codon, sequence can help mRNA interact with complex and start translation
Euk initiation- The 5’ cap and polyA tail of eukaryotic mRNA is important in initiation of translation, how so?
5’ cap and polyA tail are recognized and proteins bind to each site
these proteins on 5’ and 3’ end interact with one another and makes the mRNA fold on itself to form a closed loop
this helps the binding of the ribosome to the 5’ end of the mRNA
Euk elongation - 3 sites that can be occupied by tRNAs (A, P, E sites), 3 main elongation factors?
What are the 3 main steps of elongation?
A site - aminoacyl, P site - peptidyl, E site - exit
EF elongation factors - Tu, Ts, G
- EF-Tu, GTP, charged tRNA form a complex and enters A site, the GTP transforms to GDP and EF-Tu-GDP is released
- peptide bonds form between amino acids in P and A sites and tRNA in the P site releases the amino acid to the growing polypeptide chain
- translocation occurs - the ribosome moves down the mRNA in 5’-3’ direction, the tRNA in the P site moves to the E site and exits into the cytoplasm
*the next tRNA in the A site moves to the P site
*both GTP and ATP can be used
