DNA translation Flashcards
Most mRNAs in __________________ are translated without further modification. Protein synthesis begins before transcription is complete.
Prokaryotes
In eukaryotes, before translation can occur, mRNA must be modified. What 4 events ready a mRNA molecule for translation?
- Addition of a 5’ cap (7-methylguanine added to 5’ end of mRNA)
- Addition of a polyA tail (a long stretch of adenine residues added to the 3’ end of mRNA)
- Intron splicing (intervening sequences - introns - that are not expressed must be removed, and exons are joined together)
- mRNA translocation to the cytosol
The addition of a 5’ cap, polyA tail, and intron splicing is known as ________________ processing.
Post-translational
The ____________ code allows for the correspondence between nucleic acids and polypeptide sequences.
Genetic
The genetic code is read in nucleotide triplets called _________.
Codons
The code is read in a ______________ non-overlapping fashion.
Successive
The reading frame establishes the manner in which codons will be read. An ___________________ (ORF) is approximately 50 consecutive codons within a stop.
Open reading frame
A _____________________ mutation is the insertion or deletion of one or two nucleotides that results in a displacement of the open reading frame.
Frameshift
The third position of a codon is known as the ______________ and changes to this position often do not result in significant mutations.
Wobble
The genetic code is _______________, meaning that there are many more codons for each amino acid.
Degenerate
How many codons are possible based on the triplet code and four DNA bases?
4 x 4 x 4 = 64
The start codon is ___________. The stop codons are _______, __________, and ________.
AUG
UGA, UAA, UAG
The genetic code is “standard” but not ____________ as the mitochondria has a slightly different genetic code.
Universal
The arrangement of codons is random or non-random?
Non-random
Suppose a point mutation converts a CUU to a CUA codon. What amino acid substition occurs?
Leucine to leucine
This is known as a silent mutation
Suppose a point mutation converts a GAU to a GAA codon. What amino acid substitution occurs?
Aspartic acid to glutamic acid
This is a conservative substitution as the two amino acids while different have similar characteristics
__________________ are adaptor molecules that carry an enzymatically added amino acid to the corresponding mRNA codon.
transfer RNAs (tRNAs)
tRNAs interaction with the codon of mRNAs via complementary base pairing. If the codon on an mRNA is CGA, what is the anticodon sequence of the tRNA?
5’ UCG 3’
What amino acid does the tRNA carry?
Arginine
The mRNA codon - not the tRNA anticodon - determines the amino acid
tRNAs can also interaction with condons through non-Watson-Crick base pairing or ___________ pairing. Hypoxanthine or inosine (when connected to a ribose) is a nitrogenous base that is sometimes found in tRNAs and can pair with A, U, or C. Show the base pair between inosine and adenine.
________________________ (aaRSs) are enzymes that add amino acids to the 3’ terminal ribose of a cognate tRNA to form an aminoacyl-tRNA.
Aminoacyl-tRNA synthetases
The reaction between aaRS and tRNA ultimately forms a __________ tRNA.
Charged
You should know that the amino acid becomes attached to the L shape of tRNA, not the clover leaf shape of tRNA.
______________________ are protein synthesis machinery composed ot 2 subunits containing rRNA and proteins.
Ribosomes
Prokaryotic ribosome contains a 30S and ____ subunit. The 30S subunit is the small subunit; the other is the large subunit.
50S
The 30S and 50S subunits combind to form the _____ prokaryotic ribosome.
70S
The 30S subunit or small subunit contains 16S rRNA and 21 proteins designated S1, S2, etc.
The 50S subunit or large subunit contains 5S and 23S rRNA and 33 proteins designated by L1, L2, etc.
The eukaryotic ribosome also has a small subunit ____ and a large subunit ____, which combine to form the 80S ribosome.
40S
60S
What are the functions of the ribosome during protein synthesis?
- Matches codon on mRNA with anticodon on tRNA
- Contains three sites for tRNAs
- Binds several translation factors
- Catalyzes peptide bond formation
- Translocates by one codon on mRNA
What is the most important function of the ribosome?
Catalysis of peptide bond formation
What are the three binding sites for tRNA in the ribosome?
Exit “E”
Peptidyl “P”
Aminoacyl/acceptor “A”
In prokaryotic ribosome, the ______ rRNA is the catalyst for peptide bond formation. This means that the ribosome functions as a ___________.
23S
Ribozyme
What are some of the translation factors required for protein synthesis?
Initiation factors
Elongation factors
Release factors
How does protein synthesis know where to start in prokaryotes?
A specific sequence on the mRNA transcript is required; it is a purine-rich sequence in the 5’ untranslated region (UTR) about 10 nucleotides upstream of the start codon, AUG. This sequence is known as the Shine-Dalgarno sequence
The ribosome scans the mRNA for the ___________________ sequence, a purine-rich sequence in the 5’ _______________ (UTR) about ____nucleotides upstream of the start codon, _______.
Shine-Dalgarno sequence
Untranslated region
10 nucleotides
AUG
The Shine-Dalgarno sequence is ___________________.
UAAGGAGGU
What tRNA is required for prokaryote protein synthesis?
tRNAfMet
N-formylmethionine
Make sure you know what the initation complex looks like in prokaryotes.
In eukaryotes, translation initiation requires the 5’ cap; there is no _____________ sequence or equivalent. The small ribosomal subunit simply binds the 5’ cap and scans the mRNA transcript until the first start codon is located.
No Shine-Dalgarno sequence
What tRNA is required for eukaryotic translation initiation?
tRNAiMet
There are three stages of translation: initiation, _____________, and termination.
Elongation
You must be able to identify the electron movement in peptide bond formation.
The N-terminus of the amino acid in the A site acts as a nucleophile and attacks the C-terminus carbonyl carbon, which ultimately releases a water molecule
mRNA is read in the ____ to ____ direction; the polypeptide is made in the _______ to C-terminus direction.
5’ to 3’
N-terminus to C-terminus
Termination of protein synthesis occurs when a ____ codon is found in the A site of the ribosome. A release factor binds, peptidyl transfer of water occurs, and the polypeptide chain is released along with the translation machinery.
Stop
The peptide bond is catalyzed by _______________.
Peptidyl transferase
It is the amino acid in the ____ site that attacks the amino acid in the ____ site to form the peptide bond.
A site
P site
After the peptide bond forms, the tRNA is rendered _______, and it then moves to the E site.
Deacylated
