Lecture 14 Flashcards
In prokaryotes, transcription and translation occur –
simultaneously
Messenger RNA (mRNA): carries genetic information transcribed from DNA in the form of a series of 3-nucleotide sequences, called –, each of which specifies a particular amino acid.
codons
Transfer RNA (tRNA): small RNA chain ( –nucleotides) that is key to deciphering the codons in mRNA
74-93
Each amino acid contains its own subset of –.
tRNAs
The correct tRNA with its attached amino acid is selected at each step (Each tRNA molecule contains a three-nucleotide sequence, an –, that can base-pair with its complementary codon in the mRNA.
anticodon
– associates with a set of proteins to form ribosomes that composed of a large and small subunit
Ribosomal RNA (rRNA)
Ribosomes bind tRNAs associated with amino acids and – an mRNA molecule, catalyzing the assembly of amino acids into
physically move along
The genetic code is –
universal (with some exceptions… mitochondria, protozoa)
The DNA code is – (there is more than one codon for each aa)
degenerate
All 64 codons are used: 61 of them can be assigned to certain amino acids, the other three are –
stop signals
One of the codons can act both as an amino acid codon (for – ) and as a start signal.
Met
The different amino acids have different numbers of
–
accompanying codons.
The frequency of the codons and the frequency of their amino acid is –.
correlated
An exception is Arg, that has six codons but is – regarding its frequency in proteins.
underrated
T/F: the codons are assigned randomly
false
The first two nucleotides of a codon have a – than the third one.
higher informational value
Synthesis of all polypeptide chains in prokaryotic and eukaryotic cells begins with the amino acid – .
methionine
In most mRNAs, the start (initiator) codon specifying this amino-terminal methionine is –.
AUG
Exceptions of star codons:
GUG & UUG in prokaryotes and CUG in eukaryotes
stop (termination) codons that mark the – of polypeptide chains.
carboxyl terminus
An – is the nucleotide sequence between a start codon and a stop codon.
open reading frame (ORF)
As seen from studies of mutant proteins, such as hemoglobin from sickle cell anemia, the mutant form contains – amino acid substitution
ONLY ONE
The genetic code is – because each nucleotide is part of only one codon, resulting in only one amino acid replacement
non-overlapping
Depending on where you start, any nucleotide sequence can be read as – different “reading frames”
three
The vast majority of mRNAs can be read in only one frame (ORF) because stop codons encountered in the other two possible reading frames – before a functional protein is produced.
terminate translation
Insertions or deletions of bases not in multiples of 3 will result in a frameshift.
Frameshift mutations
All tRNAs are about the same length – & structure
80 nt long
tRNA contains – loops
3
the anticodon loop contains an anticodon region that – the codon in mRNA.
complements
An amino acid is covalently attached to the acceptor stem at the 3 tail of –
CCA
each tRNA is matched with its amino acid long before it reaches the ribosome…this is done with a collection of 20 enzymes called .
aminoacyl-tRNA synthetases
ARS charge each tRNA with the – , thus allowing each tRNA to make the proper translation from the genetic language of DNA into the amino acid language of proteins
proper amino acid
Most cells make – different aminoacyl-tRNA synthetases, for each type of amino acid.
20
ARS recognize their tRNA molecules
using the –
anticodon
Each aminoacyl tRNA synthetase recognizes – and all tRNAs that recognize codons for that aa
one particular amino acid
tRNA molecules are also recognized using segments on the acceptor end and bases elsewhere in the molecule, particularly – (discriminator base)
nucleotide 73
An amino acid is covalently linked to tRNAs at the – by aminoacyl-tRNA synthetases (an ATP requiring reaction)
2’ or 3’ OH
ARS can proofread and remove incorrect aa
– specifies the amino acid incorporation
tRNA
Fritz and Lipmann discovered that Amino acids are
illiterate
– different tRNAs have been identified in bacterial cells
30-40
A single tRNA anticodon is able to recognize more than one codon corresponding to a given amino acid due to
nonstandard pairing between bases in the wobble position
wobble position
the 3rd base (3’) in an mRNA codon and the corresponding first base (5’) in the tRNA anticodon
prok and euk wobble codon base: U
possible anticodons: A, G, I
prok and euk wobble codon base: C
possible anticodons: G or I
prok wobble codon base: A
possible anticodons: U, I
prok wobble codon base: G
possible anticodons: C or U
euk wobble codon base: A
possible anticodons: U
euk wobble codon base: G
possible anticodons C
unusual nucleotide
inosine
A site
new aminoacyl-tRNA comes in
P site
growing polypeptide
E site
exit
- finding the start codon and assembling the ribosomal subunits
Initiation
- reading the mRNA sequence and polymerizing the addition of corresponding amino acids to growing polypeptide chain
Elongation
- recognition of the stop codon and release of the new polypeptide
Termination
