4-5-additional Flashcards
In order to code for the 20 amino acids found in living things, a “word” in the genetic code must consist of at least
3 bases ( a “triplet”)
how many possible code words are there in the genetic code.
64 (explanation: each word is three bases long, and there are four alternatives for each base, so 4X4X4 = 64)
a 3-base sequence on the mRNA codes for either …
a specific amino acid or a control word
who broke the genetic code
Nirenberg and Matthaei
The genetic code consists of …
(1) 61 amino-acid coding codons
(2) three termination codons that stop the process of translation.
what does it mean that the genetic code is redundant (sometimes referred to as degenerate),
there are multiple code words for the same amino acid (for example, glycine coded for by GGU, GGC, GGA, and GGG codons).
promoters
sequences of DNA that are the start signals for the transcription of mRNA
terminators
the transcription stop signals
Ribosomes consist of
a small and a large sub-unit.
The smaller sub-unit of a ribosome has a binding site for…
the mRNA.
The larger sub-unit has… .
two binding sites for tRNA
Transfer RNA (tRNA): shape and function
the shape of a cloverleaf and carries the proper amino acid to the ribosome
how many tRNAs and how are they different
61 different tRNAs, each having a different binding site for the amino acid and a different anticodon.
Amino acid linkage to the proper tRNA is controlled by ….
aminoacyl-tRNA synthetases.
Energy for binding the amino acid to tRNA comes from …
ATP by conversion to Adenosine Monophosphate (AMP).
The initiator codon (Which triplet?)
(AUG)
(It codes for the amino acid N-formylmethionine (f-Met). No transcription occurs without the AUG codon. f-Met is always the first amino acid in a polypeptide chain, although it is frequently removed after translation).
Initiation complex (translation)
The initiator tRNA, mRNA, and the small ribosomal unit
The initiation complex joins with the
large sub-unit of the ribosome
the kind of bond that forms between the amino acids
peptide bond
What happens when the ribosome moves to the next triplet on the mRNA .
That opens up the A site and a new tRNA enters at the A site
What happens when the codon in the A site is a termination codon?
a releasing factor binds to the site, stopping translation and releasing the ribosomal complex and mRNA.
polysome
more than one ribosome, sometimes many, reading the same messenger RNA. In this way, a cell may rapidly make many proteins at once.
Mutation (revised definition for what mutation is at the molecular level)
a mutation is a change in the DNA base sequence that results in a change of amino acid(s) in the polypeptide coded for by that gene.
point mutation
mutation involving the substitution of a single base.
frame shift mutation
when the reading frame of the gene is shifted by the addition or deletion of one or more bases
powerful evidence for the common ancestry of all living things.
With the exception of mitochondria, all organisms use the same genetic code.
