The genetic code Flashcards
What does the base sequence determine?
Which amino acids joined together therefore determining which proteins are made as well as which reactions can take place in an organism.
What is the gene?
It is a length of DNA which codes for one polynucleotide.
What is the codon?
It is a triplet of bases in mRNA that codes for a specific amino acid or punctuational signal.
What is the genetic code described as?
A triplet code
What would happen if three bases were removed from a polynucleotide?
It would have one fewer amino acid.
What would happen if three bases were added to polynucleotide?
It would have one more amino acid.
Why would three bases have to code for one amino acid?
As there are four different bases in DNA with over just 20 different amino acids. One base can’t code one amino acid as there would only be 4 amino acids made. If two bases coded for one amino acid that would only be 16 amino acids. Therefore three bases have to code each amino acid which would give 64 combinations which is more than enough to code 20 amino acids.
What is the genetic code?
It is the DNA and mRNA base sequences which determine the amino acid sequences in an organisms proteins.
What does the code being punctuated mean?
It is when triplets don’t code for an amino acid, there are three triplets which do this. In mRNA they are called stop codons and mark the end of the portion which gets translated.
Why is the code described as ‘degenerate’ or ‘redundant’?
There is one more than one triplet which can encode each amino acid as there are 64 possible codes with only 20 found proteins.
Why is the code universal?
It is universal as all organisms known have the same triplet code for the same amino acid.
What does it mean when the code is non-ambiguous?
Each triplet only codes for one amino acid.
Why is the coding non overlapping?
Each base and because in only one triplet.
What is an Intron?
Is it a non-coding nucleotide sequence in DNA and pre-RNA which is removed from pre-mRNA to produce mature mRNA. These introns can be removed from the mRNA before it leaves the nucleus this is called RNA splicing.
What is an exon?
It is the nucleotide sequence in DNA and pre-M RNA which remains present in the final mature and after the introns have been spliced. This is the region of DNA that codes for the proteins.
In prokaryotes, what RNA directs the synthesis of polypeptides?
mRNA
What is the difference between making polypeptides with RNA in prokaryotes and eukaryotes?
In eukaryotes the RNA needs to be processed before it can be used to synthesise the polypeptide. This is due to the initial version of the code being much longer and contains sequences which need to be removed compared to prokaryotes which don’t need to be processed.
What happens to the introns in the sequence?
The introns can be cut out of pre-mRNA using endonucleases and the sequences left are the exons which can be joined or spliced by ligases.
How many bases are introns normally?
20–40 bases long
What are intron is made up of?
They make up 3 to 5 nucleotide sequences which are repeated several times. In DNA they are called STRs which means Short Tandem Repeats
What shows the difference in individuals?
Individuals acquire different lengths of non-coding sequences from their parents. It is the number of times these non-coding DNA lengths are repeated which shows the difference in individuals.
What do you most prokaryotes not have in their DNA?
Introns, so their genes are entirely transcribed and translated without editing or splicing.
How can one gene make up a variation of polypeptides?
As the various exons produced can be spliced together in many ways creating different polypeptides.
