Chapter 8 Flashcards
What is a gene?
A section of DNA that contains the coded information for making polypeptides and RNA
What is a locus?
The particular position on a DNA molecule that a gene is located
Why did scientists decide there must be a minimum of three bases that code for each amino acid?
Only 20 amino acids regularly occur in proteins, each requiring it’s own code of bases on the DNA.
Only four different types of bases are present in DNA, and if each base coded for a different amino acid only four could be coded for.
Why is the genetic code degenerate?
Most amino acids are coded for by more than oen triplet
Why is the code non overlapping?
Each base in the sequence is only read once.
Why is the code universal?
Each triplet codes for the same amino acid in all organisms
What are the features of the genetic code?
A few amino acids are coded for by a single triplet, the remaining are coded for by between two and six triplets.
A triplet is always read in one particular direction.
The start of the DNA sequence is always the same triplet that codes for methionine, this is later removed if it does not form part of the final polypeptide.
Three triplets are stop codons and they mark the end of the polypeptide chain.
Why does some of the DNA in eukaryotes not code for polypeptides?
There are non coding sequences between genes made up of multiple repeats of base sequences called exons. These are seperated by other non coding sequences introns.
Some genes code for ribosomal and transfer RNA
