Genes and the genetic code Flashcards
What is a gene?
A gene is a section of DNA that contains coded information for making polypeptide and functional RNA.
The coded information is in forms of a specific sequence of bases on the DNA molecule.
How are genes responsible for the proteins in an organism?
Genes determine the sequence of polypeptide and polypeptides make up proteins so genes determine the proteins in an organism.
How can genes determine the nature and development of all organisms along with some environmental factors?
Enzymes are proteins and enzymes control chemical reactions, therefore, it is responsible for the organism’s development and activities.
What is a locus?
A particular position where the gene is located on the section of DNA.
What can gene code for?
Gene is a base sequence of DNA that codes for:
- The amino acid sequence of a polypeptide
- Functional RNA, including rRNA and tRNA
Why must there be a minimum of 3 bases which codes for each amino acid?
- Only 20 different amino acids regularly occur in proteins.
- Each amino acid must have its own code of bases on the DNA.
- Only 4 different bases are present in DNA (A,T,C,G).
- If each base code for an amino acid, only 4 different amino acids could be coded for.
- If using a pair of bases 4^2, that’s only 16 different codes so it’s not enough.
- Using 3 bases 4^3 would give 64 codes, more than 20, which was what we needed.
What is each set of amino acid called and why?
Triplet as there are 3 bases for each amino acid.
As there are 64 different codes but we only need 20 amino acids, it means that some triplets codes for the same amino acid.
What is degenerate code?
Degenerate code is a code where most amino acids are coded by more than one triplet.
What is at the start of each DNA sequence?
The start is always coded by the same triplet. The code for the amino acid methionine - triplet AUG.
If the amino acid methionine does not form part of the final polypeptide, it is later removed.
What are the 3 triplets that do not code for any amino acid?
UAA
UAG
UGA They are stop codes which mark the end of a polypeptide chain.
What does it mean of which the code is non-overlapping?
Each base in the sequence is read only once. e.g. 123456
It is read as 123,456 not 123,234,345,456…
What does it mean that the code is universal?
Each triplet codes for the same amino acid in all organisms. This is indirect evidence for evolution.
What are exons and introns?
Exons are coding sequences and introns are non-coding sequences.
