8.1 Gene and the genetic code Flashcards
What is a gene?
A section of DNA on a chromosome coding for one or more polypeptides.
What is the function of genes? Why?
They determine the proteins of an organism because polypeptides make up proteins.
Which fixed position is gene occupied (佔據) ?
Locus on a particular DNA molecule
What does gene code for?
- amino acid sequence of a polypeptide
- a functional RNA (eg. rRNA and tRNA)
How many bases are needed to code for one amino acid?
3
How many possible amino acids are there?
20
How many different bases are present in DNA? What are they?
4 - adenine, thymine, cytosine, guanine
What is a sequence of three DNA bases called?
Triplet
How many possible triplets are there?
64
What does triplet do?
It codes for a specific amino acid.
What words are used to describe genetic code?
- universal
- non-overlapping
- degenerate
Why is genetic code described as ‘universal’ ?
Because there are only a few minor exceptions that each triplet codes for the same amino acid in all organisms.
Why is genetic code described as ‘non-overlapping’ ?
Because each base in the sequence is read only once.
Why is genetic code described as ‘degenerate’ ?
Because most amino acids are coded for by more than one triplet.
What are exons?
Base sequences that code for amino acid sequences.
What are introns?
Non-coding base sequences
