Flashcards in 2: The Genetic Code Deck (10):
Why do codons have to be 3 groups of 3 bases and not more or less?
definitely couldn't be less than 3 because:
- there are 4 bases
- 4^2 = 16, 16 different base combinations
- 20 is the number of amino acids needed to make most polypeptides, so 16 is too few base combinations
shouldn't be more than 3 because:
- 4^3 = 64, 64 different base combinations
- 64 possible codons easily covers 20 diff amino acids
- occam's razor: it would be wasteful/pointless for a codon to be bigger
How many codons are there for each amino acid?
two or more codons for most amino acids
- exceptions: methionine (start codon), tryptophan
Know how to read a 'meaning of codon' table. (p31)
What is human insulin? Why would scientists want to transfer the gene that codes for insulin (in humans) to the bacterium E.Coli and other organisms? How come a bacteria produces the same thing (insulin) as humans?
- a protein that contains just 51 amino acids
- to produce the insulin that is needed to treat diabetes
- amino acid sequence of insulin produced in E.Coli = identical to the sequence produced in humans. This is because of the: universality of the genetic code
Are there any exceptions to 'the universality of the genetic code'?
- in some yeasts, CUG codes for serine rather than leucine
- in some organisms, a stop codon is used for a non-standard amino acid
What is polymerase chain reaction (PCR) used for?
used for copying DNA artificially
Why might polymerase chain reaction (PCR) be useful?
- for gene transfer procedures: many copies of the desired gene are needed
- forensic analysis: small sample (from crime scene) can be replicated as larger amount is needed for analysis
What are eppendorfs?
small tubes in which DNA is copied (in PCR)
How many copies of a gene might there be in an eppendorf by the end of PCR?
100mil+ in a 0.2ml eppendorf