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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'?

yes: e.g.
- 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


How can PCR be sped up? What change is necessary for this to condition to work?

- by carrying it out at high temperatures
- special type of heat-stable DNA polymerase has to be used: Taq DNA polymerase. Obtained from Thermus aquaticus, a bacterium adapted to hot springs

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