Features of the genetic code

Question 1

What is the “start codon?”

Answer 1

• 3 base triplet at the start of every gene
• This codes for an amino acid that is later removed from the chain (not part of polypeptide.)

() - extra info for clarification

Question 2

What is a “stop codon?”

Answer 2

• 3 base triplet at the end of every gene that donnot code for an amino acid.
• Stop codons mark end of polypeptide chain/ cause ribosomes to dettach - stopping translation.

Question 3

What is meant when we say the genetic code is “degenerate?”

Answer 3

• Degenerate means that each amino acid is coded for by more than one triplet of bases.

Question 4

Explain why the genetic code is degenerate.

Answer 4

• Three bases are needed to make enough combinations for 20 amino acids.
• 4(to the power of n)
• 4(power of 2) = 16 combinations (NOT ENOUGH)
• 4(power of 3) = 64 combinations
• 64 combinations is more than is needed to code for 20 amino acids.

Question 5

Why is it important that the genetic code is degenerate?

Answer 5

• If a base is substitiuted for another base (ie. a mutation occurs), even though the triplet of bases will be different, it may still code for same amino acid (so will have no effect on the polypeptide chain formed.)

Question 6

What is meant when we say the genetic code is “universal?”

Answer 6

• The same triplet of bases codes for the same amino acid in ALL organisms, this is why the genetic code is described as being universal.

Question 7

Why is it an advantage that the genetic code is universal?

Answer 7

• It means that genetic engineering is possible.
• Ie. you are able to insert the human gene for insulin to bacteria (for mass production of insulin because the gene for inslulin is same in humans as bacteria.)

() - extra info for clarification.

Question 8

What is it called when ONE BASE in a codon changes to another base?

Answer 8

• This is called a “Substitution mutation.”

Question 9

What is meant when we say the genetic code is “non-overlapping?”

Answer 9

• Each base in a gene is only part of one triplet of bases that codes for one amino acid.
• Therefore, each . triplet of bases is read as a discrete unit.

Question 10

Why is it an advantage that the genetic code is “non-overlapping?”

Answer 10

• If a point mutation occurs, it will only affect ONE codon/ therefore one amino acid (this makes the mutation less severe.)

() - extra info for clarification.

Question 11

What is a sequence of three DNA bases called?

Answer 11

• A triplet

Question 12

Give three features of the genetic code

Answer 12

• Universal
• Degenerate
• Non- overlapping.

Question 13

What are “introns?”

Answer 13

• Introns are sections of genes that do not code for amino acids and therefore doesn’t code for polypeptide chains.

Question 14

True or False

Introns are found in both prokaryotic and eukaryotic DNA.

Answer 14

• False.
• Introns are only found in eukaryotic DNA, not prokaryotic DNA.

Question 15

True or False

Introns are found in the DNA/ mRNA of eukaryotic cells.

Answer 15

• False.
• Introns are only found in DNA of eukaryotic cells: they get removed/ are spliced out of mRNA molecules.

Question 16

What are exons?

Answer 16

• Exons are sections of genes that do code for amino acids.

Question 17

What are between different genes on DNA?

Answer 17

• Non-coding, multiple repeats of base sequences between genes.

Question 18

What are exons separated by in a gene?

Answer 18

• Exons are separated by one or more non-coding sequences, called introns.

Question 19

What is the “genome?”

Answer 19

• Genome is the complete set of DNA/ genes (ie. genetic material) in one cell.

() - extra info for clarification.

Question 20

What is the “proteome?”

Answer 20

• Proteome is full range of proteins that a cell is able to produce.

Question 21

Difference between proteome vs genome?

Answer 21

• Genome of cell should never change (unless there has been a mutation) whereas, proteome of cell is constantly changing depending on which proteins are needed in a given moment.