5.i./j. The genetic code

Question 1

The genetic code mnemonic: No, Please Don’t Talk. Understood?

Answer 1

1. Non-overlapping
2. Punctuated
3. Degenerate/Redundant
4. Triplet code
5. Universal

Question 2

Why is the genetic code a triplet code?

Answer 2

Because three bases encode each amino acid (AA)

Question 3

Why is the genetic code redundant/degenerate?

Answer 3

Because more than one triplet can code for each amino acid (64 triplets but only 20 AAs)

Question 4

How is the genetic code punctuated?

Answer 4

There are 3 triplets that don’t code for an AA called ‘stop’ codons

Question 5

Name the three stop codons using only three of the base letters (out of G, C, A, T, U)

Answer 5

UAA
UAG
UGA

Question 6

Why is the genetic code universal?

Answer 6

Because in all organisms the same triplet codes for the same AA

Question 7

How is the genetic code non-overlapping?

Answer 7

Because each base occurs in only one triplet

Question 8

When AAs are joined together (translated) what do they form?

Answer 8

A polypeptide

Question 9

If one base coded for one AA how many possible combinations of AA would there be?

Answer 9

4 possible AAs

because 4^1

Question 10

If two base coded for one AA how many possible combinations of AA would there be?

Answer 10

16 possible AAs

because 4^2

Question 11

If three base coded for one AA how many possible combinations of AA would there be?

Answer 11

64 possible AAs

because 4^3

Question 12

What is the name of the monomer that makes up a polynucleotide?

Answer 12

A nucleotide

Question 13

Finish this sentence: A polynucleotide strand always has 3x the number of bases than…

Answer 13

…the AA that it codes for

Question 14

What would happen if 3 bases were removed from a polynucleotide chain?

Answer 14

The polypeptide made would have one less AA

Question 15

What would happen if a polynucleotide had three extra bases?

Answer 15

The polypeptide formed would have one more AA

Question 16

The code is sometimes quoted as ___________ but can also be quoted as ___________

Answer 16

The code is sometimes quoted as DNA TRIPLETS but can also be quoted as RNA CODONS

Question 17

What does the enzyme helicase do?

Answer 17

Causes the DNA double-helix to unwind

Question 18

What does the enzyme DNA polymerase do?

Answer 18

Catalyses the condensation reaction (between the 5’ phosphate group of a free nucleotide to the 3’ OH on the growing DNA chain)

Question 19

Define ‘codon’

3 points

Answer 19

• A triplet of bases in mRNA
• that codes for a particular AA
• or a punctuation signal

Question 20

Define ‘genetic code’

3 points

Answer 20

• DNA and mRNA base sequences
• that determine the AA sequence
• in an organism’s proteins

Question 21

Define ‘intron’

4 points

Answer 21

• *Regions of DNA that don’t code for proteins
• in DNA and pre-mRNA
• removed from pre-mRNA
• to produce mature mRNA

Question 22

The initial RNA version of the code is ________ than the final mRNA so introns are ________ .

Answer 22

The initial RNA version of the code is MUCH LONGER than the final mRNA so introns are REMOVED

Question 23

Define ‘exon’

points

Answer 23

• *Exons are regions of DNA that contain the code for proteins
• and remain present in mature mRNA after introns are removed