The Genetic Code

Question 1

What happens in transcription?

Answer 1

• In the nucleus DNA is copied into RNA
• A protein coding gene in DNA which is identified by protein factors is subsiquently unwound and opened up by helicase (stabilised by topoisomerase (prevents supercoils))
• The DNA template strand is read 3’ to 5’ so the Pre-mRNA is coded in the 5’ to 3’ direction (Coding strand is not used but is identical to the subsequent Pre-mRNA formed but with uracil present in the place of thymine in the Pre-mRNA)
• RNA polymerase identifies the protein coding gene (by identifying the promoter region) and binds to the specific DNA region and travels along the DNA in a 3’ to 5’ direction, synthesising Pre-mRNA in a 5’ to 3’ direction (same length as gene being transcribed)
• RNA polymerase transverses the the RNA coding sequence laying down complimentary RNA nucleotides in a 5’ to 3’ direction which are bound together by ligase
• Once the RNA polymerase has transversed the RNA coding sequence and the terminator region is identified the Pre-mRNA formed is released
• As the Pre-mRNA is released the double helical DNA can reform
• Pre-mRNA is then processed to produced mRNA which can then be exported out of the nucleus and into the cytoplasm where translation can occur

Question 2

What happens in translation

Answer 2

• In the RER in the cytoplasm RNA is read and proteins are made

Question 3

What is the structure of an amino acid?

Answer 3

• Central carbon
• Carboxyl group
• Variable R group
• Amino group

Question 4

How do 2 amino acids join and what is the bond formed?

Answer 4

A peptide bond forms between the carboxyl group of one amino acid and the amino acid of the adjacent amino acid in a condensation reaction

Question 5

What is the start codon

Answer 5

Methylamine AUG

Question 6

What are the stop codons

Answer 6

UAA
UAG
UGA

Question 7

Structure of Glycine

Answer 7

• Small

Question 8

Structure of Serine

Answer 8

• Nucleophilic

Question 9

Structure of Val

Answer 9

• Hydrophobic

Question 10

Structure of Met

Answer 10

• Hydrophobic

Question 11

Structure of Phe

Answer 11

• Aromatic

Question 12

Structure of Tyr

Answer 12

• Aromatic

Question 13

Structure of Gln

Answer 13

• Amide

Question 14

Structure of Glu

Answer 14

• Acidic

Question 15

Structure of Lys

Answer 15

• Basic

Question 16

What are essential amino acids

Answer 16

Amino acids that have to be provided through diet

Question 17

What are non-essential amino acids

Answer 17

Amino acids that are made in the body

Question 18

What is the genetic code?

Answer 18

Made up of triplet codes (codons) RNA that code for specific amino acids

Question 19

Triplet code

Answer 19

Each triplet on the DNA CODES for a SPECIFIC amino acid in the RNA when it is translated

Question 20

Degeneracy

Answer 20

Most amino acids have more than one codon

- Partial – 1st two bases in the codon are the same and the third is one of three bases
- Complete - 1st two bases in the codon are the same and the third is any of the four bases

Question 21

Non-overlapping

Answer 21

Adjacent codons do not overlap so no single base can take part in the formation of more than one codon.

Question 22

Non-ambiguous

Answer 22

While the same amino acid can be coded by more than one codon (the code is degenerate), the same codon shall not code for two or more different amino acids (non-ambiguous).

Question 23

Universal

Answer 23

Same sequence of 3 bases encodes the same amino acids in all life forms

Question 24

Polar

Answer 24

Reads in a 5’ to 3’ direction

Question 25

How many possible reading frames are there

Answer 25

3 per strand (starting at a different base)

Question 26

What is an open reading frame?

Answer 26

A run of codons that starts with ATG and ends with a termination code (TGA,TAA,TAG)
Before the ORF is the leader sequence and after is the trailer sequence

Question 27

How to locate the ORF?

Answer 27

• Contains ATG
• Has a termination code (TGA,TAA,TAG)
• Has the longest peptide chain