Transcription, Translation, and Mutation

Name:_______________________________ Date:_________
Section:__________________ Lab 5: Human genetics and variation
Exercise 1: Transcription, Translation, and Mutation
The processes of transcription and translation allow an organism’s genotype (genetic code) to be expressed as its phenotype (physical trait).
1 Starting material: DNA strands made up of nucleotide bases (A, C, T, and G)
2 Transcription: DNA is transcribed into mRNA
DNA base

RNA Base

C

G

G

C

T

A

A

U

3 Translation: mRNA is translated 3 bases at a time (3 bases = a codon) into a corresponding amino acid
4 Translation begins with a “start” codon and ends with a “stop” codon
5 Result: A chain of amino acids becomes the protein that defines the phenotype.
Figure 1: Transcription & Translation
Mutations are random changes to the genetic sequence.
There are two basic types of mutations in the genetic sequence:
1 SNPs = Single Nucleotide Polymorphisms
This means that only a single base has been changed (mutated) in the sequence. A SNP mutation can result in the production of:
* an entirely new amino acid (a nonsynonymous mutation), which may be a premature stop codon (which causes translation to end) OR
* the production of the same amino acid (a synonymous mutation), which is possible because of redundancies in the genetic code (i.e. sometimes multiple codons code for the same amino acid)
2 INDELs = INsertion or DELetion events
This occurs when a base is inserted into or deleted from the sequence.
Therefore, INDELs cause frameshifts (i.e. a disruption of the grouping of codons), which:
* result in a completely different sequence of amino acids OR
* introduce a premature stop codon into the sequence
Table 1: List of amino acids
Amino Acid

Abbreviation

Amino Acid

Abbreviation

Alanine

Ala

Threonine

Thr

Leucine

Leu

Tyrosine

Tyr

Isoleucine

Ile

Cysteine

Cys

Valine

Val

Asparagine

Asn

Proline

Pro

Glutamine

Gln

Phenylalanine

Phe

Aspartic Acid

Asp

Tyrptophan

Trp

Glutamic Acid

Glu

Methionine

Met

Lysine

Lys