Download The Genetic Code

The Genetic Code
Essential Questions
1. Use the Genetic Code to identify condons,
anti-codons and amino acids from a DNA
sequence. (Essential Skill 2-2)
The Universal Genetic Code
• Codon = every 3 bases
on mRNA that codes for
a specific amino acid.
– Start Codon = AUG =
Methionine
– Stop Codons = (UAA, UAG,
UGA)
• This is what the tRNA reads
The Genetic Code is the same for all organisms!!!
tRNA – “reads” the codons
• Anticodon = 3 bases on
tRNA that are
complementary to the
codon on mRNA.
• tRNA brings the correct
amino acid to the
ribosome/protein.
• The correct amino acid
depends on the mRNA
codons
How to Use the Genetic Code
• Each codon has 3 letters
(nucleotides: G, C, A & U)
– 1st letter can be found along
the left side of the chart
– 2nd letter can be found along
the top of the chart
– 3rd letter can be found along
the right side of the chart
• it must be in the same row as
the first letter
• Where all three letters
intersect is the name of the
amino acid this codon codes
for!
– Each code always starts with
AUG (start) and ends with a
stop codon!
• NOTE: The Genetic
Code always uses the
mRNA sequence!!!
Basic Decoding Example
tDNA
TAC TCT GGG CTG ACT
ATC
mRNA AUG AGA CCC GAC UAG
AA
Met Arg Pro Asp
AA
Letter
Letter
(start)
W
H
S
!
How Mutations Affect the Amino Acid
Sequence
• A mutation (change in the
nucleotide sequence) can
affect protein structure in
3 ways:
– No Change: It doesn’t
change the amino acid
sequence
– Small Change: It changes
only 1 amino acid
– Large Change: It changes
the whole protein
Protein Synthesis Review
DNA  mRNA  protein
Transcription vs. Translation
• Transcription = DNA into
mRNA (occurs in nucleus)
• Translation = mRNA into
Protein (occurs at
ribosome)
– tRNA carries the amino
acids
– rRNA makes up the
ribosomes
Protein Synthesis Review