Download One Gene -One polypeptide

Chapter 11.4
One gene=one polypeptide
Overview of Protein Synthesis
11.4 One Gene One Polypeptide
Each gene codes for a polypeptide
(protein).
 A polypeptide is made up of amino
acids (monomer)
 Proteins can have 1,2,3,or 4
polypeptides,
 Human traits can have more than 1
gene.

 Examples4
genes for eye color.
 3 genes for height.
The genetic code is universal.
 What
does this mean?
 It arose very early in the history of
life and has been passed on to all
living organisms on Earth.
 All organisms have the same
nucleotides- A,C,T,G
 We share 31% of a yeast’s genes,
40% of a worm’s genes, 50% of a
fly’s genes.
Overview:
Information Flows from
DNA to RNA to Protein
RNA- Ribonucleic Acid Nucleic Acid- 1, single, twisted strand
(chain) of nucleotides.
 Nucleotide- 3 parts
 Sugar-
ribose
 Phosphate group
 Nitrogen bases
 Adenine,
Guanine, Cytosine, and Uracil(instead of thymine).
Overview of Protein Synthesis2 main parts
1.Transcription -nucleus
 a sequence of DNA nucleotides (a gene)
is converted to a single-stranded RNA
molecule (mRNA)
 mRNA leaves the nucleus to go to the
ribosomes. DNA remains in the nucleus.
 2.Translation –ribosomes
 mRNA is translated into amino acids that
combine to form a polypeptide (protein)

 Codons-
three-base nucleotides “words” that
code for one amino acid.
The Triplet Code
There are 20 amino acids.
 The A,C,T,G must combine in groups of three
to have enough amino acid codes.
 4 3 = 64 triplet codes

61 of them code for amino acids
 Each codon represents an amino acid.
 Some amino acids have more than 1 codon




Ex. Leucine can result from CUU, CUC, CUA, CUG.
Each codon is specific- CUU is always leucine and not a
different amino acid.
3 “stop” codons which do not code for an amino
acid. They stop the gene sequence= stops
assembling the protein
1 Start codon- AUG= methionine.