Translation- taking the message of
DNA and converting it into an
amino acid sequence.
Genes (DNA) to RNA to Proteins
(Traits)
Overview
 Protein synthesis can be summarized in 2 main steps:
 Transcription: One of the 2 strands of DNA is
transcribed into a single stranded messenger RNA,
which carries the DNA message to the ribosome.
 Translation:The ribosome reads the messenger RNA
and assembles the appropriate sequence of amino
acids
Post-transcription Processing
 Process between transcription and
translation
 Pre-mRNA molecule produced and
undergoes processing and editing.
 Introns – cut out and discarded
 Exons – remaining pieces spliced back
together to form mRNA
• mRNA travels through nuclear membrane
pore into cytoplasm
Genes Contain Introns
 Introns and exons why?
 Evolution, spliced in different ways in different tissues
enabling one gene to produce several forms of mRNA,
which can make several forms of a protein.
 Takes a lot of energy to make initial large molecule.
Rule for gene expression, use to state until the 1990s:
1 gene = 1 protein
Not true any more
1 gene = can make many proteins
Translation
 Occurs at the Ribosome in the Cytoplasm
 Necessary materials: Ribosomes (rRNA and proteins),
mRNA, tRNA, amino acids
 Produces proteins (traits) by connecting amino acids
together with peptide bonds
 Uses codons on mRNA to determine amino acid
sequence = genetic code
Codons
 Codon= sequence of 3 nucleotides on mRNA that
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codes for one amino acid or a start or stop signal
during translation.
Each codon 3-lettered (bases) code codes for one
amino acid
4 x 4 x 4= 64 possible triplet combinations
First codon discovered- UUU= phenylalanine
Codon-Amino Acid chart or wheel.
Codon-Amino Acid Table
How many start and stop codons are present?
Practice
 mRNA
 AUGUCCACGGGAUGA
 AUGGGAAGACUAUAA
 All living organisms and viruses use this triplet
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genetic code - its that "biological unity" idea again!!!
How does translation relate to YOUR life? (Why do you
need to know this, anyway?) All the proteins that make
up YOU, your cells, your body, the foods you eat, all the
living cells in the world, etc - are made this way! Every time
your body needs more of a protein muscle protein,
hair protein,
enzymes,
hormones,
hemoglobin molecules,
a gene carrying the information for that protein is
transcribed into mRNA, and the mRNA is made into
protein!
Structure of Ribosomes
tRNA (anti-codons, amino acids)
and mRNA (codons)
Translation
 Ribosome has 3 sites.
 Ribosome can hold 1
mRNA strand and 2
tRNA molecules at a
time.
 400 amino acids in 20
seconds
The steps of translation:
 1. Initiation: mRNA enters the cytoplasm and becomes
associated with ribosomes (rRNA + proteins).
 2. Elongation: addition of amino acids one-by-one:
As the ribosome moves along the mRNA, the tRNA
transfers its amino acid to the growing protein chain,
producing the protein - codon by codon!
 3. Termination: when the ribosomes hits a stop codon UAA, UGA, or UAG - the ribosome falls apart!
 The same mRNA may be used hundreds of times during
translation by many ribosomes before it is degraded
(broken down) by the cell.
 http://glencoe.mcgraw-
hill.com/sites/0078802849/student_view0/unit3/chap
ter12/concepts_in_motion.html#
Practice – DNA-mRNA-tRNA-amino
acid
 DNA
TACAATGCCGTAATT
 mRNA (codon)
 tRNA (anti-codon)
 Amino acids
 Protein
 Be able to determine patterns in all directions
 Practice-Keratin
Types of Mutations
Point mutation
Substitution- wrong nucleotide
base put in place
No protein made
Protein made without function
(different AA in place)
No effect (ie 2 different codons
for same AA)
Insertion/Duplicaton (addition)extra nucleotide placed in
sequence- frameshift mutation
Deletion (subtraction)- one fewer
nucleotide is placed in sequenceframeshift mutation
One mutation, can cause a completely new
amino acid sequence to form: often called
frameshift mutations
 Shift triplet codes
 Example CCUAGCAUUGCA
 CCUGCAUUGCA
Mutations
Other Chromosomal Mutations
Inversion- reverses the direction
of parts of a chromosome
Translocation- part of a
chromosome breaks off and
attaches to another
i.e. Down’s syndrome
Extra piece of C. 21 is found.
Gene Regulation
 Genes are turned on and off as needed by the cell.
 Prokaryotes
 Promoter, operator, repressor protein, genes
 Ex. Lac operon- if lactose present E. coli makes
proteins to break down lactose- lactose binds to
repressor protein which detaches from the operator –
the operator is switched on and RNA polymerase can
move along gene making mRNA.
Lac operon
Operon continued
Eukaryotes- regulation
 More complicated with more regulatory proteins.
 Regulatory proteins= transcription factors
 Enhancer, activator, promoter, transcription factor,
RNA polymerase. No operator
 Activators increase attraction of RNA polymerase for
the promoter
 Textbook page 215