Chapter 11
(Part 3)
Translation
From Gene to Protein
Honors Biology
Ms. Gaynor
Lecture for 3/24/09
REVIEW…
Translation
mRNA  polypeptide
(protein)
Type of RNA
Function Job
mRNA
Brings message
from DNA (DNA
instructions) to
ribosome to
make protein
(messenger RNA)
tRNA
(transfer RNA)
Transfers/moves
amino acids to
ribosomes
Makes up
rRNA
ribosomes along
(ribosomal RNA)
with proteins
Picture
tRNA
 A cell translates mRNA message
into protein with help from transfer
RNA (tRNA)
 Type of RNA
 ~80 nucleotides
 “t” shape
 Carries amino acids
 Matches codons to
anticodons
tRNA
 Molecules of tRNA are not all
identical
 Each carries a specific amino acid
 Each has an specific anticodon on
the other end
 Aminoactyl Synthase
(enzyme) puts tRNA together
with it amino acid
tRNA Assembly
Aminoactyl
tRNA Synthase
ACTIVATED tRNA
Ribosomes
Help bind tRNA anticodons
with mRNA codons during
translation
Anticodon (tRNA) = codon (mRNA)
Found on ROUGH Endoplasmic
Reticulum RER (“bound”) or in
cytoplasm (“free”)
AMINO ACIDS
tRNA
(with
anticodons)
mRNA
(with
codons)
REVIEW…The Genetic
Code
 It’s a table used that TRANSLATES
RNA nucleotides called CODONS
(or mRNA “letters”) into one of the
20 amino acids
 3 letter mRNA “word” = 1
amino acid
 There are 4 different RNA
“letters” that can be used

A, U, C, and G
THE
GENETIC
CODE
Ribosomes
 There are 2 ribosomal subunits
 Constructed of proteins and
ribosomal RNA or rRNA
Binding Sites in a Ribosome
 The ribosome has three binding sites for
tRNA



P site (Peptide Bond-tRNA
binding site)
The P site
The A site
The E site
E site
(Exit site)
E P A
mRNA
binding site
A site (Amino acidtRNA binding site)
Large
subunit
Small
subunit
Amino acid
Growing polypeptide
Next amino acid
to be added to
polypeptide chain
tRNA
mRNA
3
Codons
5
\
Building a Polypeptide
Translation can be
divided into 3 phases
Initiation
Elongation
Termination
Initiation of Translation
 initiation stage brings together
 mRNA
bearing 1st amino acid
(“start”) called MET
 2 subunits of a ribosome come
together
 tRNA
3 U
A C
5
5 A U G
3
Large
ribosomal
subunit
P site
Initiator tRNA
GTP
GDP
E
A
mRNA
5
3
5
3
Start codon
mRNA binding site
Small
ribosomal
subunit
Translation initiation complex
Elongation
 Amino acids are added one by one
to the preceding amino acid
 Peptide bonds are formed
Amino
acid
Termination of Translation
 When the ribosome reaches a stop
codon on the mRNA
 There
are 3 stop codons
 UAA, UAG, and UGA
 Release factor (protein) binds to
stop codon in A site (NOT tRNA) 
polypeptide released
Termination of Translation
Release
factor
Free
polypeptide
5
3
3
5
5
Stop codon
(UAG, UAA, or UGA)
3
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Amino
acids
Polypeptide
“EMPTY”
tRNA
Ribosome
tRNA with
amino acid
attached
Gly
tRNA
A A A
U G G U U U G G C
5
Codons
Figure 17.13
mRNA
Anticodon
3
Polypeptide  3D Protein
 Primary Structure

Amino acids is a row (LINEAR)
 Secondary Structure

Amino Acids BEND and FOLD
towards each other
 Tertiary Structure
Amino acids BIND to each other
 3D shape made

 Quartnary structure (only some)

2 or more polypeptides BIND to
each other
1
3
2
4
Translation (Protein Synthesis)
Animation
 http://www.wisc-
online.com/objects/index_tj.asp?objID=AP13
02
 http://highered.mcgrawhill.com/sites/0072437316/student_view0/cha
pter15/animations.html#
 http://www.ucopenaccess.org/courses/APBiol
ogyI/course%20files/multimedia/lesson13/les
sonp.html
Chapter 11
(Part 7)
Translation & Mutations
From Gene to Protein
Honors Genetics
Ms. Gaynor
Review…
Review…
Review…
DNA Template (Gene)
TAC GGG CTC AAA TAC ACG ACT
What is the mRNA transcript?
5’
AUG CCC GAG UUU AUG UGC UGA
3’
What is the amino acid sequence?
START- Pro- Glu-Phe- Met-Cys-STOP
Mutations
 Mutations
 Are
changes in the genetic
material (DNA) of a cell
2 TYPES
 1. Point mutations can affect
protein structure and function
 Are changes in just one base pair
of a gene
POINT MUTATIONS
The change of a single
nucleotide in the DNA’s
template strand
Can lead to the
production of
an abnormal protein or…
the same protein
Point Mutations
Point mutations within a gene
can are called
Base-pair substitutions
Can results in a mutation
(change) that is
harmful
 neutral (not harmful or helpful)
 beneficial

Substitutions
 2 TYPES
 missense
(wrong aa)
 1 wrong aa is added to
polypeptide
 nonsense (prematurely STOP)
 The change in DNA leads to an
early STOP codon  polypeptide
is SHORTEN!!
POINT MUTATION
ANALOGY…
 TEMPLATE:
THE CAT ATE THE RAT
 POINT MUTATION: THE CAT ATE THE RAT
 THE CAT ATE THE BAT  What kind of point
mutation is this?


MISSENSE
THE CAT ATE THE XAT  What kind of point
mutation is this?

NONSENSE
What is the “wobble”
effect?
 The last base (nucleotide) in a codon is said to
be in the WOBBLE position.
 codon mutation may encode the same amino
acid
 Leads to NEUTRAL or SILENT mutations
 Not harmful or helpful
 SILENT MUTATIONS
 Mutation does not change “end
result”…change in DNA still makes the SAME
amino acid
 NO noticeable change occurs

a change from AUU to AUC will still encode
What is a neutral
mutation?
 May or may not affect the resulting
protein.



For example, if the codon AAA is mutated
to AGA, arginine would be used in the
resulting protein instead of lysine
These amino acids are chemically similar
and may not have a large effect in the
protein or its function
IF this change cause the protein to not
function (and be LETHAL to organism) then
it is not a neutral mutation but rather a
missense mutation
2. Frameshift Mutations
Insertions and deletions
Are
additions or losses of
nucleotide pairs in a gene
produce frameshift
mutations

2 TYPES
Insertions
Deletions
FRAMESHIFT MUTATION
ANALOGY…
 TEMPLATE:
THE CAT ATE THE RAT
 ADDITION of “B” MUTATION: THE CAT ATE THE RAT

THE CAT BAT ETH ERA T  What kind of
frameshift mutation is this?
INSERTION
 SUBTRACTION of “A” MUTATION: THE CAT ATE THE RAT


THE CAT TET HER AT  What kind of frameshift
mutation is this?

DELETION
Which is more harmful?
 Typically, frameshift mutations
are more harmful BUT some point
mutations can be LETHAL
 Ex: Tay Sachs and Cystic
Fibrosis
Other Types of
Mutations
 Inversions
 “Flip
Flops”
 Nucleotides trade places on
each strand
 Deletions (2+ nucleotides)
 Many nucleotides are deleted at
once
Causes of Mutations
 Inherited mutations
 From
mom and dad
 Spontaneous mutations
 occurs during DNA replication
 Environmental mutations
(Mutagens)
 physical or chemical agents that can
cause mutations

Ex: Sun, viruses, chemicals