LECTURE #25: Translation

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Transcript LECTURE #25: Translation

Making Proteins:
Translation
Lecture #25
Honors Biology
Ms. Day
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)
 Each carries a
specific amino acid
 “t” shape
 Carries amino acids
 Matches codons to
anticodons
tRNA delivers amino
acids to ribosomes
Amino

acid comes on and off!
OR
Ribosomes
Help bind tRNA anticodons
with mRNA codons during
translation
Anticodon (tRNA) = codon (mRNA)
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
AMINO ACIDS
tRNA
(with
anticodons)
mRNA
(with
codons…co
des for aa)
Ribosomes
 There are 2 ribosomal subunits
 Constructed of proteins and
ribosomal RNA or rRNA
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
Large
ribosomal
subunit
3 U
A C
5
5 A U G
3
Initiator tRNA
GTP
GDP
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 (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
 https://www.youtube.com/watch?v=5bLEDd-
PSTQ
 http://highered.mcgraw-
hill.com/sites/0072437316/student_view0/cha
pter15/animations.html#