Chapter 11(Part 3)

TranslationFrom Gene to Protein

Honors BiologyMs. Gaynor

Lecture for 3/24/09

REVIEW…Translation

mRNA polypeptide (protein)

Type of RNA Function Job Picture

mRNA (messenger RNA)

Brings message from DNA (DNA instructions) to

ribosome to make protein

tRNA (transfer RNA)

Transfers/moves amino acids to

ribosomes

rRNA (ribosomal RNA)

Makes up ribosomes along

with proteins

tRNA

A cell translates mRNA message into protein with help from transfer RNA (tRNA)Type of RNA ~80 nucleotides“t” shapeCarries amino acidsMatches codons to anticodons

tRNA

Molecules of tRNA are not all identicalEach carries a specific amino acidEach has an specific anticodon on

the other endAminoactyl Synthase (enzyme) puts tRNA together with it amino acid

tRNA Assembly

ACTIVATED tRNA

Aminoactyl tRNA Synthase

RibosomesHelp bind tRNA anticodons with mRNA codons during

translation

Found on ROUGH Endoplasmic Reticulum RER (“bound”) or in cytoplasm (“free”)

Anticodon (tRNA) = codon (mRNA)

tRNA(with

anticodons)

mRNA(with

codons)

AMINO ACIDS

REVIEW…The Genetic Code

It’s a table used that TRANSLATES RNA nucleotides called CODONS (or mRNA “letters”) into one of the 20 amino acids3 letter mRNA “word” = 1 amino acid

There are 4 different RNA “letters” that can be used

A, U, C, and G

THE GENETIC

CODE

RibosomesThere 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 The P site The A site The E site

E P A

P site (Peptide Bond-tRNAbinding site)

E site (Exit site)

mRNAbinding site

A site (Amino acid-tRNA binding site)

Largesubunit

Smallsubunit

\

Amino acid Growing polypeptide

Next amino acidto be added topolypeptide chain

tRNA

mRNA

Codons

3

5

Building a Polypeptide

Translation can be divided into 3 phasesInitiationElongationTermination

Initiation of Translation

initiation stage brings togethermRNAtRNA bearing 1st amino acid

(“start”) called MET2 subunits of a ribosome come

together

Large ribosomal subunit

Initiator tRNA

mRNA

mRNA binding site Smallribosomalsubunit

Translation initiation complex

P site

GDPGTP

Start codon

MetMet

U A C

A U G

E A

3

5

5

3

35 35

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 mRNAThere are 3 stop codons

UAA, UAG, and UGARelease factor (protein) binds to stop codon in A site

(NOT tRNA) polypeptide released

Termination of Translation

Release factor

Freepolypeptide

Stop codon(UAG, UAA, or UGA)

5

3 35

35

Figure 17.13

TRANSCRIPTION

TRANSLATION

DNA

mRNA

Ribosome

Polypeptide

Polypeptide

Aminoacids

tRNA with amino acid attachedRibosome

tRNA

Anticodon

mRNA

Trp

Phe Gly

A G C

A A A

C C G

U G G U U U G G C

Codons5 3

“EMPTY”tRNA

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 2

34

Translation (Protein Synthesis) Animation

http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html#

http://www.ucopenaccess.org/courses/APBiologyI/course%20files/multimedia/lesson13/lessonp.html

Chapter 11(Part 7)

Translation & Mutations

From Gene to ProteinHonors 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

MutationsMutations

Are changes in the genetic material (DNA) of a cell

2 TYPES1. Point mutations can affect protein

structure and functionAre changes in just one base pair of a

gene

POINT MUTATIONSThe change of a single nucleotide in the

DNA’s template strandCan lead to the production of

an abnormal protein or…the same protein

Point Mutations

Point mutations within a gene can are calledBase-pair substitutions

Can results in a mutation (change) that is

harmfulneutral (not harmful or helpful) beneficial

Substitutions2 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

Isoleucine

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 deletionsAre additions or losses of nucleotide pairs

in a geneproduce frameshift mutations

2 TYPESInsertionsDeletions

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 LETHALEx: 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 dadSpontaneous mutations

occurs during DNA replicationEnvironmental mutations

(Mutagens)physical or chemical agents that can

cause mutations Ex: Sun, viruses, chemicals