Translation- taking the message of DNA and converting it into an amino acid sequence.

Genes (DNA) to RNA to Proteins (Traits)

OverviewProtein 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 ProcessingProcess between transcription and

translationPre-mRNA molecule produced

and undergoes processing and editing. Introns – cut out and discardedExons – remaining pieces spliced back

together to form mRNA

• mRNA travels through nuclear membrane pore into cytoplasm

Genes Contain IntronsIntrons 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 proteinNot true any more 1 gene = can make many proteins

TranslationOccurs at the Ribosome in the CytoplasmNecessary materials: Ribosomes (rRNA and

proteins), mRNA, tRNA, amino acidsProduces proteins (traits) by connecting

amino acids together with peptide bondsUses codons on mRNA to determine amino

acid sequence = genetic code

Codons Codon= sequence of 3 nucleotides on mRNA

that 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 combinationsFirst codon discovered- UUU= phenylalanineCodon-Amino Acid chart or wheel.

Genetic Code

Codon

Codon-Amino Acid TableHow many start and stop codons are present?

PracticemRNA AUGUCCACGGGAU

GA

AUGGGAAGACUAUAA

All living organisms and viruses use this triplet 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)

TranslationRibosome 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.

Summary

http://glencoe.mcgraw-hill.com/sites/0078802849/student_view0/unit3/chapter12/concepts_in_motion.html#

Practice – DNA-mRNA-tRNA-amino acidDNA TACAATGCCGTAATTmRNA (codon)tRNA (anti-codon)Amino acids Protein

Be able to determine patterns in all directions

Practice-Keratin

Types of MutationsPoint mutation

Substitution- wrong nucleotide base put in place

No protein madeProtein 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 mutationDeletion (subtraction)- one fewer nucleotide is placed in sequence- frameshift 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 MutationsInversion- reverses the direction of parts of a chromosome

Translocation- part of a chromosome breaks off and attaches to anotheri.e. Down’s syndrome Extra piece of C. 21 is found.

Gene RegulationGenes are turned on and off as needed by the

cell.ProkaryotesPromoter, operator, repressor protein, genesEx. 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- regulationMore complicated with more regulatory

proteins.Regulatory proteins= transcription factorsEnhancer, activator, promoter, transcription

factor, RNA polymerase. No operatorActivators increase attraction of RNA

polymerase for the promoterTextbook page 215