Chapter 11 (Part 3) Translation From Gene to Protein Honors Biology Ms. Gaynor Lecture for 3/24/09

mRNA  polypeptide (protein) REVIEW… Translation mRNA  polypeptide (protein)

Brings message from DNA (DNA instructions) to ribosome to make 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” 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

Aminoactyl tRNA Synthase tRNA Assembly Aminoactyl tRNA Synthase ACTIVATED tRNA

Ribosomes Help bind tRNA anticodons with mRNA codons during translation Found on ROUGH Endoplasmic Reticulum RER (“bound”) or in cytoplasm (“free”) Anticodon (tRNA) = codon (mRNA)

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 The P site The A site The E site P site (Peptide Bond-tRNA binding site) E site (Exit site) mRNA binding site A site (Amino acid- tRNA binding site) Large subunit Small E P A

tRNA mRNA Growing polypeptide Amino acid Next amino acid to be added to polypeptide chain tRNA mRNA Codons 3 5 \

Building a Polypeptide Translation can be divided into 3 phases Initiation Elongation Termination

Initiation of Translation initiation stage brings together mRNA tRNA bearing 1st amino acid (“start”) called MET 2 subunits of a ribosome come together

Translation initiation complex Large ribosomal subunit Initiator tRNA mRNA mRNA binding site Small Translation initiation complex P site GDP GTP Start codon Met U A C G E 3 5 Figure 17.17

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 Stop codon (UAG, UAA, or UGA) 5 3

Phe tRNA Anticodon 5 3 Amino acids “EMPTY” tRNA tRNA with amino acid TRANSCRIPTION TRANSLATION DNA mRNA Ribosome Polypeptide Amino acids tRNA with amino acid attached tRNA Anticodon Trp Phe Gly A G C U Codons 5 3 “EMPTY” tRNA Figure 17.13

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 4 3

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 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 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 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