Translation SBI4U1

Components of Translation mRNA Determines amino acid sequence tRNA Contains anticodon that pairs w/ a codon on mRNA w/ amino acid attached Ribosomes Made of rRNA and proteins (protein synthesis) Translation factors Proteins needed for translation

Transfer RNA (tRNA) Composed of single strand of RNA Acceptor stem Composed of single strand of RNA Two functional regions Anticodon loop 3 nucleotides complementary to mRNA codon Acceptor stem 3’ single stranded w/ amino acid at the end

Aminoacyl-tRNA synthetase Enzymes that attach appropriate amino acid to tRNA 20 enzymes  one for each amino acid Example: If mRNA codon is 5’-CGG-3’, what is the corresponding anticodon? What amino acid should it carry? Anticodon = 3’to 5’- GCC – therefore arginine is the corresponding a. a 3’-GCC-5’, arginine

Ribosomes Made up of proteins and ribosomal RNAs (rRNAs) Two subunits Large subunit of 60S & small subunit of 40S Subunits bind to mRNA, clamping it b/t them Note: S is a measure of size (based on rate at which components sediment when centrifuged)

There are 3 binding sites for tRNA molecules Allows for complementary base pairing mRNA codon  tRNA anticodon Reading frame depends on starting point Example: If ribosome reads from 1st nucleotide... mRNA strand: AUUGCGCAAC reading frame: AUU GCG CAA But, if the ribosome reads from the 2nd nucleotide... reading frame: UUG CGC AAC

Ribosome moves along mRNA is 5’-3’ direction -Polyribosomes- multiple ribosomes along a strand of mRNA. -synthesizes several copies of polypeptides

3 Stages in Translation: Initiation Elongation Termination Note: these are NOT similar to DNA replication and transcription

1. Initiation Initiation factors assemble the following: Small ribosomal sub-unit mRNA Initiator tRNA Large ribosomal sub-unit Ribosome binds to mRNA at the start codon (AUG). Initiator tRNA has complementary anticodon (UAC)

The start codon sets the reading frame for the gene The start codon sets the reading frame for the gene. The reading frame establishes how subsequent codons in the sequence will be read to produce an amino acid sequence.

The reading frame establishes how all the following codons should be determined. Example: If ribosome reads from 1st nucleotide... mRNA strand: AUGGCGCAAC reading frame: AUG GCG CAA But, if the ribosome reads from the 2nd nucleotide... reading frame: UGG CGC AAC

There are 3 binding sites for tRNA molecules A site: acceptor site P site: peptide site E site: ejection site

2. Elongation Protein synthesis each amino acid is added one by one they form peptide bonds Polypeptide chain grows

3. Termination Stop codon on mRNA is reached Release factor cleaves polypeptide Protein is modified, folded and sent to appropriate area of the cell

Translation Animation http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf For Prokaryotes (similar): https://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__how_translation_works.html

DNA Mutations and Effects of Mutagens Mutation: permanent change in nucleotide sequence in DNA Mutations are copied during DNA replication Mutations in reproductive cells are passed on to future generations Mutations in somatic cells don’t effect future generations

Mutations are grouped into 2 categories: Single Gene Mutations -changes in nucleotide sequence -involves 1 gene 2) Chromosomal Mutations -changes in chromosomes -involves many genes

(1)Single Gene Mutations: Silent Mutation: no change in amino acid sequence Missense Mutation: changes amino acid sequence and can be harmful Nonesense Mutation: converts codon for amino acid to a stop codon

Single Gene Mutations cont’d… Point mutation  change in a single base pair Frameshift Mutation: causing entire reading frame to be altered. This will change the amino acids and therefore the protein.

(2)Chromosome Mutations Rearrangement of genetic material on chromosome structure deletion or duplication of portions of chromosomes inversions (a chromosome segment is broken and re-inserted in the opposite direction) translocations (a section of one chromosome is broken and fused to another chromosome

Causes of Mutations Mutations can be either spontaneous or induced. Spontaneous mutations may be caused by: a) incorrect base pairing by DNA polymerase during replication b) “transposition”; in which specific DNA sequences (called transposons) move within and between chromosomes

Induced mutations may be caused by: Induced Mutagens Induced mutations may be caused by: Physical mutagens X-rays tear through DNA and change structure UV radiation distorts DNA molecule Chemical mutagens Molecule that enters nucleus and reacts w/ DNA Nitrites (cured meats), gasoline fumes, cigarettes

DNA Repair Recall: DNA polymerase “proof reads” as a mismatch repair mechanism Specific and non-specific repair mechanisms also fix mutations

Photorepair Specific mechanism Repairs damage from UV Excision Repair Non-specific mechanism Fixes variety of damage

Learning Expectations... Components of translation (structure/functions) mRNA tRNA Ribosomes 3 stages in translation (in detail) Be able to go from DNAmRNAA.A. sequence All single gene and chromosomal mutations Example of mutagens