1. Translation
SBI4U1

2. 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

3. 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

4. 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

5. 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)

6. 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

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

8. 3 Stages in Translation:
Initiation
Elongation
Termination
Note: these are NOT similar to DNA replication and transcription

9. 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)

10. 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.

11. 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

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

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

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

18. Translation Animation
For Prokaryotes (similar):

19. 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

20. 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

21. (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

23. 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.

24. (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

26. 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

27. 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

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

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

30. 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