Necessary Components for Translation 1.Messenger RNA (mRNA): Encodes for a specific protein sequence.Encodes for a specific protein sequence. Variable length (depending on protein size).Variable length (depending on protein size). Information is read in triplets (codons) 64 possible codons (4 x 4 x 4 = 64 = 4 3 ) 61 codons specify amino acids 3 codons are termination signals.Information is read in triplets (codons) 64 possible codons (4 x 4 x 4 = 64 = 4 3 ) 61 codons specify amino acids 3 codons are termination signals.

mRNA is complementary to DNA and read in triplets (codons)

Necessary Components for Translation 2. Transfer RNA (tRNA): Brings one amino acid at a time to the growing polypeptide chain.Brings one amino acid at a time to the growing polypeptide chain. Small molecule (70 to 90 nucleotides).Small molecule (70 to 90 nucleotides). Forms a cloverleaf structure.Forms a cloverleaf structure. Anticodon: Base pairs to mRNA codon during translation.Anticodon: Base pairs to mRNA codon during translation. Amino acid binding site: At 3’ end of molecule.Amino acid binding site: At 3’ end of molecule.

Transfer RNA (tRNA) Carries Amino Acids to the Growing Polypeptide Chain

Necessary Components for Translation 3. Ribosomal RNA (rRNA): Ribosome is the site of protein synthesis.Ribosome is the site of protein synthesis. Facilitates coupling of mRNA to tRNA.Facilitates coupling of mRNA to tRNA. Huge molecule: Large and small subunits must assemble for translation.Huge molecule: Large and small subunits must assemble for translation. Ribosome composition: 60% rRNA and 40% proteinRibosome composition: 60% rRNA and 40% protein Transfer RNA (tRNA) Carries Amino Acids to the Growing Polypeptide Chain

Ribosome is the Site of Translation

STEPS OF TRANSLATION 1.INITIATION: Messenger RNA (mRNA) and ribosome come together.Transfer RNA (tRNA): Carrying first amino acid (methionine) has anticodon which binds to start codon (AUG). 2.ELONGATION One amino acid at time is added and linked to growing polypeptide chain by a peptide bond. 3.TERMINATION-Stop codons: UAA, UAG, or UGA Ribosome/mRNA complex dissociates.

Translation: Initiation at Start Codon

Translation: During Elongation one Amino Acid is Added at a Time

Elongation: Ribosome Travels Down mRNA, Adding One Amino Acid at a Time

Termination: Once Stop Codon is Reached, Complex Disassembles

Mutations DNA replication is never 100% accurate.DNA replication is never 100% accurate. Bases may be inserted, deleted, or mismatched during replication.Bases may be inserted, deleted, or mismatched during replication. Mutations: are permanent changes in DNA.Mutations: are permanent changes in DNA. Any mistakes that cause changes in the nucleotide sequence of DNA.Any mistakes that cause changes in the nucleotide sequence of DNA. Mutations may be either harmful, beneficial, or have no effect on a cell or individual.Mutations may be either harmful, beneficial, or have no effect on a cell or individual.

Mutations There are several possible types of mutations: I.Substitution mutation: One nucleotide is replaced by another. May result in: 1. Missense: Different amino acid. May or may not have serious consequences. Example: Sickle cell anemia. 2. Nonsense: Stop codon. Protein is truncated. Usually has serious consequences. 3. Silent: No change in amino acid. No consequence.

Missense Mutation in Sickle Cell Anemia Base substitution results in a single amino acid change Glu ---> Val

Mutations 2. Frameshift Mutation: Nucleotides which are inserted or deleted may change the gene’s reading frame. Usually serious, because entire protein sequence after mutation may be disrupted.2. Frameshift Mutation: Nucleotides which are inserted or deleted may change the gene’s reading frame. Usually serious, because entire protein sequence after mutation may be disrupted.

Effects of Different Types of Mutations