Necessary Components for Necessary Components for TranslationTranslation

1.1. Messenger RNA (mRNA):Messenger RNA (mRNA): • Encodes for a specific protein sequence. Encodes for a specific protein sequence. • Variable length (depending on protein Variable length (depending on protein

size).size).• Information is read in Information is read in tripletstriplets ( (codonscodons) )

64 possible codons (4 x 4 x 4 = 64 = 464 possible codons (4 x 4 x 4 = 64 = 433) ) 61 codons specify amino acids 3 codons 61 codons specify amino acids 3 codons are termination signals. are termination signals.

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

Necessary Components for Necessary Components for TranslationTranslation

2. Transfer RNA (tRNA):2. Transfer RNA (tRNA): • Brings one amino acid at a time to the growing Brings one amino acid at a time to the growing

polypeptide chain.polypeptide chain.• Small molecule (70 to 90 nucleotides).Small molecule (70 to 90 nucleotides).• Forms a cloverleaf structure.Forms a cloverleaf structure.• AnticodonAnticodon: Base pairs to mRNA codon during : Base pairs to mRNA codon during

translation. translation. • Amino acid binding siteAmino acid binding site: At 3’ end of molecule. : At 3’ end of molecule.

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

Necessary Components for Necessary Components for TranslationTranslation

3. Ribosomal RNA (rRNA):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 moleculeHuge molecule: Large and small subunits must : Large and small subunits must

assemble for translation. assemble for translation. • Ribosome compositionRibosome composition: 60% rRNA and 40% : 60% rRNA and 40%

proteinprotein• Transfer RNA (tRNA) Carries Amino Acids to

the Growing Polypeptide Chain

Ribosome is the Site of Translation

STEPS OF TRANSLATIONSTEPS OF TRANSLATION

1.1. INITIATION: INITIATION: Messenger RNA (mRNA) and Messenger RNA (mRNA) and ribosome come together.ribosome come together.Transfer RNA Transfer RNA (tRNA):(tRNA): Carrying first amino acid Carrying first amino acid (methionine) has(methionine) has anticodonanticodon which binds towhich binds to start codonstart codon (AUG). (AUG).

2.2. ELONGATION ELONGATION One amino acid at time is One amino acid at time is added and linked to growing polypeptide added and linked to growing polypeptide chain by a peptide bond. chain by a peptide bond.

3.3. TERMINATION-TERMINATION-Stop codonsStop codons: UAA, UAG, or : UAA, UAG, or UGA Ribosome/mRNA complex dissociates. 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

MutationsMutations

• DNA replication is never 100% accurate.DNA replication is never 100% accurate.• Bases may be inserted, deleted, or mismatched Bases may be inserted, deleted, or mismatched

during replication. during replication. • Mutations:Mutations: are permanent changes in DNA.are permanent changes in DNA.• Any mistakes that cause changes in the Any mistakes that cause changes in the

nucleotide sequence of DNA. nucleotide sequence of DNA. • Mutations may be either harmful, beneficial, or Mutations may be either harmful, beneficial, or

have no effect on a cell or individual.have no effect on a cell or individual.

MutationsMutations

There are several possible types of mutations: There are several possible types of mutations: I.I. Substitution mutation:Substitution mutation: One nucleotide is One nucleotide is

replacedreplaced by another. May result in: by another. May result in: 1. 1. Missense:Missense: Different amino acid. May or Different amino acid. May or may not have serious consequences. may not have serious consequences. Example: Sickle cell anemia.Example: Sickle cell anemia.2. Nonsense:2. Nonsense: Stop codon. Protein is Stop codon. Protein is truncated. Usually has serious consequences.truncated. Usually has serious consequences.3. Silent:3. Silent: No change in amino acid. No No change in amino acid. No consequence.consequence.

Missense Mutation in Sickle Cell Anemia

Base substitution results in a single amino acid change Glu ---> Val

MutationsMutations

• 2. Frameshift Mutation:2. Frameshift Mutation: Nucleotides Nucleotides which are which are insertedinserted or or deleteddeleted may may changechange the gene’s the gene’s reading framereading frame. Usually . Usually serious, because entire protein sequence serious, because entire protein sequence after mutation may be disrupted. after mutation may be disrupted.

Effects of Different Types of Mutations