2 Part I: TRANSCRIPTION- the building of mRNA, tRNA, and rRNA (takes place in the NUCLEUS)Initiation:RNA polymerase binds to the gene’s promoter on the template strand of DNA(a specific sequence of the DNA that acts as a “start signal” for transcription)RNA polymerase unwinds and separates the two strands of the DNA.Elongation:RNA polymerase adds and then links complementary RNA nucleotides as it “reads” the gene” on the template strand.Termination:A “stop” signal on the DNA tells the RNA polymerase to detach from the DNA and release the RNA molecule
4 RNA Processing Before leaving the nucleus…….. A cap (methyl-guanine or mG) is added by enzymes to the starting end of the mRNA moleculeA poly-A tail is added to the end of the mRNAThe molecule is spliced. Introns are removed (non-coding nucleotides) and exons remain.
6 TranslationThe assembly of a protein (occurs on the ribosome in the cytoplasm)Translation DetailmRNA leaves the nucleus through the nuclear pore and forms a functional ribosome with two ribosomal subunits, and a tRNAInitiation: The mRNA “start” codon AUG is oriented in a region of the ribosome called the P site where the tRNA molecule carrying methionine can bind to the start codon.
7 Translation- cont.3. The codon in the area of the ribosome called the A site is ready to receive the next tRNA.Elongation: Both the A site and the P site are holding tRNA molecules- each carrying a specific amino acid. A peptide bond forms between the adjacent amino acidsThe tRNA in the P site detaches and leaves its amino acid behindThe tRNA in the A site moves to the P site. The tRNA carrying the amino acid specified by the codon in the A site arrives.Termination: Steps 4-6 are repeated until a stop codon is reached.
8 Translation animation One more Translation animation
9 The mRNA strand would be: AUG UUU CAU UGA If a segment of DNA is:TAC AAA GTA ACTThe mRNA strand would be:AUG UUU CAU UGAThis would code for the following amino acids:Met Phe His Stop
10 Types of Mutations Point Mutations- a change of one or just a few nucleotides in a geneSubstitution-one nucleotide is replaced by another.sometimes called a “missense” mutationInsertion –an extra nucleotide is added.Deletion-a nucleotide is omitted.
11 Frame shift mutations are caused by deletions and insertions Original Strand AUG AAU GCG GAC UAAStart Asparagine - alanine –aspartate –stop Ex. DeletionAUG -AU GCG GAC UAAbecomes AUG AUG CGG ACU AAStart -methionine -arginine- threonine-
12 becomes AUG AAU GCG GGA CUA A Ex. InsertionAUG AAU GCG GGAC UAAbecomes AUG AAU GCG GGA CUA AStart- Asparagine- alanine - glycine- Leucine -