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4th hour






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    4th hour 4th hour Presentation Transcript

    • 4.3 Protein Synthesis
      • 4.3.1 TRANSCRIPTION (Nucleus)
      • - DNA mRNA
      4.3.2 TRANSLATION (Cytoplasm) - mRNA protein
    • Overview the roles of transcription and translation in the flow of genetic information
    • Importance of Protein Synthesis
      • Production of hormones
      • Production of enzymes
      • 4.3.1Transcription
      • Definition :
      • the synthesis of mRNA on a DNA template
      • which is take place in nucleus
      • information that has been transcribed from DNA to mRNA can then be translated and thereby expressed by the formation of specific protein.
      • (DNA mRNA protein)
    • Transcription
      • RNA polymerase enzyme involved
      • Specific sequences of nucleotides along the DNA mark where the transcription begin ( promoter site ) and ends ( terminator site )
      • The stretch of DNA that is transcribed into mRNA is called a transcription unit
      • mRNA elongates in its 5’ to 3’ direction
      • 3 steps involves in transcription
      • RNA polymerase binding and initiation
      • RNA polymerase recognize and attaches to promoter site on DNA.
      • Enzyme begins to separate the DNA strand .
      • Segment of DNA strand unwind.
      • 2. Elongation Of RNA strand
      • As RNA polymerase moves along the template of DNA, complementary RNA nucleotides pair with DNA nucleotides of the strand
      • RNA polymerase joins the RNA nucleotides together in the 5’ to 3’ direction
      • 3. Termination
      • Elongation of mRNA continues until RNA polymerase reaches a terminator site on the DNA
      • Terminator site causes the RNA polymerase to stop transcribing DNA and release the mRNA
      • mRNA will leave the nucleus through the nucleus pore to the cytoplasm
    • RNA Splicing (RNA Processing)
      • Exon : A nucleotide sequence in a gene that codes for parts or all of the gene
      • product and is therefore expressed in
      • mature mRNA.
      • Intron : A nucleotide sequence in a gene that does not code for gene product.
      • : It usually transcribed in eukaryotes into
      • mRNA but subsequently removed from
      • transcript before translation.
      • Genetic code
      • Genetic code: Base triplet in DNA provides a template for ordering the complementary triplet in mRNA molecule.
      • Every base triplet is amino acid.
      • Three bases of an mRNA codon are designated as first, second and third bases .
    • Genetic code
      • There are only four nucleotide to specify 20 amino acids; A-adenine, C-cytosine, G-guanine, T-thymine (unique to DNA), U-uracil (unique to RNA) [pyrimidine, very similar to thymine].
      • Flow of information from gene to protein is based on triplet code.
      • A cell cannot directly translate a gene’s base triplets into amino acids.
      • An mRNA molecule is complementary rather than identical to its DNA template according to base-pairing rules.
      • A-U, T-A, C-G, G-C
      • mRNA base triplets are called codons.
      • Noticed that U only can be found on mRNA strand, substitute for T (only on DNA strand).
      • U on mRNA pairs with A on DNA strand, while T on DNA strand pairs with A on mRNA.
      • Two important codons in protein synthesis are initiation codon (start signal) and termination codon or stop signal.
      • Initiation codon
      • Codon AUG is a starter to the process of translation.
      • Codon AUG has dual function, as a start signal / initiation codon and it also code for amino acid methionine (Met).
      • Polypeptide chains begin with methionine
      • An enzyme may subsequently remove starter amino acid from chain.
      • 2. Termination codon
      • Three triplet bases of stop signal: UAA, UAG, UGA .
      • marking the end of a genetic code.
      • Genetic massages begin with the mRNA codon AUG, which signals the protein- synthesizing machinery to begin translating the mRNA at the location.
      • Three of 64 codons function as stop signal or termination codon. They are UAA, UAG and UGA . Any one of these termination codons marks the end of a genetic massage, and the completed polypeptide chain is released from the ribosome.