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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
      • ELONGATION OF RNA STRAND
      • TERMINATION
    THE PROCESS OF 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.