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DNA Replication and Protein Synthesis

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    DNA Replication and Protein Synthesis DNA Replication and Protein Synthesis Presentation Transcript

    • Processes of DNA Replication and Protein Synthesis
    • DNA Replication
    • Replication
      • Makes duplicate copies of DNA in the process of replication
      • DNA replication involves separating the DNA molecule into 2 strands.
      • Each strand than serves as a pattern, or template, to make a new DNA molecule.
      • The result is 2 identical double-stranded molecules of DNA
    • Replication (con’t)
      • Because each of these double-stranded molecules of DNA consists of a single strand of old DNA (the template) and a single strand of new, replicated DNA (the complement), this is called semi-conservative replication.
    • Steps
      • Helicase unwinds DNA, creating a replication fork. Proteins bind to the single strand to keep the DNA from recombining.
      • RNA primase starts replication at special base sequences by adding RNA primers.
      • DNA polymerase attaches to the RNA primers and begins elongation. (Elongation = the adding of DNA nucleotides to the complement strand)
    • Steps (con’t)
      • The leading complementary strand is assembled continuously as the DNA uncoils.
      • The lagging complementary strand is assembled in short pieces called Okazaki fragments. The pieces are joined together by DNA ligase.
      • The RNA primers are replaced by DNA nucleotides.
    • Protein Synthesis
    • Protein Synthesis
      • Proteins can function as:
        • Enzymes
        • Repairing agents for the cell
      • Proteins determine the shape and function of organisms.
      • Each gene is responsible for one protein. So, the message of the DNA code is information for building proteins.
    • Protein Synthesis (con’t)
      • How do genes code for proteins? THE GENETIC CODE!!!
      • Genetic code: sequence of nitrogen bases along one of the two strands that codes for the synthesis of proteins.
      • The nitrogen bases set up in sets of 3 that are known as codons.
    • Protein Synthesis (con’t)
      • Because the sequence of 3 nitrogen bases forms the code for an amino acid, the DNA code is often called the triplet code.
      • 64 combinations are possible when a sequence of 3 bases is used. So, 64 different codons are in the genetic code.
      • 61 of the codons code for amino acids, and the other 3 code for protein synthesis to start or stop.
    • Protein Synthesis (con’t)
      • More than one codon can code for an amino acid; however, for any one codon, there can only be one amino acid.
      • The genetic code is universal. Universal means that the codons represent the same amino acids in all organisms.
      • Protein synthesis: process that describes how enzymes and other proteins are made from DNA.
    • Protein Synthesis (con’t)
      • Steps of Protein Synthesis:
        • Transcription
        • RNA processing
        • Translation
      • There are 3 types of RNA:
        • mRNA (messenger): provides the instructions for assembling amino acids into a polypeptide.
        • tRNA (transfer): delivers amino acids to a ribosome for their addition into a growing polypeptide chain
        • rRNA (ribosomal): combines with proteins to form ribosomes
    • Transcription: From DNA to RNA RNA is transcribed from a DNA template by a process that resembles DNA replication.
    • Steps of Transcription:
      • Initiation
        • The “start transcribing” signal is a nucleotide sequence called the promoter, located in the DNA at the beginning of the gene. Promoter is a specific place where RNA polymerase attaches.
        • RNA polymerase attaches to the promoter
        • Start of RNA synthesis
    • Steps of Transcription (con’t)
      • RNA Elongation
        • During the 2 nd phase of transcription, elongation, the RNA grows longer.
        • As RNA synthesis continues, the RNA peels away from DNA and allows the DNA strand to rejoin.
      • Termination
        • The 3 rd and final phase, RNA polymerase reaches the terminator sequence of bases in DNA.
        • This sequence signals the end of the gene and the polymerase molecules detaches from the RNA molecule and the gene.
      Steps of Transcription (con’t)
    • RNA Processing The RNA copy that is formed is called mRNA. The mRNA carries the information for making the protein chain to the ribosomes, where it goes through RNA processing.
    • Translation Conversion between different languages – from nucleic acid to protein. Occurs on the ribosomes and uses tRNA. End product is a very long protein chain.
    • tRNA
      • Composed of about 75 nucleotides
      • Each tRNA recognizes only one amino acid.
      • The amino acid becomes bonded to the top of the tRNA.
      • Located on the bottom of the tRNA are 3 nitrogenous bases, called an anticodon, which pairs with mRNA codons during translation.
    • Steps of Translation
      • Initiation
        • 1 st phase brings together:
          • mRNA
          • 1 st amino acid with its attached tRNA, and
          • The 2 subunits of a ribosome
    • Steps of Translation (con’t)
      • Elongation
        • Amino acids are added one by one in a 3-step process
          • Step 1
            • Codon recognition
          • Step 2
            • Peptide bond formation
          • Step 3
            • Translocation
      • Termination
        • Elongation continues until a stop codon (UAA, UAG, or UGA) is reached.
        • Polypeptide is released.
        • Ribosome splits into subunits and falls off.
      Steps of Translation (con’t)