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    Chapter 10 Chapter 10 Presentation Transcript

    • CHAPTER 10 DNA STRUCTURE AND REPLICATION
      • DNA 2. DNA Replication
      • 3. From DNA to RNA to Protein
      • 4. Mutations
    • 1. DNA
      • DNA
      • Has the capacity to store genetic information.
      • Can be copied and passed from generation to generation.
    • DNA is a nucleic acid It consists on a long chain of molecules called nucleotides . The nucleotides are joined by a sugar - phosphate backbone. 4 nucleotides Differ in their nitrogenous bases Thymine (T) Cytosine (C) Adenine (A) Guanine (G) !
        • 2 DNA strands join together to form a double helix.
      ONLY PAIRS FORMED BETWEEN A-T AND G-C A T G C T A C G Hydrogen Bond
    • James WATSON and Francis CRICK determined that DNA is a double helix .
    •  
    • 2. DNA Replication
    • 2. DNA Replication When a cell or whole organism reproduces, a complete set of genetic instructions must pass from one generation to the next.
    • DNA is split in 2 strands and each strand is copied to form a new DNA molecule
    • DNA replication: - starts at specific sites ( origin of replication ) - goes in both directions
    • 3. From DNA to RNA to PROTEIN
    • From DNA to RNA to PROTEIN How an Organism’s Genotype Produces Its Phenotype GENOTYPE : is the Genetic Constitution of an organism or cell , its genetic make up . It is the sequence of nucleotide bases in DNA PHENOTYPE : is the organism’s specific traits , the organism’s total physical appearance and constitution. It is the result of the actions of proteins.
    • GENOTYPE: eye color gene called: bey2 PHENOTYPE: Example for phenotype and genotype
    • Nucleus Cytoplasm DNA specifies the synthesis of proteins in 2 stages : DNA Protein 2. TRANSLATION 1. TRANSCRIPTION RNA
    • TRANSCRIPTION : DNA  RNA TRANSLATION : RNA  PROTEIN From Nucleic Acid to Amino Acid Different Molecules - Different Languages 1 gene – 1 polypeptide hypothesis: The function of an individual gene dictates the production of a specific polypeptide.
    • CODONS: triplets of bases Each codon corresponds to an Amino Acid
      • DNA has 2 strands .
      • 4 bases combining in pairs in DNA:
          • A-T
          • G-C
      • RNA has 1 strand .
      • 4 bases combining in pairs in DNA:
          • A-U
          • G-C
    •  
    • The genetic code is shared by all organisms. GENETIC CODE: It is the set of rules relating nucleotide sequence to amino acid sequence.
    • Transcription: From DNA to RNA
      • In transcription:
      • Genetic information is transferred from DNA to RNA.
      • An RNA molecule is transcribed from a DNA template.
    • Transcription done by RNA Polymerase which adds RNA nucleotide 1 by 1 to the newly made RNA sequence. The base of the nucleotide is complementary to the DNA base.
    • DNA Promoter Terminator RNA polymerase DNA of a gene RNA Initiation Elongation Completed RNA Single strand Termination
    • 1. INITIATION: The “start transcribing” signal is a nucleotide sequence called a promoter . The first phase of transcription is initiation: RNA polymerase attaches to the promoter. RNA synthesis begins. 2. ELONGATION: Second phase. The RNA gets longer. 3. TERMINATION: RNA polymerase reaches a sequence of DNA bases called a terminator . 3 PHASES OF TRANSCRIPTION
    • But RNA is not ready yet… It needs to be processed.
    • The eukaryotic cell processes the RNA after transcription by: The Processing of Eukaryotic RNA
          • Adding a cap and tail
          • Removing introns
          • Splicing exons together
    • What does this mean? What are caps and tails? A cap and a tail are added at the extremities of the newly RNA molecule. It protects the RNA from enzymes; and help the ribosomes recognize it.
    • A gene contains EXONS and INTRONS What are EXONS and INTRONS? EXONS are kept and will be translated into polypeptides (EX for EXiting the nucleus) INTRONS are rid of. Exon Exon Exon Intron Intron
    • Remember… 1 gene – 1 polypeptide hypothesis: The function of an individual gene dictates the production of a specific polypeptide. ACTUALLY, it could be several….. 1 gene can give different versions of a protein. By combining (splicing) different exons.
    • DNA READY TO GO! Exon Exon Exon Intron Intron RNA Transcription Cap and Tail added Introns removed Splicing of exons Coding sequence
    • Translation: From RNA to PROTEIN From nucleic acid to amino acid
    • THE PLAYERS:
      • Messenger RNA (mRNA):
        • - carries the coding sequence to be translated into a protein
      • Transfer RNA (tRNA): The translator.
        • - Each carries a specific amino acid (aa)
        • - Matches it with codons in mRNA using anticodons
      • Ribosomes :
        • - 2 subunits
        • made of proteins and ribosomal RNA (rRNA)
        • brings tRNA and mRNA together. Has 2 sites and can hold 2 tRNA.
        • catalyze the peptide bonds to form polypeptide
      aa
    • codons ribosome mRNA tRNA Growing polypeptide Next amino acid to be added Formation of a Protein aa
    • Translation: The Process Translation is divided into 3 phases: 1. Initiation 2. Elongation 3. Termination
    • 1. Initiation
        • The mRNA (recognized by its cap and tail)
        • The first amino acid with its attached tRNA (the first codon is always the same (AUG), it marks the starts of the coding sequence and is therefore called start codon )
        • The two subunits of the ribosome
        • Step 1, codon recognition
          • The anticodon of an incoming tRNA pairs with the mRNA codon.
        • Step 2, peptide bond formation
          • The ribosome catalyzes bond formation between amino acids. The polypeptide grows.
        • Step 3, translocation
          • A tRNA leaves the P site of the ribosome.
          • The ribosome moves down the mRNA.
      2. Elongation 3 steps:
    • 1. codon recognition codons Empty site New codon mRNA moves 2. peptide bond formation 3. translocation
    • 3. Termination Elongation continues until the ribosome reaches a stop codon and the polypeptide is released.
    • Review: DNA  RNA  Protein
    • 4. Mutations
    • A mutation is any change in the nucleotide sequence of DNA. Mutations
    • Types of Mutations
        • A base can be replaced by another one
        • A base can be inserted
        • A base can be removed
      • Any of these change the reading frame of the genetic message
      • which can result in changes in the amino acids in proteins
      • and therefore change the function of the protein
      • can be disastrous
      • Errors in DNA replication.
      • Physical or chemical agents called mutagens.
      Mutations may result from Although mutations are often harmful, They are also the source of the rich diversity of genes in the living world.