6-NUCLEIC ACIDS AND PROTEIN SYNTHESIS

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  • Purines
    • Adenine (A)
    • Guanine (G)
    Larger nitrogenous base (Purine )
    2 ring structure
  • Pyrimidine
    • Cytosine (C)
    • Uracil (U)
    • Thymine (T)
    Smaller nitrogenous base
    1 ring structure
  • name of sugars in
    DNA = deoxyribose sugar
    RNA = ribose sugar
  • DNA has T
    RNA has U
  • A-T has 2 hydrogen bonds
    C-G has 3 hydrogen bonds
  • New nucleotides are always added in a 5' to 3' direction
  • DNA STRANDS
    made up of DNA nucleotides joint by phosphodiester bonds and the 2 strands are connected by hydrogen bonds via complementary base pairing
    DNA strands are anti-parallel to each other
  • why is DNA replication carried out
    Because it is used to prepare the cell for mitosis or meiosis and happens in the S phase
  • Which enzyme is used to unzip 2 DNA strands?
    Helicase
  • Phosphodiester bonds are made using DNA polymerase enzyme
  • Leading strand: Formation of new strand is continuous
    Lagging strand: The new strand is fragmented and these fragments are known as the okazaki fragments
  • 3 types of RNA
    a)messenger RNA - Carries code from DNA to ribosome for protein synthesis
    It has a linear shape
    b)Transfer RNA - Transports specific amino acids to ribosome for protein synthesis
    It has a clover shape and has only 1 anti codon
    c)Ribosomal RNA - Assembles amino acids brought by RNA in a specific order from mRNA to make proteins of RNA by the nucleus
  • tRNA can fold within its self unlike mRNA
  • TRANSCRIPTION
    happens in the nucleus
    1)the gene gets unwind
    2)the RNA nucleotides form complementary base pairing with the template strand (template strands are non-coding strands of a certain gene)
    3)mRNA detaches from the template strand
  • RNA polymerase: forms the phosphodiester bonds between RNA nucleotides
  • Gene: A length of DNA that codes for a particular polypeptide or protein
  • An anticodon is a sequence of 3 unpaired bases on a tRNA molecule that binds with a codon on mRNA
  • Translation
    happens in the cytoplasm
    The tRNA brings the amino acids to the ribosome
  • Start codon: The codon that starts the translation process
    Stop codon: The codon that stops the translation process
  • AUG is the universal start codon and it codes for methionine
    stop codons : UGA, UAA, UAG
  • Gene mutation : Random change in the base sequence of the gene/DNA

    Causes
    1. error during DNA replication
    2. damage due to mutagens such as radiation or carcinogens
    Types of mutations

    1. Base substitution : A base is randomly substituted (silent mutation)
    2. Base addition : A base is randomly added (Frame shift)
    3. Base deletion : A base is randomly deleted (Frame shift)
  • In eukaryotes
    A mature mRNA is formed when an exon is spliced/joined
    When exons are arranged differently it is exon shuffling
  • How the ribosome synthesizes a protein

    -mRNA binds to a small subunit
    -codons are exposed to the large subunits
    -tRNA carries the amino acid to the ribosome
    -anticodons and codons form complementary base pairing
    -Ribosome links 2 amino acids together with peptide bonds
    -Ribosome moves along the mRNA translating more codons and the polypeptide chain becomes longer
    -Once the translation process stops the polypeptide chain has been synthesized