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    Central Dogma

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    hoàng linh
    The central dogma describes how DNA is transcribed into mRNA which is then translated into proteins. Transcription occurs from 3' to 5' on one strand of DNA to produce mRNA. Translation begins at the start codon where the first tRNA binds and elongation continues until a stop codon is reached, at which point the ribosome dissociates and protein synthesis is complete. Experiments by Khorana, Nirenberg and others determined the genetic code by which codons correspond to specific amino acids.

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    Central Dogma

    Uploaded by

    hoàng linh
    12 views32 pages
    The central dogma describes how DNA is transcribed into mRNA which is then translated into proteins. Transcription occurs from 3' to 5' on one strand of DNA to produce mRNA. Translation begins at the start codon where the first tRNA binds and elongation continues until a stop codon is reached, at which point the ribosome dissociates and protein synthesis is complete. Experiments by Khorana, Nirenberg and others determined the genetic code by which codons correspond to specific amino acids.

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    The central dogma describes how DNA is transcribed into mRNA which is then translated into proteins. Transcription occurs from 3' to 5' on one strand of DNA to produce mRNA. Translation begins at the start codon where the first tRNA binds and elongation continues until a stop codon is reached, at which point the ribosome dissociates and protein synthesis is complete. Experiments by Khorana, Nirenberg and others determined the genetic code by which codons correspond to specific amino acids.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    12 views32 pages

    Central Dogma

    Uploaded by

    hoàng linh
    The central dogma describes how DNA is transcribed into mRNA which is then translated into proteins. Transcription occurs from 3' to 5' on one strand of DNA to produce mRNA. Translation begins at the start codon where the first tRNA binds and elongation continues until a stop codon is reached, at which point the ribosome dissociates and protein synthesis is complete. Experiments by Khorana, Nirenberg and others determined the genetic code by which codons correspond to specific amino acids.

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    Central Dogma

    Review question 1
    • In what direction is RNA polymerized?
    • N to C
    • 3 to 5
    • 3' to 5'
    • 5' to 3'
    Review question 2
    • True or False: More than one codon typically
    encodes each amino acid.
    • True
    • False
    Review question 3
    • Where does translation begin, as indicated
    on the mRNA transcript?
    • terminator
    • start codon
    • transcription start site
    • promoter
    Review question 4
    • If the following were a complete mRNA,
    which codon would be recognized as the stop
    codon? 
    5' UAAUGCUGACUAGUUAAGCCCGAGCGAA-3'
    • UAA
    • UGA
    • UAG
    Review question 5
    Review question 6
    Learning objectives
    • What is the central dogma?
    • How is an RNA chain synthesized?
    • How is transcription /translation initiated,
    elongated and terminated?
    Watson &Crick
    • Solving DNA three-dimensional structure: does
    not end.
    • DNA is the hereditary molecule of the cell,
    they reasoned that the sequence of
    nucleotides in the molecule must function as
    a code, able to direct the synthesis of proteins

    DNA ---- ? -------- PROTEINS


    ????????How DNA can direct the synthesis of
    proteins that are made exclusively in the cell’s
    cytoplasm
    • A candidate for
    this information
    carrier was
    ribonucleic acid –
    RNA that found
    mostly in the
    cell’s cytoplasm
    • DNA &RNA use the same nitrogenous
    bases except that DNA uses thymine,
    whereas RNA uses uracil
    • Uracil can hydrogen bond with adenine
    just like thymine
    • DNA is usually a double-stranded
    molecule. RNA is usually single-stranded
    ??????????How did the amino acids interact
    with the carrier RNA?
    • There must be adaptor molecules; in fact there
    must be 20 different adaptors, one for each
    amino acid.
    • Har Khorana and Nirenberg figured out how the
    nucleotide language of mRNA is “translated”
    into the amino acid language of proteins.
    • Three nucleotides form a “codon” – an mRNA
    word that specifies one amino acid.
    • A codon made from only one or two
    nucleotides would not produce enough
    combinations (words) to code for all 20 of the
    known amino acids.
    • A three-nucleotide codon produces 64
    combinations.
    • This would produce a redundant code where
    several different codons specify the same
    amino acid.
    • They made synthetic mRNA
    composed entirely of uracil,
    then added this poly-U to the
    cell-free extract.
    • When they examined the
    products produced in this cell-
    free system, they found
    polypeptides composed
    entirely of the amino acid
    phenylalanine (PHE)
    • From this result, they concluded that a
    sequence of three uracils – UUU- must code
    for phenylalanine -> determined one of the 64
    triplet codons
    • Matthaei and Nirenberg
    tried other polynucleotide
    chains. Poly –C made a
    proline (PRO) chain;
    • Poly-A made a lysine (LYS)
    chain
    • No protein was made with
    the poly –G chain
    • Using RNA templates containing different
    nucleotide combinations. They assigned
    amino acids to about 50 triplet codons
    • This is genetic code table
    • To find a specific codon, look down the left
    hand side for the first letter of the codon. For
    the second letter, look across the table. For
    the last letter, look down the right hand side
    of the table.
    • The codon C G A codes for the amino acid
    arginine (ARG).
    • Phil Leder help Nirenberg with
    the rest of the genetic code.
    • Some of the codons were hard
    to decipher, because they
    could not establish their order
    biochemically.
    • For example: a triplet with
    two Gs and one C could be in
    the order CGG or GCG or GGC
    • They used the activation of tRNA to
    solve this problem.
    • tRNA is the molecule that carries amino
    acids to the ribosomes for protein
    synthesis.
    • tRNA is single stranded, stretches of
    complementary nucleotides hydrogen
    bond to form short double-stranded
    regions, which bend the tRNA into a
    characteristic cloverleaf shape
    • At a position on one of the
    leaves, a sequence of three
    nucleotides forms an anti-
    codon, which base pairs with
    a specific mRNA codon.
    -> there is a different tRNA
    molecule corresponding to each
    mRNA codon
    • tRNA becomes activated when the amino
    acid binds to the tRNA’s stem.
    • They found the translation
    starts with a specific codon
    AUG – the only unique codon –
    and there are stop codons that
    end translation.
    • Within the nucleus, the DNA
    code is transcribed into a
    complementary mRNA molecule
    • The mRNA enters the cytoplasm, where it
    associates with a ribosome. The mRNA code
    is then translated into a polypeptide chain
    • The codon AUG signals the
    start of translation.
    • An activated tRNA ferries
    the first amino acid –
    methionine – to the
    ribosome.
    • The tRNA anti-codon binds
    to the AUG codon on the
    mRNA
    • The whole complex
    shiffts, and the next codon
    is read by another tRNA
    • As two amino acids are held in position, a
    peptide bond is formed between them. The
    second tRNA accepts the growing protein
    chain, and the methionine tRNA is released
    • The process is repeated until stop codon is
    encountered
    • When stop codon is reached,
    translation is finished.
    • Stop codon do not have
    matching tRNAs
    • The ribosome disassembles
    to be reused for translating
    another mRNA and one
    complete peptide chain is
    released
    Genetic code
    Keynote
    • Transcription is the process of transferring the genetic information
    in DNA into RNA base sequences. The DNA unwinds in a short
    region next to a gene, and an RNA polymerase catalyzes the
    synthesis of an RNA molecule in the direction along the template
    strand of the DNA. Only one strand of the double stranded DNA is
    transcribed into an RNA molecule.
    • Translation is a complicated process requiring many RNAs, protein
    factors, and energy. The AUG (methionine) initiator codon signals
    the start of translation in prokaryotes and eukaryotes. Elongation
    proceeds when a peptide bond forms between the amino acid
    attached to the tRNA in the A site of the ribosome and the growing
    polypeptide attached to the tRNA in the P site. Translocation occurs
    when the now-uncharged tRNA in the P site is released from the
    ribosome and the ribosome moves one codon down the mRNA.
    Termination occurs as a result of the interaction of a protein release
    factor with a stop codon.

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