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Ch.4 2






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    Ch.4 2 Ch.4 2 Presentation Transcript

    • Ch. 4 Section 2 How DNA Works
    • RNA - R ibo n ucleic A cid
      • How is RNA similar to DNA?
        • It is a nucleic acid
        • It is made of nucleotide subunits
        • Contains the nucleotides Adenine (A), Cytosine (C), and Guanine (G)
    • How is RNA different from DNA?
      • RNA has the 5-carbon sugar ribose instead of deoxyribose
      • RNA has the nucleotide Uracil (U) instead of Thyamine (T)
      • RNA is single stranded….DNA is double, hence the name “double helix”
    • 3 Types of RNA
      • messenger RNA (mRNA)
      • ribosomal RNA (rRNA)
      • transfer RNA (tRNA)
      • All of these types are involved in
      • Protein Synthesis
    • What is Protein Synthesis?
      • The assembly of amino acids into proteins
      • Most genes contain instructions for assembling amino acids into proteins
      • This process is controlled by RNA
    • There are 2 Parts to Protein Synthesis
      • Transcription - making RNA from
      • DNA
      • Translation - making proteins
      • from RNA
    • Protein Synthesis Part I: Transcription
      • What’s the purpose??
      • *DNA makes RNA
      • *Occurs in the nucleus
    • Steps of Transcription
      • 1. DNA unwinds and unzips exposing the bases (and the genes)
      • 2. Only one DNA strand acts as a template
      • 3. An enzyme reads off the template sequence and brings in free nucleotides that follow base pairing rules
      • 4. As nucleotides line-up, bonds form the backbone of the new mRNA
      • 5. The DNA re-zips and rewinds itself!
      • Let's take a closer look!
    • Protein Synthesis Part II: Translation
      • What’s the purpose??
      • *RNA makes protein
      • *Occurs in the cytoplasm
      • (specifically at ribosomes)
    • Steps of Translation
      • 1.MRNA leaves the nucleus and parks itself at a ribosome
      • *ribosomes are composed of protein & RNA
      • (rRNA)
      • * remember ribosomes may be “free” or
      • attached to the rough ER
      • 2. Ribosomes read mRNA as CODONS
      • (sets of 3 nucleotides)
      • *mRNA is a strand of codons
      • *Each codon specifies a start signal, an
      • amino acid, and finally a stop signal
    • mRNA is divided into codons
      • A
      • U Codon
      • G
      • C
      • A Codon
      • A
      • C
      • G Codon
      • U
      *Codons “code” for an amino acid *Amino acids “code” for proteins
    • Step of Translation Cont.
      • 3. Individual tRNA come along and match
      • the codon with their ANTICODON
      • *tRNA is made up of an anticodon
      • (set of 3 nucleotides), RNA, and an
      • amino acid
      t U A C Amino Acid RNA Anticodon
      • 4. When the correct tRNA appears, it attaches its
      • amino acid to the growing polypeptide (protein)
      • chain with a peptide bond.
      • 5. After dropping its amino acid off, the tRNA
      • breaks free
      • 6. The ribosome moves down the mRNA strand by
      • 3 nucleotides to the next codon.
      • 7. A new tRNA arrives, and the cycle continues
      • until a “STOP” codon is reached
      • Let's see how it really works!