ORGANIC CHEMISTRY 3540

NUCLEIC ACIDS

STRUCTURE

FUNCTION

NUCLEIC ACIDS

• DNA (MOLECULAR WEIGHT UP TO 150 BILLION)
  • ASSOCIATED WITH CHROMOSOMES

  • GENETIC INFORMATION

• RNA (MOLECULAR WEIGHT AS LOW AS 35,000)
  • FOUND IN NUCLEUS, CYTOPLASM, MITOCHONDRIA

  • PROTEIN SYNTHESIS

COMPLETE HYDROLYSIS OF DNA GIVES:

• PHOSPHORIC ACID

• A SUGAR, 2-DEOXYRIBOSE

• FOUR NITROGEN BASES, C, T, A, G
  • (BASED ON PYRIMIDINE OR PURINE)

PARTIAL HYDROLYSIS OF DNA GIVES:

• PHOSPHORIC ACID

• FOUR DIFFERENT N-GLYCOSIDES OR NUCLEOSIDES
  • HYDROLYSIS GIVES C, T, A, OR G AND 2-DEOXYRIBOSE

  • NUCLEOSIDES ARE NITROGEN ACETALS

MILD HYDROLYSIS OF DNA GIVES:

• 4-12 NUCLEOTIDES
  • HYDROLYSIS GIVES PHOSPHORIC ACID AND 4 NUCLEOSIDES

  • NUCLEOTIDES ARE PHOSPHATE ESTERS

DNA IS A POLYNUCLEOTIDE

• PHOSPHATE ESTER CHAIN IS THE PRIMARY STRUCTURE

DNA COMPOSITION

• FOR A GIVEN ORGANISM, MOLE PERCENT OF EACH BASE IS THE SAME IN EVERY CELL

• MOLE PERCENT OF EACH BASE VARIES FROM SPECIES TO SPECIES

• SIMILAR SPECIES HAVE SIMILAR MOLE PERCENT OF A GIVEN BASE

• FOR A GIVEN SPECIES
  • MOLE PERCENT T = MOLE PERCENT A
  • MOLE PERCENT G = MOLE PERCENT C

• X-RAY ANALYSIS
  • DNA IS LONG (UP TO 12 CM) AND STRAIGHT
  • ABOUT 12 ATOMS THICK
  • THICKNESS IS SAME FOR ALL SPECIES

• WATSON AND CRICK (EARLY '50'S) USING:
  • FRANKLIN'S X-RAY IMAGES

  • MOLECULAR MODELS

  • PAULING'S ALPHA HELIX FOR PROTEINS

• PROPOSED A DOUBLE HELIX
  • HELD TOGETHER BY HYDROGEN BONDING BETWEEN T AND A AND BETWEEN G AND C
    • G & C, INTERACTIVE
    • A & T, INTERACTIVE

  • IONIC PHOSPHATES ON OUTSIDE (IN WATER)

  • EXAMPLE (1.8 MB, INTERACTIVE)

  • PAULING IN 1938 HAD PROPOSED A TRIPLE HELIX WITH PHOSPHATES ON THE INSIDE

RNA

• COMPLETE HYDROLYSIS OF RNA GIVES:
  • PHOSPHORIC ACID

  • RIBOSE

  • C, A, G (NO THYMINE) BUT URACIL U

• RNA COMPOSITION
  • MOLE PERCENT U DOES NOT EQUAL MOLE PERCENT A

  • MOLE PERCENT G DOES NOT EQUAL MOLE PERCENT C

• RNA IS SINGLE STRANDED
  tRNA, INTERACTIVE

DNA REPLICATION

• NEW DNA IS MADE AT A RATE OF 45,000 NUCLEOTIDES PER MINUTE
  • TWO NEW STRANDS ARE MADE WHICH COMPLEMENT ORIGINAL TWO STRANDS
    • SEMICONSERVATIVE REPLICATION
      (EXPERIMENT)
      (EVIDENCE)

  • DNA IS SO LARGE IT WOULD TAKE TWO MONTHS IF IT REPLICATED ONE NUCLEOTIDE AT A TIME.
    • PARTIAL UNWINDING OF THE DNA HELIX AT MANY SITES (GROWTH FORK)

    • COMPLEMENTARY STRANDS ARE MADE OF THE TWO ORIGINAL STRANDS (EVIDENCE)

    • PRODUCES TWO NEW HELICES

DNA TRANSCRIPTION

• SMALL PORTION OF DNA DOUBLE HELIX UNWINDS

• A COMPLEMENTARY RNA (CALLED MESSENGER RNA) IS SYNTHESIZED

• mRNA IS RELEASED AND MIGRATES TO RIBOSOMES

TRANSLATION AND PROTEIN SYNTHESIS

• IN THE RIBOSOMES (60% RIBOSOMAL RNA AND 40% PROTEIN)
  • mRNA IS "READ"
    • GROUPS OF THREE BASES (CODON) CODE FOR A PARTICULAR AMINO ACID

  • TRANSFER RNA (INTERACTIVE) BRINGS THE REQUIRED AMINO ACID

  • NEXT CODON IS "READ"

  • TRANSFER RNA BRINGS NEXT AMINO ACID AND AMIDE BOND IS MADE

  • PROCESS REPEATS ITSELF UNTIL COMPLETE PEPTIDE IS SYNTHESIZED

  • PEPTIDE IS RELEASED

  • PROCESS REPEATS

THE ROLE OF DNA AND RNA IS PEPTIDE SYNTHESIS

• DNA CONTAINS THE INFORMATION

• RNA CARRIES INFORMATION AND HELPS IN THE SYNTHESIS