The Nature of Genetic Material

Prokaryotic genetics

            single chromosome

            changes in genetic material yield immediate characteristic changes (no masking)


The Structure of Deoxyribonucleic Acid

            double strand--double helix--polynucleotide


1)      nitrogenous base--purine or pyrimidine

2)      pentose (5 C CHO) deoxyribose

3)      phosphate molecule


Nitrogenous bases

            purines—adenine and guanine

            pyrimidines—cytosine and thymine






                        Nucleic Acid Structure

                                    Phosphodiester linkage--3’ linked to 5’ carbon

                                    Complementary base pairs

                                                A-T    2 hydrogen bonds

                                                C-G    3 hydrogen bonds

                                    Antiparallel helix 3’-5’ and 5’-3’

                                                3’ hydroxyl group

                                                5’ phosphate group



Structure of Ribonucleic Acid

            RNA differs from DNA by:

1)      single strand

2)      ribose sugar (hydroxyl group at 2nd carbon)



Biosynthesis of DNA

            Absorption vs. Synthesis of nucleotides

                        glucose--ammonium sulfate--minerals

            Activated nucleotides (precursor synthesis)

                        phosphate attachment reactions




Replication of DNA (Semiconservative theory)

            Bacterial chromosome--circular--2.5 X 109 daltons--

                        4 X 106 base pairs--linear length 1250 um

            Unidirectional/Bidirectional replication--origin

                        DNA polymerase--3’ end

            Discontinuous--small fragments--Okazaki fragments

                        DNA ligase

            Replication initiation--primer

                        Primer--RNA--RNA polymerase--complementary to DNA

                        DNA polymerase constructs deoxyribonucleotides

                                    RNA polymerase replaced with DNA


Biosynthesis of Proteins--polypeptides

            Transcription--rRNA (90% of total cellular RNA)

                        “sense” strand--initiation site--termination site

                                    RNA polymerase


                        triplet bases--codon


            Initiation codons--AUG & GUG

            Termination codons--UAA, UAG & UGA (nonsense codons)

            Degenerate code--more than one amino acid per codon


            Protein Synthesis

                        Activation of amino acid

                        Terminal sequence of tRNA--ACC



            Activity of rRNA 30 S and 50 S subunits (70 S)

                        synthesis from 5’ to 3’ ends

1)      rRNA-mRNA binding

2)      tRNA attaches to chain initiation codon

3)      tRNA attaches to next codon

4)      amino acids form peptide bond

5)      mRNA and rRNA advance as last tRNA is freed


Polysomal synthesis

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