CHEM  30 B  Dr. R. Rinehart

 Ch. 21 Nucleic Acids & Protein Synthesis 

I. Nucleic Acids and their components

A. DNA:  polymer of deoxynucleotides; primarily in cell nucleus
            B. RNA:  polymer of nucleotides; primarily in cytoplasm, but made in nucleus
            C. Nucleotide composition = base + 5C sugar + phosphate
                                    (a nucleoside is just base + 5C sugar)

1. Base: heterocyclic group, attached to 1’ position of sugar
                        a. Purines:  Adenine [A] and Guanine [G]
                        b. Pyrimidines: Cytosine [C]  Uracil [U]  Thymine [T]
            2. Sugar: 5C in 1-b-furanose form
                                    a. DNA:  D-2’-deoxyribose
                                    b. RNA:  D-ribose
            3. Phosphate: attached  at  5’ position  of  sugar  by  phosphoester  linkage  

See my table of bases, base pairs, nucleosides, nucleotides, and coenzymes

II. DNA :  the  “hard drive” of  genetic  information  (with “auto-backup” features!) 
            A. Backbone:  alternating sugar and phosphate groups
            B. Phosphodiester linkages connecting 3’ of one sugar to 5’ of next sugar
                  note 5’ à 3’ direction of chain:  the termini are defined by the free –OH groups

            C. Secondary structure:  double helix held by specific H-bonds and nonspecific
                               hydrophobic interactions (pi-stacking of bases)
            D. Antiparallel, complementary strands with base-pairing
                        A=T  has 2 H-bonds   and G☰C has 3 H-bonds
            E. Chromosomes    tertiary structure; each has many genes

            F.  Replication
                        uses DNA polymerase, unwinding proteins, gyrases, swivelases, etc. etc.
                               and deoxynucleoside triphosphates 

III. RNA:   Three classes with different specialized functions. 
      Each class is transcribed by a different RNA polymerase using nucleoside triphosphates.   
            A. Messenger RNA (mRNA):   gene copy;  directs amino acid sequence of protein
            B. Ribosomal RNA (rRNA):   structural framework of ribosome and possible catalysis
                        1. Ribosomes contain small and large rRNAs  and  >30 proteins/enzymes
                        2. Bacterial ribosomes different from eukaryotic ones; antibiotics like
                                    chloramphenicol and erythromycin inhibit theirs, but not ours
            C. Transfer RNA (tRNA): brings in amino acids
                        1. specific “ligases” attach specific proper amino acids to tRNAs using ATP energy
                        2. “anticodon loop”  reads codons in mRNA

D. Flow of genetic information: 
                            DNA à RNA à protein   this is called the “central dogma” of  molecular biology
                             what about reverse transcriptase???       

E. Transcription:  RNA synthesis
                        in eukaryotes, there are separate RNA polymerases for mRNA, tRNA, and rRNA

F. “Processing” of mRNA
                        Get those damn introns out of here!  dice and splice!   

IV. Translation and Protein Synthesis           

A. The GENETIC CODE [see table below]
                        1.  Each amino acid has at least one specific “codon”
                        2.  Codons are “triplets”  4x4x4 = 64 possible
                        3.  some are “degenerate”, but at least 40 different tRNA’s needed to read them
                        4.      there is one INITIATION codon (AUG)
                                and three TERMINATION codons (UAA, UAG, UGA) 

B. TRANSLATION (of mRNA): protein synthesis by ribosomes
                        1. Initiation
                        2. Elongation: energy from GTP
                        3. Termination
                        4. Post-translational modifications    

            C. Mutations and their consequences
                        1. Point mutations
                        2. Insertions and deletions           

D. Recombinant DNA: genetic engineering

V. Applications: scholarly, medical, forensic, agricultural, ...

 © Ronald W. Rinehart, 2002-2007