PBIO 100 Lecture Notes

I. Heredity and Environment

• A. DNA determines the entire structure of an organism
  • 1. Heredity includes the blueprints for arranging an organism
    2. An organism's genes (DNA) are inherited from parents

  B. Both heredity and environment are critical determinants of an organism's structure and behavior

  • 1. If it's not in your genes, you can't have it
    2. Everything that is inherited can only be expressed in the proper environment
    • a. Example: you have genes to be very healthy, but if you only eat Big Macs, you won't reach your potential

II. DNA structure and replication (a complex summary, consult later)

• A. Polymer of nucleotides
  • 1. Each nucleotide composed of phosphate, sugar (deoxyribose), and organic base
    2. Four kinds of bases- A, T, G, C
    3. DNA consists of 2 strands held together by base pairing
    • a. adenine pairs with thymine
      b. guanine pairs with cytosine
      c. each differs chemically
      

    4. Each strand is the complement of the other
    

    • 
                ORIGINAL   --A T--    MATCHING
                           --C G--
                           --G C--
                           --T A--
      

    5. See this illustration of DNA structure and see how DNA duplicates itself

  B. Replication of DNA (in nucleus)

  • 1. Each strand becomes a template - parent comes apart
    2. Proper base-pairs are assembled on that template (w/proper enzymes)
    
    • a. Pool of nucleotides in nucleus

    3.The nucleotides are connected together to make a new strand complimentary to the old one - new identical to old
    4. Called semi-conservative replication half old, half new DNA on each strand (half original)

III. RNA structure and synthesis

• A. Similar to DNA with the following differences (RNA nucleic acid composed of repeating subunits - nucleotides - base, sugar, phosphate)
  • 1. Each RNA nucleotide contains a different sugar (ribose - DNA deoxyribose) and the bases are A, G, C, and U (uracil)
    A--U, G--C
    2. RNA is single-stranded and shorter in length
    3. RNA doesn't persist in the cell for very long (sometimes only for a few seconds), while DNA persists for the life of the cell

IV. What is the central dogma?

• A. 3 different RNA molecules are involved in protein synthesis
  B. Process of making proteins - summary of steps - but there are some exceptions, see the NEW dogma
  • 1. Transcription- making an RNA copy (mRNA) of a small part of the DNA molecule - at nucleus
    
    • a. mRNA- carries the message about what type of protein to make from the DNA in the nucleus to the ribosome
      b. The sequence of nucleotides in RNA and in the DNA is the same (in RNA substituting uracil for thymine)
      c. mRNA is synthesized from DNA using base pairing
      d. DNA unwinds in a section
      

                --T--A--
                --G--C--
                --C-   -G--
                --A-     -T--     Formation of a strand of RNA
                --A--U--   -T--   
                --G--C--   -C--
                --G--C--   -C--   Only one strand used to make RNA
                --A--U--  -T--
                --C-RNA -G--
                --T-   -A--
                --A--T--
                --G--C--
                   DNA 
      

    2. Translation- synthesizing a protein from amino acids according to the sequence of nucleotides in mRNA - at the ribosomes
    

    • a. components of translation
      
      • i. rRNA- part of the ribosome- needed for protein synthesis (helps mRNA bind to ribosome)
        ii. tRNA- brings (transfers) specific amino acids to the ribosome to be assembled as proteins
        iii. amino acids - the repeating sub-units of protein molecules, the order determines the protein
        • 1) 20 amino acids common in all life forms
          2) 2 functional groups:-NH₂ (amino group) & -COOH (acid group)
          3) Order of amino acids is important- order determines the 3-dimensional shape of the molecule. This is significant because function follows form: the biological activity of a protein depends largely on its 3-dimensional structure
          

      b. steps in translation
      

      • i. the mRNA leaves the nucleus and migrates to a ribosome
        ii. the mRNA binds to the small ribosomal subunit
        iii. a tRNA brings an amino acid to the ribosome where the anticodon on the tRNA binds to the codon of the mRNA
        iv. the amino acid bonds to its adjoining amino acid to form a growing polypeptide molecule
        v. the tRNA without the amino acid is released from the ribosome
        vi. other tRNA's bring amino acids to the ribosome to complete the protein molecule
        

    3. The genetic code
    

    • a. Every three nucleotides on mRNA codes for a particular amino acid - reads 3 at a time

      • 
                  U - G - C - C - A - C - G - C - A   mRNA
                  ^ codon ^   ^ codon ^   ^ codon ^
                  Cytosine    Histidine    Alanine    amino acids
        

        
        

      b. The code is universal - all living things have the same codes

      • i. Example- UUG in mRNA always codes for the amino acid phenylalanine
        ii. This is true for all organisms- bacteria, plants, animals, and so on

    The Discovery of DNA a review of the major events
    
    Other sites of Interest:
    Glossary of terms
    A good review
    A simplified review
    Review of the Central Dogma
    A review of what DNA and RNA does
    Review of DNA and RNA structure
    
    

    

    
    

    Last revised: 30 Jan 1997 - Bottino