• The Graphics Gallery at Access Excellence (lots of neat illustrations here).
• BioTech's Dictionary. A biotechnology reference tool from Indiana University
• Transcription and Translation from the University of Texas, Austin.
• MIT's Central Dogma Directory
• Human Biology (BIOL121) from the University of Virginia with lots of nice slides.
• BioTech's "An Introduction to Translation" by Indiana University
• What are genes? ( A good review of terminology!)

1. Describe what is meant by the semi-conservative replication of DNA, and explain the roles of DNA, unattached DNA nucleotides, and enzymes in this process.

2. Draw a diagram, create a concept map, or write a paragraph that explains the relationships among these terms: chromosome, allele, gene expression, trait, DNA, RNA polymerase, messenger RNA, transfer RNA, ribosomal RNA, codons, anticodons, ribosomes, transcription, translation, RNA processing, amino acids, peptide bonds, primary stucture, secondary structure, tertiary structure, quaternary structure.

3. Explain how the sequence of DNA nucleotides for a specific allele, such as the allele for Cystic Fibrosis, is related to the production of a specific membrane protein.

4. Explain transcription and translation, and the roles of RNA polymerase, messenger RNA, transfer RNA, ribosomal RNA, and ribosomes in carrying out these two processes.

5. Describe the basic changes in substrate molecules that may occur as they are converted to products by reactions catalyzed by the action of enzymes.

• each time a cell divides, its DNA must replicate, so that each daughter cell receives the same set of genetic instructions.
• relies on complementary base pairing
• replication is semi-conservative. Each new double helix has one parent strand and one new strand.
• many different enzymes are involved
• at 50 bases/sec, human DNA would require 3.8 years for one replication, so replication begins at multiple sites within each chromosome
• DNA polymerase "proofreads" as it goes, excising mismatched bases and inserting correct ones
  • An introduction to nucleic acid sequences from BioTech at Indiana University
  • A View of a DNA Molecule from Access Excellence
  • The collaboration of proteins from Access Excellence
  • DNA replication from MIT
  • Semi-Conservative DNA Replication movie
  • DNA replication diagram of last lecture

• The flow of genetic information from DNA to RNA to protein. DNA codes for the production of RNA, which in turn codes for the production of protein.
  • Proteins and Gene Expression
  • How are genes linked to disease? (from Access Excellence)
  • Central Dogma from Access Excellence
  • Illustration from the University of Texas at Austin
  • Diagram of a Retrovirus

• is the synthesis of a molecule of RNA that is complementary in sequence to one strand of the DNA double helix
• "a mobile copy of a gene's information"
• proteins called transcription factors determine which genes are expressed in which tissues at which stages of development. The promotor, a control sequence near the start of the gene, attracts RNA polymerase and transcription factors. It tells the RNA polymerase where to begin transcription.
• enzymes unwind the DNA strand, and RNA polymerase builds the RNA chain. Base pairing is complementary (A with U, and G with C). Synthesis is single-stranded, and proceeds in one direction.

  
  This animated graphic is from the University of Texas, Austin

• RNA differs from DNA
  • RNA and DNA from Access Excellence. RNA is single-(and not double-)stranded, has uracil (instead of thymine) as a base, and ribose (instead of deoxyribose) as the sugar.

• The three types of RNA from the University of Virginia
  • Messenger RNA (mRNA) is a "photocopy" of a gene by having its sequence complementary to one strand of the DNA molecule. It acts as a "busboy" to carry information stored in the DNA in the nucleus to the cytoplasm where the ribosomes on the E. R. can translate it for protein synthesis. Each three mRNA bases in a row forms a codon that specifies a particular amino acid.

  • Transfer RNA (tRNA) is small and has a very specific secondary and tertiary structure such that it can bind an amino acid at one end and mRNA at the other. It carries each amino acid to the ribosome. tRNA contains a sequence of 3 nucleotide bases called an anticodon. This anticodon is complementary to a particular codon of the mRNA.
    tRNA Structure from Plant Bio 100

  • Ribosomal RNA (rRNA) is one of the structural components of a ribosome. Ribosomes structurally support and catalyze protein synthesis. In eukaryotes, a ribosome has two subunits (large and small), containing 82 proteins and four rRNA molecules altogether (see Fig. 16.8, text).
    The Ribosome from Plant Bio 100

• RNA undergoes processing after transcription
  • noncoding sequences called introns are removed, and the 5' and 3' ends are modified
  • a "cap" is added to the 5' end of the molecule, and a "poly-A tail" is added to the 3' end.

• Check out these links:
  • Transcription of DNA to mRNA from Access Excellence
  • Processing of the primary RNA transcript from the University of Arizona (showing the 5' cap and 3' poly-A tail)
  • Control of Gene Expression from the University of Arizona

• The Genetic Code
  • three consecutive bases (a codon) code for one amino acid
  • the code is redundant, with some amino acids having more than one codon
  • the first and second bases of each codon are more important than the last
  • the codon AUG starts translation, and the codons UGA, UAA, and UAG stop translation

    • The 20 Amino Acids from the University of Virginia
    • The 3-base genetic code in RNA format, from the University of Virginia
    • Relationship among DNA, mRNA, and amino acid sequences from the University of Virginia
    • RNA transcript of the beta-globin gene and corresponding amino acid sequence, from the University of Virginia

• Translation
  • the formation of protein from mRNA
  • occurs in the ribosomes on the E. R. in the cytoplasm
  • a chain of amino acids is assembled according to the sequence of base triplets (codons) in the mRNA
  • the amino acids are carried to the ribosome by tRNAs

  • there are three basic stages to protein synthesis:
    • Initiation: the first mRNA codon AUG forms a complex with an initiator tRNA (carrying the amino acid methionine) and the small ribosomal subunit. The large ribosomal subunit then joins this complex to begin the next stage.

    • Elongation: the stepwise addition of amino acids to a growing polypeptide chain. The ribosome moves along the mRNA one codon at a time, transferring new amino acids to the growing polypeptide chain via peptide bonds.

    • Termination: elongation stops at an mRNA stop codon, and the new polypeptide is released. The ribosome breaks into its large and small subunits, releasing the new protein and the mRNA.

  • lastly, additional changes may be made to the protein before it carries out its function.

  • The process: (We thank T. Jacobs, Plant Biology 100, for the use of these figures)
    • Translation 1
    • Translation 2
    • Translation 3 and peptide bond formation
    • Translation 4
    • Translation 5
    • Translation 6
    • Translation 7

  • Animation of Translation from the University of Virginia

Another illustration from Biol 121, Human Biology, at the University of Virginia.

Protein Synthesis from Access Excellence: (This is the same figure Ed asked you to print out last lecture!

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(See Fig. 3.28, text, for examples)
• Primary Structure: The order (sequence) of amino acids in the polypeptide chain.
• Secondary Structure: The barrels, loops, coils, sheets, or corkscrews created when amino acids close to each other in the primary sequence interact.
• Tertiary Structure: The 3-D folded structure of the polypeptide chain. Remember that a protein's conformation (structure) determines its function.
• Quaternary Structure: The interconnections and organization of two or more polypeptide chains, if present.
  • MIT's Protein Structure
  • Protein Molecules, a link from last lecture.

• a protein that speeds the rate of a specific chemical reaction without being consumed in the process.
• Enzyme Example
• Characteristics of Enzymes
• Some Enzymes Split Molecules
• Some Enzymes Join Molecules
• Some Enzymes Rearrange Molecules
• Some Enzymes Need a Cofactor

Take me home, right now!