Biology 102 Gene Regulation and Expression Part 1

Lecture Outline 1.The relationship of genes and proteins 2.Overview: From gene to protein 3.Transcription

1. The relationship of genes and proteins Review: Role of proteins Review: Role of proteins Structure Structure Skin (collagen); hair and nails (keratin); cytoskeleton Skin (collagen); hair and nails (keratin); cytoskeleton Movement Movement Proteins in muscle (actin and myosin) Proteins in muscle (actin and myosin) Defense Defense Antibodies Antibodies Signals Signals Several hormones (growth hormone, insulin) Several hormones (growth hormone, insulin) Receptors for neurotransmitters Receptors for neurotransmitters Channels in membranes Channels in membranes Catalysis Catalysis Enzymes Enzymes

How did we learn that genes coded for proteins? Beadle and Tatum experiments Beadle and Tatum experiments Created mutants of the mold Neurospora Created mutants of the mold Neurospora Different mutants had different nutritional needs Different mutants had different nutritional needs Deduced which enzymes were missing from each mutation, based on nutritional needs Deduced which enzymes were missing from each mutation, based on nutritional needs

Beadle and Tatum Experiment

Beadle and Tatum (cont.) Theory: One gene, one enzyme Theory: One gene, one enzyme Later changed to one gene, one protein (or polypeptide) Later changed to one gene, one protein (or polypeptide) NOTE: They assumed the mutants were all “single-gene” mutants. Didn’t know for sure! NOTE: They assumed the mutants were all “single-gene” mutants. Didn’t know for sure!

2. Overview: From Gene to Protein RNA serves several functions in the process of building proteins from the DNA blueprint (Fig. 10-2) RNA serves several functions in the process of building proteins from the DNA blueprint (Fig. 10-2) mRNA mRNA rRNA rRNA tRNA tRNA

RNA differs from DNA RNA differs from DNA Single strand Single strand Different sugar (ribose rather than deoxyribose) Different sugar (ribose rather than deoxyribose) Uracil replaces Thymine (RNA has no thymine) Uracil replaces Thymine (RNA has no thymine) Uracil pairs with Adenine! Uracil pairs with Adenine!

2. Overview: From Gene to Protein Two major steps from DNA to protein Two major steps from DNA to protein

2. Overview: From Gene to Protein (cont.) The genetic code The genetic code Every three bases codes for an amino acid Every three bases codes for an amino acid Remember that a protein is just a long chain of them! Remember that a protein is just a long chain of them! 64 combinations 64 combinations Start and stop sequences also coded Start and stop sequences also coded Redundancy Redundancy Artificial mRNA allowed Francis Crick and co- workers to crack the code Artificial mRNA allowed Francis Crick and co- workers to crack the code Code is written based on mRNA triplets, called codons Code is written based on mRNA triplets, called codons

The genetic code (mRNA!)

3. Focus on first major part: Transcription Initiation of transcription Initiation of transcription RNA polymerase binds to promotor region on the DNA molecule RNA polymerase binds to promotor region on the DNA molecule Forces local unwinding of the double helix (Fig. 10-4) Forces local unwinding of the double helix (Fig. 10-4)

3. Transcription (cont.) Elongation (building the mRNA strand) Elongation (building the mRNA strand) RNA polymerase travels in one direction along only one strand-- the template strand--of the DNA RNA polymerase travels in one direction along only one strand-- the template strand--of the DNA RNA polymerase facilitates pairing of nucleotides (complementary base pairing (Fig. 10-4) RNA polymerase facilitates pairing of nucleotides (complementary base pairing (Fig. 10-4) Note free end of mRNA Note free end of mRNA

Transcription (cont.) Termination Termination RNA polymerase reaches termnation signal on DNA  mRNA released RNA polymerase reaches termnation signal on DNA  mRNA released

Further modification of RNA Introns are cut out, leaving only exons Introns are cut out, leaving only exons What is the function of introns, if they are not needed for making the protein? What is the function of introns, if they are not needed for making the protein? Gene can be cut different ways to make different proteins Gene can be cut different ways to make different proteins Mechanism for rapid evolution? Mechanism for rapid evolution?