Biology 102Biology 102

Gene Regulation and ExpressionGene Regulation and Expression

Part 1Part 1

Lecture OutlineLecture Outline

1.1. The relationship of genes and proteinsThe relationship of genes and proteins

2.2. Overview: From gene to proteinOverview: From gene to protein

3.3. TranscriptionTranscription

1. The relationship of genes and 1. The relationship of genes and proteinsproteins

Review: Role of proteinsReview: Role of proteins StructureStructure

Skin (collagen); hair and nails (keratin); cytoskeletonSkin (collagen); hair and nails (keratin); cytoskeleton MovementMovement

Proteins in muscle (actin and myosin)Proteins in muscle (actin and myosin) DefenseDefense

AntibodiesAntibodies SignalsSignals

Several hormones (growth hormone, insulin)Several hormones (growth hormone, insulin) Receptors for neurotransmittersReceptors for neurotransmitters Channels in membranesChannels in membranes

CatalysisCatalysis EnzymesEnzymes

How did we learn that genes coded How did we learn that genes coded for proteins?for proteins?

Beadle and Tatum experimentsBeadle and Tatum experimentsCreated mutants of the mold Created mutants of the mold NeurosporaNeurosporaDifferent mutants had different nutritional Different mutants had different nutritional

needsneedsDeduced which enzymes were missing from Deduced which enzymes were missing from

each mutation, based on nutritional needseach mutation, based on nutritional needs

Beadle and Tatum ExperimentBeadle and Tatum Experiment

Beadle and Tatum (cont.)Beadle and Tatum (cont.)

Theory: One gene, one enzymeTheory: One gene, one enzymeLater changed to one gene, one protein (or Later changed to one gene, one protein (or

polypeptide)polypeptide)NOTE: They assumed the mutants were all NOTE: They assumed the mutants were all

“single-gene” mutants. Didn’t know for sure!“single-gene” mutants. Didn’t know for sure!

2. Overview: From Gene to Protein2. Overview: From Gene to Protein

RNA serves several RNA serves several functions in the functions in the process of building process of building proteins from the proteins from the DNA blueprint (Fig. DNA blueprint (Fig. 10-2)10-2) mRNAmRNA rRNArRNA tRNAtRNA

RNA differs from DNARNA differs from DNASingle strandSingle strandDifferent sugar (ribose rather than Different sugar (ribose rather than

deoxyribose)deoxyribose)Uracil Uracil replacesreplaces Thymine (RNA has no Thymine (RNA has no

thymine)thymine)Uracil pairs with Adenine!Uracil pairs with Adenine!

2. Overview: From Gene to Protein2. Overview: From Gene to Protein

Two major steps from DNA to proteinTwo major steps from DNA to protein

2. Overview: From Gene to Protein 2. Overview: From Gene to Protein (cont.)(cont.)

The genetic codeThe genetic codeEvery three bases codes for an amino acidEvery three bases codes for an amino acid

Remember that a protein is just a long chain of Remember that a protein is just a long chain of them!them!

64 combinations64 combinationsStart and stop sequences also codedStart and stop sequences also codedRedundancyRedundancy

Artificial mRNA allowed Francis Crick and co-Artificial mRNA allowed Francis Crick and co-workers to crack the codeworkers to crack the codeCode is written based on mRNA triplets, called Code is written based on mRNA triplets, called

codonscodons

The genetic code (mRNA!)The genetic code (mRNA!)

3. Focus on first major part: 3. Focus on first major part: TranscriptionTranscription

Initiation of transcriptionInitiation of transcription RNA polymerase binds to promotor region on the DNA RNA polymerase binds to promotor region on the DNA

moleculemolecule Forces local unwinding of the double helix (Fig. 10-4)Forces local unwinding of the double helix (Fig. 10-4)

3. Transcription (cont.)3. Transcription (cont.)

ElongationElongation (building the mRNA strand) (building the mRNA strand) RNA polymerase travels in one direction along only one strand--RNA polymerase travels in one direction along only one strand--

the the templatetemplate strand--of the DNA strand--of the DNA RNA polymerase facilitates pairing of nucleotides RNA polymerase facilitates pairing of nucleotides

(complementary base pairing (Fig. 10-4)(complementary base pairing (Fig. 10-4) Note free end of mRNANote free end of mRNA

Transcription (cont.)Transcription (cont.) TerminationTermination

RNA polymerase reaches termnation signal on DNA RNA polymerase reaches termnation signal on DNA mRNA released mRNA released

Further modification of RNAFurther modification of RNA Introns are cut out, leaving only exonsIntrons are cut out, leaving only exons

What is the function of introns, if they are not needed for making What is the function of introns, if they are not needed for making the protein?the protein?

Gene can be cut different ways to make different proteinsGene can be cut different ways to make different proteins Mechanism for rapid evolution?Mechanism for rapid evolution?