Genetics: Chapter 7

What is genetics?

• The science of heredity; includes the study of genes, how they carry information, how they are replicated, how they are expressed

What do you know about DNA?

• Chromosomes made of DNA contain an organism’s entire genome

• DNA codes for genes….genes code for proteins

• Chemical composition is nucleotides• It exists in most cells as a double stranded

structure

DNA is used for many things

DNA Structure

DNA Replication

Enzymes necessary for DNA replication

• Primase

• DNA Polymerase

• DNA gyrase

• DNA ligase

• Helicase

Nucleotides are added to the 3’ position (OH group)

DNA replication…a closer look

DNA replication…closer look

Gene Expression…why is it important?

• Transcription

• Translation

What do you know about gene expression?

• Work with a partner to make a list about what you already know about gene expression

Transcription: RNA is transcribed from DNA

Transcription: Promoter orients direction of transcription

Transcription: DNA to RNA

• Requires an enzyme…..

• RNA nucleotides

• Base pairing rules for building RNA from a DNA template

• Process proceeds in the direction 5’--->3’• Process begins at the promoter region and

ends at the terminator sequence

Transcription: RNA synthesis

What are the possible products from transcription?

• Messenger RNA (mRNA)

• Transfer RNA (tRNA)

• Ribosomal RNA (rRNA)

Quick check…..

• Do we have a protein yet?

• What have we made?

• What is next?

Translation: RNA to protein

• What is needed for the process?– mRNA– Ribosomes– Amino acids– tRNA

Translation: RNA to protein

• What is needed for the process?– mRNA– Ribosomes– Amino acids– tRNA

Translation: reading frame determines the protein

The Genetic code

Translation

Translation

Both processes occur at the same time in bacteria…why??

Eukaryotic cells differ in transcription and translation

• Ribosomes are different size

• 5’ end of mRNA has cap (methylated guanine)

• 3’ end of mRNA has poly A tail

• Introns are excised, exons spliced together

• Translation is monocystronic

Is it important to regulate protein synthesis?

• Yes!

• Three types of protein regulation– Enyme inhibition (feedback inhibition)– Repression (tryptophan operon)– Induction (lactose operon)

Are all genes under regulation?

• No!

• Genes to produce enzymes for glucose metabolism are constitutive (always made)

• Other genes are induced…only made when needed

• Other genes are repressed…turned off when not needed

Models for transcriptional regulation with repressors

Transcriptional regulation by activators

Lactose Operon as a model

• Used to understand control of gene expression in bacteria

• Operon consists of three genes needed to degrade lactose

• Repressor gene(codes for repressor protein) outside of operon coding region inhibits transcription unless something else bind to the repressor protein

Lactose Operon

Diauxic growth curve of E. coli

What conditions are needed for the lactose operon to be turned “on”?

• No glucose

• Lactose present

• Increasing levels of cAMP

• cAMP binds to CAP, then complex binds next to lactose operon promoter at the activator region

• RNA polymerase binds to promoter

How do organisms adapt to other changes in their environment?

• Some organisms turn genes on/off as needed

• Some organisms alter gene expression

Gene regulation systems in bacteria

• Signal transduction– Two component

regulatory system

Gene regulation systems in bacteria

• Signal transduction

- Quorum sensing

Gene expression is influenced by natural selection

• Random changes enhance survival of some cells in population

• Antigenic variation of pathogens

• Phase variation– Switching on/off of certain genes