Chapter 7: The Blueprint of Life, from DNA to Protein

Where we’ve been… Our bacterium has –Entered the host’s body through the Portal of Entry. –Adhered to the host’s cells –Competed with host’s normal microbiota –Successfully defended itself against the host immune system (more in Stage 03…) –Found the right environment (pH, temperature, oxygen requirement, and water availability) –Found and transported in the right nutrients –And, finally, through catabolic reactions, harvested energy and made precursor metabolites that were made into subunits.

Metabolism The sum total of ALL chemical reactions within a cell –Catabolic –Anabolic

Where we’re going… Now we are going to take those subunits (nucleotides, amino acids, monosaccharides, glycerol and fatty acids) and put them together to make macromolecules so we can make another bacterial cell. Nucleotides --> nucleic acids (RNA, DNA) Amino acids --> proteins Monosaccharides --> polysaccharides Glycerol + fatty acids --> lipids

Where we’re going… Now we are going to take those subunits (nucleotides, amino acids, monosaccharides, glycerol and fatty acids) and put them together to make macromolecules so we can make another bacterial cell. Nucleotides --> nucleic acids (RNA, DNA) Amino acids --> proteins Monosaccharides --> polysaccharides Glycerol + fatty acids --> lipids

Making macromolecules! DNA nucleotide subunits --> DNA Replication to make DNA. RNA nucleotide subunits --> Transcription to make RNA. amino acid subunits --> Translation to make proteins.

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 Structure DNA Base Pairing A-T G-C

DNA Structure DNA Base Pairing A-T G-C

DNA Replication

Enzymes necessary for DNA replication: more about enzymes! DNA gyrase, Helicase, Primase, DNA polymerase, DNA ligase Enzymes can break molecules apartEnzymes can put molecules together From:

Nucleotides are added to the 3’ position (OH group) DNA Base Pairing A-T G-C

DNA replication…a closer lookreplication…a closer look DNA polymerase polymerizes DNA nucleotides together in the 5’ -> 3’ direction to make DNA. DNA polymerase requires a primer (short stretch of nucleotides) and a template in order to begin work.

DNA replication…closer look

Where we’re going… We just put DNA nucleotides together to make DNA during DNA Replication. Now we have to make more proteins needed to build our new cell.

Gene Expression…why is it important? Transcription Translation In order for our cell to replicate, it needs to make the proteins that are needed to build that new cell. DNA has the blueprints (genes) for making these proteins.

Transcription: RNA is transcribed from DNA Comparing bases: DNA: G, A, T, C RNA: G, A, U, C Base Pairing: DNA-RNA G-C A-U T-A C-G

Transcription: DNA to RNA Requires an enzyme - RNA polymerase 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 Base Pairing: DNA-RNA G-C A-U T-A C-G

Transcription: Promoter orients direction of transcription

What are the possible products from transcription? Messenger RNA (mRNA) –Encodes the message for a protein. Transfer RNA (tRNA) –Essential component to translate RNA language into amino acid language during translation. Ribosomal RNA (rRNA) –Together with protein, this makes up the structure of a ribosome.

Translation: RNA to protein What is needed for the process? –mRNA –Amino acids –tRNA –Ribosomes “Speaks” both amino acid language AND RNA language! Able to translate the RNA code into amino acids!

Translation: RNA to protein What is needed for the process? –mRNA –Amino acids –tRNA –Ribosomes Connects amino acids together to make a protein! Prokaryotic ribosome Small subunit Large subunit

The Genetic code: Translating RNA to amino acids

Translation

Translation: reading frame determines the protein

Both processes occur at the same time in bacteria… …because the DNA is not separated from the ribosomes (like in eukaryotic cells!)

Is it important to regulate protein synthesis? Yes! Genes to produce enzymes for glucose metabolism are constitutive (always made) Other genes are inducible…only made when needed (lactose operon) Other genes are repressible…turned off when not needed (tryptophan operon)

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 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 Lactose present Allolactose binds to repressor, keeping it from binding to the operator RNA polymerase can transcribe the gene

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 E. coli use this system to sense if nitrate is present when in an anaerobic environment. It turns on genes to use nitrate as the terminal electron acceptor for use in anaerobic respiration!

Gene regulation systems in bacteria Signal transduction - Quorum sensing Quorum sensing turns on biofilm production!

Metabolism The sum total of ALL chemical reactions within a cell –Catabolic –Anabolic DNA Replication Transcription Translation