Gene Expression Ch 11

Gene expression Genes to proteins –Genotype to phenotype Produce specific proteins when and where they are needed

lac Operon E. Coli make enzymes to utilize lactose sugars –Dependent on presence/absence of lactose 3 enzymes to take up and metabolize lactose –Genes that code for enzymes located next to each other in DNA

Fig. 11-1b DNA RNA polymerase cannot attach to promoter Lactose-utilization genes Promoter Operator Regulatory gene OPERON Protein mRNA Inactive repressor Lactose Enzymes for lactose utilization RNA polymerase bound to promoter Operon turned on (lactose inactivates repressor) mRNA Active repressor Operon turned off (lactose absent) Protein

lac Operon Control sequence –Promoter –Operator Operon –Genes, promoter and Operator ***Exist almost solely in prokaryotes

lac Operon Repressors –Block RNA polymerase from binding –Regulatory genes code for repressors Located outside the operon

Fig. 11-1b DNA RNA polymerase cannot attach to promoter Lactose-utilization genes Promoter Operator Regulatory gene OPERON Protein mRNA Inactive repressor Lactose Enzymes for lactose utilization RNA polymerase bound to promoter Operon turned on (lactose inactivates repressor) mRNA Active repressor Operon turned off (lactose absent) Protein

Repressors trp operon –repressor is inactive alone When tryptophan present, binds to repressor, enabling it to switch transcription off

Fig. 11-1c DNA Inactive repressor Active repressor Inactive repressor Active repressor Lactose Promoter Tryptophan OperatorGene lac operon trp operon

Activators –Turn operons on by binding to DNA –Make it easier for RNA polymerase to bind

Differentiation Specialized in structure and function –Results from selective gene expression –Variety of cell types, expressing different combination of genes Muscle cellPancreas cellsBlood cells Fiure 11.2

Root of carrot plant Root cells cultured in nutrient medium Cell division in culture Plantlet Adult Plant Single cell Figure 11.3 Differentiation Differentiated cells may retain all of their genetic potential Most differentiated cells retain a complete set of genes

The Chromosome Packaging helps regulate expression Histone proteins –Aid in packaging and ordering DNA DNA double helix (2-nm diameter) Histones Linker “Beads on a string” Nucleosome (10-nm diameter) Tight helical fiber (30-nm diameter) Supercoil (300-nm diameter) Metaphase chromosome 700 nm TEM

The Chromosome Nucleosome –DNA-histone complex involving DNA wound around 8 histone protein core Resembles beads on a string Linkers –Join consecutive nucleosomes Packing presumably prevents access of transcription proteins DNA double helix (2-nm diameter) Histones Linker “Beads on a string” Nucleosome (10-nm diameter) Tight helical fiber (30-nm diameter) Supercoil (300-nm diameter) Metaphase chromosome 700 nm TEM

X chromosome In females, 1 x inactive in each cell –Barr body Early embryo X chromosomes Allele for orange fur Allele for black fur Cell division and random X chromosome inactivation Two cell populations in adult Active X Inactive X Active X Orange fur Black fur Figure 11.5

Proteins controlling transcription Regulatory proteins turn off/on gene transcription Transcription factors Enhancers Silencers RNA splicing Enhancers Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Figure 11.6

Proteins controlling transcription Enhancers –Activators bind and bend DNA –Interact with other transcription factor proteins –Bind as complex to promoter Silencers RNA splicing Enhancers Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Figure 11.6

Proteins controlling transcription Silencers –Bind to DNA and inhibit start of transcription Enhancers Promoter Gene DNA Activator proteins Other proteins Transcription factors RNA polymerase Bending of DNA Transcription Figure 11.6

Splicing Alternate RNA splicing –Splicing can occur in more than 1 way –Different mRNA from same RNA transcript DNA RNA transcript mRNA Exons or RNA splicing Figure 11.7

Small RNA’s miRNA RNA interference miRNA 1 Translation blockedORmRNA degraded Target mRNA Protein miRNA- protein complex 2 3 4

Regulation of translation Breakdown of mRNA Initiation of translation Protein activation Protein breakdown Folding of polypeptide and formation of S—S linkages Initial polypeptide (inactive) Folded polypeptide (inactive) Cleavage

Cascades Protein products from one set of genes activate another set Homeotic gene Egg cell within ovarian follicle Follicle cells “Head” mRNA Protein signal Gene expression 1 Cascades of gene expression 2 Embryo Body segments Adult fly Gene expression 3 4 Egg cell

Signal transduction pathways Series of molecular changes that converts signal on cell surface to specific response inside cell Signaling cell Signal molecule Receptor protein Plasma membrane Target cell Relay proteins Transcription factor (activated) Transcription Nucleus DNA mRNA New protein Translation Figure 11.14

Cloning A clone is an individual created by asexual reproduction and thus is genetically identical to a single parent

Cloning Regeneration Nuclear Transplantation –Reproductive and Therapeutic cloning Remove nucleus from egg cell Add somatic cell from adult donor Grow in culture to produce an early embryo (blastocyst) Implant blastocyst in surrogate mother Remove embryonic stem cells from blastocyst and grow in culture Induce stem cells to form specialized cells (therapeutic cloning) Clone of donor is born (reproductive cloning) Donor cell Nucleus from donor cell Figure 11.10

Reproductive Cloning Not exact copy –Behavioral differences Ethical questions

Therapeutic Cloning Medical potential Embryonic stem cells Adult stem cells –Replace non- reproducing specialized cells as needed –Only give rise to certain tissues Adult stem cells in bone marrow Cultured embryonic stem cells Different culture conditions Heart muscle cells Different types of differentiated cells Nerve cells Blood cells Figure 11.12

Cancer Divide uncontrollably –Mutations whose protein products affect the cell cycle Oncogene –Can cause cancer when present in a single copy

Cancer Proto-oncogene –Gene that has potential to become oncogene –Mutation or virus Proto-oncogene DNA Mutation within the gene Multiple copies of the gene Gene moved to new DNA locus, under new controls Oncogene New promoter Hyperactive growth- stimulating protein in normal amount Normal growth- stimulating protein in excess Figure 11.16A

Cancer Tumor-suppressor genes –Help prevent uncontrolled growth Tumor-suppressor gene Mutated tumor-suppressor gene Normal growth- inhibiting protein Cell division under control Defective, nonfunctioning protein Cell division not under control Figure 11.16B

Oncogene proteins and faulty tumor-suppressor proteins can interfere with normal signal transduction pathways Growth factor Target cell Receptor Hyperactive relay protein (product of ras oncogene) issues signals on its own Normal product of ras gene Relay proteins Transcription factor (activated) DNA Nucleus Transcription Translation Protein that stimulates cell division Figure 11.17A Growth-inhibiting factor Receptor Nonfunctional transcription factor (product of faulty p53 tumor-suppressor gene) Relay proteins Transcription factor (activated) Transcription Translation Protein that inhibits cell division cannot trigger transcription Protein absent (cell division not inhibited) Normal product of p53 gene Figure 11.17B

Cancer Series of genetic changes –Colon cancer Colon wall Cellular changes: DNA changes: 1 Increased cell division Oncogene activated 2 Growth of polyp Tumor-suppressor gene inactivated 3 Growth of malignant tumor (carcinoma) Second tumor- suppressor gene inactivated

Cancer Series of mutations Chromosomes mutation mutations Normal cell Malignant cell Figure 11.18B

Table 11.20