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Ch Review Lecture
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1. Name the two types of operons that we have studied and by what mechanism do they work?
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(a) Regulation of enzyme activity (b) Regulation of enzyme production
Fig. 18-2 Precursor Feedback inhibition trpE gene Enzyme 1 trpD gene Regulation of gene expression Enzyme 2 trpC gene trpB gene Figure 18.2 Regulation of a metabolic pathway Enzyme 3 trpA gene Tryptophan (a) Regulation of enzyme activity (b) Regulation of enzyme production
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2. What are the major parts of an operon?
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Polypeptide subunits that make up enzymes for tryptophan synthesis
Fig. 18-3 trp operon Promoter Promoter Genes of operon DNA trpR trpE trpD trpC trpB trpA Regulatory gene Operator Start codon Stop codon 3 mRNA 5 mRNA RNA polymerase 5 E D C B A Protein Inactive repressor Polypeptide subunits that make up enzymes for tryptophan synthesis (a) Tryptophan absent, repressor inactive, operon on DNA No RNA made Figure 18.3 The trp operon in E. coli: regulated synthesis of repressible enzymes mRNA Protein Active repressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off
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3. What are the categories for each type of operon
3. What are the categories for each type of operon? Define what they mean.
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Repressible and Inducible Operons: Two Types of Negative Gene Regulation
A repressible operon is one that is usually “on”; binding of a repressor to the operator shuts off transcription The trp operon is a repressible operon An inducible operon is one that is usually “off”; a molecule called an inducer inactivates the repressor and turns on transcription
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(a) Lactose absent, repressor active, operon off
Fig. 18-4 Regulatory gene Promoter Operator DNA lacI lacZ No RNA made 3 mRNA RNA polymerase 5 Active repressor Protein (a) Lactose absent, repressor active, operon off lac operon DNA lacI lacZ lacY lacA RNA polymerase Figure 18.4 The lac operon in E. coli: regulated synthesis of inducible enzymes For the Cell Biology Video Cartoon Rendering of the lac Repressor from E. coli, go to Animation and Video Files. 3 mRNA mRNA 5 5 -Galactosidase Permease Protein Transacetylase Allolactose (inducer) Inactive repressor (b) Lactose present, repressor inactive, operon on
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4. Which metabolic pathway does each operon operate. Explain how?
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Inducible enzymes usually function in catabolic pathways; their synthesis is induced by a chemical signal Repressible enzymes usually function in anabolic pathways; their synthesis is repressed by high levels of the end product Regulation of the trp and lac operons involves negative control of genes because operons are switched off by the active form of the repressor
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5. Name two secondary messengers
5. Name two secondary messengers. Explain what occurs if lactose is present but glucose is scarce.
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(a) Lactose present, glucose scarce (cAMP level
Fig. 18-5 Promoter Operator DNA lacI lacZ CAP-binding site RNA polymerase binds and transcribes Active CAP cAMP Inactive lac repressor Inactive CAP Allolactose (a) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized Promoter Operator DNA lacI lacZ Figure 18.5 Positive control of the lac operon by catabolite activator protein (CAP) CAP-binding site RNA polymerase less likely to bind Inactive CAP Inactive lac repressor (b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized
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6. How many ways can gene regulation be controlled in the nucleus
6. How many ways can gene regulation be controlled in the nucleus? How is DNA controlled?
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1. Chromatin Modification
Histone acetylation occurs on histones and increases gene expression DNA methylation occurs primarily on the DNA and reduces gene expression.
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7. What is important further up the DNA for transcription?
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2. Regulation of Transcription Initiation
Associated with most eukaryotic genes are control elements, segments of noncoding DNA that help regulate transcription by binding certain proteins Control elements and the proteins they bind are critical to the precise regulation of gene expression in different cell types
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Promoter Activators Gene DNA Enhancer
Fig Promoter Activators Gene DNA Distal control element Enhancer TATA box General transcription factors DNA-bending protein Group of mediator proteins RNA polymerase II Figure 18.9 A model for the action of enhancers and transcription activators RNA polymerase II Transcription initiation complex RNA synthesis
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(distal control elements)
Fig Poly-A signal sequence Enhancer (distal control elements) Proximal control elements Termination region Exon Intron Exon Intron Exon DNA Upstream Downstream Promoter Transcription Primary RNA transcript Exon Intron Exon Intron Exon Cleaved 3 end of primary transcript 5 RNA processing Intron RNA Poly-A signal Figure 18.8 A eukaryotic gene and its transcript Coding segment mRNA 3 Start codon Stop codon 5 Cap 5 UTR 3 UTR Poly-A tail
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8. What occurs before the RNA can leave the nucleus?
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3. Mechanisms of Post-Transcriptional Regulation
Figure Degradation of a protein by a proteasome
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9. Explain what function miRNA serves.
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(b) Generation and function of miRNAs
Fig Hydrogen bond Dicer miRNA miRNA- protein complex Figure Regulation of gene expression by miRNAs mRNA degraded Translation blocked (b) Generation and function of miRNAs
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10. What is the name of the enzyme that degrades proteins?
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Non-Coding RNA and gene expression regulation
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11. Give three things that must occur for a zygote to become an embryo.
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A Genetic Program for Embryonic Development
The transformation from zygote to adult results from : Cell division-is the series of mitotic divisions that increases the number of cells Cell differentiation Morphogenesis What controls cell differentiation and morphogenesis?
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11. What are the two things that control morphogenesis?
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(a) Cytoplasmic determinants in the egg
Fig a Unfertilized egg cell Sperm Nucleus Fertilization Two different cytoplasmic determinants Zygote Mitotic cell division Figure Sources of developmental information for the early embryo Two-celled embryo (a) Cytoplasmic determinants in the egg
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12. How do cells communicate. Name the four ways. 13
12. How do cells communicate? Name the four ways Differentiate between plant and animal cell communication.
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(b) Induction by nearby cells
Fig b NUCLEUS Early embryo (32 cells) Signal transduction pathway Signal receptor Figure Sources of developmental information for the early embryo Signal molecule (inducer) (b) Induction by nearby cells
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Sequential Regulation of Gene Expression During Cellular Differentiation
Determination commits a cell to its final fate and is irreversible Cell differentiation is marked by the production of tissue-specific proteins (found only in a specific cell type and give the cell its characteristic structure and function.
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(fully differentiated cell)
Fig Nucleus Master regulatory gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF mRNA OFF MyoD protein (transcription factor) Myoblast (determined) Figure Determination and differentiation of muscle cells mRNA mRNA mRNA mRNA Myosin, other muscle proteins, and cell cycle– blocking proteins MyoD Another transcription factor Part of a muscle fiber (fully differentiated cell)
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14. Define pattern formation and positional formation
14. Define pattern formation and positional formation. Give an example of a gene involved in this process.
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Pattern Formation: Setting Up the Body Plan
Pattern formation is the development of a spatial organization of tissues and organs In animals, pattern formation begins with the establishment of the major axes Positional information, the molecular cues that control pattern formation, tells a cell its location relative to the body axes and to neighboring cells
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Bicoid: A Morphogen Determining Head
Structures One maternal effect gene, the bicoid gene, affects the front half of the body An embryo whose mother has a mutant bicoid gene lacks the front half of its body and has duplicate posterior structures at both ends
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Homeotic genes in animals are called Hox genes
An identical or very similar nucleotide sequence has been discovered in the homeotic genes of both vertebrates and invertebrates Homeotic genes in animals are called Hox genes Sometimes small changes in regulatory sequences of certain genes lead to major changes in body form For example, variation in Hox gene expression controls variation in leg-bearing segments of crustaceans and insects
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15. What is cell death? How it is used in our bodies? Describe.
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Apoptosis- programmed cell death
suicide genes code for products that activate proteins present in the cell and cause the self-destruction of the cell very common in vertebrate development of nervous system -failure of apoptosis in human development --> webbed hands and feet!
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16. Are viruses alive? Why? 17. Give the three major parts of a virus.
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Structure of Viruses Viruses are not cells
Viruses are very small infectious particles consisting of: nucleic acid enclosed in a protein coat in some cases, a membranous envelope
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18. Give two examples and describe the structure of common viruses.
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RNA DNA Membranous envelope Head RNA Capsomere DNA Capsid Tail sheath
Fig. 19-3 RNA DNA Membranous envelope Head RNA Capsomere DNA Capsid Tail sheath Capsomere of capsid Tail fiber Glycoprotein Glycoproteins 18 250 nm 70–90 nm (diameter) 80–200 nm (diameter) 80 225 nm Figure 19.3 Viral structure 20 nm 50 nm 50 nm 50 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4
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19. Explain why viruses cannot reproduce forever.
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Concept 19.2: Viruses reproduce only in host cells
Viruses are obligate intracellular parasites, which means they can reproduce only within a host cell Each virus has a host range, a limited variety of host cells that it can infect
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20. Explain the four step process of the virus reproductive cycle.
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Fig. 19-4 VIRUS Entry and uncoating 1 DNA Capsid Transcription and manufacture of capsid proteins 3 2 Replication HOST CELL Viral DNA mRNA Viral DNA Capsid proteins Figure 19.4 A simplified viral reproductive cycle Self-assembly of new virus particles and their exit from the cell 4
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21. Explain the two phage reproductive cycles.
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The phage injects its DNA.
Fig. 19-6 Daughter cell with prophage Phage DNA The phage injects its DNA. Cell divisions produce population of bacteria infected with the prophage. Phage DNA circularizes. Phage Bacterial chromosome Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Lytic cycle Lysogenic cycle The bacterium reproduces, copying the prophage and transmitting it to daughter cells. The cell lyses, releasing phages. Lytic cycle is induced or Lysogenic cycle is entered Figure 19.6 The lytic and lysogenic cycles of phage λ, a temperate phage Prophage New phage DNA and proteins are synthesized and assembled into phages. Phage DNA integrates into the bacterial chromosome, becoming a prophage.
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22. Explain the HIV reproductive cycle.
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Fig. 19-8a Glycoprotein Viral envelope Capsid RNA (two identical strands) Reverse transcriptase HOST CELL HIV Reverse transcriptase The viral DNA that is integrated into the host genome is called a provirus Unlike a prophage, a provirus remains a permanent resident of the host cell Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation Figure 19.8 The reproductive cycle of HIV, the retrovirus that causes AIDS mRNA New virus
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