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Q1 vs. Q2 Grades Grade1 st Quarter2 nd Quarter A5575 B3227 C2116 D78 F195.

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Presentation on theme: "Q1 vs. Q2 Grades Grade1 st Quarter2 nd Quarter A5575 B3227 C2116 D78 F195."— Presentation transcript:

1 Q1 vs. Q2 Grades Grade1 st Quarter2 nd Quarter A5575 B3227 C2116 D78 F195

2 Figure 18.6 The lytic cycle of phage T4, a virulent phage Attachment. The T4 phage uses its tail fibers to bind to specific receptor sites on the outer surface of an E. coli cell. Entry of phage DNA and degradation of host DNA. The sheath of the tail contracts, injecting the phage DNA into the cell and leaving an empty capsid outside. The cell’s DNA is hydrolyzed. Synthesis of viral genomes and proteins. The phage DNA directs production of phage proteins and copies of the phage genome by host enzymes, using components within the cell. Assembly. Three separate sets of proteins self-assemble to form phage heads, tails, and tail fibers. The phage genome is packaged inside the capsid as the head forms. Release. The phage directs production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts, releasing 100 to 200 phage particles Phage assembly Head Tails Tail fibers

3 Figure 18.7 The lytic and lysogenic cycles of phage, a temperate phage Many cell divisions produce a large population of bacteria infected with the prophage. The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages. Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Certain factors determine whether The phage attaches to a host cell and injects its DNA. Phage DNA circularizes The cell lyses, releasing phages. Lytic cycle is induced Lysogenic cycle is entered Lysogenic cycleLytic cycle or Prophage Bacterial chromosome Phage DNA

4 Figure The reproductive cycle of HIV, a retrovirus Vesicles transport the glycoproteins from the ER to the cell’s plasma membrane. 7 The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER). 6 The double-stranded DNA is incorporated as a provirus into the cell’s DNA. 4 Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins. 5 Reverse transcriptase catalyzes the synthesis of a second DNA strand complementary to the first. 3 Reverse transcriptase catalyzes the synthesis of a DNA strand complementary to the viral RNA. 2 New viruses bud off from the host cell. 9 Capsids are assembled around viral genomes and reverse transcriptase molecules. 8 mRNA RNA genome for the next viral generation Viral RNA RNA-DNA hybrid DNA Chromosomal DNA NUCLEUS Provirus HOST CELL Reverse transcriptase New HIV leaving a cell HIV entering a cell 0.25 µm HIV Membrane of white blood cell The virus fuses with the cell’s plasma membrane. The capsid proteins are removed, releasing the viral proteins and RNA. 1

5 The Genetics of Viruses & Bacteria 1.What do you know about viruses? 2.How big are viruses? 3.What are the components of a virus? 4.How do viruses identify appropriate cells to infect? 5.What is the lytic cycle of a bacteriophage? 6.What is the lysogenic cycle of a bacteriophage? 7.How do retroviruses (like HIV) reproduce? 8.How do “new” viruses emerge? -Mutation of an existing virus since there is no proofreading -Spread of an existing virus from 1 host species to another -Spread of viral disease from a small isolated population 9. What is the difference between horizontal & vertical transmission? -Horizontal – 1 organism spreads to another -Vertical – 1 organism inherits disease from parent 10. What are viroids & prions? -Viroids – tiny molecules of naked, circular RNA that infect plants, several hundred nucleotides long -Prions – infectious proteins (NO genetic material) -Slow incubation period – at least 10 yrs -Virtually indestructible Nobel Prize in Medicine – Stanley Prusiner

6 The Genetics of Viruses & Bacteria 1.What do you know about viruses? 2.How big are viruses? 3.What are the components of a virus? 4.How do viruses identify appropriate cells to infect? 5.What is the lytic cycle of a bacteriophage? 6.What is the lysogenic cycle of a bacteriophage? 7.How do retroviruses (like HIV) reproduce? 8.How do “new” viruses emerge? 9. What is the difference between horizontal & vertical transmission? 10. What are viroids & prions? 11. How is bacterial DNA different from eukaryotic DNA? (refer to Ch. 19 notes) BacterialEukaryotic Circular chromosomeLinear chromosomes Nucleoid regionNucleus No introns (all exons)Introns & exons Transcription coupled w/ translationTranscription & translation separate More mutations Fewer mutations (proofreading) 12.How does bacterial DNA replicate its circular chromosome? - Figure 16.16

7 Figure Generalized transduction Phage DNA Donor cell Recipient cell A+A+ B+B+ A+A+ B+B+ A+A+ A+A+ B–B– A–A– B–B– A+A+ Recombinant cell Crossing over Phage infects bacterial cell that has alleles A + and B + Host DNA (brown) is fragmented, and phage DNA and proteins are made. This is the donor cell. A bacterial DNA fragment (in this case a fragment with the A + allele) may be packaged in a phage capsid. Phage with the A + allele from the donor cell infects a recipient A – B – cell, and crossing over (recombination) between donor DNA (brown) and recipient DNA (green) occurs at two places (dotted lines). The genotype of the resulting recombinant cell (A + B – ) differs from the genotypes of both the donor (A + B + ) and the recipient (A – B – )

8 Figure Bacterial conjugation Sex pilus 1  m

9 Figure Conjugation and recombination in E. coli 1 A cell carrying an F plasmid (an F + cell) can form a mating bridge with an F – cell and transfer its F plasmid. A single strand of the F plasmid breaks at a specific point (tip of blue arrowhead) and begins to move into the recipient cell. As transfer continues, the donor plasmid rotates (red arrow). 2 DNA replication occurs in both donor and recipient cells, using the single parental strands of the F plasmid as templates to synthesize complementary strands. 3 The plasmid in the recipient cell circularizes. Transfer and replication result in a compete F plasmid in each cell. Thus, both cells are now F +. 4 F Plasmid Bacterial chromosome F – cell F + cell Hfr cell F factor The circular F plasmid in an F + cell can be integrated into the circular chromosome by a single crossover event (dotted line). 1 The resulting cell is called an Hfr cell (for High frequency of recombination). 2 Since an Hfr cell has all the F-factor genes, it can form a mating bridge with an F – cell and transfer DNA. 3 A single strand of the F factor breaks and begins to move through the bridge. DNA replication occurs in both donor and recipient cells, resulting in double-stranded DNA 4 The location and orientation of the F factor in the donor chromosome determine the sequence of gene transfer during conjugation. In this example, the transfer sequence for four genes is A-B-C-D. 5 The mating bridge usually breaks well before the entire chromosome and the rest of the F factor are transferred. 6 Two crossovers can result in the exchange of similar (homologous) genes between the transferred chromosome fragment (brown) and the recipient cell’s chromosome (green). 7 The piece of DNA ending up outside the bacterial chromosome will eventually be degraded by the cell’s enzymes. The recipient cell now contains a new combination of genes but no F factor; it is a recombinant F – cell. 8 Temporary partial diploid Recombinant F – bacterium Conjugation and transfer of an F plasmid from an F + donor to an F – recipient (a) Conjugation and transfer of part of the bacterial chromosome from an Hfr donor to an F – recipient, resulting in recombination (b) A+A+ B+B+ C+C+ D+D+ F – cell A–A– B–B– C–C– D–D– A–A– B–B– C–C– D–D– D–D– A–A– C–C– B–B– D–D– A–A– C–C– B–B– A+A+ B+B+ C+C+ D+D+ A+A+ B+B+ C+C+ D+D+ A+A+ B+B+ D+D+ C+C+ A+A+ A+A+ B+B+ A–A– B–B– C–C– D–D– A–A– B+B+ C–C– D–D– A+A+ B+B+ B–B– A+A+ A+A+ B+B+ F + cell Mating bridge Plasmid – extra-chromosomal, small, circular, self-replicating DNA

10 Figure The trp operon: regulated synthesis of repressible enzymes (a) Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA at the promoter and transcribes the operon’s genes. Genes of operon Inactive repressor Protein Operator Polypeptides that make up enzymes for tryptophan synthesis Promoter Regulatory gene RNA polymerase Start codon Stop codon Promoter trp operon 5 3 mRNA 5 trpD trpE trpCtrpB trpA trpR DNA mRNA ED C BA

11 DNA mRNA Protein Tryptophan (corepressor) Active repressor No RNA made Tryptophan present, repressor active, operon off. As tryptophan accumulates, it inhibits its own production by activating the repressor protein. (b)

12 Figure The lac operon: regulated synthesis of inducible enzymes DNA mRNA Protein Active repressor RNA polymerase No RNA made lacZ lacl Regulatory gene Operator Promoter Lactose absent, repressor active, operon off. The lac repressor is innately active, and in the absence of lactose it switches off the operon by binding to the operator. (a) 5 3

13 mRNA 5' DNA mRNA Protein Allolactose (inducer) Inactive repressor lacl lacz lacYlacA RNA polymerase PermeaseTransacetylase  -Galactosidase 5 3 (b) Lactose present, repressor inactive, operon on. Allolactose, an isomer of lactose, derepresses the operon by inactivating the repressor. In this way, the enzymes for lactose utilization are induced. mRNA 5 lac operon

14 Before the invention of antibiotics, the clean modern hospitals of India, which were mostly reserved for Europeans, reported cholera death rates of 86%. Meanwhile, in other more crowded and less hygienic hospitals, the death rate from cholera was only 27%. WHY? Based on knowledge gained from the case study, explain the most likely process that occurred in the crowded hospitals that led to such a low death rate from cholera.

15 Figure 21.4a, b Animal development. Most animals go through some variation of the blastula and gastrula stages. The blastula is a sphere of cells surrounding a fluid-filled cavity. The gastrula forms when a region of the blastula folds inward, creating a tube—a rudimentary gut. Once the animal is mature, differentiation occurs in only a limited way—for the replacement of damaged or lost cells. Plant development. In plants with seeds, a complete embryo develops within the seed. Morphogenesis, which involves cell division and cell wall expansion rather than cell or tissue movement, occurs throughout the plant’s lifetime. Apical meristems (purple) continuously arise and develop into the various plant organs as the plant grows to an indeterminate size. Zygote (fertilized egg) Eight cells Blastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell movement Gut Cell division Morphogenesis Observable cell differentiation Seed leaves Shoot apical meristem Root apical meristem Plant Embryo inside seed Two cells Zygote (fertilized egg) (a) (b)

16 Chapter 21: The Genetic Basis of Development 1.How do we study development in the genetics-based lab? 2.How does a zygote transform into an organism? 3.How do cells become differentiated? -All cells have the same DNA, so differential gene expression must be the explanation!

17 Nucleus removed Mammary cell donor Egg cell donor Egg cell from ovary Cultured mammary cells are semistarved, arresting the cell cycle and causing dedifferentiation Nucleus from mammary cell Grown in culture Early embryo Implanted in uterus of a third sheep Surrogate mother Embryonic development Lamb (“Dolly”) genetically identical to mammary cell donor Cells fused APPLICATION This method is used to produce cloned animals whose nuclear genes are identical to the donor animal supplying the nucleus. TECHNIQUE Shown here is the procedure used to produce Dolly, the first reported case of a mammal cloned using the nucleus of a differentiated cell. RESULTS The cloned animal is identical in appearance and genetic makeup to the donor animal supplying the nucleus, but differs from the egg cell donor and surrogate mother. Nucleus removed Figure 21.7

18 Chapter 21: The Genetic Basis of Development 4. What is a stem cell? -a relatively unspecialized cell Figure 21.9 Early human embryo at blastocyst stage (mammalian equiva- lent of blastula) From bone marrow in this example Totipotent cells Pluripotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cells Nerve cells Blood cells Embryonic stem cells Adult stem cells -can differentiate into cells of different types under specific conditions -Embryonic = totipotent -Adult = pluripotent (can produce some, but not all, cell types)

19 Chapter 21: The Genetic Basis of Development 5. What type of genetic signal leads to cell differentiation? -Step 1: Cell receives signals from other cells DNA OFF mRNA Another transcription factor MyoD Muscle cell (fully differentiated) MyoD protein (transcription factor) Myoblast (determined) Embryonic precursor cell Myosin, other muscle proteins, and cell-cycle blocking proteins Other muscle-specific genesMaster control gene myoD Nucleus Determination. Signals from other cells lead to activation of a master regulatory gene called myoD, and the cell makes MyoD protein, a transcription factor. The cell, now called a myoblast, is irreversibly committed to becoming a skeletal muscle cell. 1 Differentiation. MyoD protein stimulates the myoD gene further, and activates genes encoding other muscle-specific transcription factors, which in turn activate genes for muscle proteins. MyoD also turns on genes that block the cell cycle, thus stopping cell division. The nondividing myoblasts fuse to become mature multinucleate muscle cells, also called muscle fibers. 2 -Step 2: A regulatory gene is turned “on”, and a protein is made that activates other genes. (“point of no return”) -Step 3: Activated genes make proteins that determine cell type/ structure/behavior.

20 Figure 21.16b Epidermis GonadAnchor cell Signal protein Vulval precursor cells Inner vulva Outer vulva Epidermis ADULT Induction of vulval cell types during larval development. (b)

21 Figure EXPERIMENT RESULTS CONCLUSION Spemann and Mangold transplanted a piece of the dorsal lip of a pigmented newt gastrula to the ventral side of the early gastrula of a nonpigmented newt. During subsequent development, the recipient embryo formed a second notochord and neural tube in the region of the transplant, and eventually most of a second embryo. Examination of the interior of the double embryo revealed that the secondary structures were formed in part from host tissue. The transplanted dorsal lip was able to induce cells in a different region of the recipient to form structures different from their normal fate. In effect, the dorsal lip “organized” the later development of an entire embryo. Pigmented gastrula (donor embryo) Dorsal lip of blastopore Nonpigmented gastrula (recipient embryo) Primary embryo Secondary (induced) embryo Primary structures: Neural tube Notochord Secondary structures: Notochord (pigmented cells) Neural tube (mostly nonpigmented cells)

22 Chapter 21: The Genetic Basis of Development -cytoplasmic determinants in the unfertilized egg regulate gene expression in the zygote that affects differentiation/development Figure 21.11a Unfertilized egg cell Molecules of a a cytoplasmic determinant Fertilization Zygote (fertilized egg) Mitotic cell division Two-celled embryo Cytoplasmic determinants in the egg. The unfertilized egg cell has molecules in its cytoplasm, encoded by the mother’s genes, that influence development. Many of these cytoplasmic determinants, like the two shown here, are unevenly distributed in the egg. After fertilization and mitotic division, the cell nuclei of the embryo are exposed to different sets of cytoplasmic determinants and, as a result, express different genes. (a) Nucleus

23 Chapter 21: The Genetic Basis of Development -Cytoplasmic determinants from mother’s egg initially establish the axes of the body of Drosophila. -bicoid gene Head Wild-type larva Tail Mutant larva (bicoid) Drosophila larvae with wild-type and bicoid mutant phenotypes. A mutation in the mother’s bicoid gene leads to tail structures at both ends (bottom larva). The numbers refer to the thoracic and abdominal segments that are present. (a) T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8 A7A6A7 A8 Tail Figure 21.14a

24 Translation of bicoid mRNA Fertilization Nurse cells Egg cell bicoid mRNA Developing egg cell Bicoid mRNA in mature unfertilized egg 100 µm Bicoid protein in early embryo Anterior end (b) Gradients of bicoid mRNA and Bicoid protein in normal egg and early embryo Figure 21.14b

25 Chapter 21: The Genetic Basis of Development -7. How does morphogenesis (pattern formation) occur in animals? After the body’s axes are determined (by cytoplasmic determinants)… -Segmentation genes produce proteins that direct formation of body segments. Hierarchy of Gene Activity in Early Drosophila Development Maternal effect genes (egg-polarity genes) Gap genes Pair-rule genes Segment polarity genes Homeotic genes of the embryo Other genes of the embryo Segmentation genes of the embryo -Then, the development of specific features of the body segments is directed by HOMEOTIC GENES (Hox genes.)

26 Chapter 21: The Genetic Basis of Development 8. What is the relationship among the genetic basis of development across organisms? -Molecular analysis of the homeotic genes in Drosophila has shown that they all include a sequence called a homeobox -An identical (or very similar) DNA sequence has been discovered in the homeotic genes of vertebrates and invertebrates Figure Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse

27 Chapter 21: The Genetic Basis of Development 9. What is apoptosis? -programmed cell death (cell suicide) Ced-9 protein (active) inhibits Ced-4 activity Mitochondrion Death signal receptor Ced-4Ced-3 Inactive proteins (a) No death signal Ced-9 (inactive) Cell forms blebs Death signal Active Ced-4 Active Ced-3 Activation cascade Other proteases Nucleases (b) Death signal Figure Molecular basis of apoptosis in C. elegans

28 Chapter 21: The Genetic Basis of Development 8. What is apoptosis? -programmed cell death (cell suicide) -necessary for development of hands/feet in vertebrates Figure Interdigital tissue 1 mm


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