BSC 2010 Integrated Principles of Biology I - Genetics

1. BSC 2010 Integrated Principles of Biology I - Genetics • Lecturer: Dr. J. C. Herrera, Zoology • Office: 3175 McCarty Hall • Office Hours: TWTh 3rd and 5th periods, and by appointment • Phone: 213-2498, Email: herrera@zoo.ufl.edu • Course Home Page: http://nersp.nerdc.ufl.edu/~herrera/bsc.html • Lectures • Tuesday, Wednesday, Thursday, McCarty C 100 (MCC 100) • Discussions • Friday, MCC 100; May include lectures as needed.

2. Exam II Lectures and Text Pages • I. Cell Cycles • Mitosis (218 – 228) • Meiosis (238 – 249) • II. Mendelian Genetics • III. Chromosomal Genetics • IV. Molecular Genetics • Replication • Transcription and Translation • V. Microbial Models • VI. DNA Technology

3. Figure 12.1 The Key Roles of Cell Division • The continuity of life • Is based upon the reproduction of cells, or cell division

4. 100 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). Figure 12.2 A Unicellular organisms • reproduce by cell division

5. 200 µm 20 µm (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Figure 12.2 B, C Multicellular organisms • depend on cell division for • Development from a fertilized cell (zygote) • Growth • Maintenance and repair

6. The Cell Cycle • The cell cycle is the life of the cell from its formation to its own division. • Cell division is just a portion of the cell’s lifecycle (cell cycle) • Some cells go through repeated cell cycles. • Other cells never or rarely divide once they are formed (e.g., vertebrate nerve and muscle cells).

7. Mitotic cell division • produces genetically identical daughter cells • Cells precisely duplicate their genetic material • They allocate the two copies to opposite ends of the cell • Then they divide into two new daughter cells

8. Figure 12.3 50 µm Cellular Organization of Genetic Material • A cell’s total endowment of genetic information • Is called its genome • The DNA in a cell • Is packaged into chromosomes

9. Eukaryotic chromosomes • Eukaryotic chromosomes • Are supercoils of chromatin, a complex of DNA and protein that condenses durnig cell division • Allow duplication and distribution of large genomes • In animals • Somatic cells have two haploid sets of chromosomes • Gametes have one haploid set of chromosomes

10. Chromosomes • Each chromosomes has: • A single, long, molecule of DNA, segments of which are genes. • Proteins which maintain the structure of the chromosome or are involved with the expression of genes, DNA replication, and DNA repair • Each species: has a characteristic number of chromosomes • The chromosomes: are in different states at different stages of the cell cycle. • Interphase:  loosely folded; not visible. • Mitotic phase: highly folded and condensed; visible with a light microscope (basis of karyotype)

11. 0.5 µm A eukaryotic cell has multiplechromosomes, one of which is represented here. Before duplication, each chromosomehas a single DNA molecule. Chromosomeduplication(including DNA synthesis) Once duplicated, a chromosomeconsists of two sister chromatidsconnected at the centromere. Eachchromatid contains a copy of the DNA molecule. Centromere Sisterchromatids Separation of sister chromatids Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Centromeres Sister chromatids Figure 12.4 Distribution of Chromosomes During Cell Division • During S-phase of interphase, DNA is replicated and the chromosomes condense • Each duplicated chromosome • Has two sisterchromatids, attached at the centromere

12. Important Note • chromosome, chromatid, chromatin • The course includes several sets of words which are very similar – be sure you know the differences among each set of similar words. • Another example: centromere, centrosome, centriole

13. Two Types of Eukaryotic Cell Division • Mitotic cell division (occurs only in eukaryotes) consists of • Mitosis - the division of the nucleus - sister chromatids pulled apart into two sets of chromosomes, one at each end of the cell. • Cytokinesis - the division of the cytoplasm into two separate daughter cells, each containing 1 nucleus with 1 diploid set of single-copy chromosomes. • Animal cells - cytokinesis = cleavage • Plant cells - cytokinesis = cell plate formation • Not all cells undergo cytokinesis following mitosis. • Meiotic cell division • Gametes are produced after a reduction in chromosome number • Gametes each have 1 haploid set of chromosomes

14. Key Haploid gametes (n = 23) Haploid (n) Ovum (n) Diploid (2n) Sperm Cell (n) FERTILIZATION MEIOSIS Diploid zygote (2n = 46) Ovary Testis Mitosis and development Multicellular diploid adults (2n = 46) Figure 13.5 Human Life Cycle • Adult inherits 46 chromosomes (2n) • Meiosis in gonads halves chromosome number (n) • Sperm cell (23 chromosomes) • Ovum (23 chromosomes) • Fertilization restores the chromosome number to 46 and results in a zygote • Mitosis produces genetically identical daughter cells. Mitosis is responsible for growth and development.

15. INTERPHASE S(DNA synthesis) G1 CytokinesisMitosis G2 MITOTIC(M) PHASE Figure 12.5 Phases of the Mitotic Cell Cycle • The cell cycle consists of • Interphase • The mitotic phase (m-phase)

16. Interphase • Interphase is 90% of the cell cycle and can be divided into 3 sub-phases • G1 phase – Growth 1 (Gap 1) cell grows • S phase – Synthesis phase – DNA replicates (cell continues to grow) • G2 phase - Growth 2 (Gap 2) cell grows

17. The Mitotic (M) Phase • The mitotic phase - 10% of the cell cycle, and • Is made up of mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm) • Mitosis is unique to eukaryotes and thought to be an evolutionary adaptation to handle large amounts of genetic material • Mitosis is a very reliable process, only 1 error in about 100,000 cell divisions • Mitosis is a continuous process, and cytokinesis usually begins during telophase

18. G2 OF INTERPHASE PROMETAPHASE PROPHASE Centrosomes(with centriole pairs) Aster Fragmentsof nuclearenvelope Early mitoticspindle Kinetochore Chromatin(duplicated) Centromere Nonkinetochoremicrotubules Kinetochore microtubule Chromosome, consistingof two sister chromatids Nuclearenvelope Plasmamembrane Nucleolus Figure 12.6 Mitosis • Mitosis begins with a cell just leaving G2 of Interphase Nucleus: well-defined Nucleoli: visible Centrosomes: two, adjacent to nucleus A pair of centrioles: in each centrosome An aster: a microtubular array around each centrosome Chromosomes: duplicated, but cannot be distinguished individually.

19. G2 OF INTERPHASE PROMETAPHASE PROPHASE Centrosomes(with centriole pairs) Aster Fragmentsof nuclearenvelope Early mitoticspindle Kinetochore Chromatin(duplicated) Centromere Nonkinetochoremicrotubules Kinetochore microtubule Chromosome, consistingof two sister chromatids Nuclearenvelope Plasmamembrane Nucleolus Figure 12.6 The Five Phases of Mitosis - Prophase In the cytoplasm: Mitotic spindle (microtubules) forms. Centrosomes move apart due to lengthening of spindle fibers between them. In the nucleus: Nucleoli disappear Chromatin fibers condense into visible doubled chromosomes

20. G2 OF INTERPHASE PROMETAPHASE PROPHASE Centrosomes(with centriole pairs) Aster Fragmentsof nuclearenvelope Early mitoticspindle Kinetochore Chromatin(duplicated) Centromere Nonkinetochoremicrotubules Kinetochore microtubule Chromosome, consistingof two sister chromatids Nuclearenvelope Plasmamembrane Nucleolus Figure 12.6 The Five Phases of Mitosis - Prometaphase Nucleus: envelope disintegrates Spindle fibers: extend from centrosome at each pole toward the cell’s equator. Each chromatid:  has a kinetochore, at the centromere region = spindle attachment site. By the end of prometaphase the chromosomes are aligned at the center of the cell. Spindle microtubules: Kinetochore microtubules: become attached to the kinetochores. Nonkinetochore microtubules: radiate from each centrosome toward the equator without attaching to chromosomes. They overlap with those from opposite pole.  May be attached by protein bridges.

21. METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Metaphaseplate Cleavagefurrow Nucleolusforming Nuclear envelopeforming Daughter chromosomes Centrosome at one spindle pole Spindle Figure 12.6 The Five Phases of Mitosis - Metaphase Centrosomes: alreadyat opposite poles. Chromosomes: already lined up at the metaphase plate. Centromeres: aligned on  metaphase plate. The long axis of each chromosome: at a right angle to the spindle axis Kinetochores: (structures of proteins and DNA that are part of the centromere) of sister chromatids face opposite poles.

22. METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Metaphaseplate Cleavagefurrow Nucleolusforming Nuclear envelopeforming Daughter chromosomes Centrosome at one spindle pole Spindle Figure 12.6 The Five Phases of Mitosis - Anaphase Paired centromeres: of each chromosome separate and move apart. Sister chromatids: split apart - move towards opposite poles. Kinetochore microtubules: shorten at the kinetochore end. Nonkinetochore microtubules: move cell ends further apart.

23. METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Metaphaseplate Cleavagefurrow Nucleolusforming Nuclear envelopeforming Daughter chromosomes Centrosome at one spindle pole Spindle Figure 12.6 The Five Phases of Mitosis - Telophase Nonkinetochore microtubules further elongate cell. Daughter nuclei form, from fragments of the parent nucleus, at poles. Nucleoli reappear There is a set of chromosomes at each pole of the cell, and the chromatin uncoils and chromosomes no longer visible. By the end of telophase: Mitosis is complete. Cytokinesis has begun.

24. The Mitotic Spindle • Events of mitosis depend on the spindle, which forms in the cytoplasm from microtubules and other proteins. • Microtubules of the cytoskeleton: partially disassembled during spindle formation. • alpha- and beta-tubulin • Fibers: elongate by adding tubulin subunits at the end away from the centrosome • Assembly begins in the centrosome (microtubule organizing center).

25. Aster Centrosome MetaphasePlate Sisterchromatids Kinetochores Overlappingnonkinetochoremicrotubules Kinetochores microtubules 0.5 µm Microtubules Chromosomes Figure 12.7 Centrosome 1 µm The Mitotic Spindle • The spindle arises from the centrosomes • And includes spindle fibers and asters

26. The Mitotic Spindle • The kinetochoremicrotubules of the spindle attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate • In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell • Current model: Kinetochore microtubules shorten by depolymerizing at the kinetochore ends, and motor proteins “walk” the chromosomes poleward. The microtubules of a cell in early anaphase were labeled with a fluorescent dye that glows in the microscope (yellow). Kinetochore Spindlepole Figure 12.8

27. The Mitotic Spindle • Nonkinetechoremicrotubules from opposite poles • Overlap and push against each other, elongating the cell in preparation for cytokinesis. Probably attached to each other by protein bridges. • Cytokinesis usually begins during telophase

28. Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells Figure 12.9 A (a) Cleavage of an animal cell (SEM) Cytokinesis • In animal cells • Cytokinesis occurs by a process known as cleavage, first forming a cleavage furrow • Actin microfilaments form a ring just under the plasma membrane. They constrict and pinch the cell in two.

29. Cytokinesis • In plant cells • Vesicles from the Golgi apparatus carrying cell wall material converge at the center of the cell • The vesicles fuse forming the cell plate • The plate grows and connects to the existing cell wall forming new cell wall. Vesiclesforming cell plate Wall of patent cell 1 µm Cell plate New cell wall Daughter cells (b) Cell plate formation in a plant cell (SEM) Figure 12.9 B

30. 2 3 5 1 4 Chromatinecondensing Nucleus Chromosome Nucleolus Metaphase. The spindle is complete,and the chromosomes,attached to microtubulesat their kinetochores, are all at the metaphase plate. Prophase. The chromatinis condensing. The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is staring to from. Prometaphase.We now see discretechromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelop will fragment. Telophase. Daughternuclei are forming. Meanwhile, cytokinesishas started: The cellplate, which will divided the cytoplasm in two, is growing toward the perimeterof the parent cell. Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomesare moving to the ends of cell as their kinetochoremicrotubles shorten. Figure 12.10 Mitosis in a plant cell

31. Origin of replication Cell wall Plasma Membrane E. coli cell Bacterial Chromosome Two copies of origin Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1 Replication continues. One copy ofthe origin is now at each end of the cell. 2 Origin Origin Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. 3 4 Two daughter cells result. Binary Fission – Prokaryotic Cell Division • In binary fission • The single circular bacterial chromosome replicates • The two daughter chromosomes actively move apart Figure 12.11

32. The Evolution of Mitosis • Since prokaryotes are simpler and preceded eukaryotes by billions of years • It is likely that mitosis evolved from bacterial cell division • Certain protists • Exhibit types of cell division that may represent intermediates between binary fission and the type of mitosis carried out by most eukaryotic cells

33. (a) Prokaryotes. During binary fission, the origins of the daughter chromosomes move to opposite ends of the cell. The mechanism is not fully understood, but proteins may anchor the daughter chromosomes to specific sites on the plasma membrane. Bacterial chromosome Chromosomes (b) Dinoflagellates. In unicellular protists called dinoflagellates, the nuclear envelope remains intact during cell division, and the chromosomes attach to the nuclear envelope. Microtubules pass through the nucleus inside cytoplasmic tunnels, reinforcing the spatial orientation of the nucleus, which then divides in a fission process reminiscent of bacterial division. Microtubules Intact nuclear envelope (c) Diatoms. In another group of unicellular protists, the diatoms, the nuclear envelope also remains intact during cell division. But in these organisms, the microtubules form a spindle within the nucleus. Microtubules separate the chromosomes, and the nucleus splits into two daughter nuclei. Kinetochore microtubules Intact nuclear envelope Kinetochore microtubules (d) Most eukaryotes. In most other eukaryotes, including plants and animals, the spindle forms outside the nucleus, and the nuclear envelope breaks down during mitosis. Microtubules separate the chromosomes, and the nuclear envelope then re-forms. Centrosome Fragments of nuclear envelope A hypothetical sequence for the evolution of mitosis Figure 12.12 A-D