UNIT V Review Baby Campbell Ch 9 10

UNIT V - Review Baby Campbell – Ch 9 , 10, 13 Big Campbell – Ch 12, 13, 16

I. Chi Square (Goodness Of Fit) Analysis • A coin is flipped repeatedly. 65 heads are obtained. 45 tails are obtained. How do we determine if the coin is normal? • Determine the expected outcome – Find the total number and multiply by the expected fraction to get expected numbers – Example: 110 coin flips X 0. 50 = 55 heads, 55 tails • Calculate the chi squared value – Sum of (observed-expected)2/expected – Higher deviation from expected means greater Chi 2 • Determine degrees of freedom (categories – 1) • Compare to critical value for a given p value and Degrees of freedom – If chi squared > critical value, difference is significant, reject null – If chi squared <= critical value, difference can happen by chance with given p value.

I. CHI SQUARE, cont

II. ASEXUAL cell division • Purpose Ø Unicellular Organisms ØReproduction Ø Multicellular Organisms ØGrowth and development ØRenewal and repair ØHealing ØRenewing skin cells

III. THE CELL CYCLE • Can be divided into: Ø Interphase Ø G 1, S, G 2 Ø Longer Ø Mitosis/M Ø Condensation and segregation of previously replicated genetic material

Interphase § DNA found in chromatin form § 3 sub-phases Ø G 1 Ø Growth Ø Normal cell function Ø G 1 Checkpoint ØS Ø DNA synthesis—DNA replication Ø Chromosomes replicated to make two identical sister chromatids. Ø Chromatid cohesion established Ø G 2 Ø Synthesis of microtubules for spindles and other mitotic proteins Ø Replication of centrioles and other organelles Ø G 2 Checkpoint—DNA damage

Formation of chromatids G 1 Phase • 1 chromosome • Not condensed yet G 2 Phase through Metaphase • 1 chromosome • Composed of sister chromatids Anaphase • Resolved into 2 daughter chromosomes

Chromatid components § Cohesion § Mediated by cohesion complexes § Cleaved by separase at metaphase § Centromere § Closest association of chromatids § Kinetochore § Protein complex that mediates interaction between centromere and spindle fibers

Mitosis • Mitosis § “Nuclear division” (really condensation and segregation of DNA) § Requires all the cell’s energy, resources § Last step is cytokinesis – splitting of the cell

III. CELL CYCLE, cont

III. Cytokinesis • Cytokinesis – Division of cytoplasm – Happens in parallel with telophase, sometimes anaphase • Animal Cells – Cleavage furrow produced by actin microfilament contractile ring

III. Cytokinesis • Cytokinesis – Division of cytoplasm – Happens in parallel with telophase, sometimes anaphase • Plant Cells – Cellulose cellulose fibers deposited by Golgi-derived vesicles – Cell Plate

IV. MEIOSIS – A SPECIAL TYPE OF CELL DIVISION • Somatic Cells o Body cells o Human somatic cells contain 46 chromosomes, 23 from mom, 23 from dad o 2 n or diploid o Matched pairs of chromosomes called homologous pairs. Each chromosome making up a homologous pair is known as a homologue. Both carry genes for same traits. The location of a gene on a chromosome is known as a locus. Ø 44 Autosomes Ø 2 Sex chromosomes v. XX = v. XY =

IV. MEIOSIS, cont • Gametes o Egg and sperm cells o Haploid or n o Contain 23 chromosomes o In fertilization, haploid (n) sperm fuses with haploid (n) egg → diploid (2 n) zygote

IV. MEIOSIS, cont • Description of Meiosis o Special type of cell division that occurs to produce gametes o Involved specialized cells o DNA replicated once, cell divides twice o Produces 4 cells with ½ the original chromosome number o In humans, Ø Occurs in ovaries, testes only

IV. MEIOSIS, cont

IV. MEIOSIS, cont

IV. MEIOSIS, cont • Crossing Over o Further increases genetic variability o Occurs during prophase I when tetrads are forming o Piece of one sister chromatid breaks off & exchanges places with piece of sister chromatid of homologue o Known as chiasma o Occurs very frequently

IV. MEIOSIS, cont

IV. MEIOSIS, cont Spermatogenesis vs Oogenesis in Humans

Male spermatogenesis Female oogenesis • Begins at puberty • One diploid primary spermatocyte gives rise to 4 genetically unique spermatozoa (sperm) • Meiosis begins before birth • Cells arrested in Meiosis I • During ovulation, Meiosis I completes, producing one haploid cell with polar body, arrested in metaphase II • After fertilization, anaphase II commences. • A second polar body forms • One genetically unique ovum

V. A COMPARISON OF MEIOSIS & MITOSIS Formation of tetrads is a deadgiveaway of Metaphase I. To differentiate Metaphase and Metaphase II, look at the diploid number given.

VI. DNA – THE MOLECULE OF INHERITANCE • Discovery • Structure of DNA Ø Each strand of nucleotides held together with Ø Double helix Ø 2 nucleotide strands are antiparallel Ø Each strand has a 3’ end (terminus) and a 5’end; named for carbon on deoxyribose

VI. DNA, cont • Base Pairing

VI. DNA, cont • Chromosome o Single molecule of DNA wrapped in histone proteins. Proteins maintain chromosome structure & control DNA activity o Gene

VI. DNA, cont • Genome o All of an organism’s DNA o Provides working instructions for cell through m. RNA. o Must be copied prior to cell division Euchromatin—less dense, more actively transcribed

VII. DNA REPLICATION • DNA Replication o Prior to cell division, DNA must be replicated o Occurs during S or Synthesis phase of mitosis, meiosis o Known as semiconservative model of replication Ø Meselson-Stahl Experiment Ø Two double helices produced, each containing old DNA and new DNA

VII. DNA REPLICATION, cont. • Steps of Replication: Ø DNA helicase unwinds the DNA double helix Ø Replication begins at specific points on the DNA molecule known as origins of replication. The Y-shaped region where new strands of DNA are elongating are called replication forks

VII. DNA REPLICATION, cont. Ø As DNA is “unzipped”, single-strand binding proteins hold the DNA open Ø A topoisomerase relieves tension creating by unwinding of DNA by making cuts, untwisting, & rejoining the nucleotide strand. Ø DNA polymerase can only add nucleotides to an already-existing strand so an RNA primer is synthesized to get replication going

VII. DNA REPLICATION, cont. Ø DNA polymerases add complementary nucleotides to each side of the DNA molecule. Ø DNA polymerase can only add nucleotides to the 3’ end of the growing strand, so the daughter DNA is synthesized 5’ – 3’, which means parental DNA is “read” 3’-5’. Ø This means only one side of the DNA (3’ – 5’) molecule can be replicated as a continuous strand. Known as the leading strand.

VII. DNA REPLICATION, cont. • Synthesis of lagging strand Ø To synthesize the other new strand of DNA, DNA polymerase must work away from the replication fork. Leads to synthesis of short pieces of DNA known as Okazaki fragments. Ø DNA ligase binds fragments together to form a continuous strand of nucleotides.

VII. DNA REPLICATION, cont. An Overview of Replication

VII. DNA REPLICATION, cont. • Proofreading & Repair Ø DNA Polymerase proofreads nucleotides as they are added

VII. DNA REPLICATION, cont. • Telomeres Ø 5’ ends of daughter strands cannot be completed because DNA polymerase needs primer upstream of start site Ø Results in shorter and shorter DNA molecules with jagged ends Ø To protect genetic integrity, ends of chromosomes do not contain genes – instead there are nucleotide sequences known as telomeres

VII. DNA REPLICATION, cont. • Telomeres, cont Ø Telomeres shorten each time cell divides - limits the number of times a cell can divide; thought to protect organism from cancer Ø Telomerase Ø Enzyme that lengthens telomeres. Required in stem cells. Ø Cancer cells up-regulate telomerase activity

IX. REGULATION OF CELL CYCLE • Highly regulated by chemical messengers. v Cell Signaling Ø Autocrine Signaling Ø Paracrine Signaling Ø Endocrine Signaling v Allosteric Regulation v Cyclins and CDK’s

IX. CELL CYCLE REGULATION, cont • Internal Signals o Three major checkpoints in cell cycle Ø G 1 Ø DNA damage and lack of activators of cell cycle prevent progression Ø Passing this checkpoint and entering S phase is the “point of no return” Ø G 2 Ø DNA damage checkpoint that prevents cells with damaged chromosomes to enter mitosis. ØM o Spindle checkpoint (metaphase) o Ensures all kinetochores are attached to spindle fibers before proceeding to anaphase

IX. CELL CYCLE REGULATION, cont o Regulated by enzymes known as cyclin -dependent kinases or Cdks • Activated when bound to proteins known as cyclins • Kinase concentrations fairly constant; cyclin concentrations vary

IX. CELL CYCLE REGULATION, cont CDK activity decreases once its activating cyclin is destroyed

IX. CELL CYCLE REGULATION, cont • External Signals o Growth Factors (stimulate cell cycle) Ø Proteins released by certain cells that stimulate other cells to divide. Ø Cells stop dividing when growth factor is depleted. Ø Examples include erythropoetin, interleukin, pdgf

IX. CELL CYCLE REGULATION, cont • External Signals o Density-dependent Inhibition Ø Results from crowded conditions Ø When one cell touches another, cell division stops o Anchorage Dependence Ø Most cells must be in contact with solid surface to divide

IX. CELL CYCLE REGULATION, cont • Cell Cycle Out of Control = CANCER o Uncontrolled growth o Deprive normal cells of nutrients o Cancer cells do not respond to normal cell cycle controls

IX. CELL CYCLE REGULATION, cont o Cancer cells do not respond to normal cell cycle controls Ø Apoptosis

IX. CELL CYCLE REGULATION, cont