Cellular Reproduction All of Chapter 8 Recall that… nucleotide – a monomer of DNA or RNA consists of nitrogen base, a sugar, and a phosphate group DNA or deoxyribonucleic acid – a double helix nucleic acid – hereditary information RNA or ribonucleic acid – nucleic acid consisting of single strand with ribose and uracil unlike DNA Nucleic acid – organic molecule that stores & carries important info for cell function Cell Division: All cells are derived from preexisting cells (Cell Theory) Cell division - process where cells produce new cells Cell division differs in prokaryotes (bacteria) & eukaryotes (protists, fungi, plants, & animals) Some tissues must be repaired often i.e. lining of gut, white blood cells, skin cells w/a short lifespan Other cells do not divide at all after birth i.e. muscle & nerve Reasons for Cell Division: Cell growth Repair & replacement of damaged cell parts Reproduction of/ species Copying DNA: each new cell must get a complete set of the DNA molecules b/c instructions are in DNA DNA must be copied (replicated, duplicated) before cell division Chromosomes & Their Structure: The plans for making cells are coded in DNA DNA, deoxyribose nucleic acid, a long thin molecule that stores genetic info DNA in human cell consists of ~ six billion pairs of nucleotides DNA is organized into giant molecules called chromosomes Chromosomes are made of protein & a long, single, tightly-coiled DNA molecule visible only when the cell divides http://highered.mcgraw-hill.com/olc/dl/120073/bio14.swf mitosis When a cell is not dividing DNA is less visible & is called chromatin DNA in eukaryotic cells wraps tightly around proteins called histones to help pack the DNA during cell division Nonhistone proteins help control the activity of specific DNA genes Kinetochore proteins bind to centromere and attach chromosome to the spindle in mitosis Centromeres hold duplicated chromosomes together before they separate in mitosis Telomeres are the ends of chromosomes which are important in cell aging When DNA makes copies of itself before cell division, each half of the chromosome is called a sister chromatid DNA of prokaryotes (bacteria) is one, circular chromosome attached to/ inside of/cell membrane Chromosome Numbers: Human body cells have 23 pairs of chromosomes or 46 chromosomes (diploid or 2n number- cells that have 2 sets of chromosomes) The 2 chromatids of a chromosome pair are called homologues (have genes for the same trait at the same location) Homolog Human body cells are somatic cells undergo mitosis. Human reproductive cells or gametes (sperms & eggs) have one set or 23 chromosomes (haploid or n number) Organism Chromosome Number (2n) Human 46 Fruit fly 8 Lettuce 14 Goldfish 94 Fertilization, joining o/egg & sperm, restores diploid chromosome number in/zygote (fertilized egg cell) Sex chromosomes, either X or Y, determine the sex o/organism XX = female XY = male autosomes – all other chromosomes, except X & Y Karyotype – a photomicrograph of chromosomes from a dividing cell arranged in pairs by size, long to short, ending w/sex chromosomes A human karyotype has 22 pairs of autosomes and 1 pair of sex chromosomes (23 total) What sex is this organism? Genes: gene - section of DNA which codes for a protein Each gene codes for ONE protein Humans have ~ 50,000 genes or 2000/ chromosome About 95% o/DNA in chromosome is "junk" that does not code for any proteins References http://sps.k12.ar.us/massengale/cell_division_notes.htm Cell Division 8.2 Cell Cycle: Cells go thru phases or a cell cycle during their life before they divide to form new cells The cell cycle includes 2 main parts -- interphase, and cell division Cell division includes – mitosis (nuclear division) – cytokinesis (division of the cytoplasm) Interphase – "resting stage" longest part of a cell's life cycle – cell isn't dividing – Cells grow, develop, & carry on all their normal metabolic functions – 3 parts --- G1, S, & G2 phases Interphase: G1 or 1st Growth Phase occurs after a cell division – Cells mature & inc in size by making more cytoplasm & organelles while carrying normal metabolic activities S or Synthesis Phase follows G1 and the genetic material of the cell (DNA) is copied or replicated Interphase cont’: S or Synthesis Phase follows G1 – genetic material of the cell (DNA) is copied or replicated G2 or 2nd Growth Phase - occurs after S Phase - cell makes all structures needed to divide Cell division in Prokaryotes: Prokaryotes i.e.bacteria don’t have a nucleus Binary fission – process of dividing into 2 identical new cells - asexual method of reproduction Binary fission cont’ chromosome (attached to cell membrane) makes a copy of itself and cell grows to 2X normal size Next, a cell wall forms btw/chromosomes & parent cell splits into 2 new identical daughter cells (clones) Cell Division in Eukaryotes: Eukaryotes have a nucleus & membranebound organelles which must be copied exactly so the 2 new cells formed from division will be exactly alike original parent cell & 2 new daughter cells must have identical chromosomes DNA is copied in the S phase o/cell cycle & organelles, found in the cytoplasm, are copied in the Growth phases Both the nucleus (mitosis) and the cytoplasm (cytokinesis) must be divided during cell division in eukaryotes Stages of Mitosis: Mitosis - Division o/nucleus occurs 1st –asexual method of reproduction –4 stages Prophase Metaphase Anaphase Telophase Prophase: Chromosomes become visible when they condense into sister chromatids Sister chromatids attach to each other by the centromere Centrioles in animal cells move to opposite ends of cell Spindle forms from centriole (animals) or microtubules (plants) Kinetochore fibers of spindle attach to centromere Polar fibers of spindle extend across cell from pole to pole Nuclear membrane dissolves Nucleolus disintegrates Metaphase: Chromosomes line up in center or equator of the cell attached to kinetochore fibers of the spindle Anaphase: Kinetochore fibers attached to the centromere pull the sister chromatids apart Chromosomes move toward opposite ends of cell Telophase: Nuclear membrane forms at ea end o/cell around the chromosomes Nucleolus reforms Chromosomes become less tightly coiled & appear as chromatin again Cytokinesis begins Cytokinesis: Cytoplasm of the cell and its organelles separate into 2 new daughter cells In animals, a groove called the cleavage furrow forms pinching the parent cell in two Cytokinesis cont’ In plants, cell plate forms down the middle o/cell where the new cell wall will be Summary of Mitosis: Interphase Cell matures & carries on normal activities DNA copied & appears as chromatin Nucleolus visible Early Prophase Chromosomes condense & become visible Centrioles separate & spindle starts forming Late Prophase Spindle forms with aster at each pole Nuclear membrane & nucleolus disintegrate Centromere of chromosomes attaches to spindle fibers Metaphase Chromosomes line up at the equator of the cell attached to kinetochore fibers of spindle Anaphase Centromeres split apart Homologs move to opposite poles of the cell Telophase/Cytokinesis Nuclear membrane & nucleolus reform Cell pinches into 2 cells in animals In plants, a cell plate separates the 2 new cells Cancer is Uncontrolled Mitosis: Mitosis must be controlled, otherwise growth will occur w/out limit (cancer) Control is by special proteins produced by oncogenes Mutations in control of proteins can cause cancer Meiosis 8.3 Similar Several to mitosis- nuclear division differences – Involves 2 cell divisions - Results in 4 cells with 1/2 the normal chromosome number for DNA. Meiosis & Sexual Reproduction Reduces the number of chromosomes in new cells by half o/ original cell New cells have a single copy of chromosomes (23 total) but are not identical to each other or parent cell Used for making gametes ( sperm and eggs) w/haploid or n number Recall Vocabulary: – Diploid (2N) - Normal amount of genetic material – Haploid (N) - 1/2 the genetic material. In Meiosis cells divide twice after single DNA duplication Produces 4 haploid cells or gametes MEIOSIS I MEIOSIS II separates homologs separates sister chromatids Crossing over No crossing over Half # of chromosomes 23 Same # chromosomes 46 Stages: Prophase I Metaphase I Anaphase I Telophase I Stages: Prophase II Metaphase II Anaphase II Telophase II When sperm fertilizes an egg to form zygote, the diploid number of chromosomes is restored (23 + 23 = 46) Egg cells or ova (ovum, singular) are larger, nonmotile cells Oogenesis - meiosis producing eggs occurs in female's ovaries Oogenesis Sperms contain less cytoplasm – smaller – flagellum to swim to the egg Spermatogenesis meiosis producing sperm cells & occurs in the testes Spermatogenesis Meiosis I: The cell that undergoes Meiosis I is a primary spermatocyte or oocyte Remember –cyte or -cyto means cell/hollow container Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. Oocyte: A female germ cell in the process of development. The oocyte is produced in the ovary by an ancestral cell called an oogonium and gives rise to the ovum (the egg) which can be fertilized. Prophase I: Chromosomes coil tightly & are visible Nuclear membrane & nucleolus disintegrate Spindle forms Synapsis (joining) of homologous chromosomes occurs making tetrads Kinetochore fiber forms on ea chromosome Chromosomes in tetrad exchg frag by crossing over Metaphase I: Tetrads become aligned in/center o/cell attached to spindle fibers Telophase I: May not occur in all species Cytokinesis - producrs 2 cells In females, 2nd cell in females is called the 1st Polar Body 1st Polar Body dies due to uneven splitting of the cytoplasm Anaphase I: Homologous chromosomes separate Prophase II: Cells called Secondary spermatocytes or oocytes DNA is NOT copied before cell divides Chromatids attach to spindle fiber Metaphase II: Chromosomes become aligned in the center of the cell attached to spindle fibers Anaphase II: Sister chromatids separate randomly Called independent assortment Telophase I: Cytokinesis occurs producing 4 cells in males called spermatids Spermatids mature & form flagellum to become sperm Cytokinesis in females produces a 2nd Polar Body (that dies) and an ootid Ootids mature to become ovum or egg Asexual & Sexual reproduction: Evolution is the slow process of change in living populations over time Variations are differences that occur due to crossing-over among members of a sexually reproducing population Variations are important to the survival of individuals in a population (some must survive to reproduce) Asexually reproducing organisms rarely show variations because the organisms have identical genes REVIEW animations View 1st – http://highered.mcgraw-hill.com/olc/dl/120074/bio19.swf – Stages of meiosis View 2nd – http://highered.mcgraw-hill.com/olc/dl/120074/bio18.swf – Random orientation of chromosomes in meiosis View 3rd – http://highered.mcgraw-hill.com/olc/dl/120074/bio16.swf – Unique features of meiosis View last – http://highered.mcgraw-hill.com/olc/dl/120074/bio17.swf – comparison of mitosis and meiosis