Cell Reproduction

Chromosomes rod-like structures made of DNA and protein 2 Kinds of proteins in chromosomes A. histones- proteins that DNA wraps around, helps hold shape of chromosome and allows DNA to pack tightly B. nonhistones- Do not aid in packing of DNA, instead they control specific regions of the DNA

Chromosomes Chromosomes consist of two identical halves (each half is called a chromatid) Chromatids form when DNA makes a copy of itself prior to cell division When the cell divides each new cell receives one chromatid

Chromosomes Chromatids are held together by a centromere

Chromosomes Prokaryote DNA consists of a single chromosome that is attached to inside of cell membrane

Chromosome Number Each species has a characteristic number of chromosomes in each cell Ex: Humans46 Dogs78 Adder’s tongue fern 1,262 Chromosome # has nothing to do with complexity of organism

Types of Chromosomes 1.Sex chromosomes- determine sex of organism (could carry other genes as well) -Human sex chromosomes are either X or Y Females XX Males XY

Types of Chromosomes 2.Autosomes- all other chromosomes in an organism -Of the 46 human chromosomes, 2 are sex chromosomes, the other 44 are autosomes

Types of Chromosomes Every cell of an organism produced by sexual reproduction has 2 copies of each autosome (one from each parent) The two copies of each chromosome are called homologous chromosomes- same shape and size and carry genes for same trait

Karyotypes Picture of an individual’s chromosomes (cells are treated with chemicals to start mitosis, photos are taken during metaphase, and pictures are cut out and matched up)

Diploid vs. Haploid Cells Diploid cells- cells with two sets of chromosomes (2n) Diploid cells have both chromosomes for each pair as well as the sex chromosomes Diploid cells in humans have 23 pairs, or 46 chromosomes 2n = 46

Diploid vs. Haploid Cells Human gametes, or sex cells, are haploid sperm- male gamete egg- female gamete Haploid cells contain only one set of chromosomes, n Have half the # of chromosomes as diploid cells and only have one sex chromosome

Diploid vs. Haploid Cells When sperm and egg unite during fertilization, first cell of new organism will be diploid (2n) If gametes were not haploid, the new cell would be 4n and not functional

Cell Division in Prokaryotes Binary fission- Division of prokaryotes into two identical offspring cells 3 Stages 1. Chromosome makes a copy of itself 2. Cell grows until approximately 2X size of original 3. Cell wall forms between two chromosomes forming 2 new identical cells

Cell Division in Eukaryotes Cell Cycle- events that make up the life of a cell 2 Main Parts: A. Interphase-cell growth and DNA replication B. Mitosis- nuclear and cytoplasmic division

Interphase most of cell’s time spent in this part of cycle A. G 1 - cell grows in size and carries on metabolism B. S- DNA is copied C. G 2 - cell grows some more and prepares to divide *Some cells enter G 0 phase where they remain and no longer grow or divide (Ex: nerve cells)

Mitosis 4 Stages of Mitosis 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

Prophase first and longest stage of mitosis chromatin coils into rod-shaped chromosomes Nucleus disappears Centrioles move to opposite ends of cell Spindle begins to form

Metaphase double chromosomes become attached to spindle by centromere chromosomes line up on mid-line or equator of cell

Anaphase sister chromatids separate and move to opposite poles of cell

Telophase final stage of mitosis chromosomes reach opposite poles spindle disassembles nuclear envelope reappears and nucleolous forms

Cytokinesis Cytoplasm divides **Different between plant and animal cells In animal cells, cell membrane pinches in midway between two poles creating a cleavage furrow

Cytokinesis In plant cells, vesicles formed by golgi fuse together at mid-line forming a cell plate **Each cell formed by mitosis receives an exact copy of original cell’s chromosomes and approximately half of the parent cell’s cytoplasm and organelles.