Overview of Cell Division Mechanisms Chapter 9.1 Overview of Cell Division Mechanisms AP Biology Fall 2010

Objectives Determine the function of mitosis, meiosis, and prokaryotic fission Analyze the structural components of chromosomes

Mitosis, Meiosis, and Prokaryotes Before cells reproduce, there must be a division of the nucleus and its DNA

Mitosis, Meiosis, and Prokaryotes Mitosis and meiosis are eukaryotic nuclear division mechanism that lead to the distribution of DNA to new nuclei in forthcoming daughter cells

Mitosis Mitosis is used by multicelled organisms for growth by repeated divisions of somatic cells Responsible for: Increases in body size during growth Replacement of worn out or dead cells Tissue repair

Mitosis Used by multicelled organisms Plants, animals, fungi and single celled protists produce asexually by mitosis

Meiosis Meiosis occurs only in reproductive cells that divide to form gametes or spores Sexual reproduction Gemetes kown as sperm and eggs develop from germ cells Spores form in life cycle of protists, plants, and fungi

Meiosis

Prokaryotes Prokaryotic cells reproduce asexually by an entirely different mechanism called prokaryotic fission

Prokaryotes

Chromosome Structure Each chromosome is a molecule of DNA complexed with proteins Eukaryotic species have a characteristic number of chromosomes Before cell enters nuclear division, duplicates every chromosome Forms two sister chomatids held together by centromere

Chromosome Structure

Chromosome Structure During early stages of mitosis and meiosis: Duplicated chromosomes coil back on itself into highly condensed form

Chromosome Structure Proteins called histones tightly bind to DNA and cause spooling into structural units called nucleosomes Prevent tangling during nuclear division DNA winds twice around histones

Chromosome Structure Nucleosome: consists of part of DNA molecule looped twice around a core of histone proteins

Chromosome Structure Centromere: constricted region Location is different for each type of chromosome, unique characteristic Kinetochore: during nuclear division, located at centromere Is docking station for microtubules that help move chromatids

Chromosome Structure

Review What is the point of structural organization of chromosomes? What is the function of mitosis?

Answers Tight packaging keeps chromosomes from getting tangled, also between cell divisions nucleosome packaging can be loosened in specific regions (enzymes gain access to heredity information that cell requires). The function of mitosis is to increase in body size during growth, replacement of dead or worn-out cells, and repair of damaged tissues.