5 CELL AND NUCLEAR DIVISION

5 CELL AND NUCLEAR DIVISION

LO:explain the importance of mitosis in the production of genetically identical cells, growth, repair and asexual reproduction; describe, with the aid of diagrams the behaviour of chromosomes during the mitotic cell cycle and the associated behaviour of the nuclear envelope, cell membrane, centrioles and spindle (names of the main stages are expected)

Historic video from 1960

Importance of mitosisGrowthAllows a zygote to produce more cell in order to grow; daughter cells are genetically identicalRepair and replacementAllow the multicellular organism maintain its tissues, example skin cells and bloodAsexual reproductionclone

CHROMOSOMESCHROMOSOMES

Thread like structures in the nucleusHuman cells 46 chromosomesKaryogram all the chromosomes rearranged so that there are matching pairs of chromosomes = homologous pairs (on of each pair comes from the mother and the other one from the father)last pair = sex chromosomes determine the sex of the individual (XX female, XY male)All the other chromosomes = autosomes

Each chromosome has a characteristic set of genes which code for different featuresDown syndrome trisomy of the 21st pairCystic fibrosis chromosome 7

Diploid cells (2n) = contain two sets of chromosomes; somatic cells (46 in humans)Haploid cells (n) = contain only one set of chromosomes; gametes (23 in humans)

Chromosome before cell division is a double structure made of two identical chromatids joined together by the narrow region = centromereEach chromatid contains one DNA moleculeDNA is made up of genes; each gene is a unit of inheritance = coding for one polypeptideThe gene for one characteristic is always found at the same position = locus

Homologous chromosomes

Homologous pairs of chromosomesSimilar in structure and compositionEach member comes from one of the parentsEach homologous pair possesses genes controlling the same characteristics (may exist in different forms = alleles); a change in allele is called mutation

TYPES OF NUCLEAR DIVISIONGROWTHNew cells are genetically identical, with the same number of chromosomes = MITOSISSEXUAL REPRODUCTIONNumber of chromosomes is halved = MEIOSIS; gametes are always haploid; reduction division

LO:outline the cell cycle, including interphase (growth and DNA replication), mitosis and cytokinesis outline the significance of telomeres in permitting continued replication and preventing the loss of genes outline the significance of mitosis in cell replacement and tissue repair by stem cells and state that uncontrolled cell division can result in the formation of a tumour

describe, with the aid of photomicrographs and diagrams, the behaviour of chromosomes in plant and animal cells during the mitotic cell cycle and the associated behaviour of the nuclear envelope, cell surface membrane and the spindle (names of the main stages of mitosis are expected) observe and draw the mitotic stages visible in temporary root tip squash preparations and in prepared slides of root tips of species such as those of Vicia faba and Allium cepa

MITOSIS IN AN ANIMAL CELL= Nuclear division that produces two genetically identical daughter nuclei, each containing the same number of chromosomes as the parent nucleus

CELL CYCLE

Cell growsCell cycle - The period that extends from the time a new cell is produced until the time the cell completes a cell division.Mitosis: nuclear divisionCytokinesis: cytoplasmic division

The cell cycle is divided into two major phases:InterphaseMitosis

InterphaseThe period between division, divided into 3 sub phases (G1, S and G2):

G1- cells grow rapidly and new organelle are synthetized

S - synthesis of DNA and chromosomes are replicated (2 chromatids)

G2 - cells prepare for mitosis, synthesis protein and mitotic spindle begin to form; DNA is checked and errors are erased

MitosisMitosis is a division of the nucleus to produce two new daughter cells containing chromosomes identical to the parent cell.Mitosis is a continuous process and divided into 4 main phases based on the appearance and behavior of the chromosomes.Prophase, PMetaphase, MAnaphase, ATelophase, T

ProphaseEarly prophaseChromosome condense and appear shorter and thicker and become visible in a light microscopeEach chromosome now consists of a pair of sister chromatids joined together at centromere.Nucleolus disappears & nuclear membrane disintegrates.Paired centrioles move to opposite ends of the cell

Late prophaseNuclear membrane disappearsSpindle form

Centrioles

Centromere

Metaphase Spindle fibres are fully formSister cromatids line up at the spindle equator/ metaphase plate.Two sister chromatids are still attached to one another at the centromere.At the end of metaphase, the centromers divide.

Anaphase Anaphase begin with the separation of the centromersThe sister cromatids are drawn to opposite poles of the cell by shortening of spindle fibres.Once separated, chromatids are referred to as daughter chromosome.End anaphase: the poles of the cell have complete and equivalent sets of chromosome.

Telophase Telophase begin when the two sets of daughter chromosomes have reached the two poles of the cell.The spindle fibres disintegrate, the nuclear membrane forms around each set of daughter chromosomes and the nucleoli reappear.The nucleolus also re-forms in each nucleus.The chromosomes uncoil and become less visible under the light microscope.Mitosis process is now completed.

Cytokinesis process of cytoplasmic division to form two daughter cells.

Different in animals and plants.Animal cells, the cytoplasm contracts to pull the plasma membrane inwards, forming groove called a cleavage furrow In plant cells, cytokinesis in cells is markedly different.A cleavage furrow does not form. Instead, membrane-enclosed vesicle gather at a plant cells equator between the two nuclei.Vesicle fuse to form a cell plate

outline the significance of telomeres in permitting continued replication and preventing the loss of genes

The importance of controlled mitosisControlled mitosis: the ability of the cell to divide at its own rate and time.Crucial to normal growth, development and maintenance for the perpetuity of living things.Eg: in plants controlled mitosis occurs at shoots results in growth of plants.in human Malphigian layer of skin divides actively to replace dead and damaged cells.

The effects of uncontrolled mitosis in living things

Mutation is the change in the DNA structure of the cell.This change in the DNA corrupts the coded genetic instructions for mitosis control.This leads to uncontrolled mitosis, which is the non-stop division of cells, producing a mass of new daughter cells, called tumour.

Uncontrolled mitosis

Causes of CancerGenetic- some forms of cancer like prostate, colon, breast, skin, ovary are suspected to be inherited from the parents

Carcinogens- these are chemicals which affect genetic activity and cause cancer, e.g. of carcinogen a diesel exhaust, cigarette smoke, hair dyes, soot, arsenic, benzene and formaldehyde.

Radiation- excess exposure to x-ray, gamma-rays and ultra violet rays lead to increase cancer risk.

Viruses- some viruses (such as the HPV and HIV-1) cause cancer.

Application of Mitosis in CloningMitosis is used to improve the quality, to produce new species and to ensure uniformity in the traits.Cloning: process of artificially creating a new individual that is genetically identical to an existing individual.Technique in application of mitosis in cloning tissue culture.

Application on mitosis in cloning

Plant tissueSkin tissue

HW:End of chapter questions