Topic 2.3 Eukaryotic cell cycle and division Flashcards
State what the cell cycle is and outline its stages
Regulated cycle of division with intermediate growth periods.
- Interphase
- Mitosis or meiosis (nuclear division)
- Cytokinesis (cytoplasmic division)
Outline what happens during interphase
G1(Gap 1): cell synthesises proteins for replication e.g. tubulin for spindle fibres and cell size doubles
S (Synthesis of DNA): DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere
G2(Gap 2): organelles divide
What is the purpose of mitosis?
Produces 2 genetically identical diploid daughter cells for:
* Growth
* Cell replacement/ tissue repair
* Asexual reproduction
What are diploid cells
Cells that have two complete sets of chromosomes
Name the stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Remember order through PMAT
Outline what happens during prophase
- Chromosome condense, becoming visible. (X-shaped: 2 sister chromatids joined at centromere)
- Centrioles move to opposite poles of cell (animal cells) and mitotic spindle fibres form
- Nuclear envelope and nucleolus break down = chromosomes free in cytoplasm
Outline what happens during metaphase
Sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres
Outline what happens during anaphase
Requires energy from ATP hydrolysis
- Spindle fibres contract = centromeres divide
- Sister chromatids separate into 2 distinct chromosomes and are pulled to opposite poles of cells. (looks like ‘V’ shapes facing each other)
- Spindle fibres break down
Outline what happens during telophase
- Chromosomes decondense, becoming invisible again
- New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome
What happens during cytokinesis?
- Cell membrane cleavage furrow forms
- Contractile division of cytoplasm
Explain how to prepare a temporary root tip squash
- Place root in hydrochloric acid to halt cell division and hydrolyse middle lamella
- Stain root tip with a dye that binds to chromosomes
- Macerate tissue in water using mounted needle
- Use mounted needle at 45o to press down cover slip and obtain a single layer of cells. avoiding trapping air bubbles
Explain the procedure for a root tip squash experiment
- Prepare a temporary mount of root tissue
- Focus an optical on the slide. Count total number of cells in the field of view and number of cells in a stage of mitosis
- Calculate mitotic index (proportion of cells undergoing mitosis
Name two dyes that bind to chromosomes
Toluidine blue (blue)
Acetic orcein (purple-red)
Why is only the root tip used when calculating a mitotic index?
Meristematic cells at root tip are actively undergoing mitosis.
Cells further from root tip are elongating rather than dividing.
What is meiosis?
A from of cell division that produces four genetically different haploid cells known as gametes
What are haploid cells?
Cells with half the number of chromosomes found in the parent cell
What happens during meiosis I?
- Homologous chromosomes pair to form bivalents
- Crossing over (exchange of sections of genetic material) occurs at chaismata
- Cells divide into two. Homologous chromosomes separate randomly. Each cell contained either maternal or paternal copy
What happens in meiosis II?
- Independent segregation of sister chromatids
- Each cell divides again, producing 4 haloid cells
Draw diagrams to show cells after each stage of meiosis
Parent cell: XXXX
After meiosis I: 2 XX cells
After meiosis II: 4 II cells
How does meiosis produce genetic variation?
- Crossing over during meiosis I
- Independent assortment (random segregation) of homologous chromosomes and sister chromatids
Results in new combinations of alleles.
What is a chromosome mutation?
Name the types
Involves section of a chromosome rather than 1 base.
Types include: deletion, inversion, duplication, translocation.
What is a translocation mutation?
A base sequence from one chromosome fuses with a non-homologous chromosome.
What is a non-disjunction mutation?
Chromosomes fail to separate correctly in meiosis.
Gametes have at least one more (polysomy) or one less (monosomy) chromosomes than normal.
Give examples of conditions caused by non-disjunction
trisomy-21 = Down’s syndrome
X-monosomey of sex chromosomes = Turner’s syndrome
Give various methods of asexual reproduction, and the organisms that use that method
- Binary fission - simple microbes - a single microbe splits into two daughter cells
- Budding - other microbes e.g. hydra - two daughter cells form but they aren’t the same size
- Vegative reproduction - higher organisms (especially plants) e.g. strawberry runners
Asexual reproduction in animals is rare on higher animals, but is known in lizards. It’s more common in lower animals e.g. the green fly
