BIO; Cell Cycles

when eukaryotic cells enter the cell cycle what do they divide by

mitosis or meiosis

when prokaryotic cells enter cell cycle what do they divide by

binary fission

why do viruses not undergo cell division

bc they are non living

how does binary fission in prokaryotic cells work

1. circular DNA and plasmids replicate

2. cytoplasm splits to create 2 daughter cells

3. each daughter cell has one copy of the circular DNA but a variable number of plasmid copies

what are the 3 key stages of the cell cycle

1. interphase - G1, S, G2 i.e growth/DNA synthesis/growth and preparation for mitosis

2. cell division - mitosis/meiosis

3. cytokinesis - division of the cytoplasm to create new cells

what’re the key events of interphase for mitosis

G1 (growth) - cell increases in size and organelles, such as mitochondria and chloroplasts, are replicated

S (synthesis) - DNA is replicated; each chromosome is copied, resulting in two identical sister chromatids attached at the centromere

G2 (growth+preparation) - cell continues to grow and synthesizes more ATP, providing energy for cell division

what the difference between mitosis and meiosis

mitosis creates 2 identical diploid cells for growth and repair

meiosis creates 4 genetically different haploid cells - gametes

whats mitosis

part of the cell cycle in which a eukaryotic cell divides to produce two identical diploid daughter cells,

each with the identical copies of DNA produced by the parent cell during DNA replication

what are the 4 stages of mitosis

prophase

metaphase

anaphase

telophase

how many rounds of division occur during mitosis

one

describe 1st stage of mitosis

prophase;

• chromatin condenses into chromosomes

• nucleolus disappears and chromosomes become visible

• centrioles separate and move to opposite poles of the cell

describe second stage of mitosis

metaphase;

• chromosomes align along the equator of the cell

• spindle fibres are released from the poles and attach to the centromere and chromatid

describe 3rd stage of mitosis

anaphase;

• spindle fibres retract and pull the centromere and sister chromatids apart

• sister chromatids are pulled to opposite poles of the cell

• stage requires ATP provided by respiration in mitochondria

(sister chromatids now referred to as ‘chromosomes’ )

describe the 4th stage of mitosis

telophase;

• chromosomes becomes longer and thinner

• spindle fibres disintegrate and nucleus starts to reform

what happens during cytokinesis in mitosis

• cytoplasm splits in two

• myosin II and actin filament ring contract to cleave cell in two

• creates 2 new genetically identical diploid cells

how to calculate mitotic index

by counting how many cells are visible in the field of view and the number of cells visible that are in a stage of mitosis;

mitotic index = no. cells in mitosis / total no. cells

how to standardise mitotic index

only count cells that are fully visible in the sample field of view

whats uncontrolled cell division

unregulated control of mitosis

whats a tumour

mass of cells resulted of uncontrolled cell division

either benign (non cancerous) or malignant (cancerous)