5 all cells arise from other cells

how do eukaryotic cells reproduce?

they entered the cell cycle and divide by mitosis or meiosis

how do prokaryotic cells reproduce?

replicate by binary fission

how do viruses reproduce?

they don’t undergo cell division as they’re not living. they replicate inside of host cells they invade by injecting their nucleus acid into a cell to replicate the virus particles

what are the three stages of the cell cycle?

• interphase (G1, S, G2)

• nuclear division (mitosis and meiosis)

• cytokinesis

what happens during interphase?

• interphase is the longest stage in the cell cycle

• the cell grows, organelles double, then DNA replicates

• G1 - growth (all organelles in cell double and cell grows in size)

• S - DNA synthesis (SNA replication)

• G2 - growth and preparation for mitosis (some growth, but DNA is checked for mutations. mutation detected = cell destroyed)

what are the stages in mitosis?

• prophase

• metaphase

• anaphase

• telophase

what does mitosis produce?

two genetically identical daughter cells

what’s mitosis for?

growth and repair such as clonal expansion of B cells

what’s the centromere?

a circular pinch point in the middle of the chromosome

what’s the chromatid?

the arms of the chromosome

what happens in prophase?

• chromosomes condense and become visible

• in animal cells, centrioles separate and move to opposite poles of the cells

• the centrioles are responsible for creating spindle fibres which are released from both poles to create a spindle apparatus, these will attach to the centromere and chromatids on the chromosome later

• plants have a spindle apparatus, but lack centrioles

• nuclear envelope starts to disintegrate

what happens in metaphase?

• chromosomes align along the equator (centre) of the cell

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

what happens in anaphase?

• spindle fibres start to detect and pull the centromere and chromatids they are bonds to towards opposite poles

• this causes the centromere to divide in two and the individual chromatids and pulled to each opposite pole

• these separated chromatids are now referred to as chromosomes

• this stage requires energy in the form of ATP which is provided by respiration in the mitochondria

what happens in telaphase?

• the chromosomes are now at each pole of the cell and become longer and thinner again

• the spindle fibres disintegrate and the nucleus starts to reform

what happens in cytokinesis?

cytoplasm splits in two to create the two new genetically identical daughter cells

how can the mitotic index be calculated?

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

what’s the equation for mitotic index?

mitotic index = the number of cells in mitosis/the total number of cells x 100

mitosis is a controlled process, what can happen if it’s uncontrolled?

can lead to the formation of tumours and cancers. many cancer treatments are directed at controlling the rate of cell division

what does binary fission in prokaryotic cells involve?

• replication of the circular DNA and of plasmids

• division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids