AQA A-Level Biology Mitosis and Cell Division

what are the phases of the cell cycle?

• interphase

• mitosis

• cytokinesis

which phases make up interphase?

• G1 (growth) phase

• S (synthesis) phase

• G2 (growth) phase

which phase makes up the majority of the cell cycle?

interphase

what happens in G1 phase?

• cells grow

• new organelles and proteins are made

what happens in S phase?

• DNA replication occurs

• completed as quickly as possible to prevent exposed bases being exposed to mutagens - chromatids now

what happens in G2 phase?

• microtubules produced

• lots of protein synthesis occurs to increase organelle numbers

• more ATP produced

define mitosis

• process of cell division

• in which two identical daughter cells are produced

why is mitosis required?

• needed for growth of multicellular organisms

• repair of tissues

what are the stages of mitosis?

• prophase

• metaphase

• anaphase

• telophase

describe what happens in prophase

• chromatin condenses into visible chromosomes, each made up of two chromatids (identical)

• centrioles move towards poles of the cell

• this forms a network of protein fibres across cell called spindle fibres

• nuclear envelope breaks down

describe what happens in metaphase

• chromosomes line up in the centre of the cell

• centromeres attach to the spindle

describe what happens in anaphase

• centromeres divide which separates sister chromatids

• spindle fibres contract

• pulls sister chromatids to opposite poles of the cell - ensures genetically identical

describe what happens in telophase

• separated chromatids group together at opposite ends of the cell

• chromosomes unwind and become indistinct

• spindle fibres disappear

• nuclear membrane reforms

describe what happens in cytokinesis

• cytoplasm of cell divides

• two new cells formed

describe the process of viral replication

• attachment proteins on the virus bind to complementary receptors on the host cell

• viral DNA/RNA is injected into the host cell

• host cell uses ribosomes to synthesize viral proteins and nucleic acids

• new viral particles are assembled

• the viral particles are released from the cell by cell lysis/budding

• budding - cell membrane is converted to viral envelope

how do bacteria divide?

by binary fission

describe the process of binary fission

• cell elongates and DNA is replicated (circular and plasmids)

• cell wall and plasma membrane constrict

• cytoplasm divides between 2 daughter cells

• cell wall and membrane close around 2 daughter cells forming 2 new cells

• cells can divide up to every 20 mins

how is cancer caused?

• caused when there are mutations in genes that control cell division

• causes cells to divide uncontrollably, forming a tumour, invading nearby tissues

how do cancer treatments work?

• aimed at controlling rate of cell division - either affect G1 or S phase

• G1 - prevent synthesis of enzymes needed for DNA replication, prevents S phase, causes cell death

• S - drugs damage DNA, during replication DNA is checked for damage, if severe damage is detected, the cell dies

describe the mitosis root tip practical

• cut off root tip of garlic bulb

• place in 1moldm-3 HCl for 5 mins

• swirl in distilled water briefly

• use a scalpel to cut off the yellowish very tip - meristem region - of the root tip

• place on a slide, squish it, add a few drops of ascetic stain

• leave for 2 mins then slowly place a coverslip on top, using it to gently squash cells

• use filter paper to absorb any excess stain

• look at cells under microscope

how would you calculate mitotic index?

cells in mitotis/all cells