Mitosis Flashcards
Why is the cell cycle needed?
• Growth of tissue/organism
• Replacement of worn out/damaged cells
• Repair of body tissues
• Asexual reproduction
What happens in growth stage one (G1)?
• Protein synthesis
• Organelles replicate
• Cell increases in size
What happens in the synthesis phase (S)?
• Replication of each chromosome in the nucleus (now called sister chromatids joined at the centromere)
What happens in growth stage two (G2)?
• Cell continues to grow in size
• Duplicated DNA is checked for errors
• Energy stores are increased
Why would cells be in G0 (resting state)?
• Differentiation (and no longer able to divide)
• DNA may be damaged
What may happen if the DNA is not checked at checkpoints?
• Mutations in the DNA sequence
• Faulty DNA produced
• Error in copying daughter cells
• Daughter cells will not receive identical genetic information
• Proteins not made or do not function properly
What is the difference between sister chromatids and homologous chromosomes?
A homologous pair of chromosomes contain one maternal and one paternal chromatid. They carry the same genes although may have different alleles of these genes. Members of a homologous pair pair up during meiosis. Sister chromatids are the exact copy of each other and have the exact same alleles as well as genes.
What are the four phases of mitosis?
PMAT
• Prophase
• Metaphase
• Anaphase
• Telophase
What happens during prophase?
• Chromosomes condense and thicken (becoming visible)
• Two centrioles migrate to opposite poles of the cell (in animal and some plant cells)
• Spindle fibres attach to specific areas on the centromeres and start to move the chromosomes to the centre (equator) of the cell
• Nuclear envelope disappears
What happens during metaphase?
• Individual sister chromatids are moved by the spindle fibres to align at the metaphase plate/equator at the centre of the cell
• Sister chromatids are attached to the spindle fibres by the centromere
What happens during anaphase?
• Centromeres holding the pairs of chromatids in each chromosome divide
• Sister chromatids separate
• Spindle contracts (fibres shorten)
• Each chromatid is pulled by their centromere to the opposite poles of the cell
What happens during telophase?
• Chromatids have reached opposite poles of the cell. They uncoil and become long and thin again
• Now called chromosomes
• Spindle fibres disappear
• Nuclear envelope reforms and enclose around the chromosomes at each pole
What forms during cytokinesis in animal cells?
A cleavage furrow
What forms during cytokinesis in plant cells?
A cell plate
