Cell division and Cellular Organization Flashcards
What is the stages of the cell cycle
G1, G1 checkpoint, S, G2, G2 checkpoint
What happens during G1
Cell grows and new organelles and proteins are made
What happens during G1 checkpoint
The cell check that the chemicals needed for replication are present and for any damage to the DNA before enters S phase
What happens during S phase
Cell replicates its DNA ready to divide by mitosis
What happens during G2
Cell keeps growing and proteins needed for cell division are made
What happens during G2 checkpoint
The cell checks whether all the DNA has been replicated without any damage. If it has, the cell can enter mitosis.
What happens during M phase
Mitosis and cytokinesis
What are the stages of mitosis
Interphase, prophase, metaphase, anaphase, telophase, cytokinesis
What happens during interphase
The cell carries out normal functions but also prepares to divide. The DNA is unraveled and replicated to double its genetic content. Organelles are replicated and ATP is increased
What happens during prophase
The chromosones condense getting shorter and fatter. Centrioles (bundles of protein) start moving to opposite ends of the cell forming a protein network - spindle. The nuclear envelope breaks down and chromosomes lie free in the cytoplasm
What happens during metaphase
The chromosomes line up along the middle of the cell and become attached to the spindle by their centromere. The cell check all the chromosomes are attached to the spindle before mitosis can continue
What happens during anaphase
The centromeres divide separating each pair of sister chromatids. The spindles contract, pulling chromatids to opposite ends of the cell, centromere first
What happens during telophase
The chromatids reach the opposite poles on the spindle. They uncoil becoming long and thin now called chromosomes. A nuclear envelope forms around each group of chromosomes so now two nuclei
What happens during cytokinesis
The cytoplasm divides. In animals a cleavage furrow forms now two genetically identical daughter cells are formed.
How do you observe the cell cycle
By staining the chromosomes so you can see them under a microscope and therefore be able to watch what happens during mitosis
What does meiosis produce and where
The reproductive organs producing gametes
What type of division is meiosis
Reduction division. This is where the cells that are formed have half the number of chromosomes (diploid)
What happens in meiosis I
Prophase I = Chromosomes condense, getting shorter and fatter then arrange themselves into homologous pairs. Centrioles move them to opposite ends forming spindle fibres. Nuclear envelope breaks down
Metaphase I = The homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres
Anaphase I = The spindles contract separating the pairs one chromosome to each end of the cell
Telophase I = A nuclear envelope forms around each group
Cytokinesis = two haploid daughter cells produced
What are homologous pairs
Pairs of chromosomes one from mum and one from dad
What happens during meiosis II
Daughter cells undergo the stages again. In anaphase II the pairs of sister chromatids are separated and each new daughter cell inherits one chromatid from each chromosome
What happens to homologous pairs during meiosis I
Come together and pair up, the chromatids twist around each other and bits of chromatids swap over. The chromatids still contains the same genes but now a different combination of alleles
What are the two main events during meiosis that lead to genetic variation
Crossing over of chromatids - daughter cells formed contain chromatids with different alleles
Independent assortment of chromosomes
What are stem cells
Unspecialized cells that can develop into different types. They divide to become new cells which specialize for a certain job called differentiation.
Why does the independent assortment of chromones lead to genetic variation
1) Each homologous pair is made from one chromosome that is maternal and one paternal chromosome
2) When pairs line up in metaphase I and separated in anaphase I it is completely random which chromosome from each pair ends up in which daughter cell
3) The four daughter cells have different combinations of maternal and paternal
4) This is an independent assortment of chromosomes
5) The shuffling leads to genetic variation
