Cell Cycle And Cell Division Flashcards
What protein is DNA made up of?
Histone
When do chromosomes become visible?
Chromatin condenses prior to cell division
What does haploid mean and what symbol is associated with it?
Having a single set of chromosomes. Symbol= n
What does Diploid mean and what is the symbol associated with it?
Having two complete sets of chromosomes. Symbol= 2n
What is used to describe the number of complete sets of chromosomes in an organism?
The Ploidy level
How are organisms with more than two complete set of chromosome described as?
Polyploid
What are the 3 steps to the cell cycle?
Interphase
Mitosis
Cytokinesis
Describe the process of Prophase:
The chromosomes condense-> becoming distinguishable as pairs of chromatids
Centrioles separate and move to opposite ends of the cell-> As they move they organise a partner so by the time they reach the poles their in pairs again
Protein microtubules form-> Making the spindle. Spindle fibres extend from pole to pole and from pole to the centromere of each chromosome
Nuclear envelope disintegrates-> The nucleolus disappears (late prophase)
Describe what happens at Metaphase:
Chromosomes line up at the equator of the cell. Spindle fibres attach to the centromere and chromatids of the chromosomes.
How do chromosomes in metaphase look like when viewed from different points?
From the poles= spread out
From the side= in a line
Describe what happens at anaphase:
The spindle fibres shorten and the centromeres separate. Pulling the now separated chromatids to the poles, centromere first.
Describe what happens at telophase:
Chromatids are referred to as chromosome again.
- Chromosomes uncoil and lengthen
- The spindle fibres break down
- The nuclear envelope reforms
- The nucleolus reappears
Describe cytokinesis and how it differs in animal and plant cells:
Cytokinesis= the division of the cytoplasm to make new cells
Animal cells= Occurs by constriction of the parent cell around the equator, from outside inwards
Plant cells= a cell plate form across the equator of the parent cell from the centre outwards and they extend and join to form the new cell wall
Name some key differences between mitosis in animal cells and plant cells:
Shape= animal cell becomes rounded before mitosis, where’s in plant there is no change
Centriole= in animal is present, in plant absent from higher plant cells
Cytokinesis= Cleavage furrow, Cell plate. Cleavage furrow develops from outside inwards, Cell plate develops from the centre outwards
Spindle= in animal degenerates at telophase, in plant it remains throughout new cell wall formation
Occurrence= bone marrow/hair follicles/ sites of tissue repair, in meristems
The significance of mitosis:
Produces cells that are genetically identical to the parent (same number of chromosomes)
Growth- can repair tissue and replace dead cells. Some tissues are constantly worn away and need replacing like the gut lining.
Asexual reproduction- produces complete offspring that is genetically identical to the parent
What is the name given to the genes that prevents the cell cycle from repeating continually?
Tumour suppressing genes
When a gene is mutated but does not cause cancer what is it called?
Porto-oncogenes
When a gene is mutated and does cause cancer what is it called?
oncogenes
Where does DNA replication occur?
Within interphase before mitosis/meiosis
Describe what happens at prophase I of meiosis I:
- Paternal and maternal chromosomes come together in homologous pairs (synapsis), each chromosome pair is a bivalent
- The centrioles move to opposite poles and form the spindle fibres
- Chiasmata occurs when the chromatids wrap around each other
-Crossing over happens as DNA from one chromatid may be exchanged causing a source of variation
-This allows ‘genetic recombination’ which produces new combinations of alleles, single cross over in meisosis one can result in four haploid gametes having a different genetic composition
- By the end of prophase I, the nuclear envelope disintegrated and the nucleolus has disappeared
Describe what happens at metaphase I:
- Pairs of homologous chromosomes arrange themselves at the equator of the spindle.
- Independent assortment happens, each combination of paternal and maternal chromosomes faces each pole, so the combination of chromosomes that enters each daughter cell at meiosis 1 is random
With 3 pairs of chromosomes, how many possible combinations are there of maternal and paternal chromosomes?
2 to the power of 3 = 8 possible combinations
Describe what happens at anaphase I:
- Spindle fibres shorten which separates each chromosome in the bivalent resulting in each pole receiving only one of each homologous pair of chromosome.
Describe what happens at telophase I:
In some species the nuclear envelope reforms around the haploid group of chromosomes and the chromosomes decondense making them no longer visible, but in many species the chromosomes stay in their condensed form.
Are the daughter cells in meiosis I diploid or haploid?
Haploid after cytokinesis
What happens at prophase II?
The centrioles separate and organise a new spindle at right angles to the old spindle.
Describe what happens at Metaphase II:
The chromosomes line up on the equator with each chromosome attached to a spindle fibre by its centromere. Independent assortment happens as the chromatids can face either pole.
Describe what happens at Anaphase II:
The spindle fibres shorten and the centromeres separate, pulling the chromatids to opposite poles.
Describe what happens at telophase II:
At the poles, the chromatids lengthen and can no longer be distinguished in the microscope. The spindle disintegrates and the nuclear envelope and nucleoli reform.
What is the significance of meiosis?
- Keeps the chromosome number constant from one generation to the next
- Generates genetic variation in the gametes, in two ways (Crossing over in Prophase I or Independent assortment)
