1.6 - The Cell Cycle and Cell Division Flashcards
What are chromosomes made of?
DNA and the protein histone
When are chromosomes visible?
When chromatin condenses prior to cell division
What do chromosomes replicate to become?
They replicate to become chromatids, joined by a centromere
What is the haploid number?
The number of chromosomes in a complete set
What are homologous pairs?
When organisms receive 1 chromosome from each parent
What is the ploidy level?
The number of complete sets in an organism
How many complete chromosome sets are in a haploid level?
1, example being human gametes
How many complete chromosome sets are in a diploid level?
2,example human body cells
How many complete chromosome sets are in a triploid level?
3, example a banana
What is the definition of mitosis?
A type of cell division in which 2 daughter cells have the same number of chromosomes and are genetically identical with each other and the parent cell
It is a continuous process
What are the 3 broad stages of mitosis?
Interphase (synthesis and growth)
Mitosis (formation of 2 nuclei)
Cytokinesis (division of the cytoplasm)
What are the 4 stages of interphase?
G1 - growth
S - DNA synthesis
G2 - growth and prep for mitosis
M- beginning of prophase
Longest phase of the cell cycle with much metabolic activity
Name all the phases of mitosis.
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
What is prophase?
- The chromosomes condense
- Centrioles are present in animal cells, moving to opposite ends of the cell
- Protein microtubules form, radiating from each centriole, making the spindle
- nuclear envelope disintergrates and the nucleolus disappears
What is metaphase?
Chromosomes attach to the spindle fibres at their centromeres and align along the equator
What is anaphase?
- very rapid stage
- the centromere seperates and the spindle fibres shorten, pulling the now separated chromatids to the poles, centromere first
What is telophase?
- final stage of mitosis
- chromatids can be referred back to as chromosomes
- chromosomes uncoil and lengthen
- the spindle fibres break down
- nuclear envelope reforms
- nucleolus reappears
What is cytokinesis?
- division of the cytoplasm to make 2 cells
- animal cells : constriction around the equator from the outside
- plant cells: cell plate forms across the equator and extends to form a new cell wall
How does cancer occur?
- proto-oncogenes control the cell cycle by acting as a break, preventing the cell from repeating continually (tumor supressing genes)
- if these genes become damaged, a tumour can form, forming onco-genes
- some genes have the potential to cause cancer if mutated or infected with a virus
What is an oncogene?
A gene with the potential to cause cancer
What is a proto-oncogene?
A gene that currently does not have the ability to cause cancer, unless mutated
What is the definition of meiosis?
A 2 stage cell division in sexually reproducing organisms that produces 4 genetically distinct daughter cells, each with half the number of chromosomes of the parent cell
What happens in prophase 1? (meiosis)
- Paternal and maternal chromosomes come together in pairs, the pairing of chromosomes is called synapsis and each homologous pair is a bivalent
- The chromosomes coil up and condense to become shorter and thicker, visible as 2 chromatids, a spindle forms
- the chromatids wrap around eachother and then partially repel eachother but remain joined at points called chiasmata
- at the chiasmata, a segment of DNA may be exchanged, this swapping is called crossing over and is a form of genetic variation
- this genetic recombination produces a mixture of new alleles
- the nuclear envelope disintergrates and nucleolus disappears
What is metaphase 1? (meiosis)
- Pairs of homologous chromosomes arrange themselves at the equator of the spindle
- Independant assortment occurs, which is the random arrangement of chromosomes along the equator
What is anaphase 1? (meiosis)
- The chromosomes in each bivalent separate and as the spindles shorten, one of each is pulled to one pole and the other to the opposite
- Each pole only receives 1 of each homologous pair of chromosomes and because of their random assortment at metaphase, there is a random assortment
What is telophase 1? (meiosis)
- in some species the nuclear envelope reforms and the haploid group of chromosomes and the chromosomes condense and become invisible
- many species keep chromosomes in a condensed form
What is cytokinesis 1? (meiosis)
Division of the cytoplasm occurs making 2 haploid cells
What is prophase II (meiosis)
The centrioles separate and organise a new spindle at right angles to avoid the old spindle
What is metaphase II (meiosis)
The chromosomes line up along its equator, with each chromosome attached to a spindle fibre by its centromere
Independant assortment occurs because the chromosomes can face either pole
What is anaphase II? (meiosis)
The centromeres divide and the spindle fibres shorten, pulling the chromatids to different poles
What is telophase II? (meiosis)
At the poles, the chromatids lengthen and no longer can be distinguished in the microscope. The spindle disintergrates and the nuclear envelope and nucleoli reforms
What is cytokinesis II? (meiosis)
Produces 4 haploid cells from the division of the cytoplasm
What is significant about meiosis?
- the number of chromosomes remain constant from one generation to the next
- creates genetic variation (crossing over and independant assortment)
- helps keep species adaptable in changing environments
