Cell Division Flashcards
What is dna
DNA is a molecule which carries the instructions (genes) which controls the activity if the cell
What is a chromatin
In eukaryotes DNA is tightly wrapped around proteins called histones. The DNA and histone proteins together are called chromatin which can be made visible by staining
What is a single chromosome
 Is one long linear double stranded molecule of DNA. single chromosomes are relaxed and not visible under a light microscope
What is a duplicated chromosome (relaxed)
Chromosomes are replicated before a cell divides each chromosome consists of two genetically identical copies called sister chromatids how together by a shared centromere
What is a duplicated chromosome (supercoiled)
During mitosis chromosomes shorten and thicken so they are sturdy enough to move around the cell. individual chromosomes are only visible when they are super coiled
In humans the normal diploid number of chromosomes is
46
Chromosomes exist in pairs called
homologous pairs. human cells normally contain 23 pairs of chromosomes
Homologous chromosomes are
The same size and same shape and carry the same genes
Sex cells are
Haploid cells
The cell cycle is divided into what is three main stages
Interphase, mitosis and cytokinesis
Describe what happens during interphase
During stage G1 Proteins are synthesised and organelles are replicated (5hr)
During stage S DNA is replicated (7hr)
During stage G2 the cell grows (3hr)
Describe what happens in mitosis
Mitosis has four stages prophase metaphase anaphase and telophase and it involves the division of a nucleus into two genetically identical nuclei
Describe what happens during cytokinesis👍🏻
The cytoplasm divides to produce 2 genetically identical cells
How can cells in interphase be recognised
- they have no visible chromosomes because they’re relaxed
- they have a visible nucleus because the nuclear envelope is still intact
Mitosis increases cell number for
- tissue growth
- tissue repair
- asexual reproduction in some organisms
Describe what happens during prophase
Chromosomes shorten and thicken (supercoil) So become visible. Each consists of two chromatids joined by a centromere and the nuclear envelope disintegrates. centrioles move to opposite poles of the cell and they start to make spindle fibres
Describe what happens during metaphase
Chromosomes attach to spindle fibres by the central mass and move towards the cell equator and they align on the equator
Describe what happens during anaphase
The centromere split and the spindle fibres contract and shorten the chromatids are then pulled apart and move to opposite poles of the cell. The centromeres move first
What happens during telophase
Chromosomes relax (uncoil)at this cell pose meaning they become indistinct and the nuclear envelopes form around each set of chromosomes to nuclei form and cell goes into cytokinesis
What is meiosis? 
Meosis this a type of cell division which involves two divisions of the parent cells to produce for genetically different daughter cells.
What happens during meiosis?
Homologous chromosome pairs, separate during the first division and sister chromatids separate during the second division these daughter cells are called gametes which are sex cells and therefore the parent cells diploid. The daughter sex cells will be haploid. This is important as it leads to sexual reproduction and genetic variation.
Compare mitosis and meiosis
Mitosis has one division meiosis has two divisions
Mitosis produces two genetically identical daughter cells. Where as meiosis produces four genetically different cells
In mitosis, the number of chromosomes that the daughter cell has is the same as the parent cells in meiosis, it is not
Mitosis is used for growth and repair and asexual reproduction. Where is meiosis is used for sexual reproduction and genetic variation. 
What is a tumour?
A Mass of abnormal and differentiated cells produced by uncontrolled cell division 
What is a malignant tumour?
-malignant tumours cause cancer
-grow rapidly
-Invade and destroy surrounding tissues
-Cancer cells can break off from the tumour and migrate to other parts of the body and blood or lymph to set up secondary tumours elsewhere in the body. This process is called metastasis. 
What is a benign tumour
-they do not cause cancer
-Grow slowly
-Do not invade and damage surrounding tissues?
-Do not undergo metastasis?
-Are usually harmless
-May damage organs are found in or cause blockages or pressure on surrounding organs
The rate of the normal cell cycle is controlled by
Regulatory genes called Proto-oncogenes and tumour suppressor genes. These genes code for proteins to ensure that the cell cycle starts and stops when it should.
Mutation of these regulatory genes is characterised by
An unusually large proportion of cells undergoing mitosis, leading to unusually rapid cell division
What do proto-oncogenes code for?
Regulatory proteins that stimulate cell division. Mutated proto-oncogenes are called oncogenes. They overproduce the regulatory proteins, so that so division occurs too rapidly.
What do tumour suppressor genes code for
Regulatory proteins that inhibit cell division. Mutated tumour, suppressor genes produce a non-functional regulatory protein that fails to inhibit so division division occurs to rapidly.
What are the genetic factors that cause cancer?
Some cancers are caused by inheriting, mutated alleles of the genes that controls cells division. These are called hereditary gene mutations.
What environmental factors cause cancer
Some cancers are caused by a car acquired Jean mutations of the genes that controls cell division. Exposure to radiation, mutagenic, chemicals, and high fat diet will increase the chances of a person developing certain cancers. Environmental changes can cause epigenetic changes during a persons lifetime such as Abnormal methylation of genes control inside a vision. These changes can also be inherited. 
What prevents getting cancer from genetic factors?
-genetic screening to identify people who carried the mutated allele
-Regular screening for signs of cancer because the earlier the diagnosis is May, the greater the chance of effective treatment and recovery
-Preventative surgery for example, women with the BRCA1 mutation may choose to have their breast removed

What helps prevent environmental factors from causing cancer?
UV radiation in sunlight is a mutagen, its genes that controls cell division in the skin. White people are more at risk of developing skin cancer as the skin has less melanin. Melanin protect the skin from the UV radiation in sunlight. Avoiding excessive exposure to the Sun or using sunscreen is the block UV radiation reduces the risk of developing skin cancer
