2.2 All cells arise from other cells (including Required Practical 2) Flashcards
What is the cell cycle?
Cells that don’t divide continuously but undergo a regular cycle of division separated by periods of cell growth are said to have a cell cycle
What are the three stages of the cell cycle?
- interphase
- nuclear division
- cytokinesis
What is interphase? (Cell cycle)
It occupies most of the cell cycle and is sometimes known as the resting phase because no division takes place
What is nuclear division?
When the nucleus divides either into two during mitosis or four during meiosis
What is cytokinesis?
Division of cytoplasm which follows nuclear division
What is the length of the cell cycle?
- complete cycle length varies greatly between organisms
- typically, a mammalian cell takes about 24 hours to complete a whole cycle (90% of this time the cell is in interphase)
What are the 5 stages of mitosis?
- interphase
- prophase
- metaphase
- anaphase
- telophase
Describe interphase.
- occupies most of the cell cycle, and is sometimes known as the resting phase because no division takes place
- lots of cellular activity which includes the replication of DNA
Describe prophase.
- the chromosomes condense (shorten and thicken) so that they can be seen
- centrioles move to opposite ends of the cell and spindle fibres develop from them. Together spindle fibres are known as spindle apparatus
- nucleolus disappears and nuclear envelope breaks down
Describe metaphase.
- the chromosomes are pulled along the spindle apparatus by their centromeres and arrange themselves along the equator of the cell
Describe anaphase.
- the centromeres divide in two and the spindle fibres pull the chromatids apart
- the chromatids move to their respective poles and we now refer to them as chromosomes again
- the energy for this process is provided by the mitochondria
Describe telophase.
- chromosomes reach their respective poles and become longer and thinner, finally disappearing completely (leaving widespread chromatin)
- spindle fibres disintegrate and the nuclear envelope and nucleolus reform
- cytoplasm divides in a process called cytokinesis
What is mitosis?
Division of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell (except for mutations which are rare)
What is the importance of mitosis?
- growth
- repair
- reproduction (single cells organisms)
How can cell division take place?
Either by mitosis or meiosis
Factors of mitosis (x11)
- DNA is copied exactly (if there are no mutations)
- the daughter (new) cells are copies of the parent cell
- daughter cells have the same number of chromosomes as the parent cell
- chromosomes of the parent cell are duplicated in the daughter cells
- enables a species to colonise an area quickly using asexual reproduction
- important for the growth of plants and animals
- produces clones
- important for the repair of damaged tissue where new cells must be identical to damaged cells
- the original (parent cells) become 2 daughter cells
- when out of control, a cancerous tumour may result
- produces cells with the diploid number of chromosomes
Factors of meiosis (x11)
- 4 daughter cells are made
- cell division by reduction
- forms gametes (sex cells)
- increases the variety of offspring - provides a varied stock of individuals
- happens only in gamete producing organs (testes, ovaries, pollen, sacs, ovules)
- the daughter cells contain half the number of chromosomes as the parent cell
- produces new genetic combinations in individuals
- ensures that the number of chromosomes remains the same in sexually reproducing organisms
- enables a species to adapt to a changing environment or to colonise new environments
- halves the number of chromosomes in cells
- produces cells with the haploid number of chromosomes
Describe stem cells
- the first group of cells in an embryo are initially identical
- all cells are produced through mitosis division and contain the same genes
- only some genes are switched on
- different genes are switched on depending on the cells specialism
What is cancer?
- group of diseases caused by a growth disorder of cells
- it is the result of damage to the genes that regulate mitosis and the cell cycle
- if the cell cannot regulate its growth this could lead to uncontrolled growth and division of cells. These uncontrolled cells form a growth (tumour) which keeps growing
Where can tumours develop?
- they can develop in any organ in the body
Where a tumours most commonly found?
- most commonly in; lungs, prostate gland (in males), breasts and ovaries (in females), large intestine, stomach, oesophagus and pancreas
When do tumours become cancerous?
- if they change from benign to malignant
What are the problems with treating cancer?
- using these kinds of drugs also disrupts the cell cycle of normal cells
- however the drugs are more effective against rapidly dividing cells such as cancer cells
- normal body cells that divide rapidly include hair-producing cells which explains hair loss during cancer treatment
What are the treatments for cancer?
-often involves killing dividing cells by blocking part of the cell cycle
- drugs used to treat cancer (chemotherapy) usually disrupt the cell cycle by preventing DNA from replicating and inhibiting the metaphase stage of mitosis by interfering with spindle formation
