π©Ά 3.2.2 All Cells Arrise From Other Cells Flashcards
(25 cards)
Can all multicellular organisms divide?
No, within multicellular organisms, not all cells retain the ability to divide
What do eukaryotic cells that do determine the ability to divide show?
They show a cell cycle
When does DNA replication occur?
It occurs during interphase of the cell cycle
What is the purpose of mitosis?
- For eukaryotes to grow
- For eukaryotes to replace damaged cells
- For eukaryotes to asexually reproduce
Define mitosis
The process of cell replication in eukaryotes resulting into genetically identical daughter cells
Define chromosome
Double or single structure composed of linear DNA wrapped around histone proteins
Define chromatid
Identical sister chromatids make up the double structure of a chromosome when joined together with a centromere
Define centromere
These join the identical sister chromatids together
Define centriole
Organelles which produce spindle fibres in order to make the chromosomes
Define spindle fibres
Proteinous structures which connect the centrioles to the centromeres
Define cytokinesis
Division of the cytoplasm during telophase
What is the first step of mitosis called and what happens during it ?
It is called prophase.
- the chromosomes shorten, thicken and therefore condense thus becoming more visible
- each chromosome can be seen to consist of two identical, sister chromatids joined via a centromere
- the nuclear membrane breaks down and centrioles move towards either pole
What is the second step of mitosis called and what happens during it?
It is called metaphase.
- each chromosome is joined, via its centromere, by spindle fibres to the centrioles
- the chromosomes are lined up in single file along the equator of the cell
What is the third step of mitosis called and what happens during this stage ?
This step is called anaphase.
- the spindle fibres contract and each of the identical, sister chromatids are pulled to the opposite pole
- the centromeres divide
- the chromatids form a characteristic β V β shape
What is the fourth step of mitosis called and what happens during this stage?
It is called telophase.
- the identical sister chromatids now start to be referred to as chromosomes again
- the chromosomes start to lengthen again
- the cytoplasm divides (cytokinesis) and the cell membrane of the two identical, daughter cells (clones) reforms
- the nuclear membrane reforms in the two new cells
What is the product of mitosis?
Two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication
What kind of process is mitosis?
It is a controlled process
What can uncontrolled cell division lead to ?
The formation of tumours of cancer
What do many cancer treatments focus on doing ?
Many cancer treatments are directed at controlling the rate of cell division
Which organisms donβt undergo cell division and why?
Viruses donβt undergo cell division as they are non living. Instead, after the injection of their nucleic acid, the infected host cell replicates the virus particles
Which organisms do binary fission?
Prokaryotes - specifically bacteria cells
Give the method for binary fission
1- circular DNA replicates
2- plasmids replicate many times unpredictably
3- semi conservative replication occurs
4- circular DNA moves to either pole
5- plasmids move to poles
6- the cell elongates
7- cytoplasm divides
8- cell wall reforms
9- plasmids may divide unequally so they are not referred to as clones or identical cells
Describe the steps of how to prepare a temporary mount and estimate the size of a cell
- cut the specimen thinly to allow light to penetrate the single layer of cells
- a drop of water can assist this
- when adding the specimen to the slide, add stain to make organelles visible and supply contrast
- add the coverslip to the specimen, lowering it with a mounted needle, and press firmly down to ensure the specimen is one cell thick and so any air bubbles are removed
- the microscope needs to be calibrated in order for cells to be measured
- a random number generator can be used to choose the cells to measure in order to not be biased
- many cells need to be measured in order to make the sample representative
(The above two points are done to increase reliability) - a mean size of cells can be calculated
When measuring an organism on the stage what do you use ?
An eye piece graticule