Cell Division Flashcards
The cell cycle
- Interphase
This is the period between divisions. The majority of the life of the cell is spent in INTERPHASE G1,
G1 phase- Cell increases in size and new biomass is made
S phase- DNA replicates by semi-conservative DNA replication
G2 phase- Cell gets ready for division, synthesis & stores of ATP and new organelles synthesised.
- Nuclear Division (Mitosis or Meiosis)
Period when the nucleus divides into two, or 4. - Cell Division (Cytokinesis)
Division of the cytoplasm to produce two new cells or four new cells.
Gene definition
section of DNA that codes for one polypeptide
Chromosome definition
independent DNA molecule which has been supercoiled into a condensed form
Chromosome structure
During semi conservative DNA replication, 2 genetically identical copies of the DNA molecule are made.
They remain attached at a central point called the centromere.
Each of the DNA copies now supercoils using histones
While they are still joined, the two condensed DNA molecules are called identical sister chromatids.
The whole structure is the chromosome.
Homologous chromosomes definition
have the same genes in the same gene loci but may have different alleles of the genes.
Calculating diploid and haploid cells
diploid = 2n
haploid = n
n = number of chromosomes
What is mitosis used for?
- Increasing cell numbers and growth of an organism
- Repair of damaged tissues (not cells)
- Replacement of worn out/ dead cells
What is mitosis?
DNA molecules are replicated, the identical copies separated and are passed on to the two daughter cells.
The 2 daughter cells are genetically identical.
They have the same number of chromosomes as the parent cell.
They are genetic clones of each other.
It is also used by some organisms for asexual reproduction
Prophase
1) The nuclear membrane starts to break down.
2) The centrioles start to move to the poles of the cell and make spindle fibres
3) The chromosomes supercoil and condense
4) Each chromosome appear as 2 identical sister chromatids joined at the centromere
Metaphase
1)The centrioles complete the production of spindle fibres
2)The chromosomes are attached to the spindle fibres by their centromere
3) the chromosomes align down the equator of the cell.
Anaphase
1) The spindle fibres contract/shorten.
2)The centromere splits
3)The identical sister chromatids are pulled to
opposite poles
4) making a “V” shape
Telophase
1)A nuclear membrane starts to reform around each set of chromosomes
2)The chromatids unwind and become invisible
Unregulated Mitosis
- Tumour suppressor genes code for proteins that slow down the cell cycle.
- Proto-onco genes code for proteins that speed up the cell cycle
Mutation= uncontrolled cell division= tumour develops
Treating cancer
One method is to give drugs that inhibit cell division
These drugs may stop:
DNA replication, spindle formation, Cytokinesis or other processes linked to mitosis
Binary Fission
- Replication of (circular) DNA;
- Replication of plasmids;
- Division of cytoplasm to produce daughter cells
Virus Replication
Being non-living, viruses do not undergo cell division.
Following injection of their nucleic acid, the infected host cell replicates the virus particles.
Viruses can only replicate inside host cells.
use the host cell enzymes to replicate and transcribe viral DNA and translate viral proteins, making more virus particles, which then burst out of the cell.
Preparation of plant roots
50 °C Hydrochloric acid:
To break down the cellulose cell walls, ensuring the stain can enter and the tissue and the root tissue can be squashed into a layer one cell thick so that light passes through the thin sample of tissue
Ethano-orcein stain:
To stain the chromosomes so they can be viewed under the microscope.
Mitotic Index
Number of cells with condensed chromosomes / total number of cells
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.
- Examine many cells;
- To ensure representative sample;
OR
3. Repeat count;
4. To ensure figures are correct;
Serial Dilution
M1 X V1 = M2 X V2
M1 = Desired diluted concentration (mol dm-3)
V1 = Desired Volume (cm3)
M2 = Original concentration (mol dm-3)
V2 = Unknown Volume of stock solution (cm3)
Meiosis
used by diploid organisms to produce haploid gametes for sexual reproduction.
increases variation within the population.
Meiosis results in four genetically different daughter cells.
halves the chromosome number before fertilisation to restore the full chromosome number at fertilisation 2n.
Meiosis process
DNA is replicated in S phase (interphase) of the cell cycle. The chromosomes then go through two nuclear divisions.
Each division has a prophase, metaphase, anaphase and telophase.
In the first meiotic division, the homologous chromosomes pair up and are separated
In the second division, the chromatids are separated.
Causes of Variation
mutations
random fertilisation
crossing over (occurs in meiosis 1)
independent segregation (occurs in meiosis 1)
Crossing over
- The homologous chromosomes associate. Bivalent is formed
- Chiasmata form
- Equal lengths of alleles are exchanged.
- Producing new combinations of alleles.
(during prophase or metaphase)
INDEPENDENT SEGREGATION
homologous chromosomes attach to the spindle fibres and they pair up side by side and can be reshuffled in any combination.
- maternal and paternal chromosomes are arranged in any order
Give two differences between mitosis and meiosis.
Mitosis given first
1. One division, two divisions in meiosis;
2. (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
3. Two cells produced, (usually) four cells produced in meiosis;
4. Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
5. Separation of homologous chromosomes only in meiosis;
6. Crossing over only in meiosis;
7. Independent segregation only in meiosis;
