Cell Cycle and Cell Division Flashcards
Interphase
This is the period between divisions.
G1 phase
Cell increases in size
New proteins are made
S phase
DNA replicates by semi-conservative DNA replication
G2 phase
Cell prepares for division
New organelles synthesised.
Phases within interphase
G1 phase
S phase
G2 phase
Cell cycle stages
- Interphase
- Nuclear Division
- Cytokinesis
Nuclear Division
Period when the nucleus divides into two (mitosis), or four (meiosis).
Cytokinesis
Division of the cytoplasm which follows nuclear division and is the process by which the cytoplasm divides to produce two new cells (mitosis) or four new cells (meiosis).
Chromosome definition
A chromosome is an independent DNA molecule which has been supercoiled into a condensed form. Chromosomes contain many different genes.
Different species may have different numbers of chromosomes and genes specific to that species.
What are replicated chromosomes attached by?
Centromere
While they are joined, what are the two condensed chromosomes called?
Identical sister chromatids
Homologous chromosomes definition
Have the same genes in the same gene loci but may have different alleles of the genes.
One chromosome is Maternal and the other is Paternal.
Mitosis is used for?
Repair of damaged tissues
Replacement of dead cells
Growth of an organism
Mitosis stages
Prophase
Metaphase
Anaphase
Telophase
Prophase in mitosis
1) The nuclear membrane starts to break down.
2) The chromosomes supercoil and condense and become visible.
3) Each chromosome appears as 2 identical sister chromatids joined at the centromere
Metaphase in mitosis
1)The chromosomes are attached to the spindle fibres by their centromere
2) the chromosomes align down the equator of the cell
Anaphase in mitosis
1) The spindle fibres contract.
2)The centromere splits
3)The identical sister chromatids are pulled to opposite poles, making a “V” shape
Telophase in mitosis
1)A nuclear membrane starts to reform around each set of chromosomes
2)The chromosomes unwind and become invisible.
Sister chromatid definition
One of the two strands of a replicated chromosome that are joined together by a single centromere prior to cell division
Gene definition
A section of DNA which codes for the primary structure of a polypeptide
Haploid cell definition
Cell that contains only a single copy of each chromosome
Diploid cell definition
Cell in which the nucleus contains two sets of homologous chromosomes.
Somatic cell definition
A normal body cell
Cancer definition
Cells that undergo rapid uncontrolled 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.
Which genes code for proteins that slow down the cell cycle?
Tumour suppressor genes
Which genes code for proteins that speed up the cell cycle?
Proto-onco genes
What occurs if the proto-onco genes or tumour suppressor genes are mutated?
1) The cell cycle occurs uncontrollably
2) It is often rapid and the cells produced are abnormal and so a tumour develops
3) If these cells start to spread into the surrounding tissues/body, the tumour is regarded as a cancer.
How can cancer be treated?
One method is to give drugs that inhibit cell division
What will the cell division inhibition drugs do?
These drugs may stop:
DNA replication, spindle formation, Cytokinesis or other processes linked to mitosis.
What does binary fission involve?
- Replication of circular DNA and plasmids
- Division of the cytoplasm to form two daughter cells, each with a copy of the circular DNA and plasmids
Virus replication (In steps)
- Attachment proteins on the virus attach to receptors of the host cell
- The viral nucleic acid enters the host cell’s cytoplasm
- The virus’ DNA is inserted into the host cell’s DNA
- The viral DNA is transcribed and translated into viral proteins
- The cell replicates the viral DNA
6.The genetic material is assembled into virions - These virions eventually burst out of the cell, destroying it
Prepartion of plant root tips to observe mitosis: what solutions should the plant be soaked in and why?
50 °C Hydrochloric acid to break down the cell wall, ensuring the stain can enter and the tissue and the root tissue can be squashed into a one cell thick layer, so that light passes through the thin sample of cells.
KI solution - To stain the chromosomes so they can be viewed under the microscope.
Mitotic Index equals to?
Number of cells in mitosis / Total number of cells
Meiosis summary
This form of cell division is used by diploid organisms to produce haploid gametes for sexual reproduction.
Why is meiosis important?
It increases variation within the population
It halves the chromosome number before fertilisation to restore the full chromosome number at fertilisation
What does meiosis result in?
4 genetically different haploid daughter cells
Prophase 1 in Meiosis
Chromosomes supercoil, condense and become visible.
Metaphase 1 in Meiosis
Homologous pairs of chromosomes pair up to form a bivalent and align along the equator.
Spindle fibres attach to the centromere.
Crossing over and independent segregation occurs here.
What is formed when the homologous chromosomes pair up?
A bivalent
Anaphase 1 in Meiosis
Spindle fibres contract and separate homologous chromosome pairs, pulling one of each pair to opposite poles of the cell.
Telophase 1 in Meiosis
Nuclear membrane reforms around the separated homologous chromosomes.
What happens at the end of Meiosis 1?
Each daughter cell is now HAPLOID (n).
Prophase 2 in Meiosis
Each daughter cell is now haploid so only contains one chromosome from each homologous pair
Metaphase 2 in Meiosis
Each chromosome aligns along the equator
Anaphase 2 in Meiosis
Non-Sister chromatids are split by their centrome and pulled to opposite poles of the cell.
Telophase 2 in Meiosis
Nuclear membrane reforms.
What is the result of Meiosis 2?
Four genetically different different haploid daughter cells are produced.
Crossing over stages
- The homologous chromosomes form a bivalent once paired along the equator
- Chiasmata forms
- Equal lengths of chromatids are exchanged.
- Producing new combinations of alleles.
What is the key word for crossing over?
It is RARE
When does crossing over occur?
Metaphase 1 in Meiosis
Independent Segregation of Homologous chromosomes
During Metaphase 1, the homologous chromosomes attach to the spindle fibres and they pair up side by side and can be reshuffled in any combination.
This increases genetic variation
What is the key word for independent segregation?
It is RANDOM
