All cells arise from other cells Flashcards
What type of cell does binary fission occur
Prokaryotic cells
Where is the genetic information stored in prokaryotic cells
Circular DNA and plasmids
Describe the process of binary fission
1) Bacteria replicates by binary fission
2) Replication of circular DNA
3) Division of cytoplasm to produce 2 daughter cells
4) Each with single copy of circular DNA
Define mitosis
Production of two genetically identical daughter cells that have the same number of chromosomes as the parent cell and each other
Where does mitosis occur
In body cells / somatic cells
Define homologous chromosomes
Two chromosomes that carry the same gene
Define interphase ( mitosis)
- Chromosomes have disappeared
- Each chromosomes replicated
- Chromosomes made up off 2 sister chromatids joined at centromere
Define prophase ( mitosis)
- Chromosomes shorten and thicken to become visible
- Nuclear envelope breaks down
- Centrioles move to the poles of the cell and start forming spindle fibers
- Chromosomes appear as chromatids joined at the centromere
Define metaphase ( mitosis)
- Chromosomes line up at the equator
- Chromosomes attach to spindle fibers by their centromere
Define anaphase ( mitosis)
- Spindle fibers contract
- The centromere splits
- Sister chromatids are pulled to opposite poles
Define telophase ( mitosis)
- Spindle fibers break down
- Nuclear envelope reforms
- Chromosomes disappear
- Chromosomes uncoil and become thinner
- Cytokinesis begins
Define meiosis
Production of four genetically different daughter cells that have half the number of chromosomes as the parent cells
Where does meiosis occur
Production to make sex cells ( gametes)
Define interphase 1 ( meiosis)
- Chromosomes are dispersed ( uncoil)
- Each chromosomes replicated
Define prophase 1 ( meiosis)
- Chromosomes shorten and thicken to become visible
- Chromosomes appear as two sister chromatids joined at centromere
- Homologous pairs of chromosomes from bivalents
- Chiasm from where the chromosomes cross over each other
- This produces a new combination of alleles
Define metaphase 1 ( meiosis)
- Homologous chromosomes ( in bivalents) line up on the equator
- Chromosomes attached to spindle fibers by their centromere
- Independent segregation of the homologous chromosomes will result in a different combination of alleles within the daughter cells
Define anaphase 1 ( meiosis)
- Homologous chromosomes are pulled apart to opposite poles
Define telophase 1 ( meiosis)
- Chromosomes uncoil and become thinner
- Cytokinesis begins
Define prophase 2 ( meiosis)
- Chromosomes shorten and thicken to become visible
- Chromosomes appear as a pair of sister chromatids joined at the centromere
Define metaphase 2 ( meiosis)
- Chromosomes line up on the equator
- Chromosomes attached to spindle fibers by their centromere
Define anaphase 2 ( meiosis)
- Chromatids are pulled to opposite poles
- By contraction of spindle fibers
Define telophase 2 ( meiosis)
- Chromosomes uncoil and become thinner
Define cytokinesis ( meiosis)
- Cytoplasm divides
- Membranes form around new cells
- 4 haploid cells produced
What is the difference between meiosis 1 and meiosis 2
Meiosis 1 - Homologous pairs of chromosomes are separated ( reductive division)
Meiosis 2 - Pairs of chromosomes are separated ( non- reductive division)
What is the difference between meiosis and mitosis
Meiosis-
1) Reduces the chromosome number
2) Crossing over and independent segregation
3) Two divisions
4) Genetically different
Mitosis-
1) Maintains the same chromosome number as in the parent nucleus
2) No crossing over nor independent segregation
3) One division
4) Genetically identical
What is crossing over
Homologous pairs of chromosomes form a bivalent. Chiasmata form alleles are exchanged. Producing new combinations of alleles
What is independent assortment
How different combination of homologous chromosomes can be separated during anaphase 1 leading to genetically unique gametes
How does meiosis result in variation
- Homologous chromosomes pair up
- Independent segregation
- Maternal and paternal chromosomes are re-shuffled in any combination
- Crossing over leads to exchange of parts of (non-sister) chromatids/ alleles between homologous chromosomes
- Both creating new combination of alleles
Why is meiosis is important in sexual reproduction
Produces haploid cells so fertilisation maintains the chromosomes number in next generation
What is the cell cycle
The cell cycle is an ordered set of events, leading to cell growth and division
Describe the cell cycle
1) Interphase occupies most of the cell cycle
- G1 phase : synthesis of proteins
- S phase : DNA is replicated
- G2 phase : Organelles grow and divide, ATP stores increased
2) Nuclear division
- Mitosis
3) Cell division
- Cytokinesis
Where are the 3 main checkpoints in the cell cycle
1) G1/S - can DNA synthesis begin?
2) G2/M - has DNA synthesis been done correctly?
3) Spindle - all chromosomes attached to spindles ( can sister chromatids separate correctly) ?
What is cancer
Is essentially the incorrect replication of DNA. It is the result of damage to the genes that control cell mitosis and the cell cycle
How is cancer often treated
By blocking some part of the cell cycle. Prevent DNA replication. Inhibiting the metaphase by interfering with spindle formation
What is the problem by using drugs that inhibit the cell cycle for treating cancer
Mostly effective against rapid cell division but they also disrupt the cell cycle of healthy cells. Hair producing cells divide rapidly, explaining hair loss
Why are tumours damaging to the body
May damage organ concerned, cause blockage and they may exert pressure on other organs
