Cell Division Flashcards
What is mitosis?
Mitosis is the division of the nucleus and is part of the cell cycle
What type of cells are produced in mitosis?
Genetically identical daughter cells
What happens in G1(growth 1)?
• organelles replicate
• increase in cell size
• protein synthesis
• respiration
What is happens in the G1 checkpoint?
• the cell size is checked
• if there is DNA damage
What happens in S phase (synthesis)?
• DNA replication
What happens in G2 (growth 2)?
• similar to G1
• synthesis of ATP
• proteins needed for cell division are made
What happens in G0 (resting stage)?
• the cell can leave the cycle
It leaves if there is any:
- DNA damage
- differentiation
- senescent cells (have reached max. Number of cell divisions)
What happens in the G2 checkpoint?
DNA replication errors are checked
What occurs in interphase in the cell cycle and how long does it take? (95%)
• Growth 1
• Synthesis
• Growth 2
12-24 hours
What stages happen in mitosis in the cell cycle and how long does it take?
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
1 hour
What happens in interphase?
The cells DNA unravels and replicates to double its genetic content and also replicated so it has spare ones. It’s ATP content is increased for cell division.
What happens in early prophase?
• nucleolus production of new ribosomes
• DNA and chromosomes condenses
• centrioles form
What happens in late prophase?
• the nucleus fades
• the nuclear membrane breaks down
• centrioles move to opposite poles of the cell
• spindle fibres form
• chromosomes continue to condense, 2 chromatids become visible
What happens in the metaphase?
M in metaphase for middle
• chromosomes align on the equator
• nuclear membrane has broken down
• each chromosome attaches to spindle fibres at the centromere
What happens in the early anaphase?
• centromeres divide and sister chromatids are pulled apart to opposite poles of the cell by the spindle fibres
What happens in late anaphase?
The spindle fibres will shorten
What happens in the telophase?
T in telophase for two cells
• chromatids reach opposite poles of the cell and chromatids unwind
• nuclear membranes reform around the two nuclei
• cytoplasm divides into 2 cells
Cytokinesis in plant cells
Microtubules transport vesicles containing cell wall material to the center of the cell creating a cell plate. The cell plate expands outward until it splits the plant cell into two daughter cells.
Cytokinesis in animal cells
A cleavage furrow forms which leaves an indentation in the plasma membrane which grows deeper and deeper until it pinches the cell into two halves
What is a centromere?
A centromere is a constricted region of a chromosome that connects sister chromatids together
How is the cell cycle regulated?
Cells can leave the cell cycle and enter the G0 or resting stage
This can be temporary this could be because the cell isn’t big enough or new cells aren’t needed at that time
It can also be permanent because the cells have undergone differentiation or bc the DNA of the cell is damaged
What is terminal differentiation?
Cells may differentiate and become so specialised that they are unable to divide anymore
E.g neurones and muscle cells
What happens if a mutation occurs?
This can result in the production of abnormal checkpoint proteins
Cancer is a group of many different diseases all cause by uncontrolled cell division resulting in a mass of undifferentiated cells called a tumour
What is meiosis for?
Meiosis is essential for sexual reproduction as it produces gametes (sex cells)
What does meiosis produce?
Gametes (sex cells) that are haploid cells which are genetically different (genetic variation)
What type of cells are gametes?
Haploid cells (2n)
What happens in prophase 1 in meiosis?
Homologous chromosomes pair up (bivalents)
What happens in metaphase 1 in meiosis?
Homologous chromosomes line up at the equator
• random arrangement and crossing over can occur (genetic variation occurs)
What happens in anaphase 1 in meiosis?
Separation of homologous chromosomes
No separation of centromeres
•independent assortment of homologous chromosomes
• many different combinations of male and female chromosomes on either side of the equator
What happens in telophase 1 in meiosis?
The formation of two daughter cells and it produces 2 haploid cells
Is there an interphase between meiosis 1 and 2?
No
What happens in prophase 2 in meiosis?
• the nuclear membrane breaks down
• DNA condenses
• centrioles move towards opposite poles
What happens in metaphase 2 in meiosis?
• chromosomes line up on the equator
• spindle fibres attach to centromeres
What happens in anaphase 2 in meiosis?
• spindle fibres shorten
• centromere splits and the chromosomes divide
• chromatids more towards poles
What happens in the telophase 2 in meiosis?
It produces 4 genetically different cells (gametes)
What are homologous chromosomes?
Chromosomes that carry genes for the same characteristics at the same gene locus (location) one is paternal and the other is maternal
What is crossing over?
• genetic variation
Spindle fibres pull apart the homologous chromosomes. The chromatids twist around each other and bits of chromatids swap over. The chromosomes still contain the same genes but now have a different combination of alleles.
What is independent assortment?
• genetic variation
When homologous chromosomes line up in metaphase 1 and are separated in anaphase 1, it’s completely random which chromosome from each pair ends up in which daughter cell.
So the four daughter cells produced by meiosis have completely different combination of those maternal and paternal chromosomes
Where and why does asexual and sexual reproduction occur?
Most common in plants as they can’t move to find mates
e.g insects, yeast, worms, jellyfish
Use an example to explain when budding may occur.
For example yeast can reproduce asexually by budding when conditions are good but will reproduce sexually when conditions are less favourable
What happens in budding?
• DNA replication in the nucleus
• Cell wall weakens causing extrusion of cytoplasm
• Chitin ring starts to form
• Nucleus migrate
• One nucleus moves into bud with organelles
• Cytokinesis - formation of new chitin cell wall between mother and daughter cell
• Daughter cell increases in size
