B3 Cell Division and Sex Determination Flashcards
what are the three stages of cell division
- interphase
- mitosis
- cell cytokinesis
summarise what happens during interphase
the cell grows and DNA is copied
what is interphase
the longest phase of the cell cycle
a period of intense metabolic activity of the nucleus
what three metabolic activities occur during interphase
- The cell grows by - replicating DNA - producing proteins and cytoplasmic organelles.
- Centrioles divide in an animal cell.
- Chromosomes appear as long thin threads called chromatin. Just before the cell divides, each chromatin thread replicates, producing two identical sister chromatids joined at the centromere.
what are the four stages of mitosis
Prophase
Metaphase
Anapahse
Telophase
what stages of mitosis is the longest
prophase
what happens in prophase
• Nuclear envelope disintegrates. Nucleolus disappears.
• Chromatin threads condense, coil
and shorten to become discrete chromosomes observable under a light microscope.
• In animal cells, centriole pairs migrate to opposite poles of the cell.
• Spindle fibres continue to develop.
what happens in metaphase
- Spindle fibres (microtubules) attach to both sides of the centromere of each chromosome.
- Chromosomes migrate and align singly at the metaphase (equatorial) plate.
what is the shortest stage fo mitosis
anaphase
what happens in anaphase
• Centromeres divide and sister chromatids are
separated to become daughter chromosomes.
• Spindle fibres (microtubules) shorten and pull
daughter chromosomes to opposite poles of the
cell.
• Daughter chromosomes move with centromeres
leading, producing a characteristic ‘V’ shape pattern.
what happens in telophase
• Spindle fibres (microtubules) break down / disassemble.
• Nucleolus and nuclear envelope re-form.
• Chromosomes uncoil and decondense to
become thin chromatin threads.
what are the three reasons for which we need mitosis
- Genetic stability
- Growth, repair and regeneration
- Asexual reproduction
how does mitosis aid genetic stability
Mitosis produces two daughter cells with the same number of chromosomes. This ensures the preservation of genetic stability across generations.
how does mitosis aid growth, repair and regeneration
o Growth – increasing cell numbers
o Repair of tissues – damaged cells are replaced by exact copies of the original
o Regeneration – replacement of worn out cells
how does mitosis aid asexual reproduction
Offspring is genetically identical to parent, ensures preservation of favourable traits from generation to generation
in terms of cell, how many cancer cells initially arise
A cell may be stimulated to divide, differentiate or die by signals released by neighbouring cells.
what are the four checkpoints
G0
G1
G2
M
what happens in the G1 checkpoint
assessment of cell growth
checks for growth factors, DNA damage and cell size
apoptosis will occur if DNA is damaged and cannot be repaired
what happens in the G2 checkpoint
assessment of DNA replication
checks if DNA is successfully replicated without damage apoptosis occurs if there is irreparable damage
what happens in the M checkpoint
assessment of mitosis
occurs at metaphase
checks for formation of spindle fibres
mitosis is arrested if spindle fibres are not formed
how does cancer cells escape cell cycle control and what does this result in
Cancer cells have escaped precise cell cycle control due to mutation in cell cycle control genes, such that they proliferate indefinitely.
o loss of function mutation of tumour suppressor gene
o gain in function mutation of proto-oncogene to form an oncogene
what is cancer the result of
Cancer is the result of changes in cells that lead to uncontrolled growth and division.
define meiosis
division that produces daughter cells, known as gametes, in which the chromosome number is halved from diploid to haploid so they have a single set of chromosomes
where does meiosis occur
• occurs only in sex cells in sexually reproducing organisms