Cell cycles Flashcards
What are the two main phases of eukaryotic cell division?
Interphase and mitotic (division) phase
Mitosis- the nucleus divides
Cytokinesis- the cytoplasm divides
What happens during interphase?
DNA is replicated and checked for errors
Mitochondria/ chloroplasts etc grow and divide, increasing in number
Protein synthesis occurs
Normal metabolic processes of the cell
What are the stages of interphase and what happens in them?
G1- growth 1 (organelle replication, cell increases in size)
S- synthesis (DNA is replicated)
G2- growth 2 (cell continues to increase in size and the replicated DNA is checked for errors)
What is G0 and why can a cell enter it?
When the cell leaves the cell cycle due to:
1- differentiation (a specialised cell is no longer able to divide so it cannot enter the cell cycle again)
2- dna may be damaged
What checkpoints occur during the cell cycle?
G1- cell size, DNA damage
G2- cell size, DNA damage, DNA replication
Metaphase- spindle assembly checkpoint (check for chromosome attachment to spindle)
What is mitosis and why is it important?
The process in which a eukaryotic cell divides to form two genetically identical daughter cells
Used for growth, replacement and repair of tissues and asexual reproduction
How do chromosomes form chromatids?
A chromosome is replicated to form two chromatids.
Two chromatids are joined together at the centromere.
What are the stages of mitosis?
Prophase- chromatin fibres begin to coil and condense to form chromosomes that are visible, nucleolus disappears, nuclear membrane and envelope breaks down, centrioles migrate to opposite poles of the cells and spindle fibres attach to them (to move chromosomes)
Metaphase- chromosomes are moved to the centre of the cell (metaphase plate) by the spindle fibres
Anaphase- the chromatids are separated and pulled to opposite ends of the cells by the spindle fibres
Telophase- chromatids are now called chromosomes again, nuclear envelope forms around the chromosomes, chromosomes begin to uncoil and nucleolus reforms
How does cytokinesis differ in animal and plant cells?
The actual division of the cell into two separate cells
Animals- cleavage furrow forms in the middle of the cell and the cell surface membrane is brought inwards by the cytoskeleton
Plants- cannot form a cleavage furrow due to their cell walls. Vesicles from the golgi apparatus fuse together and with the cell surface membrane. New sections of the cell walls form around the new sections of membrane.
What is meiosis and what is it used for?
Type of cell division used for the production of gametes.
Gametes need to have half the number of chromosomes (haploid)- reduction division
Produces 4 genetically different daughter cells
What are homologous chromosomes?
Matching sets of chromosomes, same genes but different alleles from each parent.
What happens in meiosis 1 and 2?
Meiosis 1- pair of homologous chromosomes are separated (reduction division)
Meiosis 2- chromatids are separated
Describe the process of meiosis
Prophase- DNA condenses and becomes visible as chromosomes, nucleolus disappears, nuclear envelope breaks down,spindle fibres form, homologous chromosomes pair up forming bivalents
Metaphase- homologous pairs of chromosomes line up at the equator of the cell, with spindle fibres attached at the centromere
Anaphase- homologous pairs of chromosomes are separated to opposite ends of the cell, centromeres do not divide
Telophase- nuclear membrane reforms around the two groups chromosomes and nucleoli reform
Meiosis 2 is the same as mitosis
How does genetic variation arise during meiosis?
Non sister chromatids of homologous chromosomes cross over and entangle at the chiasmata- they can exchange DNA to form recombinant chromatids
In metaphase 1 and 2, the orientation of each chromosome is independent of any other chromosome-maternal or paternal can end up facing either way
