2.1.6 Flashcards
What are the main two phases of the cell cycle?
Interphase and mitotic phase
What happens during interphase?
- DNA is replicated and checked for errors in the nucleus
- Protein synthesis occurs
- Mitochondria grow and divide
- Chloroplasts grow and divide in plant and algal cell cytoplasm
- Normal metabolic processes
What are the three stages of interphase?
G1 - first growth phase. Proteins are synthesised and organelles replicate. Cell increases in size
S - synthesis phase. DNA is replicated
G2 - second growth phase. The cell grows in size, energy stores increased, duplicated DNA is checked for errors
What is G0?
When the cell leaves the cell cycle
Why could a cell enter G0?
Differentiation, DNA is damaged, senescence
How is the cell cycle controlled?
- G1 checkpoint: At the end of the G1 phase, and checks for cell size, nutrients, growth factors, and DNA damage
- G2 checkpoint: At the end of the G2 phase checks for cell size, DNA replication, and DNA damage
- Spindle assembly checkpoint: Checks chromosome is attached to the spindle
What happens in prophase?
Chromatin fibres coil and condense, forming chromosomes. Nucleolus disappears, and nuclear membrane breaks down. Microtubules form spindles linking the poles of the poles. Spindle fibres attach to specific areas on the centromeres and start to move the chromosomes to the centre of the cell
What happens in metaphase?
Chromosomes are moved by the spindle fibres to the centre of the cell
What happens in anaphase?
Spindle fibres shorten, so centromeres divide.
What happens in telophase?
Chromatids reach the poles and are now called chromosomes. Two new sets of chromosomes assemble at each pole and the nuclear envelope reforms. Chromosomes uncoil and nucleolus forms
What happens in prophase 1?
Chromosomes condense, the nuclear envelope disintegrates, the nucleolus disappears and spindles form. Homologous chromosomes pair up, forming bivalents. Crossing over takes place
What happens in metaphase 1?
Homologous pairs of chromosomes assemble along the metaphase plate. Independent assortment takes place
What happens in anaphase 1?
Homologous chromosomes are pulled to opposite poles. Areas that have crossed over are exchanged, forming recombinant chromatids
What happens in telophase 1?
Chromosomes assemble at each pole, nuclear membrane reforms. Chromosomes uncoil. Cell undergoes cytokinesis
What happens in prophase 2?
Chromosomes condense and become visible again. Nuclear envelope breaks down and spindle formation begins
