2.1.6 Flashcards
What happens during interphase?
- dna replicated, checked for errors
- protein synthesis in cytoplasm
- mitochondria increases (grows and divides)
- chloroplasts grow and divide (in plants)
- normal metabolic processes (cell respiration)
What are the three stages of interphase?
G1 - first growth phase
S - synthesis phase
G2 - second growth phase
What happens during G1?
- proteins are produced (synthesise organelles)
- organelles replicate
- cell gets bigger
What happens during S?
DNA in nucleus is replicated
What happens during G2?
- cell gets bigger
- energy stores are increased
- duplicated DNA is checked for errors
What happens during the mitotic phase?
Mitosis : nucleus divides
Cytokinesis: cell divides
What is G0?
Phase where the cell leaves the cycle (temporarily or permanently)
When does G0 happen?
- differentiates (can no longer divide)
- cell DNA may be damaged (enters permanent arrest and no longer viable)
- age (leads to senescent cells)
What happens to lymphocytes in an immune response?
They can be stimulated to go back to cell cycle
When does a cell divide?
- at right size
- replicated Dna is error free
- chromosomes are in right position during mitosis
Why must these three characteristics be matched before a cell divides?
To ensure 2 identical daughter cells
What are checkpoints used for?
To monitor and verify whether phases have been accurately completed before going on to the next phase
What are the three checkpoints?
G1 checkpoint
G2 checkpoint
Spindle assembly checkpoint ( metaphase checkpoint)
What happens at G1 check point?
Checks for:
- cell size
- nutrients
- growth factors
- DNA damage
What happens if all is good at G1 checkpoint?
Triggers DNA replication
If not cell enters G0
What happens at G2 checkpoint?
Checks for:
- cell size
- DNA replication
- DNA damage
If all is good in G2 checkpoint then what happens?
It initiated molecular processes that signal the start of mitosis
What happens at the spindle assembly (metaphase) checkpoint?
It checks for chromosome attachment to spindle
What happens if all is good at metaphase checkpoint?
Mitosis proceeds
What is the order of stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What are the six steps that happen in prophase?
- Chromatin fibres coil and condense making chromosomes
- nucleoulus disappears
- nuclear membrane starts to break down
- Chromatin fibres coil and condense making chromosomes
- Protein microtubules form spindle shaped structures
- 2 centrioles migrate to opposite sides of the pole (help with spindle formation)
- Spindle fibres attach to specific areas on centromeres and start moving chromosomes to middle
- By the end nuclear envelope has dissapeared
What happens during metaphase?
Chromosomes in the centre of cell (metaphase plate, equator)
What happens during anaphase?
-chromosomes divide and are pulled to opposite poles (through liquid cytosol) because of shortening spindle fibres
What happens during telophase?
Chromatids that reach each pole are now called chromosomes.
-nuclear envelope forms around each set of chromosomes
(Nucleolus is formed and chromosomes start to uncoil)
What else starts in telophase?
Cytokenisis
Describe what happens in cytokinesis in animals.
Cleavage furrow forms
Cell surface membrane is pulled inwards by cytoskeleton until its close enough to fuse in the middle.
Describe cytokinesis in plants.
- vesicles from golgi assemble in same place that metaphase plate was
- they fuse together with cell membrane
- dividing cell into two
- new sections of cell wall form along new sections of membrane
What are gametes?
Sex cells
What is zygote?
Fertilised egg
What type of division is meiosis and why?
Reduction division
Because for daughter cells (haploid) are produced
What are alleles?
Different versions of the same gene (gene variants ) they have the same locus
What happens during meiosis I?
First division is reduction division
Homologous pairs are split into two cells