2.1.6 Cell division Flashcards
What are the three phases of the cell cycle
- interphase
- mitosis
- cytokinesis
What are the three phases that make up interphase
- G1 phase
- S phase
- G2 phase
What triggers movement from one phase to another
chemical signals called cyclins
What happens during the G1 phase
protein synthesised for organelles and enzymes
organelles synthesised (mitochondria and ribosomes)
ATP production for S phase
cell increases in mass and size
What happens during the S phase
DNA replication
What happens during the G2 phase
ATP production to increase energy store for division
Organelle duplication
What is the G0 phase
when a cell leaves the cell cycle either permanently or temporarily
Why might a cell enter the G0 phase
- highly specialised cells (neurones etc) stay in G0
- senescence ( most cells only divide a certain number of times - hayflick constant (50))
- DNA damage - undergoes apoptosis (programmed cell death)
What are the three checkpoints in the cell cycle
G1 checkpoint
G2 checkpoint
M checkpoint
What is checked at the G1 checkpoint
if the cell is large enough and contained needed organelles
What is checked at the G2 checkpoint
if DNA is replicated correctly
if there are negative mutations the cell moves into G0
What is checked at the M checkpoint
checks that the spindle fibres have been assembled correctly
- all chromosomes should be attatched to spindles and aligned
What are the five stages of mitosis
prophase
metaphase
anaphase
telophase
cytokinesis
Describe the process of prophase
- chromatin fibres condense into chromosomes
- the nucleolus disappears and the nuclear envelope disintegrates
- centrioles migrate to the poles of the cell
- spindle fibres attach to specific points on the centromere
Describe the process of metaphase
chromosomes are moved by fibres to form a plane in the middle of the cell
- metaphase plate
Describe the process of anaphase
centromeres divide and chromatids are pulled to opposite ends of the cell by spindle fibres
(characterised by a v shape)
Describe the process of telophase
- chromatids have reached the poles and are called chromosomes
- the nuclear envelope forms around new sets of chromosomes
- chromosomes uncoil and the nucleolus forms
Describe the process of cytokinesis
- begins during telophase
- animals: cell surface membrane is pulled in by cytoskeleton until close enough to fuse
- plants: golgi vesicles assemble at same place as metaphase plate and fuse with each other and cell membrane
new sections of cell wall are formed through osmotic lysis
Describe how to view meristem cells in garlic/onion
Place the root tip on a glass slide
add 3 drops of acetic orcein (stains chromosomes dark purple)
cover with cover slip at angle and gently press down to squash the tissues
examine tissues under a microscope and use a calibrated graticule to measure the length of a chromosome and a cell
What are the limitations of viewing mitosis through a light microscope
it can be difficult to distinguish between prophase and telophase in cells
light microscopes may prevent you from seeing particular structures
Give three reasons why mitosis is important
- allows for the growth of multicellular organisms
- allows replacement of cells and tissue replacement (essential as cells are constantly dying)
- asexual reproduction
What is a stem cell
an undifferentiated cell that has the potential to differentiate and become a range of specialised cells
Define differentiated
when a cell becomes specialised for its function
Define potency
a stem cell’s ability to differentiate into different cell types
