2.6 - Cell division, cell diversity and cell differentiation Flashcards
Interphase
- Made up of G1, S and G2 phases
- G1 – cell grows, respires, proteins made and organelles replicated
- S – DNA replication occurs, chromosomes becomes sister chromatids joined by a centromere
- G2 – DNA replication is checked for mistakes, organelles replicated
Mitosis
- Prophase – sister chromatids supercoil, nuclear envelope breaks down, spindle fibres form
- Metaphase – sister chromatids line up on equator and spindle fibres attach to centromere
- Anaphase – spindle fibres shorten and pull sister chromatids apart towards opposite poles
- Telophase – chromosomes uncoil, nuclear envelope reforms
Cytokinesis
- Cytoplasm cleaves down furrow to split cytoplasm
- Produces the 2 new genetically identical daughter cells (both identical also to the parent
cell) .
Mitosis - Prophase
- sister chromatids supercoil to shorten and thicken
- sister chromatids consist of sister chromatids joined by a centromere
- they are now visible under a light microscope
- the nuclear envelope breaks down
- centriole divides in 2 and each daughter centriole goes to a pole of the cell
- spindle fibres (microtubules) begin to form
Mitosis - Metaphase
- sister chromatids line up along, equator
- the spindle fibres attach to the centromeres
Mitosis - Anaphase
- centromere splits
- chromatids separate
- spindle fibres shorten
- pull identical chromatids move to opposite poles with the centromere leading
Mitosis - Telophase
- chromosomes uncoil
- nuclear envelope reforms
- spindle fibres break down
Mitosis compared with meiosis
Mitosis produces 2 genetically identical diploid daughter cells used for growth and repair. It
occurs in all body cells and involves only one division.
Meiosis produces 4 genetically different haploid daughter cells and is used for producing
gametes. It occurs only in the ovaries and testes and involves 2 divisions.
Cell division and budding in yeast cells
- Nuclei divided by mitosis
- Bulge in surface of the cell
- nucleus moves into bulge
- bulge nips / pinches off
- this leaves an uneven distribution of cytoplasm in the two cells
Differentiation – structure and function of specialised cells
- Red blood cells (erythrocytes)
- no nucleus or many other organelles e.g. Golgi, mitochondria and ER – provides maximum space for haemoglobin to increase the oxygen carrying capacity
- no nucleus and organelles also makes it more flexible to fit through capillaries
- Filled with haemoglobin which can bind with the oxygen to form oxyhaemoglobin to
transport it round to the aerobically respiring cells - shape is a biconcave disc in order to provide a larger s.a. to volume ratio for oxygen
exchange for more efficient uptake of oxygen into the red blood cells
Differentiation – structure and function of specialised cells
- Root hair cells
- The hair like projection into the soil provides a large surface area for osmosis and mineral uptake (active transport) into the roots.
- They also have a thin wall for a short diffusion path
- Many mitochondria to provide energy for the active transport of minerals
- Many carrier proteins for the active transport of minerals
- Many channel proteins for the uptake of water via osmosis
Differentiation – structure and function of specialised cells
- Neutrophils (phagocytes)
- Contain a lot of lysosomes containing lysin enzymes to digest pathogens)
- Multi-lobed nucleus to fit between gaps in endothelial cells of capillaries to leave blood
- Contain many mitochondria to move lysosomes and phagosomes through cell along
microtubules
Differentiation – structure and function of specialised cells - Sperm
- Haploid nucleus so when it fertilises an egg, the zygote is diploid
- many mitochondria provide energy for movement of flagellum
- Shape: long and thin - ease of movement
- enzyme contained in acrosome so when the sperm meets the egg it can penetrate it to
fertilise
