Cell Division, Cell Diversity and Cellular Organisation Flashcards
Cell cycle
- G(1): growth phase 1. Proteins are synthesised, organelles replicate, organelles and cell grows
- S: Synthesis of new DNA (replication of chromosomes). Genes are checked here by proof-reading enzymes to ensure no mutations have occured
- G(2): growth of cell, proteins are synthesised, organelles replicate and grow
- M: nuclear division (mitosis) and cytokinesis. Only takes up a small percentage of the cell cycle
Stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Prophase
Chromosomes replicated in interphase. Now, the chromosomes condense into a pair of sister chromatids. Nuclear envelope breaks down and disappears. Centrioles divide into two, and each daughter centriole moves to opposite poles of the cell to form the spindle
Metaphase
Chromosomes line up along the equator of the cell. Each chromosome becomes attached to the spindle by its centromere
Anaphase
Sister chromatids are pulled to opposite poles of the cell as spindle fibres shorten. Centromere splits to allow this. The sister chromatids (now an individual chromosome) are pulled by their centromere, and so form a V shape
Telophase
As the separated sister chromosomes reach the poles of the cell, a new nuclear envelope forms around each set. The spindle breaks down and disappears. The chromosomes uncoil, becoming indistinct again.
Cytokenisis
The cell membrane nips in at the edges, coming together to form 2 separate, identical cells. Forms a clevage furrow
Differences in mitosis between plants and animal cells
- most cells in animals are capable of mitosis, whilst only meristem cells are in plants.
- Plants don’t have centrioles - the tubulin protein threads are made in the cytoplasm
- Cytokenisis in animals begins by the nipping in of the cell membrane (clevage furrow), whilst in plants, a cell plate forms along the equator of the cell, and the materials for the cell membrane and wall are laid down here
Homologous pair of chromosomes
Chromosomes that have the same genes at the same loci. Members of an homologous pair of chromosomes pair up during meiosis. Diploid organisms, produced by sexual reproduction, have homologous pairs of chromosomes - one member of each pair from the male parent and the other member from the female parent.
Why is mitosis important?
- Asexual reproduction: single-celled organisms divide to produce 2 daughter cells that are separate organisms. Some multicellular organisms produce offspring from parts of the parent
- Growth: multicellular organisms grow by producing new extra cells. Each new cell is genetically identical to the parent cells and so can perform the same functions
- Repair: damaged cells need to be replaced by new ones that perform the same functions and so need to be identical (as with growth)
- Replacement: red blood cells and skin cells are replaced by new ones
Budding in yeast
- Method of asexual reproduction
- Nucleus divides by mitosis
- Cell swells on one side before DNA replicated
- One replicated nuclei and cytoplasm and organelles move into the bud
- Spindle apparatus forms between the bud and the parent cell
- bud pinched off, becoming a separate cell
Meiosis
Cells produced aren’t genetically identical
Stem cell
Undifferentiated cells that are capable of becoming differentiated to a number of possible cell types. Can be omnipotent, totipotent, pluripotent
Differentiation
The changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function
Production of erythrocytes and neutrophils
- Both produced from undifferentiated cells in the bone marrow
- Erythrocytes: these cells lose their nuclues, mitochondria, Golgi apparatus and rough ER. They are packed full of haemoglobin and become biconcave in shape
- Neutrophils: keep their nucleus, cytoplasm appears granular as many lysosomes are produced, filled with enzymes so the neutrophil can kill microorganisms
