L4- Cell division

What is the importance of mitosis?

• Growth

• Tissue renewal and repair

• Maintain homeostasis

Which cells cannot repair themselves, resulting in serious diseases

• Cardiomyocytes

• Neurons

• Photoreceptors

How long is interphase, and what are the three phases of interphase?

23 hours

• G1- Growth (with a checkpoint for nutrients and DNA damage)

• S- DNA synthesis

• G2- Growth and preparation for mitosis (with a checkpoint for cell size and DNA replication)

How long is mitosis, and what are the phases?

• Prophase

• Metaphase

• Anaphase

• Telophase

What happens during prophase?

Chromatin condenses into chromosomes

Centrosomes move to opposite poles

What happens during prometaphase?

Nuclear envelope fully breaks down

Spindle microtubules can access chromosomes, and attach to spindle fibres

What happens during metaphase?

Chromosomes align at the equator

Sister chromatids attach to opposite poles by spindle fibres (kinetochore microtubules)

What happens during anaphase?

Spindle fibres shorten, pulling chromosomes to opposite poles of the cell- centromeres separated

What happens during telophase?

Chromosomes reach to opposite poles (decondense to chromatin)

Nuclear envelope reforms

What happens during cytokinesis?

Cytoplasm divides

What are microtubules?

The main constituents of mitotic spindles for pulling chromosomes apart (form part of the cytoskeleton)

Label the parts of the cell?

What is the importance of meiosis?

• Maintain the same number of chromosomes across generations

• Genetic stability- all have the same diploid number after fertilisation

• Genetic diversity- crossing over/ independent assortment/ natural selection

Explain the key stages of meiosis

Interphase 1- DNA replication (two sister chromatids)

Prophase 1- Homologous chromosomes pair up, crossing over

Metaphase 1- Homologous chromosomes align randomly, independent assortment

Anaphase 1- Homologous chromosomes pulled to opposite poles

Telophase 1- Two haploid cells formed

Meiosis 2- Separation of sister chromatids, four haploid gametes formed, genetically unique

Explain the key difference between mitosis and meiosis, and the differences in the products and roles

• In mitosis, DNA replicates and the cell divides once. In meiosis, DNA replicates and the cell divides twice

Products

• Mitosis- identical cells, meiosis- genetically unique cells

• Mitosis- 2 cells, meiosis- 4 cells

• Mitosis- Same number of chromosomes as parent, meiosis- half the number of chromosomes as the parent

Roles

• Mitosis- increase number of cells in multicellular organisms, meiosis- produce gametes for reproduction