Cell Division And Cellular Organisation Flashcards
Stages of The Cell Cycle.
1- G phase 1(cell grows and new organelles and proteins are made.)
2- G1 checkpoint (The cell checks that the chemicals needed for replication are present and for any damage to the DNA).
3- Synthesis (Cell replicates it’s DNA, ready to divide by mitosis.)
4- G phase 2 (Cell keeps growing and proteins needed for cell division are made.)
5- G2 checkpoint (Cell checks whether all the DNA has been replicated without damage)
6- M phase (Mitosis and cytokinesis).
What happens during interphase?
- Cell’s DNA is unravelled and replicated to double it’s genetic content.
- Organelles are replicated.
- ATP content is increased (ATP provides the energy needed for cell division).
Significance of mitosis in life cycles.
- Needed for the growth of multicellular organisms.
- Repairs damaged tissues.
- Used to reproduced asexually by some animals, plant and fungi.
Structure of chromosomes in mitosis.
- Made up of two strands joined in the middle by a centromere.
- Separate strands are called chromatids.
- Two strands on the same chromosome are called sister chromatids.
Stages of mitosis.
- Prophase.
- Metaphase.
- Anaphase.
- Telophase.
What happens during prophase?
- Chromosomes condense and become visible.
- Nuclear envelope breaks down and chromosomes lie free in the cytoplasm.
What happens during metaphase?
- Chromosomes line up along the equator of the cell.
- They attach to the spindle via their centromere.
What happens during Anaphase?
- Centromeres divide, separating each pair of sister chromatids.
- Spindles contract, pulling chromatids to opposite ends of the cell.
What happens during Telophase?
- Chromatids reach opposite poles of the spindle.
- They uncoil and become long and thing again.
- They are now called chromosomes again.
- A nuclear envelope forms around each group of chromosomes, so there are now two nuclei.
What happens during cytokinesis?
- Cytoplasm divides.
- There are now two daughter cells which are genetically identical to each other.
- Usually begins in anaphase and telophase.
- separate to mitosis
What are gametes?
- Sperm cells in males.
- Egg cells in females.
What is sexual reproduction?
- Two gametes join together at fertilisation for o form a zygote.
- The zygote divides and develops into a new organism.
What are homologous chromosomes?
- Chromosomes which are the same size and have the same genes.
What does Meiosis 1 do?
- Halves the chromosomes number
What happens during prophase 1 do?
- Homologous chromosomes pair up.
- Spindle fibres are formed.
- Nuclear envelope breaks down.
What happens during Metaphase 1?
- Homologous pairs line up across the centre of the cell.
- They attach to the spindle fibres by their centromere.
What happens during Anaphase 1?
- Spindles contrast pulling the pairs apart.
- One chromosome goes to each end of the cell.
What happens during Telophase 1?
- a nuclear envelope forms around each group of chromosomes.
- Cytokinesis (the division of cytoplasm) occurs and two haploid daughter cells are produced.
What is the difference between Meiosis 1 and Meiosis 2?
- Meiosis 2 is with half the number of chromosomes.
- Sister chromatids are separated in Anaphase 2.
- Four haploid daughter cells are produced.
Which earners during Meiosis leads to genetic variation?
- Crossing over of chromatids.
- Independent assortment of chromosomes.
When does crossing over of chromatids occur and how does it happen?
- Prophase 1 of meiosis 1.
- Homologous pairs of chromosomes come together and pair up.
- Chromatids twist around each other and bits of chromatids swap over.
What is independent assortment of chromosomes?
- The ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring.
What are stem cells?
- Unspecialised cells that can develop into different types of cell.
What is one place that stem cells are found in adults?
- Bone Marrow.
