Cell Division: Mitosis Flashcards
what are the two types of cell division?
mitosis and meiosis
What does mitosis produce?
In mitosis a parent cell divides to produce two genetically identical daughter cells (they contain an exact copy of the DNA of the parent cell).
What is mitosis needed for?
Mitosis is needed for the growth of multicellular organisms (like us) and for repairing damaged tissues.
What do you need to remember about divsion in multicellular organisms?
In multicellular organisms, not all cells keep their ability to divide
What are the two stages of the cell cycle?
What are each of these divided into?
The cell cycle consists of a period of cell growth and DNA replication called interphase. Mitosis happens after that. Interphase (cell growth) is subdivided into three separate growth stages. These are called G₁, S and G₂.
Briefly outline what happens in the first stage of the cell cycle.
Interphase - The cell carries out normal functions, but also prepares to divide. The cell’s DNA is unravelled and replicated, to double its genetic content. The organelles are also replicated so it has spare ones, and its ATP content is increased (ATP provides the energy needed for cell division).
What are the 4 stages of mitosis?
Prophase
metaphase
anaphase
telephase
What happens in the first stage of mitosis?
Prophase-The chromosomes condense, getting shorter and fatter. Tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle. The nuclear envelope (the membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm.
Label and describe a chromosome.
There are two strands because each chromosome has made an identical copy of itself during interphase. When mitosis is over, the chromatids end up as one-strand chromosomes in the daughter cells.
What happens in the second stage of mitosis?
Metaphase - The chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.
What happens in the third stage of mitosis?
Anaphase - The centromeres divide, separating each pair of sister chromatids. The spindles contract, pulling chromatids to opposite poles (ends) of the spindle, centromere first. This makes the chromatids appear v-shaped.
What happens in the final stage of mitosis?
Telophase - The chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again. They’re now called chromosomes again. A nuclear envelope forms around each group of chromosomes, so there are now two nuclei. Division of the cytoplasm (cytokinesis, which starts in anaphase) finishes in telophase. There are now two daughter cells that are genetically identical to the original cell and to each other. Mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis.
A scientist observes a section of growing tissue under the microscope. He counts 100 cells undergoing mitosis. Of those, 10 cells are in metaphase. One complete cell cycle of the tissue lasts 15 hours. How long do the cells spend in metaphase? Give your answer in minutes.
1) The scientist has observed that 10 out of 100 cells are in metaphase. This suggests that the proportion of time the cells spend in metaphase must be 1/10th of the cell cycle.
2) You’re told that the cell cycle in these cells lasts 15 hours. That’s (15 × 60 =) 900 minutes.
3) So the cells spend: 1/10 x 900 = 90 minutes in metaphase.
What is cancer?
uncontrolled cell division that forms a mass of cells, a tumour, and invades surrounding tissue.
How do different cancer treatments work?
Cancer treatments control the rate of cell division in tumour cells by disrupting the cell cycle. This kills the tumour cells.
1) G1 (cell growth and protein production) - Some chemical drugs (chemotherapy) prevent the synthesis of enzymes needed for DNA replication. If these aren’t produced, the cell is unable to enter the synthesis phase (S), disrupting the cell cycle and forcing the cell to kill itself.
2) S phase (DNA replication) - Radiation and some drugs damage DNA. At several points in the cell cycle (including just before and during S phase) the DNA in the cell is checked for damage. If severe damage is detected, the cell will kill itself - preventing further tumour growth.
