Flashcards in 1: Mitosis Deck (27):
In eukaryotes, where is nearly all of the DNA of a cell stored?
in the nucleus
How many metres of DNA does a human nucleus contain? How long is the human nucleus in diameter? How can all the DNA fit in the small nucleus?
- DNA molecule is so narrow - its width is is 2nm (0.002um)
Is a DNA molecule visible with a light microscope?
What do DNA molecules have attached to them in eukaryotes? What structure does this form?
have proteins attached to them, forming structures called chromosomes
What happens to the chromosomes during mitosis? What is this called? How does 'this' occur?
- chromosomes become shorter and fatter
- through complex process called 'supercoiling'
When is it possible to see chromosomes through a light microscope?
when they are condensed during the early stages of mitosis
What sort of structure do chromosomes have when it is possible to see them with a light microscope?
a double structure
During the early stages of mitosis, what are the two parts of the chromosome called? What is the name of the point that holds the two parts of the chromosome together?
- sister chromatids
- the centromere
What does the term 'sister' indicate in 'sister chromatid'? How are they produced?
- that the two chromatids contain an identical DNA molecule
- produced by DNA replication before the start of mitosis
What happens to the centromere during mitosis? What is the result of this?
- centromere divides
- the sister chromatids separate
What are the sister chromatids referred to as after the centromere divides and they separate?
as chromosomes, rather than chromatids
State all the stages of mitosis.
1. early prophase
2. late prophase
5. early telophase
6. late telophase
What happens in mitosis: early prophase
- spindle microtubules are growing
- chromosomes are becoming shorter and fatter by supercoiling
What happens in mitosis: late prophase
- spindle microtubules extend from each pole to the equator
- each chromosome consists of two identical chromatids formed by DNA replication in interphase and held together by a centromere
What happens in mitosis: metaphase
- spindle microtubules from both poles are attached to each centromere, on opposite sides
- nuclear membrane has broken down and chromosomes have moved to equator
What happens in mitosis: anaphase
- spindle microtubules pull the genetically identical chromosomes to opposite poles
- centromeres have divided and the chromatids have become chromosomes
What happens in mitosis: early telophase
- spindle microtubules break down
- all chromosomes have reached the poles and nuclear membranes form around them
What happens in mitosis: late telophase
- chromosomes uncoil and are no longer individually visible
- cell divides (cytokinesis) to form two cells with genetically identical nuclei
Draw and label a cell undergoing mitosis (only include relevant parts of cell). (p14)
What is the mitotic index?
the ratio between the number of cells in mitosis in a tissue and the total number of observed cells
State the formula for mitotic index.
= number of cells in mitosis/ total number of cells
How is the mitotic index used?
by doctors to predict how rapidly a tumour will grow and therefore what treatment is needed
What does a high mitotic index indicate?
a fast-growing tumour
What is cytokinesis?
the division of the cytoplasm to form two cells
When does cytokinesis occur?
after mitosis and is different in plant and animal cells
How does cytokinesis occur in plant cells?
a new cell wall is formed across the equator of the cell, with plasma membrane on both sides. This divides the cell in two.