Cell Division Flashcards
What is the cell cycle
regulated sequence of events that occurs between one cell division and the next as one parent cell divides to form two genetically identical daughter cells.
What are the three stages
interphase
mitosis
cytokinesis
what happens to the cell in interphase
the cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis)
What are the three phases for interphase and what occurs
G1 phase - Cells make the RNA, enzymes and other proteins required for growth. At some point during the G1 phase a signal is received telling the cell to divide again.
S phase - The DNA in the nucleus replicates (resulting in each chromosome consisting of two identical sister chromatids)
G2 phase - the cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired
What generally happens in mitosis
Cell growth stops, the nucleus divides and chromatids separate
what occurs in cytokinesis
Once the nucleus has divided into two genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells. In animals cytoplasm constricts and in plants a new cell wall is formed
What is the process of mitosis
nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent cell nucleus
Explain Prophase
chromosomes condense and consist of two identical sister chromatids joined by centromere.
centrosomes move towards opposite side of poles which were replicated in G2.
spindle fibres form from centrosomes
nuclear envelope also breaks down into small vesicle
chromatids condense and become visible
Explain Metaphase
Centrosomes reach opposite poles
- chromosomes line up along the equator (of the cell) (1)
*spindle fibres (from the centrioles) attach to the {centromere / chromosome} (1)
Explain Anaphase
The sister chromatids separate at the centromere
Spindle fibres (protein microtubules) begin to shorten
The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres
Explain Anaphase
The sister chromatids separate at the centromere
Spindle fibres (protein microtubules) begin to shorten
The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres
Explain Telophase
Chromosomes arrive at opposite poles and begin to decondense
Nuclear envelopes begin to reform around each set of chromosomes
The spindle fibres break down
Cytokinesis division of cytoplasm into cell by constriction at edges. Centrosome replicate during interphase before nucleus division.
Significance of cell division
Growth. Multicellular organisms grow in size by increasing the number of cells in their bodies through mitosis.
Replacement of dead cells. Dying cells are replaced by identical cells produced through mitosis.
Repair of tissues by cell replacement. In eukaryotes, most structures which have become damaged can be replaced by new daughter cells.
Asexual reproduction. Some organisms (e.g. wasps, strawberry plants, and yeasts) reproduce asexually through mitosis (i.e. does not require the fusion of gametes). The resulting offspring will be genetically identical to its parents.
practical for identifying mitosis
Cut a small piece from the tip of a growing onion root and place it in strong acid (use this to break down middle lamella and separate layer of cells) and heat to intensify the effect
Transfer the root tip to a microscope slide.
Add a drop of stain. - toludine blue
Use a mounted needle to flatten the piece of root and place a coverslip on top and press on it to form single layer of cells
View using high power objective lens of a microscope.
Count the cells at each stage of the cell cycle.
How do you calculate mitotic index
number of cells with visible chromosomes ÷ total number of cells
Why do we use multiple root tips?
The root tips are very delicate, and can decompose. So using several increases the chances of getting good images at the end.
Why is acid used
Plant cells tend to stick together due to their cellulose cell walls. The acid separates the cells, enabling the stain to enter more easily
What does stain bind to
but many bind to chromatin DNA.
why can you not see nucleus at the end of prophase in eukaryotic cell
because the nuclear membrane is broken down (1) because DNA is { coiled / condensed } into individual chromosomes (1)
How do chromosomes look in metaphase
condensed / visible (1)
seen as pairs of chromatids (held together by a centromere) (1)
joined to the spindle (fibres) (1)
aligned on the equator of the cell (1)
difference between anaphase and telophase
In anaphase, sister chromatids (now called chromosomes) are pulled toward opposite poles. In telophase, chromosomes arrive at opposite poles, and nuclear envelope material surrounds each set of chromosomes.
advantage to reproduce both sexually and asexually
create genetically different cells and increase gene pool / increase genetic diversity
asexual doesn’t require mate, conserve advantageous allele and it is faster
explain why two different values of time in anaphase is measure
the student may have selected a different part of the root tip
OR
different plants had different {age / rates of growth / mitotic index / rates of respiration / genes}
(1)
* it is difficult to identify the correct stage of mitosis
2 things i tend to forget when talking about stages of mitosis
- remove acid with cold water
- tease with needle
role of enzyme ligase in dna replication
joins sections of DNA together / repairs breaks in the phosphodiester backbone
(1)
* by forming phosphodiester bonds
(1)
* (forms bonds) between phosphate and {deoxyribose / sugar / pentose
why does mitotic index increase as distance from root tip increases
because cells become more specialised and differentiate further from root tip
which part of plant do you use for preparing a slide during mitosis
meristem
what else can you do after adding stain to slide to show stages of mitosis
heat to intensify the stain (1)
{squash / tease) the tissue to separate the cells
(1)
apply a coverslip {in order to view at high magnification / stop evaporation}
why is an appropriate stain required
a stain is needed to see chromosomes that would not be clearly visible
(1)
because the stain must attach to {chromosomes / DNA / histone}
changes that can be implemented to allow mitosis to be seen clearly
use {5mm / shorter} piece of root tip
- add acid and then stain separately
- heat the root tip in { acid / stain }
- tease the cells apart before staining
- intensify the stain by warming (after squashing)
explain changes during cell cycle
- DNA content will double by the end of {S phase / interphase)(1)
because DNA synthesis takes place (before mitosis) (1)
- the chromosomes will now consist of pairs of chromatidsjoined together at the centromere (1)
During mitosis the chromatids separate and chromosomes now consist of one DNA molecule (by theend of mitosis (1)
DNA content will return to normal by the end of cytokinesis(1)
- because chromatids are separated into (two new) daughtercells
why do cells carry out mitosis
growth / repair / asexual reproduction
(1)
* because this needs {genetically identical cells / clones / cells with the same number of chromosomes }
Describe events take place during prophase in Animal cell
{nucleus / nuclear envelope / nucleous} breaks down
*
spindle (fibres) formed
{chromosomes / chromatids} condense
Centrioles migrate to (opposite) poles of the cell
