The Mitotic Cell Cycle Flashcards
Which organelle in the cell controls cell division and why?
The nucleus controls cell division as it contains chromosomes.
What happens to the chromosomes before nuclear division?
Chromosomes become more visible just before nuclear division.
What are chromosomes made up of?
Chromosomes are made of two identical chromatids (sister chromatids). Sister chromatids are joined together by a narrow region called the centromere which can be found anywhere along the length of the chromosome, but the position is characteristic for a particular chromosome. There are no genes in the region of the centromere. Each chromatid contains one DNA copy. Chromosomes also contain telomeres which are visible if the chromosome is stained appropriately.
When are chromatids formed?
Chromatids are formed during the interphase of the replication of the DNA strand.
What is DNA made up of?
DNA is made up of many genes, each gene is coded for one polypeptide that is involved in a specific aspect of the functioning of the organism. The gene for a particular characteristic is always found at the same position or locus on the chromosome.
What are histones?
Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
What is chromatin?
The combination of DNA and proteins is called chromatin. Chromosomes are made up of chromatin. As proteins are basic and DNA is acidic both of them can interact easily with each other. Chromatin is easily stained, the more tightly cold it is the more densely it’s stained. Chromatin exists in two forms heterochromatin and euchromatin.
How many chromosomes do human cells possess?
Human cells have 46 chromosomes in each, 44(22 pairs) autosome (control all traits except sex) and 2 sex chromosomes XY for male and XX for females.
Define mitosis
Division of a nucleus into two so that the two daughter cells have exactly the same number and type of chromosomes as the parent cell.
Define cell cycle
The sequence of events that takes place from one cell division until the next; it is made up of interphase, mitosis and cytokinesis.
What is the longest phase of the cell cycle?
Interphase is not a resting phase, but it is a stage of preparation for cell division it takes almost 90% of the cell cycle time.
What is the length of this cell cycle?
The length of the cell cycle is very very variable, depending on environmental conditions and cell type. On average root tip cells of onions divide once every 20 hours. Epithelial cells in the human intestines divide every 10 hours.
Describe interphase
During the interphase the cell goes to its normal size after cell division and carries out its normal functions. At some point during interphase a signal may be received that the cell should divide again. It has three events within preparation for the nuclear division: G1 + S + G2.
Describe the G1-phase
G1-phase(Gap 1 phase): during G1, cells make the RNA, enzymes and other proteins needed for growth. At the end of G1 the cell becomes committed to dividing or not dividing.
Describe the s-phase.
The S-phase (synthesis phase): The DNA in the nucleus replicates so that each chromosome consists of two identical chromatids. Each original chromosome has one DNA molecule after replication each chromosome has two identical molecules (2 chromatids). They are joined together at the centromere. This phase of the cell cycle is called the s phase where s stands for synthesis (of DNA). This is a relatively short phase.
Describe the G2 phase:
During the G2 phase (gap 2 phase) The cell continues to grow and the new DNA that was made during the s phase is checked, any errors are usually repaired. Preparations are also made to begin the process of division. For example there is a sharp increase in the production of the protein tubulin which is needed to make microtubules for the mitotic spindle. Organelles (mitochondria and chloroplasts) are replicated.
What phase in the cell cycle comes after interphase?
Nuclear division follows interphase. Nuclear division is referred to as the M phase (M for mitosis). Growth stops temporarily during mitosis. After the M phase when the nucleus has divided into two the whole cell divides to create two genetically identical cells.
What phase in the cell cycle comes after mitosis?
After mitosis the whole cell divides to create two genetically identical cells. In animal cells cell division involves construction of the cytoplasm between the two nuclei. Cleavage in the middle of the cytoplasm appears that constricts the cytoplasm between the two nuclei. In plant cells it involves the formation of a new cell wall between the two nucleui. Vesicles emerged from golgi body that contains cellulose, hemicellulose and pectin will move to the middle of the cell then release the contents of the vesicles to build the cell wall in the middle of the cell between two nuclei. The membrane of vesicles will form the new cell membrane The gap between vesicles will form plasmodesmata. The organelles are shared out.
What are the four stages of mitosis?
Although in reality the process is continuous it is usual to divide into the four stain mages for convenience like four snapshots from a film The four stages are called prophase, metaphase, anaphase and telophase.
Describe prophase
The first stage of mitosis is called prophase. During prophase the chromosomes condense and become visible in the nucleus. we can see that each chromosome consists of two sister chromatids joined at the centromere. The nucleolus disappears. The nuclear membrane starts to break down. A pair of centrosomes starts to move to either side of the nucleus where they will form the pole of the spindle. Proteins begin to form spindle fibers. Prophase is divided into early and late prophase.
Explain metaphase
The second stage of mitosis is called metaphase. Each centrosome will eventually reach the pole where they help to organize the production of spindle microtubules. Then chromosomes completely lined up across the equator of the spindle (centre of the cell). The centromere of chromosomes get attached to the spindle fibers, each chromosome splits at the centromere and the chromatids start to be pulled apart by microtubules. At metaphase the spindle apparatus has completely formed and the chromosomes are lined up at the center or equator of the cell.
Explain Anaphase
The third stage of mitosis is anaphase. In anaphase the chromatids continue to move to opposite poles, centromeres first and they are pulled by the shortening of the microtubules.
Describe telophase.
In telophase the chromatids have reached the poles of the cell. They will now uncoil again so that each chromatid will replicate itself during interphase before the next division. The spindle apparatus breaks down and the nuclear membranes reform. The chromosomes uncoil back to their chromatin state. The nucleolus also reappears in each nucleus. At this point the cell has now finished nuclear division by mitosis and start cytokinesis.
How does mitosis in plant cells differ from animal cells?
Plant cells do not contain centrosomes and therefore centrioles do not play a part in forming the spindle apparatus in plant cells. Secondly when plant cells undergo cytokinesis the cell membrane cannot form a furrow as in animal cells. Instead vesicles from the Golgi apparatus form membrane structures down the center of the cell. These then fused together to form a central cell membrane dividing the cytoplasm into two. A new cellulose cell wall also forms down the center.
