EduNinjaMitogens are short chains of amino acids that function as cell-signalling molecules. Mitogens are released from secretory cells and travel in the blood to target cells, where the mitogens bind to cell surface receptors. The target cells respond by progressing from the phase to the S phase of the mitotic cell cycle.
Outline what happens in the phase and S phase of the mitotic cell cycle.
phase
S phase
Prokaryotes divide by a process known as binary fission.
Fig. 1.2 shows some of the stages in binary fission.
Fig. 1.2
With reference to Fig. 1.2, identify two events that occur during binary fission that do not occur during mitosis in human cells.
A diagram of a chromosome from a dividing cell is shown in Fig. 1.1.
Fig. 1.1
Name the stage in the mitotic cell cycle during which the cytoplasm and the cell divide to produce two genetically identical daughter cells.
Fig. 1.1 shows a stage in the mitotic cell cycle in an animal cell.
Fig. 1.1
In many multicellular organisms, such as mammals, the time taken for the mitotic cell cycle varies considerably between different tissues, but is very carefully controlled in each cell.
Suggest the importance of this control in mammals.
In many multicellular organisms, such as mammals, the time taken for the mitotic cell each cell.
Suggest the importance of this control in mammals.
Human cytomegalovirus (HCMV) is a common virus affecting humans. In people with a fully functioning immune system, infection by HCMV usually causes no, or only mild, symptoms.
Fig. 2.1 A is a diagram of a section through HCMV. In Fig. 2.1B, only the outer part of HCMV is sectioned.
Fig. 2.1
The viral DNA shown in Fig. 2.1 contains genes that code for proteins important in viral replication and viral structure, including viral DNA polymerase and proteins known as tegument proteins.
Viruses can only replicate in host cells as they need to use processes and contents of the host cell. Complete viral particles that are released from the host cell are known as virions.
HCMV is known to infect some types of human cell that carry out the mitotic cell cycle.
Studies have shown that in the presence of one tegument protein, UL69, the cell cycle stops in the G1 stage.
Outline the effects the presence of UL69 will have on the normal activity of the mitotic cell cycle.
DNA replication is an important event in the cell cycle.
State when, during the cell cycle, DNA replication occurs.
Meristematic tissue is found in the growing region of plants, such as root tips.
Fig. 2.1 shows a section through the meristematic region of a root tip of onion, Allium cepa.
Fig. 2.1
Table 2.1 shows the numbers of cells in different stages of the cell cycle that were observed in sections of the meristematic regions of root tips of A. cepa.
Table 2.1
The total length of time taken for meristematic cells of A. cepa to complete one cell cycle at is 12 hours.
Using sections similar to the one in Fig. 2.1, the length of time spent in each stage of the cell cycle can be estimated. To obtain the estimate, the percentage of cells in that stage is calculated.
Using the data in Table 2.1, calculate:
- the percentage of cells in anaphase
- the mean length of time in minutes for anaphase.
Show your working.
Fig. 3.1 shows the structure of part of a seminiferous tubule of a human testis.
Fig. 3.1
Describe how cell F is produced from cell E in the process of spermatogenesis.
Cells of the immune system respond to the presence of non-self antigens.
The cell cycle can be divided into different parts.
Complete sentences A, B and C to provide more information about the mitotic cell cycle.
A The part of the cell cycle that occurs immediately after mitosis is
B The part of the cell cycle in which the S phase occurs is
C The main event that occurs during the S phase is