[Maximum number: 2]
Fig. 1.1 is a diagram showing the structure of a section of a DNA molecule.
Fig. 1.1
(a)
The telomere is a region found at the end of a chromosome.
Outline the function of telomeres.
[ 2 ]
[Maximum number: 1]
Telomeres prevent the loss of genes from the ends of chromosomes during DNA replication, but they become shorter each time they are copied.
In cancer cells and stem cells, the telomeres remain the same length.
Which statement is correct for all human cells?
A
If telomeres become too short, a cell may stop dividing.
B
Adding telomeres could increase the rate of ageing of cells.
C
Telomeres are repaired by the enzyme RNA polymerase.
D
Telomeres prevent all damage occurring to DNA molecules.
[Maximum number: 1]
The enzyme telomerase prevents loss of telomeres after many mitotic cell cycles.
Which cells need to transcribe telomerase enzyme?
1 cancer cells
2 stem cells
3 activated memory B-lymphocytes
A
1, 2 and 3
B
1 and 2 only
C
1 and 3 only
D
2 and 3 only
[Maximum number: 1]
What happens to the telomeres during mitosis of a cancer cell?
A
The length increases.
B
The length decreases.
C
They are completely lost.
D
They stay the same length.
[Maximum number: 1]
The jellyfish, Turritopsis dohrnii, is described as being immortal. If T. dohrnii is not eaten by predators or diseased, it seems to be able to live forever. There is no way to determine the biological age of a T. dohrnii individual.
Which feature of the cells in T. dohrnii could explain these observations?
A
very long G phases in the cell cycle
B
a very short S phase in the cell cycle
C
an ability to restore telomeres to their original length
D
fewer chromosomes than other eukaryotic organisms
[Maximum number: 1]
The enzyme telomerase prevents loss of telomeres after many mitotic cell cycles.
Which cells transcribe a high concentration of telomerase?
1 neutrophils
2 mature red blood cells
3 activated memory T-Iymphocytes
A
1 and 2
B
1 and 3 only
C
1 only
D
3 only
[Maximum number: 1]
Chromosome telomeres are essential for DNA replication and are not completely replaced during mitosis.
A substance X is known that completely replaces telomeres during mitosis.
What will be the effect of growing cells with and without substance X ?
with substance X
without substance X
cells divide continually
cell division eventually slows and stops
cells divide more rapidly
cells divide continually
cell division eventually slows and stops
cell division stops immediately
cell division stops immediately
cells divide continually
[Maximum number: 1]
Which cells contain telomeres that are longer than those in a helper T-lymphocyte secreting cytokines?
1 bone marrow stem cells
2 mature red blood cells
3 activated memory B-lymphocytes
A
1 and 2
B
1 and 3
C
2 only
D
3 only
[Maximum number: 1]
In which stage of the cell cycle are telomeres needed to prevent the loss of genes?
A
prophase
B
cytokinesis
C
phase
D
S phase
[Maximum number: 1]
Which statement about telomeres is correct?
A
They allow cells in culture from any age of donor to divide a fixed number of times.
B
They are genes which are present on the 5' end of every chromosome.
C
They are unpaired regions of DNA on the 3' end of every chromosome.
D
They prevent introns and exons being lost from genes during cell division.