Figure 1. The ends of linear chromosomes are maintained by the action of
the telomerase enzyme
. Telomerase is typically active in germ cells and adult stem cells.
What maintains the ends of chromosomes?
Telomeres
are repetitive nucleotide sequences at each end of chromosomes. Their function is to protect the ends of the chromosomes from deterioration or fusion to other chromosomes during cell division. With every cell division, telomeres shorten.
What enzyme extends the ends of linear chromosomes?
Some cells have the ability to reverse telomere shortening by expressing telomerase, an enzyme that extends the telomeres of chromosomes.
Which enzyme is used to maintain the ends of linear chromosomes so that they don’t keep getting shorter during rounds of replication?
Telomeres help prevent genes from being lost in this process. But this means that as your chromosomes replicate, your telomeres shorten. That’s where an enzyme called
telomerase
comes in. It’s found in certain cells and helps prevent too much wear and tear.
What enzyme restores tips of chromosomes?
This cycle was broken, however, when dicentric chromosomes were present in embryonic cells; in these cells, the broken ends were somehow “healed” (McClintock, 1941). Today, researchers know that the ends were healed by the addition of a telomere, a process that is catalyzed by an enzyme called
telomerase
.
Are telomeres on the 5 end?
After each round of DNA replication, some telomeric sequences
are lost
at the 5′ end of the newly synthesized strand on each daughter DNA, but because these are noncoding sequences, their loss does not adversely affect the cell. … Telomerase adds complementary RNA bases to the 3′ end of the DNA strand.
What enzyme adds bases to the ends of telomeres?
The ends of linear chromosomes, called telomeres, protect genes from getting deleted as cells continue to divide.
The telomerase enzyme
attaches to the end of the chromosome; complementary bases to the RNA template are added on the 3′ end of the DNA strand.
Why can nucleotides only be added to the 3 end?
DNA polymerase adds nucleotides to the deoxyribose (3′) ended strand in a 5′ to 3′ direction. … Nucleotides cannot be added to the phosphate (5′) end because DNA polymerase can only add DNA nucleotides in a 5′ to 3
‘
direction. The lagging strand is therefore synthesised in fragments.
Why Okazaki fragments are formed?
Okazaki fragments are formed
on lagging strands
, initiated by the creation of a new RNA primer by the primosome. Okazaki fragments are formed on the lagging strand for the synthesis of DNA in a 5′ to 3′ direction towards the replication fork. … The ligase enzyme joins the Okazaki fragments together, making one strand.
What binds Okazaki fragments?
On the leading strand, DNA synthesis occurs continuously. On the lagging strand, DNA synthesis restarts many times as the helix unwinds, resulting in many short fragments called “Okazaki fragments.”
DNA ligase
joins the Okazaki fragments together into a single DNA molecule.
How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
It catalyzes the lengthening of telomeres, compensating for the shortening that occurs during replication
. DNA is a self-replicating molecule.
What happens if telomeres are too long?
It was known that very short telomeres cause harm to a cell. But what was totally unexpected was our finding that damage also occurs when telomeres are very long.” … As telomeres shorten over time, the chromosomes themselves become vulnerable to damage.
Eventually the cells die
.
Which enzyme can repair mismatched nitrogenous bases?
Thus,
DNA polymerase
is able to remove the incorrectly-incorporated bases from the newly-synthesized, non-methylated strand.
What enzyme prevents aging?
Counteracting the telomere shrinking process is the enzyme,
telomerase
, that uniquely holds the key to delaying or even reversing the cellular aging process.
Are telomeres found in all chromosomes?
Telomeres are distinctive structures
found at the ends of our chromosomes
. They consist of the same short DNA sequence repeated over and over again. Telomeres are sections of DNA
?
found at the ends of each of our chromosomes
?
. They consist of the same sequence of bases
?
repeated over and over.
What cell types have stable telomeres?
Cells which are “immortal’ such as the human germ line or tumour cell lines,
established mouse cells, yeast and ciliates
, all maintain a stable telomere length through the action of telomerase.
