Multiple choice help please 1. DNA polymerases can proofread by removing mismatc
ID: 208741 • Letter: M
Question
Multiple choice help please
1.
DNA polymerases can proofread by removing mismatched bases in the _______ direction, and replacing them with a correct base synthesized in the _______ direction.
5 to 3; 5 to 3
3 to 5; 3 to 5
3 to 5; 5 to 3
5 to 3; 3 to 5
None of the other choices is correct.
2.
What is the major difference between the lagging and leading strands?
On the leading strand, DNA synthesis occurs from 5' to 3', while DNA synthesis occurs from 3' to 5' on the lagging strand.
DNA polymerase is able to continuously add new nucleotides on the leading strand while it must keep 'starting over' on the lagging strand.
The lagging strand requires only a single primer while the leading strand requires many.
Helicase opens the leading strand at a faster rate than the lagging strand.
3.
Telomerase activity in humans is generally restricted to the germ line, cancerous cells, and a few specific adult cell types. How would this be expected to impact humans?
Cancer cells can divide indefinitely.
Because there is a difference in number of divisions, sperm would be expected to have shorter telomeres than oocytes.
Rapidly dividing populations of cells have telomeres equal in size to slowly dividing populations of cells.
All of the other choices are correct.
4.
In the lagging strand, DNA is made in the direction _____ the replication fork and is made as _____.
away from, Okazaki fragments
toward, one continuous strand
away from, one continuous strand
toward, Okazaki fragments
5.
Point at which two new strands of DNA are being produced
Okazaki fragment
lagging fork
restriction fragment
replication fork
A.5 to 3; 5 to 3
B.3 to 5; 3 to 5
C.3 to 5; 5 to 3
D.5 to 3; 3 to 5
E.None of the other choices is correct.
Explanation / Answer
1 DNA polymerases (1, II and III) can have a 3’ to 5’ exonuclease activity. This allows the enzyme to check for mismatches during DNA synthesis. These mismatches are cleaved in 3’ to 5’ direction. The enzyme also cleaves the 3’ unpaired overhangs to form create blunt ends. The DNA polymerase then replaces the correct bases in 5’ to 3’ direction.
Right option is C. 3’ to 5’, 5’ to 3’
2. The major difference between leading strand and lagging strand is that leading strand has new nucleotides added continuously by DNA polymerase while lagging strand has nucleotides added at different regions. DNA synthesis in both strands is from 5’ to 3’ direction. The leading strand synthesis requires single primers while the lagging strand requires multiple primers. Bothe strand separation are caused by helicase simultaneously.
Right option is B.
DNA polymerase is able to continuously add new nucleotides on the leading strand while it must keep 'starting over' on the lagging strand..
3. Telomerase or terminal transferase is a riboprotein that adds telomere repeat TTAGGG sequences to 3’ ends of telomeres on DNA. Telomeres are shorter in oocytes than sperm, which further shorten on aging. Telomere length in sperm increases with age. Telomerase is expressed in spermatogonia in high levels. Cancer cells evade senescence due to increased cell division. They are capable of maintaining telomere length. High telomerase activity in human allows cancer cells to divide indefinitely. Rapidly dividing cells have more telomeres than non dividing cells.
Right option is A. Cancer cells can divide indefinitely.
4. The lagging strand is made from DNA strand in 3’ to 5’ direction. Hence, it is made away from the replication fork. It is composed of short fragments called okazaki fragments. The leading strand is synthesized from the 5’ to 3’ strand and hence it is synthesized continuously towards the replication fork.
Right choice is A. away from, Okazaki fragments.
5. The point at which DNA replication takes place is the replication fork. The DNA unwinds at the replication fork during replication by the helicase enzyme. It resembles a two pronged fork. The Leading strand is synthesized towards the replication fork, while lagging strand synthesis is away from the replication fork.
Right option is replication fork.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.