Question

Question 11 Not yet answered Marked out of 1.00 P Flag question The DNA of an organism is studied and found to contain 14% guanine. This organism should have __% thymine and __% cytosine in its DNA. Select one: O a. 36; 36 O b. 14; 36 O c. 14; 86 O d. 36; 14

Answer 1

11 ) The DNA of an organism is studied and found to contain 14% guanine this organism should have contain 36   % thymine and 14 % cytocine in its DNA . [option d is right option and rest options are wrong due to chargaff's rule ) ,

[ in DNA guanine attaches with cytocine and adenine attaches with thymine , hence in a  DNA , amount of guanine is equal to cytocine and amount of thymine is equal to adenine , and DNA always maintain a 1:1 ratio of pyrimidin and purin bases. yhis rule is known as chargaff's rule .]

in this problem ,applying chargaff's rule A+G=T+C ( as purin : pyrimidine =1:1 ratio)  if amount of guanine is 14% . and guanine attaches with cytocine ( with the help of 3 hydrogen bond ) then surely the amount of cytocine will be 14% . lets assume A+T+G+C=100 . amount of guanine and cytocine = 14+14 = 28%  . therefore A+T = 100- 28=72 . ( as amount of adenine and thymine is equal then we can say A+T= 2A or 2T ) therefore 2T = 72 and T = 36 .

A= 36% , T=36% , G=14% , C =14% present in this DNA.

12) The strand of DNA double helix are said to be antiparallal ,this means that

The 5' end of a strand is directly pair with 3' end of the other strand ( option b )

antiparallal means two strand runs parallaly but in opposite direction . in DNA double helix one strand is 5' to 3' and other strand is 3' to 5' i.e oppositely directed but runs parallaly .

in option a) 5' end of DNA paired with 5' end of other strand therefore it is parallal not antiparallal hence it is wrong option .

though helix are twisted but both strands runs paralally to each other in opposite direction hence this option cant be right ,

DNA strand is negatively charged due to phosphate group and phosphate group is present in both strand hence both strand negative . so option d is wrong option .

13) the energy to form new bond when a new nucleotide is added to DNA strand is provided primarily (option c) hydrolysis of bonds between nucleotide phosphates .

as the energy of replication derived from hydrolysis of triphosphate group of dNTP.

bonds present between two base are hydrogen bond hence hydrolysis of hydrogen bonds can not provide much energy for adding new nucleotide . hence wrong option .

unwinding of double helix also do not produce energy of adding nucleotide . as this energy creates supercoiling of DNA which is nutralised by topoisomerase . hence it is wrong option .

no protein gradient provide energy to DNA replication

14) The structure lebelled C in the figure of replication fork is Helicase ( option b ) as C lebelled stucture is unwinding DNA double strand and separates two single strand .

option a) primase - it synthesize new RNA strand complementary to the template DNA .and helps DNA polymerase to find separated template DNA strand to be replicated . i.e it starts DNA replication . in this figure E lebelled structure is the ptimase .

b) Helicase - it attaches near or on origin of replication and unwind DNA double helix and separate two single strands . in this figure C lebelled structure is unwinding DNA double helix and separates the two strands hence it is Helicase .

c) DNA ligase - this enzyme joins fragmented DNA , it acts like glu . in this figure A lebelled structure joins fragmented DNA (okazaki fragment) hence it is DNA ligase . i.e its function does not resembles with the function of C lebelled stucture hence it is wrong option .

d) single strand binding protein - it helps DNA single strand to be separated by stabilizing them .after unwinding . in this figure D lebelled structure stabilize the single strand after unwinding hence it is single stranded binding protein . .i.e its function also does not resembles with function og C lebelled structure hence it is wrong option .

15) the structure lebelled A in the figure of replication fork represents DNA ligase ( option d)

as A lebelled structure is joining the fragments in this figure ( joining okazaki fragments )

helicase ( option a ) is C lebelled structure as it is unwinding DNA double helix . hence it is not the right option .

primase ( option b) helps in starting of DNA replication .in this figure E lebelled structure helps starting of polymerisation hence it cant be right .

similarly single strand binding protein's function is to stabilize single strand after unwinding . here D lebelled structure is doing that therefore it cant be the A lebelled structure .

DNA ligase( option d ) joins fragmented DNA i.e ascts similar as A lebelled structure hence it is the right option .