METABOLISM OF NUCLEIC ACIDS: The Central Dogma of Molecular Biology

Question 1

_____________________ is a high-fidelity and high-accuracy semi-conservative process where one parental DNA gives
rise to two identical copies of daughter DNAs. The replication is termed ____________________ since each new cell
contains one strand of original DNA and one newly synthesized strand of DNA. The original polynucleotide strand of DNA
serves as a template to guide the synthesis of the new complementary polynucleotide of DNA.

Answer 1

DNA Replication is a high-fidelity and high-accuracy semi-conservative process where one parental DNA gives
rise to two identical copies of daughter DNAs. The replication is termed semi-conservative since each new cell
contains one strand of original DNA and one newly synthesized strand of DNA. The original polynucleotide strand of DNA
serves as a template to guide the synthesis of the new complementary polynucleotide of DNA.

Question 2

_______________: It is the first stage when several key factors are recruited to an origin of replication of the DNA
molecule. This origin of replication is unwound and unzipped by the enzyme ____________________ forming a Yshaped region called the _________________________. Each group of enzymes at the replication fork moves away
from the origin, unwinding and replicating the original DNA strands as they proceed. _______________ mark the
individual sequences and the starting points to be replicated.

Answer 2

Initiation: It is the first stage when several key factors are recruited to an origin of replication of the DNA
molecule. This origin of replication is unwound and unzipped by the enzyme DNA helicase forming a Y-shaped region called the replication fork. Each group of enzymes at the replication fork moves away
from the origin, unwinding and replicating the original DNA strands as they proceed. DNA primase mark the
individual sequences and the starting points to be replicated.

Question 3

_______________: This stage is catalyzed by an enzyme called ____________________. As nucleotides align with
complementary bases along “old” template strand of DNA, they are added by polymerase, one by one, to the growing
end of the new DNA strand. DNA polymerase, however, can catalyze the growth of the DNA chain in only ______________ as it can add subunits only to the 3’end of the chain. As a result, a new DNA chain can be synthesized only
in _____________ direction. The DNA strand whose 5’ end must grow is made discontinuously, in successive separate small
pieces called _________________________. The DNA strand that is synthesized discontinuously is called the
_________________ while the strand that is synthesized continuously is called the _________________________.

Answer 3

Elongation: This stage is catalyzed by an enzyme called DNA polymerase. As nucleotides align with
complementary bases along “old” template strand of DNA, they are added by polymerase, one by one, to the growing
end of the new DNA strand. DNA polymerase, however, can catalyze the growth of the DNA chain in only one
direction as it can add subunits only to the 3’end of the chain. As a result, a new DNA chain can be synthesized only
in 5’ to 3’ direction. The DNA strand whose 5’ end must grow is made discontinuously, in successive separate small
pieces called okazaki fragments. The DNA strand that is synthesized discontinuously is called the
logging strand while the strand that is synthesized continuously is called the leading strand.

Question 4

_______________: This last stage occurs when DNA replication forks meet one another or run to the end of a linear
DNA molecule. Also, ________________ may occur when a replication fork is deliberately stopped by a special protein, called
a ___________________________________, that binds to specific sites on a DNA molecule.

Answer 4

Termination: This last stage occurs when DNA replication forks meet one another or run to the end of a linear
DNA molecule. Also, termination may occur when a replication fork is deliberately stopped by a special protein, called
a replication terminator protein, that binds to specific sites on a DNA molecule.

Question 5

The _______________ is a complex molecular machine that carries out replication of DNA. This contains all the
necessary enzymes for replication namely:

Answer 5

The replisome is a complex molecular machine that carries out replication of DNA. This contains all the
necessary enzymes for replication namely:

Question 6

Also known as helix destabilizing enzyme. Unwinds the DNA double helix at
the Replication Fork.

Answer 6

DNA Helicase

Question 7

Builds a new duplex DNA strand by adding nucleotides in the 5’ to 3’ direction. Also performs proof-reading and error correction.

Answer 7

DNA Polymerase

Question 8

A protein which prevents DNA polymerase III from dissociating from the DNA parent strand.

Answer 8

DNA Clamp

Question 9

Bind to ssDNA and prevent the DNA double helix from re-annealing after DNAhelicase unwinds it thus maintaining the strand separation.

Answer 9

Single-Strand Binding (SSB) Proteins

Question 10

Relaxes the DNA from its super-coiled nature.

Answer 10

Topoisomerase

Question 11

Relieves strain of unwinding by DNA helicase.

Answer 11

DNA Gyrase

Question 12

Re-anneals the semi-conservative strands and joins Okazaki Fragments of thelagging strand.

Answer 12

DNA Ligase

Question 13

Provides a starting point of RNA (or DNA) for DNA polymerase to begin synthesis of the new DNA strand.

Answer 13

Primase

Question 14

Lengthens telomeric DNA by adding repetitive nucleotide sequences to the ends of eukaryotic chromosomes.

Answer 14

Telomerase