DNA The Carrier of Genetic Information

Question 1

Nucleotides

Answer 1

Adenine, thymine, cytosine and guanine. Each nucleotide subunit contains a nitrogenous base. Each base covalently links to a pentose sugar, deoxyribose, which covalently bonds to phosphate group.

Question 2

Purines

Answer 2

Adenine and guanine

Question 3

Pyrimidines

Answer 3

Thymine and Cytosine

Question 4

Backbone of each single DNA chain is formed…

Answer 4

By alternating sugar and phosphate groups, joined by covalent phosphodiester linkages. Each phosphate group attaches to the 5’ carbon of one deoxyribose and to the 3’ carbon of the neightboring deoxyribose.

Question 5

How are DNA strands oriented with respect to each other?

Answer 5

They are antiparallel (running in opposite directions); at each end of the DNA molecule, one chain has a phosphate attached to a 5’ deoxyribose carbon, the 5’ end, and the other has a hydroxyl group attached to a 3’ deoxyribose carbon, the 3’ end.

Question 6

Pairing between bases

Answer 6

Hydrogen bonding between forms links between A and T (2 hydrogen bonds) and G with C (3 hydrogen bonds)

Question 7

Chargaff’s rules

Answer 7

A equals T and G equals C. In numbers.

Question 8

Semiconservative replication

Answer 8

Each daughter double helix consists of an original strand from the parent molecule and a newly synthesized complementary strand.

Question 9

DNA replication

Answer 9

The two strands unwind. Each one serves as a template for forming new complementary strands. Replications beggins as DNA primase synthesizes a short RNA primer. DNA polymerase then adds new nucleotide subunits to the growing DNA strand.

Question 10

DNA helicases

Answer 10

They are enzymes that open the double helix.

Question 11

Topoisomerases

Answer 11

Enzymes that prevent tangling and knotting.

Question 12

Origin of replication

Answer 12

DNA replication is bidirectional, starting at the origin of replication and proceeding in both directions. Multiple origins of replication exists along the DNA.

Question 13

Direction of replication

Answer 13

DNA synthesis always proceeds in a 5’->3’ direction, which requires that one DNA strand, the lagging strand, be synthesized discontinuously, as short Okazaki fragments. Leading strand is synthesized continuously.

Question 14

Repairs in DNA made by

Answer 14

DNA polymerases prooread each newly added nucleotide against its template and correct mistakes.

Question 15

Mismatch repair

Answer 15

Enzymes recognize incorrectly paired nucleotides and remove them; DNA polymerases then fill in the missing nucleotides.

Question 16

Telomeres

Answer 16

Eukaryotic chromosome ends are short, non-coding, repetitive DNA sequences. They shorten with each cell cycle but can be extended by the enzyme telomerase, its ausence may cause aging.