Nucleotide Structure & Function

Question 1

What are nucleotides?

Answer 1

Nucleotides are the building blocks of nucleic acids.

Question 2

What are nucleotides made of?

Answer 2

Nucleotides are made of a nitrogenous base (what differs), a pentose (5-carbon sugar of backbone), and 1 to 3 phosphates (backbone and energy).

Question 3

What are purines?

Answer 3

Purines are Adenine (A) and Guanine (G) found in both DNA and RNA. (Remember: 2 syllables = 2 rings!)

Question 4

What are other purine metabolites not found in nucleic acids?

Answer 4

Xanthine, Hypoxanthine, Uric Acid

Question 5

What are pyrimidines?

Answer 5

Cytosine (C) in both DNA and RNA. Thymine (T) in DNA. Uracil (U) in RNA. (Remember: 1 ring only!)

Question 6

What is keto-enol tautomerism?

Answer 6

Electrons are floating around due to the double bonds of rings. This allows these isomers to readily interconvert, affecting the fidelity of DNA replication. (Remember: Lactam is keto. Lactim is enol.)

Question 7

What two types of pentose are found in nucleic acids?

Answer 7

DNA has 2-deoxyribose. RNA has ribose.

Question 8

Why is RNA less stable than DNA?

Answer 8

Presence of extra OH in ribose makes RNA less stable because the OH will react with highly charged phosphates of the backbone, causing the strand to break.

Question 9

What is a nucleoside?

Answer 9

Nucleosides are formed by covalently linking a base to the 1’C of a pentose. If that pentose is deoxyribose, it is a deoxyribonucleoside. If that pentose is ribose, it is a ribonucleoside.

Question 10

What configuration does the nucleoside prefer?

Answer 10

It can be in syn or anti but prefers anti.

Question 11

When does a nucleoside become a nucleotide?

Answer 11

When 1, 2, or 3 phosphates attach to the pentose (most commonly to the 5’C).

Question 12

Why are nucleoside di- and tri-phosphates high energy compounds?

Answer 12

They have hydrolytic energy associated with the acid-anhydride bonds.

Question 13

What is the most important function of nucleotides?

Answer 13

They are precursors of nucleic acids and DNA is the carrier of genetic info.

Question 14

How do nucleotides function as carriers of energy?

Answer 14

Negative oxygens repel one another so it is energetically favorable to separate but requires energy to cleave bond. Cleaving uses energy to generate a lot more energy.

Question 15

How do nucleotides function as carriers of specific building blocks?

Answer 15

A phosphate can be cleaved and still attach what is left to something else, then cleave remaining phosphates for energy there also.

Question 16

What is an example of nucleotides functioning as carriers of energy?

Answer 16

High energy bonds of ATP and GTP

Question 17

What is an example of nucleotides functioning as carriers of specific building blocks?

Answer 17

UDP-glucose donates sugars in the synthesis of glycogen and glycoproteins.

Question 18

What is an example of nucleotides functioning as regulatory signals?

Answer 18

Second messengers like cAMP and cGMP mediate the response from certain hormones.

Question 19

What is an example of nucleotides functioning as methyl donors?

Answer 19

S-Adenosylmethionine (+ ATP) donates methyl groups in certain metabolic pathways.

Question 20

What is an example of nucleotides functioning as coenzymes in oxidation-reduction reactions?

Answer 20

Niacin, Nicotinamide, or Tryptophan —> NAD+ (+ATP) —> NADP+

Riboflavin (+ ATP) —> Flavin mononucleotide (+ADP)
—> Flavin adenine dinucleotide

Question 21

What is an example of a nucleotide functioning as a coenzyme in metabolism?

Answer 21

Coenzyme A carries acyl groups (fatty acids) in metabolism.

Question 22

Why are drugs usually nitrogenous base analogs?

Answer 22

Nucleotides are so important to cell functions that biochemistry can be adjusted by adding something that looks like a nucleotide.

Question 23

What two drugs are nitrogenous base analogs?

Answer 23

5-Fluorouracil is anti-cancer agent that inhibits replication of cancer cell.

Azidothymidine (AZT) is anti-HIV drug that interrupts replication of HIV virus.

Question 24

In Keto-Enol Tautomerism, what is Lactam?

Answer 24

Lactam is Uracil in the keto form because the top group is a carbonyl (C=O).

Question 25

In Keto-Enol Tautomerism, what is Lactim?

Answer 25

Lactim is Uracil in the enol form because the top group is a hydroxyl (OH).

Question 26

What is the significance of Lactim?

Answer 26

Lactim is less thermodynamically stable so a phoshorylated compound becomes trapped. Changes in its hydrogen bonding pattern can also lead to base pair mismatch mutations.