Structure of RNA and DNA

Question 1

What are the 3 components which make up a nucleotide?

Answer 1

• A pentose sugar
• A phosphate group
• A nitrogen-containing organic base - cytosine, thymine, adenine, guanine, (uracil).

Question 2

How are the pentose sugar, phosphate group, and organic base all joint together?

Answer 2

By condensation reaction to form a single nucleotide.

Question 3

Draw the structure of a mononucleotide.

Answer 3

Draw on a piece of paper.

Question 4

What bond is formed between the deoxyribose sugar and the phosphate group to form a dinucleotide?

Answer 4

Phosphodiester bond. This is a type of covalent bond.

Question 5

What is the name for a long chain of linked mononucleotides?

Answer 5

Polynucleotide.

Question 6

What is RNA?

Answer 6

RNA is a polymer made up of nucleotides.

It’s single, quite short, with a ribose sugar, phosphate group, and bases are always A, G, C, U, where U replaces T.

Question 7

What are the 3 types of RNA?

Answer 7

1) Transfers genetic information from DNA to the ribosomes.
2) Ribosomes themselves are made up of proteins which is another type of RNA.
3) Involved in protein synthesis.

Question 8

In 1953 who worked out the structure of DNA?

Answer 8

James Watson and Francis Crick.

Question 9

What are the differences between an RNA and DNA?

Answer 9

• DNA has deoxyribose as its pentose sugar whereas RNA has ribose as its pentose sugar.
• DNA contains bases of A, T, C, G whereas RNA contains A, U, C, G.
• DNA is made up of 2 strands of nucleotides (polynucleotide) whereas RNA is just single.

Question 10

How are the 2 strands in DNA joint together?

Answer 10

Joint by hydrogen bonds formed between certain bases. Each of the strands is extremely long.

Question 11

What are the rules of the base pairing?

Answer 11

A pairs with T
G pairs with C
As a result of the base pairings, A is said to be complementary with T and G is complementary to C.

Question 12

How many hydrogen bonds are between each base pair?

Answer 12

A and T has 2 hydrogen bonds.

G and C have 3 hydrogen bonds.

Question 13

What is the structure of DNA?

Answer 13

DNA has a double helix structure, where the uprights of phosphate and deoxyribose wind around one another to form a double helix and they form the structural backbone of the DNA molecule.

Question 14

Explain why is it important for base pairings to occur by joining hydrogen bonds and not other bonds e.g. covalent bonds.

Answer 14

Because hydrogen bonds are relatively weak therefore it can be easily broken down for DNA replication.

Question 15

Describe the features of DNA which makes it suitable to store genetic information.

Answer 15

The phosphate backbones protect the bases inside so it won’t damage the genetic information.
The molecule is coiled up into a double helix, therefore, it is very compact so a lot of information can be stored into a small space.

Question 16

Why is DNA a stable molecule?

Answer 16

• The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
• C and G base pairings are connected by 3 hydrogen bonds whereas A and T are only connected 2 hydrogen bonds so more of the C and G pairings, the more stable of the DNA molecule.

Question 17

What are the functions of DNA?

Answer 17

It is the hereditary material which passes down genetic information from cell to cell.
There are around 3.2 billion base pairings so that means there’s a variety of combinations which provides genetic diversity.

Question 18

How is DNA adapted for its function?

Answer 18

• It has a very stable structure so it can pass down information from generations without change. It only rarely mutates.
• The 2 strands are joined by hydrogen bonds so it can be easily broken during DNA replication.
• It’s a large molecule, therefore, it can carry a lot of information.
• By having the base pairs inside the helical cylinder of the deoxyribose-phosphate backbone, it is protected against the chemical and physical forces.
• Base pairings allow the DNA being able to replicate and to transfer the information as mRNA.

Question 19

Describe the features of RNA which make it suitable for transferring genetic information from the nucleus.

Answer 19

• It follows the base pairing rules so it can make complimentary copies of the DNA bases.
• It’s single stranded and small so it can be easily transported out of the nucleus.

Question 20

Why is the DNA molecule antiparallel?

Answer 20

Because the nucleotides are arranged into double strands where one strand goes from 5’ to 3’ direction while the other one goes from 3’ to 5’ so it’s said to be antiparallel.