2.6 RNA/DNA Structure

Question 1

What are nucleic acids?

Answer 1

Nucleic acids are the genetic material of the cell

Question 2

What are nucleic acids composed of?

Answer 2

are composed of recurring monomeric units called nucleotides

Question 3

What is each nucleotide composed of? (3)

Answer 3

5-carbon pentose sugar (pentagon)
Phosphate group (circle)
Nitrogenous base (rectangle)

Question 4

What is the central molecule of a nucleotide and what is attached to it?

Answer 4

Both the phosphate group and nitrogenous base are attached to the central pentose sugar

Question 5

Where is the nitrogenous base attached to the pentose sugar?

Answer 5

The nitrogenous base is attached to the 1’– carbon atom (right point)

Question 6

Where is the phosphate base attached to the pentose sugar?

Answer 6

The phosphate base is attached to the 5’– carbon atom (left point)

Question 7

What two types of nucleic acid are there?

Answer 7

DNA and RNA

Question 8

What is DNA?

Answer 8

DNA (deoxyribonucleic acid) is a more stable double stranded form that stores the genetic blueprint for cells

Question 9

What is RNA? (structure and role)

Answer 9

RNA (ribonucleic acid) is a more versatile single-stranded form that transfers the genetic information for decoding

Question 10

What are both DNA and RNA polymers of?

Answer 10

Both DNA and RNA are polymers of nucleotides

Question 11

What is the key difference in the structure of DNA and RNA?

Answer 11

DNA does not have a hydroxyl group on C2, just a H

Question 12

What are 3 key structural differences between DNA and RNA? (categories)

Answer 12

Number of strands present
Composition of nitrogenous bases
Type of pentose sugar

Question 13

How does DNA and RNA differ in terms of pentose sugar?

Answer 13

DNA - deoxyribose

RNA - ribose

Question 14

How do DNA and RNA differ in terms of base composition?

Answer 14

DNA - AGCT

RNA - AGCU (uracil)

Question 15

How do DNA and RNA differ in number of strands?

Answer 15

DNA - double-stranded (double helix)

RNA - single stranded

Question 16

What are nucleic acids composed of? How are they linked?

Answer 16

Nucleic acids are composed of nucleotide monomers which are linked into a single strand via condensation reactions

Question 17

What joins in a condensation reaction to from nucleic acids?

Answer 17

The phosphate group of one nucleotide attaches to the sugar of another nucleotide (at the 3’– hydroxyl (-OH) group)

Question 18

What is the name of the bond formed between nucleotide monomers?

Answer 18

This results in a phosphodiester bond forming between the two nucleotides (and water is produced as a by-product)

Question 19

What do the successive condensation reactions between nucleotides form?

Answer 19

Successive condensation reactions result in the formation of long polynucleotide strands

Question 20

What are the polynucleotide chains held together by to form a double helix?

Answer 20

Two polynucleotide chains of DNA are held together via hydrogen bonding between complementary nitrogenous bases

Question 21

How do the bases pair?

Answer 21

Adenine (A) pairs with Thymine (T) via two hydrogen bonds

Guanine (G) pairs with Cytosine (C) via three hydrogen bonds

Question 22

In what way do the strands run and why? What is the official word?

Answer 22

In order for the bases to be facing each other and thus able to pair, the strands must be running in opposite directions

The two strands of DNA are described as being antiparallel

Question 23

How does the atomic arrangement impact the formation of the double helix?

Answer 23

As the antiparallel chains lengthen, the atoms will organise themselves into the most stable energy configuration

This atomic arrangement results in the double-stranded DNA forming a double helix (~10 – 15 bases per twist)

Question 24

What was Watson and Crick’s contribution to the discovery of DNA?

Answer 24

The structural organisation of the DNA molecule was correctly proposed in 1953 by James Watson and Francis Crick

These British scientists constructed models to quickly visualise and assess the viability of potential structures

Question 25

What was Linus Pauling’s contribution to the discovery of DNA?

Answer 25

Their (W&C) efforts were guided by an understanding of molecular distances and bond angles developed by Linus Pauling

Question 26

What was Phoebus Levene’s contribution to the discovery of DNA?

Answer 26

DNA is composed of nucleotides made up of a sugar, phosphate and base – Phoebus Levene, 1919

Question 27

What was Erwin Chargaff’s contribution to the discovery of DNA?

Answer 27

DNA is composed of an equal number of purines (A + G) and pyrimidines (C + T) – Erwin Chargaff, 1950

Question 28

What was Rosalind Franklin’s contribution to the discovery of DNA?

Answer 28

DNA is organised into a helical structure – Rosalind Franklin, 1953 (data shared without permission)

Question 29

What 3 conditions did Watson and Crick’s DNA model fulfil?

Answer 29

DNA strands are antiparallel and form a double helix

DNA strands pair via complementary base pairing
(A = T ; C Ξ G)

Outer edges of bases remain exposed (allows access to replicative and transcriptional proteins)

Question 30

What were 3 problems with the early models made by Watson and Crick?

Answer 30

The first model generated was a triple helix

Early models had bases on the outside and sugar-phosphate residues in the centre

Nitrogenous bases were not initially configured correctly and hence did not demonstrate complementarity

Question 31

How did Franklin gather her data?

Answer 31

The final construction of a correct DNA molecule owed heavily to the X-ray crystallography data generated by Franklin

Question 32

Why was Franklin’s data so crucial?

Answer 32

This data confirmed the arrangement of the DNA strands into a helical structure