DNA Structure

Question 1

DNA consists of basic units known as _____

Answer 1

Nucleotides

Question 2

A DNA nucleotide consists of _____

Answer 2

Deoxyribose sugar, a base and and a phosphate group

Question 3

The deoxribose sugar bonds with the base via a ____ reaction that occurs when the base forms a _____ bond with the C’____ of the deoxribose sugar.

Answer 3

The deoxribose sugar bonds with the base via a condensation reaction that occurs when the base forms a N-glycosidic bond with the C’1 of the deoxribose sugar.

Question 4

The term for the unit formed between the deoxribose sugar and the base (before the phosophate has bonded) is _____

Answer 4

A nucleoside.

Question 5

The bond formed between the phosphate group and the deoxribose sugars C’___ is known as a ____ and is formed via a ____ reaction.

Answer 5

The bond formed between the phosphate group and the deoxribose sugars C’5 is known as a phosphoester bond and is formed via a condensation reaction.

Question 6

Two bases are purines, meaning they are _____ structures. The purine bases are _____

Answer 6

Two bases are purines, meaning they are “two ringed” structures. The purine bases are adenine and guanine.

Question 7

Two bases are pyrimidines, meaning they are ____ structures. The pyrimidine bases are ____

Answer 7

Two bases are pyrimidines, meaning they are “single ring” structures, The pyrimidine bases are thymine and cytosine.

Question 8

Both the bond between deoxyribose sugar and the base, and the bond between the phosphoric acid and deoxyribose sugar are examples of strong ____ bonds.

Answer 8

Both the bond between deoxyribose sugar and the base, and the bond between the phosphoric acid and deoxyribose sugar are examples of strong covalent bonds.

Question 9

A DNA strand is a ____ of deoxyribonucleotides. The nucleotides are joined by bonds between the C’ ___ of the sugar of one nucleotide and the ____ of the next nucelotide.

Answer 9

A DNA strand is a polymer of deoxyribonucleotides. The nucleotides are joined by bonds between the C’ 3 of the sugar of one nucleotide and the phosphate group of the next nucelotide.

Question 10

The bond formed between two nucelotides is known as _____. It is formed via a ___ reaction.

Answer 10

A phosphodiester bond (covalent). Condensation reaction.

Question 11

A long DNA strand consists of an array of bases and a _____

Answer 11

Sugar-phosphate backbone.

Question 12

DNA forms in a ______ direction. Because the strand is elongated by ____

Answer 12

DNA forms in a 5’ to 3’ direction. Because the strand is elongated by the addition of nucelotides to the 3’ end.

Question 13

What is the difference between the 5’ end and the 3’end of a DNA strand?

Answer 13

A 5’ end consists of a hydroxl group attached via the phosphate group to the 5’ of the deoxribose sugar. The 3’ end has an unbound OH group attached to the 3’ of the deoxribose sugar.

Question 14

How is the orientation of two DNA strands described?

Answer 14

Anti-parallel

Question 15

What holds two DNA strands together

Answer 15

The bases of each DNA strand form hydrogen bonds with their complimentary base on the other strand.

Question 16

1. Why don’t pyrimidines pair with each other?

2. Why don’t purines paor with each other?

Answer 16

1. Two pyrimidines can’t pair as they wouldn’t be able to get close enough to form a hydrogen bond
2. Two purines would be too bulky to fit inside the double helix

Question 17

Why doesn’t Adenine ever pair with Cytosine?

Answer 17

Cytosine does not contain groups which can form hydrogen bonds with Adenines hydrogen bond forming groups. Steric hindrance occurs.

Question 18

Why doesn’t Thymine ever pair with Guanine?

Answer 18

Thymine only contains one group which can form a hydrogen bond with Guanine. Steric hindrance occurs.

Question 19

How many hydrogen bonds does a Adenine - Thymine pair have?

Answer 19

2

Question 20

How many hydrogen bonds does a Guanine - Cytosine pair have?

Answer 20

3

Question 21

State the four key facts of arrangement between two DNA strands.

Answer 21

1. The strands are anti-parallel to each other
2. The bases point toward the center
3. The sugar-phosphate backbone forms on the outside
4. The strands form a double helix.