1.5.3 The Structure of DNA

Question 1

The nucleic acid DNA is a

Answer 1

polynucleotide – it is made up of many nucleotides bonded together in a long chain

Question 2

A DNA nucleotide

Answer 2

Question 3

DNA molecules are made up of

Answer 3

two polynucleotide strands lying side by side, running in opposite directions

Question 4

DNA molecules are made up of two polynucleotide strands lying side by side, running in opposite directions – the strands are said to be

Answer 4

antiparallel

Question 5

Each DNA polynucleotide strand is made up of

Answer 5

alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone

Question 6

Each DNA polynucleotide strand is made up of alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone, these bonds are

Answer 6

covalent bonds known as phosphodiester bonds

Question 7

The phosphodiester bonds link

Answer 7

the 5-carbon of one deoxyribose sugar molecule to the phosphate group from the same nucleotide

Question 8

The phosphodiester bonds link the 5-carbon of one deoxyribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by

Answer 8

another phosphodiester bond to the 3-carbon of the deoxyribose sugar molecule of the next nucleotide in the strand

Question 9

Each DNA polynucleotide strand is said to have

Answer 9

a 3’ end and a 5’ end (these numbers relate to which carbon on the pentose sugar could be bonded with another nucleotide)

Question 10

As the strands run in opposite directions (they are antiparallel), one is known as

Answer 10

the 5’ to 3’ strand

Question 11

As the strands run in opposite directions (they are antiparallel), one is known as the 5’ to 3’ strand and the other is known as

Answer 11

the 3’ to 5’ strand

Question 12

The nitrogenous bases of each nucleotide project out from the backbone towards

Answer 12

the interior of the double-stranded DNA molecule

Question 13

A single DNA polynucleotide strand showing the positioning of the ester bonds

Answer 13

Question 14

The two antiparallel DNA polynucleotide strands that make up the DNA molecule are held together by

Answer 14

hydrogen bonds between the nitrogenous bases

Question 15

These hydrogen bonds always occur between the same

Answer 15

pairs of bases

Question 16

The purine adenine (A) always pairs with

Answer 16

the pyrimidine thymine (T) – two hydrogen bonds are formed between these bases

Question 17

The purine guanine (G) always pairs with

Answer 17

the pyrimidine cytosine (C) – three hydrogen bonds are formed between these bases

Question 18

This is known as

Answer 18

complementary base pairing

Question 19

These pairs are known as

Answer 19

DNA base pairs

Question 20

A section of DNA – two antiparallel DNA polynucleotide strands held together by hydrogen bonds

Answer 20

Question 21

DNA is described as a

Answer 21

double helix (this refers to the three-dimensional shape that DNA molecules form)

Question 22

DNA molecules form a three-dimensional structure known as a DNA double helix

Answer 22

Question 23

name the different components of a DNA molecule

Answer 23

sugar-phosphate backbone, nucleotide, complementary base pairs, phosphodiester bonds, hydrogen bonds

Question 24

phosphodiester bonds join

Answer 24

the nucleotides in the sugar-phosphate backbone

Question 25

hydrogen bonds join

Answer 25

the bases of the two complementary strands together

Question 26

the bases are complementary, so the number of

Answer 26

A = T and C = G