2.4

Question 1

Which bases pair up against each other in a double stranded DNA helix?

Answer 1

A and T

C and G

Question 2

Why must the bases always pair up?

Answer 2

To allow for DNA replication - otherwise we wouldn’t have identical copies.

Question 3

The two DNA strands are antiparallel, what does this mean?

Answer 3

They run in opposite directions

Question 4

What holds the two DNA strands together?

Answer 4

Hydrogen bonds

Question 5

In what sort of reaction are the phosphate, the deoxyribose and base joined to form a nucleotide?

Answer 5

Condensation, forming a phosphodiester bond

Question 6

In what sort of reaction do the nucleotides join together to form a polynucleotide?

Answer 6

Condensation, forming a phosphodiester bond

Question 7

On a polynucleotide where is the free phosphate group?

Answer 7

At the 5’ end because it is attached to the carbon 5’ of the sugar.

Question 8

On a polynucleotide where is the free hydroxide group?

Answer 8

At the 3’ end because it is attached to the carbon 3’ of the sugar.

Question 9

When a new nucleotide is added to the growing polynucleotide which end is it always added to?

Answer 9

5’ end

Question 10

What is a nucleotide?

Answer 10

Nucleic acids are polymers made up from a number of nucleotides joined to each other by condensation. Each nucleotide has three components: a five-carbon or pentose sugar ribose in RNA and deoxyribose in DNA; a phosphate group; a nucleotide base.

Question 11

What is a nucleotide base?

Answer 11

Four different nucleotide bases are found in the nucleotides which make up a DNA molecule. These are adenine, thymine, cytosine and guanine. In RNA, thymine is replaced by another base, uracil. It is the sequence of nucleotide bases in nucleic acids which forms the basis of the genetic code.

Question 12

What is a gene?

Answer 12

A sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain.

Question 13

What is transcription?

Answer 13

The process in which the genetic information contained in a DNA molecule is copied to produce messenger RNA. This is the first stage in protein synthesis.
A molecule of DNA unwinds. The sequence of nucleotides on one of the strands, called the template strand, is used to produce an mRNA molecule by complementary base-pairing.

Question 14

How is transcription catalysed?

Answer 14

By enzymes including RNA polymerase.

Question 15

Give differences between DNA and mRNA.

Answer 15

DNA contains deoxyribose sugar in its nucleotides, while mRNA contains ribose.
DNA has 2 strands in its molecules, while mRNA has one.
DNA contains ATCG. mRNA contains AUGC.
DNA is very long and mRNA is shorter

Question 16

What is DNA?

Answer 16

One type of nucleic acid, called deoxyribonucleic acid. It is a long chain polymer made of many units called nucleotides or mononucleotides.

Question 17

What is mRNA and what does it do?

Answer 17

Messenger RNA is made in the nucleus during transcription. Its three adjacent bases are called a codon. It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it’s used to make a protein during translation.

Question 18

Describe transcription

Answer 18

[describe]

Question 19

Describe translation

Answer 19

[describe]

Question 20

What is tRNA and what does it do?

Answer 20

Transfer RNA is found in the cytoplasm. It has an amino acid binding site at one end and a sequence of three bases at the other end called an anticodon. It carries the amino acids that are used to make proteins to the ribosomes during translation.

Question 21

What is an anticodon?

Answer 21

A sequence of three nucleotide bases on a transfer RNA molecule, which is complementary to the corresponding messenger RNA codon.

Question 22

What is a codon?

Answer 22

A sequence of three nucleotide bases on a messenger RNA molecule that codes for a particular amino acid.