Nucleic Acids

Question 1

What does DNA and RNA stand for?

Answer 1

DNA stands for deoxyribonucleic acid.
RNA stands for ribonucleic acid.

Question 2

Why are DNA strands known as polymers?

Answer 2

They are composed of many monomers - nucleotides.

Question 3

What bonds are formed between adjacent nucleotides?

Answer 3

Phosphodiester bonds.

Question 4

How are phosphodiester bonds formed?

Answer 4

They are formed during a condensation reaction and eliminate water.

Question 5

What are nucleotides composed of?

Answer 5

A 5 carbon pentose sugar - DNA contains a deoxyribose sugar but RNA contains a ribose sugar.

A phosphate group.

A nitrogenous base - adenine (A), guanine (G), cytosine (C), thymine (T) / uracil (U) in RNA.

Question 6

What are the purine bases?

Answer 6

They contain a double ring structure and are adenine/guanine.

Question 7

What are pyrimidine bases?

Answer 7

They contain a single ring structure and are cytosine/thymine or uracil.

Question 8

What proteins are associated with DNA?

Answer 8

Histones - proteins associated with DNA and helps them to maintain a super coiled double helix structure.

Question 9

What are the general complementary base pairings?

Answer 9

Purines will always pair with pyrimidines.
So, adenine always pairs with thymine/uracil but guanine will always pair with cytosine.

Question 10

What are formed between the complementary bases?

Answer 10

Hydrogen bonds form between them. A to T forms 2 hydrogen bonds whilst G to C forms 3 hydrogen bonds.

Question 11

How is a polynucleotide strand formed?

Answer 11

It is made of many monomers (nucleotides) that are joined together by a phosphodiester bond between adjacent nucleotides during a condensatin reaction and removes water. Many nucleotides are joined this way to form a sugar-phosphate backbone.

Question 12

How can a polynucleotide strand be broken?

Answer 12

Through a hydrolysis reaction using water to break the phosphodiester bonds and it releases the nucleotide monomers.

Question 13

What features allow genetic information to be passed from one generation to another?

Answer 13

1. Sugar-phosphate backbone - This protects coding bases on the inside of the helix.
2. Double stranded - This allows strands to act as templates in DNA replication.
3. Large molecule - It stores lots of information.
4. Double helix - This makes the molecule compact.
5. Complementary base pairing - This allows accurate DNA replication.
6. Weak hydrogen bonds - This allows strands to separate in DNA replication using the enzyme helicase.

Question 14

Why do purines and pyrimidines always form a complementary base pairing?

Answer 14

It is because it helps to maintain a constant distance between the sugar phosphate backbone and the ‘rungs of the ladder’ are the same length.

Question 15

List some similarities between DNA and RNA.

Answer 15

1. DNA and RNA both contain nucleotides that are joined together by phosphodiester bonds to form a polynucleotide strand.
2. They are both involved in storage, transmission, and expression of genetic information.
3. They both contain phosphodiester bonds between adjacent nucleotides to form the sugar phosphate backbone.
4. Both DNA and RNA contain the nitrogenous bases - A, C, G (adenine, guanine, cytosine).

Question 16

List some differences between DNA and RNA.

Answer 16

1. DNA is longer than RNA.
2. DNA contains the nitrogenous base T, thymine but RNA has U, uracil.
3. DNA is made of the sugar deoxyribose but RNA is composed of a ribose sugar.
4. DNA has one less oxygen than RNA.
5. DNA has 2 polynucleotide strands but RNA only has 1 polynucleotide strand.

Question 17

What are two major processes in protein synthesis?

Answer 17

Transcription and translation.

Question 18

What was the purpose of the Meselson and Stahl experiment.

Answer 18

To show/prove that DNA undergoes semi-conservative replication.

Question 19

Describe the general method of the Meselson and Stahl experiment.

Answer 19

1. Bacteria were grown in a medium containing, so all their DNA is ‘heavy’.
2. The bacteria were transferred to a medium with for one round of replication, so the lighter nitrogen was incorporated into any new DNA strands they made.
3. The DNA was extracted and centrifuged.
4. Steps 2-3 were repeated for another round of replication.
5. The distribution of heavy and light DNA was analysed to track how the DNA was replicating:

Results:
The heavier bands sink lower in the test tube.

The intermediate bands, made of DNA with one heavy strand and one light strand, are in the middle of the test tube.

The lighter bands are higher up in the test tube.

This experiment shows us that when DNA is replicated it contain 1 strand of original DNA and 1 new strand of DNA.

Question 20

What is formed when DNA is wound around histone proteins?

Answer 20

It forms a DNA-histone complex.

Question 21

How can the various sequences of genetic code be summarised.

Answer 21

The possible combinations of the genetic code can be assorted into a table for the triplets/codon.