Biology 2.1.3 Nucleotides And Nucleic Acids

Question 1

Describe the structure of a nucleotide

Answer 1

Phosphate group
Pentose sugar
Nitrogenous organic base

Question 2

State the difference between an RNA nucleotide and DNA nucleotide

Answer 2

RNA has a ribose pentose sugar
DNA has a deoxyribose pentose sugar

Question 3

Define purines

Answer 3

Purines are bases which contain double carbon ring structures.

Adenine and guanine are purines.

Question 4

Define pyrimidines

Answer 4

Pyrimidines are bases which contain single carbon ring structures.

Thymine and cytosine are pyrimidines.

Question 5

Outline the synthesis of polynucleotides

Answer 5

Condensation reaction between phosphate groups and carbons of pentose sugars form phosphodiester bonds between adjacent nucleotides.

This forms a sugar-phosphate backbone.

Question 6

Outline the breakdown of polynucleotides

Answer 6

Hydrolysis reactions break phosphodiester bonds to release individual nucleotides.

Question 7

Describe the structure of ATP and ADP

Answer 7

ATP
- Three phosphate groups
- Ribose sugar
- Nitrogenous base

ADP
- Two phosphate groups
- Ribose sugar
- Nitrogenous base

Question 8

Describe the structure of DNA

Answer 8

Two strands of polynucleotides coil into a helix shape
Two strands are held together by hydrogen bonding between complementary base pairs
Two strands are parallel and run in opposite directions

DNA has a double helix, anti-parallel structure.

Question 9

Explain complementary base pairing in a DNA molecule

Answer 9

Adenine and Thymine form two hydrogen bonds
Cytosine and guanine form three hydrogen bonds

Question 10

Outline the process of semi-conservative replication

Answer 10

DNA molecule is separated into two single strands
Free DNA nucleotides will form hydrogen bonds with complementary base pairings
Adjacent nucleotides will form phosphodiester bonds

Two new DNA molecules are produced, consisting of one old strand and one new strand.

Question 11

Explain the role of enzymes in semi-conservative replication

Answer 11

DNA helicase - separation of DNA strand by catalysing reactions that break down hydrogen bonds between complementary base pairs

DNA polymerase - Formation of sugar phosphate backbone by catalysing the formation of phosphodiester bonds between adjacent nucleotides

Question 12

State the importance of DNA replication

Answer 12

Cells divide to produce more cells needed for growth or repair of tissues

Cells produced as a result of cell division are genetically identical to the parent cell and each-other.

Question 13

Define mutation

Answer 13

Random and spontaneous change in the sequence of bases in a DNA molecule

Question 14

Define genetic code, triplet codon, degenerate code, universal code, gene, non-overlapping code

Answer 14

Genetic code - DNA codes for sequence of amino acids
Triplet codon - three bases code for an amino acid
Degenerate code - several triplet codons code for one amino acid
Universal - all organisms use the same genetic code
Gene - a section of DNA that codes for a protein
Non overlapping - each nucleotide is only part of one triplet of bases

Question 15

Outline the process of transcription, stating the roles of RNA polymerase and messenger (m)RNA

Answer 15

DNA molecule is separated into two strands
Free RNA nucleotides form complementary base pairing with exposed DNA bases
Adjacent RNA nucleotides form phosphodiester bonds catalysed by RNA polymerase
mRNA molecule detaches from DNA strand and leaves through nuclear pore
DNA double helix reforms

Question 16

Outline the process of translation, stating the roles of transfer (t)RNA, ribosomes and messenger (m)RNA

Answer 16

mRNA binds to the ribosome from the start codon
tRNA with complementary anticodon binds to the start codon
tRNA carries the amino acid which corresponds to the codon of the mRNA
This repeats with another tRNA molecule
The adjacent amino acids form a peptide bond
The ribosome then moves along the mRNA , releasing the first tRNA and the process repeats until a stop codon is reached

Question 17

What is produced as a result of translation?

Answer 17

A polypeptide.
The sequence of amino acids in a polypeptide is the primary structure of a protein.

Question 18

What is the process of purifying DNA by precipitation?

Answer 18

Purpose: To isolate DNA from a mixture of cellular components.

Steps:

Cell Lysis: Break open cells to release DNA, often using a detergent to dissolve cell membranes.
Removal of Proteins: Add a protease or use salt (e.g., NaCl) to separate proteins from DNA.
Precipitation: Add alcohol (e.g., ethanol) to the solution. DNA is not soluble in alcohol and precipitates out of solution.
Isolation: Use a centrifuge or careful technique to collect the precipitated DNA. It can then be spooled or washed to remove impurities.

Question 19

What aree the key concepts for the purification of DNA by precipitation

Answer 19

*DNA is insoluble in alcohol and can be precipitated by changing the solubility conditions.
*The role of salt - to separate proteins from DNA - and alcohol - DNA is insoluble in alcohol - in promoting DNA precipitation.
*The importance of maintaining cold temperatures to prevent DNA degradation.