Nucleic Acids

Question 1

What are the three components of a nucleotide?

Answer 1

A pentose sugar
A phosphate group
A nitrogen-containing organic base (C, T, U, A and G)

Question 2

How are the three components joined to make a mononucleotide?

Answer 2

Through a condensation reaction

Question 3

How are two mononucleotides joined?

What does it make and what is the bond between it called?

Answer 3

Deoxyribose sugar of one and phosphate group of another.

Bond is called a phosphodiester bond and a dinucleotide is formed.

Question 4

What is the continued linking of mononucleotides called?

Answer 4

Polynucleotides

Question 5

What are the different structures of RNA?

Answer 5

Single, relatively short, polynucleotide chain
Pentose sugar is always ribose
Uracil base instead of thymine

Question 6

How do the two strands of DNA join?

What does the overall structure look like?

Answer 6

Through hydrogen bonds

A double helix

Question 7

What are the two base pairings in DNA?

Answer 7

Adenine - Thymine
Guanine - Cytosine
THEY ARE COMPLEMENTARY

Question 8

How do the features of DNA help its stability?

Answer 8

Phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
Hydrogen bonds link the organic base pairs forming bridges between phosphodiester sides. Three h bonds between C-G, the higher the proportion of C-G pairings, the more stable the DNA molecule.

Question 9

How is the DNA molecule adapted to carry out its functions?

Answer 9

Very stable structure and does not normally mutate.
Two separate strands joined only by hydrogen bonds, and they can separate during DNA replication and protein synthesis.
Extremely large molecule so carries a lot of genetic information.
Base pairs within deoxyribose-phosphate backbone, so genetic information is somewhat protected from corruption.
Base pairings leads to DNA being able to replicate and to transfer information as mRNA.

Question 10

What are the four requirements for semi-conservative replication?

Answer 10

Four types of nucleotides, each with their bases must be present.
Both strands of DNA molecule act as a template for the attachment of these nucleotides.
The enzyme DNA polymerase.
A source of chemical energy required to drive the process.

Question 11

Explain the process of semi-conservative replication

Answer 11

DNA helicase breaks hydrogen bonds linking the base pairs
Double helix separates and unwinds
Each exposed poly nucleotide acts as a template that complementary free nucleotides bind to by specific base pairing
Nucleotides are joined in a condensation reaction by DNA polymerase
Each of the two new DNA molecules have one of the original strands of DNA

Question 12

What are the three parts of an ATP molecule?

Answer 12

adenine
ribose
phosphates

Question 13

What can we say about the bonds between phosphate groups? How does this help them?

Answer 13

The bonds are unstable and have a low activation energy.

This means they are easily broken, and can release a considerable amount of energy.

Question 14

What enzyme is used to convert ATP to ADP? And what is this type of reaction called?

Answer 14

ATP hydrolase

Hydrolysis reaction

Question 15

What is the name of the reaction that leads to the synthesis of ATP from ADP?
What enzyme catalyses this?

Answer 15

Condensation reaction

ATP synthase

Question 16

How is a phosphate added to ADP to synthesise ATP?

Answer 16

Photophosphorylation
Oxidative phosphorylation
Substrate-level phosphorylation

Question 17

Why is ATP described as a immediate energy source?

Answer 17

It has unstable phosphate bonds.
ATP energy released in smaller, more manageable quantities than glucose.
Hydrolysis of ATP to ADP is a single reaction that releases immediate energy.
It cannot be stored, must be continuously made in mitochondria (of cells that need it).

Question 18

What processes is ATP used in?

Answer 18

Metabolic processes - provides energy needed to build up macromolecules.
Movement - provides energy for muscle contraction
Active transport - provides energy to change the shape of carrier proteins in plasma membranes
Secretion - needed to form the lysosomes necessary for the secretion of cell products
Activation of molecules - the inorganic phosphate released during the hydrolysis of ATP. Can be used to phosphorylation other compounds in order to make them more reactive

Question 19

Water is dipolar. Give 8 features of water and explain briefly.

SSLMATCC

Answer 19

Specific heat capacity - high, so a buffer against sudden temperature change
Solvent - readily dissolves other substances
Latent heat of vaporisation - high, evaporation of water in mammals allows to maintain heat (sweating when hot)
Metabolite - used to break down many complex molecules by hydrolysis, made in condensation reactions
Adhesion - hydrogen bonds form between +ve and -ve poles; and they can stick together
Transparent - aquatic plants can photosynthesise
Cohesive - hydrogen bonding means water has large cohesive forces, allows it to be pulled up through a tube (xylem vessel)
Compression - not easily compressed and therefore provides support