2.2 Nucleic acids

Question 1

What does DNA stand for?

Answer 1

deoxyribonucleic acid

Question 2

What is a nucleotide made up of?

Answer 2

deoxyribose (a pentose sugar), a nitrogenous base, and one phosphate group.

Question 3

What are the names of the nitrogenous bases?

Answer 3

guanine, cytosine, adenine and thymine

Question 4

How are nucleotides joined together?

Answer 4

By phosphodiester bonds between the deoxyribose sugar and the phosphate group.

Question 5

What are phosphodiester bonds?

Answer 5

Are strong covalent bonds, which therefore help ensure that the genetic code is not broken down

Question 6

What is the sugar-phosphate backbone?

Answer 6

Describes the strong covalent bonds between the sugar and phosphate groups that hold the polymer together

Question 7

How does the structure of DNA relate to its function?

Answer 7

• Stable structure due to sugar-phosphate backbone and the double helix
  -Double stranded so replication can occur using one strand as a template
• Weak hydrogen bonds for easy unzipping of the two strands in a double helix during replication
  -Large molecule to carry lots of info
  -Complementary base pairing allows identical copies to be made.

Question 8

First step of semi-conservative replication

Answer 8

DNA Helicase breaks the hydrogen bonds between the complementary base pairs between the two strands within double helix. This causes the double helix to unwind

Question 9

Second step of semi-conservative dna replication

Answer 9

Each of separated DNA strands act as a template
Free DNA nucleotides within the nucleus are attracted to their complementary base pairs on the template strands.

Question 10

Step 3 of semi-conservative replication

Answer 10

Adjacent nucleotides are joined together by a condensation reaction.
DNA Polymerase catalyses the joining of adjacent nucleotides.

Question 11

Step 4 of semi-conservative replication

Answer 11

Two sets of daughter DNA contains one strand of the parental (original) DNA and one newly synthesised strand

Question 12

What is ATP used for?

Answer 12

ATP is an immediate source of energy for biological processes

Question 13

What is ATP comprised of?

Answer 13

Adenine
Ribose (pentose sugar)
Three inorganic phosphate groups

Question 14

How is ATP made?

Answer 14

made during respiration from ADP adenosine triphosphate, by the addition of an inorganic phosphate via a condensation reaction and using the enzyme ATP synthase.

Question 15

What happens when ATP is hydrolysed?

Answer 15

by breaking one of the bonds between the inorganic phosphate groups, a small amount of energy is released which can be used in chemical reactions

Question 16

What is phosphorylation?

Answer 16

When inorganic phosphate released during hydrolysis of ATP can be bonded onto different compounds to make them more reactive.

Question 17

Why is ATP the immediate energy source for cells rather than glucose?

Answer 17

-ATP releases energy in small manageable amount so no energy is wasted
- ATP is a small and soluble molecule so can easily be transported around the cell.
- Only one bond has to be hydrolysed to release energy which is why energy release is immediate. Glucose would need several bonds to be broken down
- It can transfer energy to another molecule by transferring one of its phosphate groups. (phosphorylation)
- ATP can’t pass out of the cell, the cell always has an immediate source of energy.

Question 18

Why is water a dipolar molecule?

Answer 18

Water has an unevenly distributed charge due to the fact that the oxygen atom is slightly negative and hydrogen atoms are slightly positive

Question 19

Why is water a metabolite?

Answer 19

Since it is involved in lots of chemical reactions or metabolism.

Question 20

Examples of when water is used in reactions?

Answer 20

photosynthesis, hydrolysis, condensation reactions

Question 21

Why is water important as a solvent in plants?

Answer 21

substances can be easily transported in the xylem and phloem

Question 22

Which type of molecules do not dissolve in water?

Answer 22

non-polar molecules, such as lipids, therefore they are described as hydrophobic.

Question 23

Why does water have a high specific heat capacity?

Answer 23

Since some of the heat energy is used to break the hydrogen bonds between water molecules.

Question 24

Why is having a high specific heat capacity useful in water?

Answer 24

Temp of water remains relatively stable even if surrounding temp fluctuates significantly. Therefore animals and plants will not get too hot or cold, so enzymes will not denature.

Question 25

Why does water have a large latent heat of vaporisation?

Answer 25

This means a lot of energy is required to convert water in its liquid state to a gaseous state. This is due to hydrogen bonds between water molecules.

Question 26

Why is water having a large latent heat of vaporisation an advantage to organisms?

Answer 26

It provides a cooling effect to both animals and plants. Eg, when humans sweat, they release water on their skin. Heat from skin is transferred to the water to evaporate it, therefore removing a lot of heat and cooling the organism.

Question 27

What is meant by cohesion?

Answer 27

Used to describe water molecules sticking together due to hydrogen bonds.

Question 28

Advantage of cohesion in water?

Answer 28

-When water moves up in xylem in plants in a continuous column of water, rather than moving up in a droplet at a time.
-Provides surface tension to water. Enables certain animals that are able to live on surface of water. Therefore they will avoid predators in the water.