1.2 (2) - Nucleic Acids

Question 1

What is a nucleic acid?

Answer 1

A complex organic substance present in living cells whose molecule consists of many nucleotides.

Question 2

What are the 3 components of a DNA nucleotide?

Answer 2

• Phosphate group
• Pentose sugar
• Organic nitrogenous base (adenine, thymine, guanine, cytosine)

Question 3

What are the 3 components of a RNA nucleotide?

Answer 3

• Phosphate group
• Pentose sugar
• Organic nitrogenous base (adenine, uracil, guanine, cytosine)

Question 4

What bond joins nucleotides together?

Answer 4

Phosphodiester bond

Question 5

Through what reaction are the bonds between the nucleotide’s components formed?

Answer 5

Condensation reaction

Question 6

Describe RNA

Answer 6

• Single-stranded polynucleotide chain
• Pentose sugar is always a ribose sugar
• Uses A, G, C and U nitrogenous bases
• Takes 3 forms:
  - Transfer (tRNA)
  - Messenger (mRNA)
  - Ribosomal (rRNA)

Question 7

Describe DNA

Answer 7

• Forms a double-stranded pair of extremely long polynucleotide chains
• Pentose sugar is always a deoxyribose sugar
• Uses A, G, C and T nitrogenous bases
• Stable molecule that is better suited to long-term storage of DNA because:
  • 2 strands of RNA are bonded together by hydrogen
    bonds between complementary base pairs
  • Phospholipid backbone is relatively unreactive and
    protects the more reactive bases

Question 8

What are some functional adaptations of DNA?

Answer 8

• Hereditary molecule
• Highly stable molecule
• Very large molecule

Question 9

What is the method of DNA replication called?

Answer 9

Semi-conservative replication

Question 10

What does ‘semi-conservative replication’ imply?

Answer 10

Every time DNA is copied, half is kept and half is made new

Question 11

Explain the stages of semi-conservative replication

Answer 11

1) DNA helicase breaks H bonds between polynucleotides
2) DNA unwinds into 2 strands
3) Each exposed strand acts as a template so that free, complementary nucleotides can bind to specific bases
4) The free nucleotides join via a condensation reaction - DNA polymerase joins the new nucleotides together
5) The template strand and the new strand of DNA rejoin via hydrogen bonds and re-coil
6) Each new DNA molecule contains one of the original DNA strands (half the original DNA)

Question 12

What is ATP?

Answer 12

An immediate source of energy used to power cellular processes

Question 13

What kind of molecule is ATP?

Answer 13

Phosphorylated molecule (phosphates are added)

Question 14

What does ATP stand for?

Answer 14

Adenosine triphosphate

Question 15

What are the 3 components of an ATP molecule?

Answer 15

• Adenine base
• Ribose sugar
• 3 phosphate groups (joined together by 2 phosphoanhydride bonds)

Question 16

What happens when ATP is hydrolysed?

Answer 16

It can turn into ADP with 1 Pi group

Question 17

What enzyme catalyses the hydrolysis reaction that causes ATP to turn into ADP?

Answer 17

ATP hydrolase

Question 18

What can happen to the Pi released during the hydrolysis of ATP?

Answer 18

It can phosphorylate other compounds, which can make them more reactive

Question 19

By what reaction does the resynthesis of ADP and Pi undergo?

Answer 19

Condensation

Question 20

What enzyme catalyses the condensation reaction between ADP and Pi, to make ATP?

Answer 20

ATP synthase

Question 21

What are some of the uses of ATP?

Answer 21

It’s used in:

 - Metabolic processes
 - Muscle movement
 - Active transport
 - Secretion of lysosomes
 - Activation of molecules (phosphorylating them makes them more reactive)

Question 22

What are 5 useful properties of water?

Answer 22

• Dipolar molecule
• Water and hydrogen bonding
• High specific heat capacity
• High latent heat of vaporisation
• Cohesion and surface tension

Question 23

What do we mean when we say that water is ‘dipolar’?

Answer 23

Even though the molecule has an overall negative charge, the Hs have a slight +ve charge and the O has a slight -ve charge, meaning it’s got +ve and -ve poles

Question 24

What is the significance of water and hydrogen bonding?

Answer 24

Hydrogen bonds form important forces that cause water molecules to stick together, giving it its unusual properties

Question 25

What is the significance of water having a high specific heat capacity?

Answer 25

Because water molecules stick together it takes more energy to separate them, so water has a high boiling point

Question 26

What is the significance of water having a high latent heat of vaporisation?

Answer 26

The H bonds between water molecules means that lots of energy is needed to evaporate 1g of water

Question 27

What is the significance of water molecules being cohesive/having surface tension?

Answer 27

Water molecules stick together (cohesion) - because of its H bonds, water has large cohesive forces that allow it to be pulled through tubes (eg. xylem)

When water meets the air, it tends to be pulled back to the water rather than escaping from it (the force is called surface tension). This ST means that water is strong enough to support small insects because it acts like a skin

Question 28

Why is water important in organisms?

Answer 28

• Used in metabolism - used and produced in hydrolysis and condensation reactions
• It’s a solvent - can dissolve:
  
  • gases
  • waste products (eg. urea)
  • inorganic ions
  • enzymes

Question 29

Where do you find organic ions?

Answer 29

In solution in the cytoplasm and body fluids (some at high concs and other at low concs)

Question 30

What is the role of inorganic ions?

Answer 30

Each type of ion has a specific role, depending on its properties