Chapter 2: Nucleic Acids

Question 1

What are nucleic acids?

Answer 1

Nucleic acids are a group of important molecules, most commonly DNA and RNA. They are information carrying molecules.

Question 2

What are ribosomes made from and where are they found?

Answer 2

Ribosomes are molecules made from RNA and proteins which transfer information from DNA to ribosomes.

Question 3

What are the 3 components of a nucleotide?

Answer 3

1) A pentose sugar
2) A phosphate group
3) A nitrogen-containing organic base

Question 4

What is the reaction which forms nucleotides?

Answer 4

Condensation reaction

Question 5

What is the bond which forms between two nucleotides joined to each other?

Answer 5

Phosphodiester bond

Question 6

What are the 4 DNA organic bases? Why do they pair together?

Answer 6

Adenine Thymine Cytosine Guanine The base pairs are complementary

Question 7

What are the 4 RNA organic bases?

Answer 7

Adenine Guanine Cytosine Uracil

Question 8

Describe the structure of DNA:

Answer 8

• Two DNA strands curled in a double helix formation. - Sugar and phosphate form a ‘sugar-phosphate backbone’. - Opposite bases are joined by hydrogen bonds.

Question 9

Who worked out the structure of DNA?

Answer 9

James Watson Francis Crick (Following the work of Rosalind Franklin)

Question 10

What is the function of DNA and where is it found?

Answer 10

DNA is a hereditary material which is responsible for passing genetic information between cells and generations.

Question 11

How is DNA adapted to carry out its function?

Answer 11

• Very stable structure
• 2 seperate strands joined by hydrogen bonds (so they can separate during replication)
• Extremely large molecule
• Base pairs ‘protected’ by helica cylinder
• Base pairing makes DNA replicatin and transfer of information easier and more efficient

Question 12

Define nuclear division:

Answer 12

The process by which he nucleus divides. This includes mitosis and meiossis.

Question 13

Define cytokinesis:

Answer 13

The process following nuclear division in which the whole cell divides.

Question 14

What is semi-conservative DNA replication?

Answer 14

Repliation of a double stranded molecule of nucleic acid, separating into single strands which serve as a replicaion template for the formation of another complementary strand onto each original strand.

Question 15

What are the four requirements for semi-conservative replication?

Answer 15

• Four types of nucleotide (A,T,C,G)
• Both strands of the DNA molecule act as a template
• The enzyme DNA polymerase
• A source of chemical energy

Question 16

Outline the process of semi-conservative replication:

Answer 16

1) The enzme DNA helicase breaks hydrogen bonds between base pairs
2) Double helix separates
3) Each exposed polynuleotide strand acts as a template for the complementary nucleotide
4) The enzyme DNA polymerase joins nucleotides together in a condensation reaction.
5) Each new DNA molecule contains one new and one old strand.

It is called semi-conservative replication as only half of the original DNA has ben saved.

Question 17

What is ATP?

Answer 17

A phosphorylated macromolecule which is the main energy source in both animal and plant cells.

Question 18

What are the three parts of an ATP moleule?

Answer 18

• Adenine: Nitrogen containing organic base
• Ribose: A sugar moleule with a pentose sugar which acts as a backbone
• Phosphates: A chain of three phosphate groups

Question 19

What is the equation for the release of energy via the hydrolysis of ATP?

Answer 19

ATP + (H₂O) —–> ADP + P_i + (energy)

Question 20

What features of ATP make it a suitable source of energy for living organisms?

Answer 20

• It has a low activation energy so is easily broken down
• It is unstable so is easily broken down
• It releases energy in small, manageable amounts
• It releases energy in a single, simple reaction
• It is an immediate energy source (isn’t stored)
• It is soluble so can be used in cells

Question 21

What reacton takes place to break down ATP?

Answer 21

Hyrolysis catalysed by ATP hydrolase

Question 22

What reaction takes place to synthesise ATP?

Answer 22

Condensation with the enzyme ATP synthase

Question 23

Where does ATP synthesis occur?

Answer 23

• In chlorophyll-containing plant cells durng photosynthesis (phosphorylation)
• In plant and animal cells during respiration (oxidative phosphorylation)
• In plant and animal cells during the transfer of phosphate groups between cells (substrate-level phosphorylation)

Question 24

Name and describe 5 energy-requiring processes where ATP is used:

Answer 24

1) Metabolic processes: building of marcromolecules
2) Movement: energy for muscle contraction (i.e. filaments sliding across each other)
3) Active transport: energy changes shape of carrier protiens and allows molecules to move against concentration gradient
4) Secretion: ATP forms lysosomes which secrete cell products
5) Activation of molecules: P_i can phosphorylate other compounds and lower their activation energy. P_i is released during the hydrolysis of ATP

Question 25

What is water?

Answer 25

Water is a major component of cells, a metabolite and a solvent for many metabolic reactions

Question 26

Why is water described as dipolar?

Answer 26

Oxygen has a slight negative charge while hydrogen has a slight positive charge

Question 27

How do different water molecules bond to each other?

Answer 27

The positive pole of one binds to the negative pole of another forming a hydrogen bond. It is a fairly weak bond but appears srong when there are many of them

Question 28

Describe the specific heat capacity of water:

Answer 28

The SHC of water is relatively high since the water molecules stick together. This means it takes a lot of energy to raise the temperature of it. This is due to the hydrogn bonds. Water, therefore, acts as a buffer against suden temperature change in an aquatic habitat and inside organisms

Question 29

Describe the latent heat of vaporisation of water:

Answer 29

The LHV of water is also relatively large as lots of energy is required to evaporate a gram of water. This means that mammals can sweat to provide a cooling effect without the issue of evaporation.

Question 30

Define cohesion:

Answer 30

The tedency of molecules to stick to one another (e.g. water)

Question 31

Why is water so cohesive?

Answer 31

Many hydrogen bonds

Question 32

Give an example of the cohesion of water:

Answer 32

Xylem vessels

Question 33

Define surface tension:

Answer 33

A force on the surfae film of a quid caused by the attraction of the particles

Question 34

Give an example of a use for the high surface tension of water:

Answer 34

Habitat fo small organisms such as pond skaters

Question 35

Why is water important to livng organisms?

Answer 35

It is the main constituent of all organisms

Question 36

How is water used in reactions (metabolism)

Answer 36

- It is used in molecule break down and building (hydrolysis and condensation) - Many chemicl reactions take place in it - It is a raw material for photosynthesis

Question 37

Give 2 examples of water as a solvent:

Answer 37

1) Removal of waste products such as ammonia and urea 2) Gases such as oxygen and carbon dioxide dissolve in water

Question 38

Why is water useful in photosynthesis (other than being a raw material)?

Answer 38

It is transparent so aquatic plants can photosynthesise in it

Question 39

Inorganic ions ocur in a range of concentrations in a water-based solution. Give 5 examples of functions of inorganic ions:

Answer 39

Iron ions in haemoglobin- oxygen transportation Phosphate ions- structural role in DNA molecules and store energy in ATP Hydrogen ions- pH Sodium ions- co transport Sodium and potassium ions- action potential (nerve impulse)