Nucleic Acids (Chapter 2)

Question 1

Describe a Nucleotide and what it made of

Answer 1

Bases units that DNA are made of.

Consists of nitrogenous base (A, T, C, G), a deoxyribose pentose sugar and a phosphate.

Question 2

What type of bond is between nucleotides?

Answer 2

Phosphodiester

Question 3

What type of reaction joins nucleotides?

Answer 3

Condensation

Question 4

Describe how the structure of DNA helps it to do its job

Answer 4

• Sugar-phosphate backbone provides strength
• Coiling gives compact shape
• Long Molecules allow large amounts of information to be stored
• Complementary base pairs allows information to be replicated accurately
• Double helix makes molecule stable
• Bases held together by H bonds - many H bonds provide strength
• Easily broken H bonds allows chains to be split for replication
• 2 strands so both act as templates for replication

Question 5

Describe the structure of DNA

Answer 5

• Double helix
• One strand runs 5’ to 3’ direction and other 3’ to 5’ direction (antiparallel)
• Adenine pairs with Thymine (2 H bonds) and Guanine pairs with Cytosine (3 H bonds)

Question 6

What are non-coding sections of DNA?

Answer 6

Introns

Question 7

What is a triplet code?

Answer 7

Each amino acid is coded for my 3 bases and some amino acids have more than one code.

Question 8

Describe how a mutation happens and the effect of this using enzymes as an example

Answer 8

1) Change in DNA base
2) Amino acid sequence is changed
3) Change in H/Ionic bonds
4) Tertiary structure is altered (which changes the active site of an enzyme)
5) Different protein is created and if for an enzyme then no E-S complexes can be formed.

Question 9

What is semi-conservative replication?

Answer 9

DNA strand separates (H bonds break) and a new molecule is formed that has one ‘old’ strand and one ‘new’ strand.

Question 10

Describe the process of DNA replication

Answer 10

1) Chains are separated by DNA helicase which breaks the H bonds.
2) Semi conservative replication occurs where each chain acts as a template.
3) Nucleotides line up with complementary bases and join to template strand.

4) DNA polymerase joins the sugar phosphate groups of the nucleotides together in the 5’ to 3’ direction.
(DNA polymerase is specific and its active site only binds to 3’ to 5’ end)

5) Phosphodiester bonds form.

Question 11

Describe the structure of an RNA molecule

Answer 11

Has nitrogenous bases of (A, U , C, G), a ribose pentose sugar and a phosphate. RNA is a relatively short nucleotide chain, single stranded and mRNA transfers the genetic code from the DNA to the ribosomes.

Question 12

How is RNA adapted to to carry out its function?

Answer 12

It is stable and single stranded which allows bonding at the ribosome.

Question 13

Compare DNA and RNA

Answer 13

• DNA is double-stranded while RNA is single stranded
• DNA has deoxyribose sugar while RNA has ribose
• DNA has thymine base while RNA has uracil base

Question 14

What is the reaction for when ATP is released?

Answer 14

ADP + Pi > ATP

Question 15

What reaction causes energy to be released from ATP?

Answer 15

Hydrolysis

Question 16

What enzyme catalyses ATP for it to release energy?

Answer 16

ATP Hydrolase

Question 17

What can Pi be used for?

Answer 17

To phosphorylate other compounds to make them more reactive e.g. channel proteins

Question 18

What reaction reforms ATP and what else is required?

Answer 18

Condensation and energy is needed

Question 19

What enzyme catalyses ATP to be reformed?

Answer 19

ATP synthase

Question 20

Why is ATP useful?

Answer 20

• Energy is released in small suitable amounts
• Broken down in one step
• Makes energy available rapidly
• Makes phosphorylated substances more reactive/lowers the activation energy
• Can be reformed/made again

Question 21

Compare ATP and DNA nucleotides

Answer 21

• ATP has ribose and DNA has deoxyribose
• ATP has 3 phosphate groups and DNA has one phosphate group
• ATP base is always adenine while DNA base is different and varies

Question 22

What are the properties of water?

Answer 22

• Polar molecules - act as a solvent
• Solvent - metabolic reactions happen faster in solution.
• Reactive - takes place in hydrolysis and condensation reactions
• Metabolite - Can take place in chemical reactions directly
• High Specific Heat Capacity - Water in and around cells absorb lots of energy without its temperature increasing too much so keeps conditions stable.
• High Latent Heat of Vapourisation - Can be used for cooling organisms through evaporation.
• Strong Cohesive Properties - Can be pulled through plants in a column as the water molecules are held together by H bonds.
• High Surface Tension - Habitats can form on the surface of the water.
• Colourless with high transmission - Light can pass through cells for photosynthesis.

Question 23

Compare transport processes between ions and water

Answer 23

• Both can move down the concentration gradient.
• Both move through protein channels in membranes.
• Ions can move against a concentration gradient by active transport.