2B

Question 1

Name the monomers that make DNA and RNA

Answer 1

Nucleotides

Question 2

Describe the basic structure of a nucleotide

Answer 2

A phosphate group, a pentose sugar and a base

Question 3

What do A, T, G, C and U stand for?

Answer 3

Adenine, cytosine, thymine, guanine, uracil

Question 4

How do DNA and RNA nucleotides differ?

Answer 4

RNA has a ribose sugar whereas DNA has a deoxyribose sugar. RNA has a uracil base whereas DNA has Thymine

Question 5

Describe the structure of RNA

Answer 5

Single polynucleotide strand of RNA nucleotides.

Question 6

Describe how nucleotides join to form polynucleotides?

Answer 6

By condensation reactions between the sugar and phosphate groups to form phosphodiester bonds and a sugar phosphate backbone.

Question 7

Which bases form complementary base pairs in DNA and RNA?

Answer 7

Adenine with Thymine (Uracil in RNA). Cytosine with Guanine.

Question 8

Briefly outline the two main stages involed in protein synthesis.

Answer 8

1. Transcription; reads DNA sequence and produces mRNA.
2. Translation; reads mRNA sequence and orders amino acids to form polypeptide.

Question 9

Describe the process of transcription.

Answer 9

DNA uncoils (DNA helicase) into two strands with exposed bases. One used as a template. Free RNA nucleotides form hydrogenn bonds with complementary bases. Nucleotides are joined together by RNA polymerase forming phospodiester bonds between the sugar and phosphate groups in a condensation reaction.

Question 10

What happens to mRNA after transcription?

Answer 10

It moves out of the nucleus into the cytoplasm and attaches to a ribosome, ready for translation.

Question 11

Describe the process of translation.

Answer 11

The anti-codon of tRNA attaches to complementary bases on the mRNA codons.
Amino acids bonded to tRNA form peptide bonds in a condensation reaction, continuing to form a polypeptide chain until a stop codon is reached.
This process requires ATP.

Question 12

Explain how bases code for amino acids

Answer 12

Three bases code for one amino acid

Question 13

Identify features of the genetic code

Answer 13

A triplet of bases codes for a particular amino acid.
Non-overlapping=each triplet is only read once.
Degenerate=more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids).

Question 14

What is a gene?

Answer 14

A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids in a polypeptide chain.

Question 15

Define dipeptide

Answer 15

Two amino acids joined by a peptide bond

Question 16

Define polypeptide

Answer 16

Two or more amino acids joined together by peptide bonds

Question 17

How are polypeptides formed from their monomers?

Answer 17

Amino acids join together in condensation reactions, forming a peptide bond.

Question 18

What is meant by the primary structure of a protein?

Answer 18

Primary = basic amino acid sequence.

Question 19

What is meant by the secondary structure of a protein?

Answer 19

Secondary = whether the polypeptide chain is arranged into a helix or pleated sheet. Held together by H bonds.

Question 20

What is meant by the tertiary structure of a protein?

Answer 20

Tertiary = 3D folding of the secondary structure into a complex shape held together by bonds between R groups of different amino acids e.g. ionic, hydrogen, disulfide bonds as well as hydrophobic and hydrophillic interactions.

Question 21

What is meant by the quarternary structure of a protein?

Answer 21

When more than one polypeptide chain in a tertiary structure bonds together

Question 22

How does the primary structure affect the tertiary (3D) structure?

Answer 22

Different amino acid sequence therefore different R groups that produce different bonds in the tertiary structure.

Question 23

Describe how the structure of fibrous proteins relates to their function.

Answer 23

Long polypeptide chains. Very little tertiary structure. Strong cross-linkages between polypeptide chains. Hydrophobic groups on outside. This makes them insoluble, and useful for providing structure.

Question 24

Give an example of a fibrous protein and explain how its properties relate to its use.

Answer 24

Collagen. Three polypeptide chains form a triple helix which creates fibres held together by strong crosslinks. This makes it useful in bones, cartilage and
other connective tissue.

Question 25

Describe how the structure of globular proteins relates to their function.

Answer 25

Compact, highly folded with complex tertiary/quaternary structures. Soluble due to hydrophillic groups on the outside. They are useful for hormones, antibodies, etc.

Question 26

Give an example of a globular protein and explain how its properties relate to its use.

Answer 26

Haemoglobin. Water-soluble, made of 4 polypeptide chains. Contains four haem groups that oxygen can bind to. It is therefore used to carry oxygen in the
blood to respiring tissues.

Question 27

What are enzymes?

Answer 27

Proteins that act as biological catalysts i.e. increase the rate of a reaction by lowering the activation energy.

Question 28

Describe the structure of enzymes

Answer 28

Globular therefore highly folded proteins with a specific active site that is complementary to a particular substrate

Question 29

How do enzymes that join two molecules together work?

Answer 29

The active site holds the two molecules in the right orientation to form new bonds.

Question 30

How do enzymes that break down molecules work?

Answer 30

A substrate molecule is held in the active site putting a strain on the bonds and breaking the two molecules apart.

Question 31

What is meant by a ‘specific’ active site?

Answer 31

That the active site is complementary to a particular substrate where a substrate bonds to form an enzyme substrate complex.

Question 32

What determines the shape of the active site of an enzyme?

Answer 32

The sequence of bases in the gene that determines the sequence of amino acids in the primary sequence of the protein. Different R groups on different amino acids form different bonds in the tertiary structure of the protein which determines the shape of the active site.

Question 33

Differentiate with examples between intracellular and extracellular enzymes.

Answer 33

Intracellular enzymes work within cells e.g. DNA helicase and extracellular work outside cells e.g. amylase