Nucleotides and Nucleic Structure

Question 1

What are the 3 components of a nucleotide from left to right?

Answer 1

Phosphate group, Pentose sugar, Nitrogenous base

Question 2

Name the pentose sugars in DNA and RNA

Answer 2

DNA - Deoxyribose
RNA - Ribose

Question 3

Describe how polynucleotide structures are formed and broken down

Answer 3

• Formed by condensation reaction between nucleotides form strong phosphodiester bonds (sugar phosphate backbone)
• Hydrolysis reactions use a water molecule to break these bonds

Question 4

Describe the structure of DNA

Answer 4

• Double helix shape
• 2 deoxyribose polynucleotide strands, so there are 2 sugar phosphate backbones
• H bonds form complementary base pairings (AT, CG)
• Strands run antiparallel

Question 5

What is the formula of the two purine bases?

Answer 5

Adedine - C5H5N5
Guanine - C5H5N5O

Question 6

What is the formula for the three pyrimidine bases?

Answer 6

Thymine - C5H6N2O2
Cytosine - C4H5N3O
Uracil - C4H4N2O2

Question 7

Name the complementary base pairs between DNA and RNA

Answer 7

DNA - AT (2 H bonds)
- CG (3 H bonds)
RNA - AU (2 H bonds)
- CG (3 H bonds)

Question 8

Why is DNA replication semi conservative?

Answer 8

• Strands from original DNA molecule act as templates
• New DNA molecules contain 1 old and one new strand

Question 9

Explain the role of DNA helicase in semi-conservative replication

Answer 9

• Break H bonds between base pairs to form 2 single strands
• Each of which can act as a template

Question 10

How is a new strand formed during semi-conservative replication?

Answer 10

• Free nucleotides attach to exposed bases by complementary base pairing
• DNA polymerase joins adjacent nucleotides on new strand in a 5’ to 3’ direction
• Forms phosphodiester bonds through a condensation reaction

Question 11

Identify features of the genetic code

Answer 11

• Non overlapping
• Degenerate - more than one triplet codes for the same amino acid
• Universal - same bases and sequences used by all species

Question 12

How does a gene determine the sequence of amino acids in a protein?

Answer 12

Consists of base triplets that code for specific amino acids

Question 13

Describe how DNA can be purified by precipitation

Answer 13

• Add ethanol and salt to aqueous solution
• Nucleic acids precipitate out of solution

Question 14

What does transcription produce and where does it occur?

Answer 14

• Produces mRNA
• Occurs in nucleus

Question 15

Outline the process of transcription

Answer 15

• RNA polymerase binds to promoter region on a gene
• Section of DNA uncoils into 2 strands with exposed bases
• Antisense strand acts as template
• Free nucleotides are attracted to complementary bases
• RNA polymerase joins adjacent nucleotides to form phosphodiester bonds

Question 16

What happens after a strand of mRNA is transcribed?

Answer 16

• RNA polymerase detaches
• H bonds reform and DNA rewinds
• mRNA moves out of nucleus via nuclear pore and attaches to ribosome

Question 17

What does translation produce and where does it occur?

Answer 17

• Produces proteins
• Occurs in cytoplasm of ribosomes

Question 18

Outline the process of translation

Answer 18

• Ribosome moves along mRNA until it reaches the start codon (AUG)
• tRNA anticodon attaches to complementary bases on mRNA
• Condensation reactions between amino acids on tRNA form peptide bonds
• Process continues to form polypeptide chain until stop codon is reached and the polypeptide is released

Question 19

Describe the difference between ATP and ADP

Answer 19

• ATP has 3 inorganic phosphate groups
• ADP has 2 inorganic phosphate groups
  Hydrolysis of ATP to ADP releases energy

Question 20

What is a mutation?

Answer 20

• An alteration to the DNA base sequence
• Often arise spontaneously during DNA replication