Module 6 - Cellular Control (6.1.1)

Question 1

How many different types of nucleotides are found in DNA

Answer 1

4 ( one for each base )

Question 2

Which two bases are purines

Answer 2

Adenine and Guanine ( the larger bases )

Question 3

What bonds join the monomers in DNA and RNA

Answer 3

Nucleotides are joined by phosphodiester bonds to form a polynucleotide

Question 4

What enzyme catalyses the formation of the sugar phosphate backbone in DNA and RNA

Answer 4

DNA Polymerase catalyses the formation of the sugar phosphate backbone in DNA.
For RNA the enzyme is RNA Polymerase

Question 5

What enzyme unwinds DNA prior to DNA replication and transcription

Answer 5

Helicase

Question 6

Which DNA strands acts as templates during semi-conservative replication

Answer 6

Both strands

Question 7

Which DNA strands act as templates during transcription

Answer 7

The antisense strand only

Question 8

What does the sequence of bases in DNA code for

Answer 8

The sequence of amino acids ( in the primary structure )

Question 9

Which part of the amino acid is different

Answer 9

The R group

Question 10

Which RNA is involved in forming the primary structure of a protein on the ribosomes

Answer 10

Each tRNA is attached to specific amino acid and has a complementary triplet called anticodon; which binds to the complementary codon on mRNA

Question 11

Fill the blanks:

• A sequence of DNA nucleotides that code for a protein is a ……1………..
• The mRNA molecule is shorter than a DNA molecule because it only copies one ……2……….
• Catalyses the formation of the sugar phosphate backbone
• The molecule is twisted into a ……3…….. in which each of the strands are ……4………..

Answer 11

1 , gene
2 , gene
3 , double helix
4 , antiparallel

Question 12

How do the bases pair together in DNA

Answer 12

• hydrogen bonds between bases
• complementary base pairs
• purine to pyrimidine
• A to T and C to G
• 2H bonds between A and T /3H bonds between C and G

Question 13

Triplet code

Answer 13

3 bases are called a triplet which code for one amino acid

Question 14

Non-overlapping

Answer 14

base triplets don’t share their bases

Question 15

Degenerate code

Answer 15

different codons can code for the same amino acid ( except for methionine which is always AUG )

Question 16

Universal code

Answer 16

generally codons code for the same amino acids in different organisms

Question 17

Explain how DNA structure determines the specific shape of proteins, e.g. enzymes

Answer 17

• DNA codes for protein / polypeptide; transcription and translation
• 3 bases ( triplet ) code for 1 amino acid
• the sequence of bases determines :
  ·the sequence of amino acid in the primary structure
  ·the coiling of the primary structure to form an α helix or β- pleated sheet ( secondary structure )
  ·determines projecting side groups which determine the folding and bonding in the tertiary structure

Question 18

Outline how DNA replicates semi-conservatively, with reference to the role of DNA polymerase

Answer 18

• The double helix is untwisted-this requires DNA helicase
• Hydrogen bonds between complementary bases e.g. A and T are broken and the DNA is unzipped
• Free DNA nucleotides link to the complementary exposed base
• Hydrogen bonds reform between complementary base pairs: 2 between A and T and 3 between C and G
• The sugar phosphate backbone is formed by covalent ( phosphodiester bonds ) between the phosphate of one nucleotide and the deoxyribose sugar of the next
• 2 new DNA molecules are formed each containing one new DNA strand and one old ( conserved strand )