topic 1.4 - DNA & protein synthesis

Question 1

structure of a nucleotide

Answer 1

• pentose sugar
  
  • phosphate group
  • base (A, T, G, C)

Question 2

bases found in DNA

Answer 2

adenine
thymine
guanine
cytosine

Question 3

phosphodiester bonds

Answer 3

form between two nucleotides in a condensation reaction

Question 4

what is DNA

Answer 4

a polynucleotide as it is made up of many nucleotides joined together in condensation reactions forming phosphodiester bonds

Question 5

structure of DNA

Answer 5

• 2 polynucleotide strands
  
  • sugar phosphate backbone on the outside and bases on the inside
  • strands held together by hydrogen bonds formed between complimentary bases

Question 6

DNA replication

Answer 6

when a cell divides, all of its DNA is copied

Question 7

how is DNA replicated

Answer 7

• the enzyme DNA helicase attaches to the DNA molecule and causes the hydrogen bonds to break between bases
  
  • two polynucleotides break into two single strands
  • free nucleotides line up with their complementary bases on the DNA strands

Question 8

role of DNA helicase

Answer 8

breaks hydrogen bonds between the bases and separates the two polynucleotide strands

unzips dna

Question 9

role of DNA polymerase

Answer 9

• copies DNA in one direction
• copies from 5’ to 3’
• works fine for one of the strands

Question 10

role of DNA ligase

Answer 10

• the other strand goes from 3’ to 5’ - opposite direction to DNA helicase
• many short strands are therefore formed
• DNA ligase joins the shorter polynucleotide strands

Question 11

what is a gene

Answer 11

sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain

Question 12

semi-conservative replication of DNA

Answer 12

• DNA polymerase synthesises new strands of DNA that are complementary to the previous strand.
• when the DNA is replicated, one of the strands is the original DNA that is copied and one of them is new synthesised DNA
• this is semi-conservative replication