cell genetic material duplication

Question 1

Write down the sequence of the complementary strand of DNA if given the sequence of the other strand, indicating polarity.

Answer 1

• growth of nucleic acid (DNA or RNA) occurs from 5’ (phosphate) to 3’ (hydroxyl)

Question 2

Explain the key features of DNA structure.

Answer 2

• made of nucleotides
• base, sugar (5C),
  phosphate group
• C2 is where the change occurs in DNA bound to hydrogen in RNA bound to hydroxyl

bases: C, T/U, A, G
- A/G are purine have 2 rings
- C,T,U- pyrimidine have 1 ring

• hydrogen bonds between bases hold strands together
• complimentary base pairing (A-T/U and C-G)
• phosphate and sugar backbone
• two strands are antiparallel, run in opposite directions
• width is same
• dna strands wrap and make right handed helix
• dna coiling creates grooves, transcription regulator interacts with major groove (wider apart) hydrogen bonds with dna sequences

Question 3

Identify the function of each of the proteins involved in DNA replication.

Answer 3

SEE DIAGRAM

3 models of replication

• complementary base pairing
• semiconservative: each daughter molecule has original strand
• TRUE MODEL
• each round of DNA rep, composed of one conserved and one newly synthesized strand
• conservative: one daughter molecule has 2 old, one has new

-dispersive: pieces of new and old strands, fragments of dna

Question 4

Explain how at each replication fork the two strands of a double helix are synthesized.

Answer 4

• replication fork is assymetical
• 2 new synthesized strands are in opposite polarities because 2 template strands are in opposite directions
• 2 strands grow differently
• leading strand is synthesized continuously (5 - 3) in direction of fork
• lagging strand is synthesized discontinuously (3 - 5) as short dna strands Okazaki fragments
• dna ligase joins Okazaki fragments together

Question 5

Explain the end-replication problem and how it is solved.

Answer 5

DIAGRAM

-leading strand has no problem, synthesizes up until last nucleotide of template

• last Okazaki fragment is removed, DNA polymerase cannot replace RNA, needs a 3’ hydroxyl group

IN MOST CELLS
- piece of template is lost because it is not synthesized, chromosome is shortened

IN STEM CELLS
- you can fill in the gap using enzyme telomerase

• telomerase uses piece of RNA it has in it, with complementary sequence to extend telomere
• telomerase moves to new end and DNA polymerase fills in gap

Question 6

Compare and contrast chromosome segregationin meiosis and mitosis.