Worksheet 1 DNA REPLICATION

Question 1

When should DNA be replicated?

Answer 1

Any time the cell needs to divide.

Question 2

What life events would include DNA replication?

Answer 2

Growth, wound healing, regeneration, gamete production

Question 3

Which enzyme acts first in DNA replication?
A. Helicase
B. Primase
C. Polymerase
D. Ligase

Answer 3

A. Helicase

Question 4

Which enzyme(s) add(s) new DNA nucleotides to an existing strand? (Select all that apply.)
A. Primase
B. Ligase
C. Polymerase
D. Helicase

Answer 4

C. Polymerase

Question 5

What is the difference between the leading strand and the lagging strand?

Answer 5

The leading strand goes in the 3’ to 5’ orientation, so it can be copied in a linear line. The lagging strand is in the 5’ to 3’ direction, so it must be copied in sections (in the opposite orientation) and those sections ‘glued’ together. Remember that DNA is always synthesized in the 5’ to 3’ direction.

Question 6

TRUE or FALSE: Replication of the leading and lagging strands requires different enzymes.

Answer 6

FALSE

Question 7

Why are there no Okazaki fragments on the leading strand?

Answer 7

Okazaki fragments are formed on the lagging strand so DNA can be synthesized in the essential 5’ to 3’ manner on the lagging strand.

Question 8

Why is it important to replicate DNA without errors?

Answer 8

Because the sequence of DNA is what makes it do what it does.

Question 9

What might happen if there were errors in DNA replication.

Answer 9

A mutation means a sequence change: in a somatic cell, this could lead to cancer;

Question 10

What happens to the original template DNA after a round of replication?

Answer 10

It is paired with a newly synthesized DNA strand

Question 11

Instead of Thymine, RNA has

Answer 11

Uracil

Question 12

Answer 12

Question 13

Draw a single nucleotide, labeling the phosphate, in the box to the right:

Answer 13

-

Question 14

Draw and label a double-stranded segment of DNA with four nucleotides (arranged in two base pairs)

Answer 14

-

Question 15

Draw and label a nucleosome

Answer 15

Question 16

What are the functions of a nucleosome?

Answer 16

Nucleosomes allow the packing/supercoiling of DNA into chromosomes for easy separation in mitosis/meiosis. When DNA is wrapped around nucleosomes, it cannot be transcribed/translated so this allows genes to be turned “off”

Question 17

Describe what is meant by “Highly-repetitive DNA sequences” and list several functions of these sequences.

Answer 17

Nucleotide sequences in DNA that do not code for the production of proteins are also called introns. Repeating base letter patterns are 5-300 letters long (ex. AGAGAG) and build up mutations quickly without affecting organism (since they don’t code for traits) which makes them helpful for DNA fingerprinting. They also makeup telomeres, produce tRNA and rRNA and help promote or silence gene expression.