Tutorial 18: DNA Replication

Question 1

semiconservative replication

Answer 1

refers to the fact that each newly formed molecule of DNA has one strand conserved from the parent molecule and one newly synthesized strand.

Question 2

Helicases

Answer 2

Enzymes that unwind the DNA double helix.

Question 3

single-strand binding proteins

Answer 3

proteins that keep the two strands of DNA separate from each other while the replication process is carried out

Question 4

primases

Answer 4

Enzymes that initiate replication

Question 5

DNA polymerase

Answer 5

the enzyme that adds nucleotides to the unwound parent molecule

Question 6

What does it mean when they say DNA strands are antiparallel?

Answer 6

• The strands of DNA have opposite chemical polarities, with one strand designated 3’-to-5’ and the other designated the 5’-3’ strand.

Question 7

What is an important limitation that DNA polymerase has?

Answer 7

DNA polymerase can only add nucleotides to the 3’ end of the newly synthesized strand of DNA.

Question 8

Leading strand

Answer 8

• the addition of nucleotides to the leading strand is smooth and continuous

Question 9

lagging strand

Answer 9

• has a discontinuous mode of replication because DNA polymerase can only work by starting from the replication fork, and progressing outward until it runs into a previously synthesized fragment.
• the lagging strand is started by primase, which has the ability to synthesize a short primer made of a few nucleotides of RNA. DNA polymerase can then add DNA nucleotides to the end of this primer sequence and synthesize relatively short stretches of DNA known as Okazaki fragments.

Question 10

Replication fork

Answer 10

the point at which the DNA double-helix is unwinding

Question 11

primer

Answer 11

Short sequences of nucleic acids that provide a starting point for DNA synthesis.

Question 12

okazaki fragments

Answer 12

Newly synthesized DNA fragments formed on the lagging template strand during DNA replication

Question 13

ligase

Answer 13

An enzyme that seals the fragments on the lagging strand into a continuous strand of DNA

Question 14

Where does DNA replication take place in eukaryotic cells?

Answer 14

The nucleus.

Question 15

Mismatch repairs

Answer 15

Repairs that occur when DNA polymerase and other proofreading enzymes remove incorrectly paired nucleotides.

Question 16

Excision repairs

Answer 16

Repairs that involve the removal of damaged nucleotides from a DNA molecule.

Question 17

What happens when errors in DNA replication are not repaired?

Answer 17

mutations

Question 18

Mutation

Answer 18

a permanent change in an organism’s DNA.

If the mutation occurs in a reproductive cell, the mutation can be passed down to future generations and potentially become established in a population (which is why mutations are the ultimate source of genetic variation in populations)

Question 19

Polymerase chain reaction (PCR)

Answer 19

• A laboratory technique that uses the basic steps and materials of DNA replication to create large numbers of copies of a small piece of DNA in a short period of time.
• PCR involves using a machine called a thermocycler to repeatedly heat and copy a segment of DNA.

Question 20

What things are added to the thermocycler during PCR?

Answer 20

• template DNA
• specific DNA primers
• DNA polymerase
• DNA nucleotides

Question 21

What are the basic steps of PCR?

Answer 21

1. denaturation
2. annealing
3. elongation
4. Repeat

Question 22

What happens in the denaturation part of the PCR process?

Answer 22

The DNA is heated to separate the two complimentary strands (in a cell, helicase would play this role).

Question 23

What happens during the annealing part of the PCR process?

Answer 23

The temperature is lowered and the DNA primers attach (or anneal) to the regions around the segment of DNA to be copied

Question 24

What happens during the elongation part of the PCR process?

Answer 24

DNA polymerase copies the template segment of DNA

Question 25

Why do you repeat the PCR process?

Answer 25

the process is repeated until the desired amount of DNA is obtained.

Question 26

Taq polymerase

Answer 26

Heat resistant DNA polymerase from a bacterium that lives in hot springs. This is the DNA polymerase that has made the PCR process faster and less labor intensive because the taq is able to survive the heating processes.