DNA Replication

Question 1

Step 1 of DNA Replication

Answer 1

DNA must unwind to expose a single stranded template

Question 2

What does helicase do?

Answer 2

• Unzips and unwinds the double helix
• Breaks hydrogen bonds

Question 3

What enzymes are used in step 1 of DNA replication?

Answer 3

• Helicase
• Toposiomerase (gyrase)

Question 4

What does topoisomerase (gyrase) do?

Answer 4

• Detangler
• Prevents supercoils by nicking and resealing DNA

Question 5

Step 2 of DNA Replication

Answer 5

DNA must be held open, not to reform a coil

Question 6

What do Single Stranded Binding Proteins do?

Answer 6

• Bind to the uncoiled DNA and keep it open

Question 7

Step 3 of DNA Replication

Answer 7

A primer must be created before DNA synthesis can occur

Question 8

What is a primer?

Answer 8

• Short sequence of RNA, complementary to template
• Provides 3’ end where DNA synthesis can begin

Question 9

What is primase?

Answer 9

Enzyme that synthesizes RNA primer

Question 10

What is RNA polymerase?

Answer 10

• Synthesizes primers on leading strand
• Type of RNA polymerase

Question 11

Leading strand

Answer 11

• New strand that is synthesized continuously
• Synthesized towards replication fork

Question 12

Lagging Strand

Answer 12

• Synthesized in short fragments called Okazaki fragments which are later joined together
• Discontinuously
• Synthesized away from replication fork

Question 13

Step 4 of DNA Replication

Answer 13

DNA synthesis begins

Question 14

What is DNA polymerase 3 (builder)

Answer 14

• Enzyme that catalyzes the addition of nucleotides complementary to the template strand

Question 15

What direction does DNA synthesis occur in?

Answer 15

5’ to 3’ direction

Question 16

DNA polymerase 1, first function

Answer 16

• Edits mistakes
• Proofreads chain
• Exonuclease activity

Question 17

Step 5 of DNA Replication

Answer 17

Synthesis of DNA occurs on both template strands

Question 18

Step 6 of DNA Replication

Answer 18

RNA primers are removed

Question 19

DNA polymerase 1, second function

Answer 19

• chews up RNA primers and replaces them with DNA nucleotides
• All primers are removed

Question 20

Step 7 of DNA Replication

Answer 20

All nicks are repaired

Question 21

What is DNA Ligase

Answer 21

• Acts like glue to make phosphodiester linkages
• Seals the nicks between Okazaki fragments

Question 22

Proofreading and repairing DNA

Answer 22

• DNA polymerase I proofread newly made DNA, replacing any incorrect nucleotides

Question 23

What happens in mismatch repair of DNA?

Answer 23

repair enzymes correct errors in base pairing

Question 24

Some reasons DNA can be damaged

Answer 24

• exposure to harmful chemical or physical agents
• can undergo spontaneous changes

Question 25

What does a nuclease do in DNA repair?

Answer 25

Cuts out and replaces damaged stretches of DNA

Question 26

What are telomeres?

Answer 26

Repeating DNA sequences at the ends of chromosomes that protect coding regions during replication

Question 27

Do telomeres prevent DNA shortening?

Answer 27

No, but they help delay the loss of important genes near the ends of chromosomes.

Question 28

What are shortened telomeres linked to?

Answer 28

Aging, including wrinkles and grey hair

Question 29

What is telomerase?

Answer 29

An enzyme that catalyzes the lengthening of telomeres in germ cells

Question 30

How is telomerase linked to cancer?

Answer 30

- Cancer cells produce telomerase in high quantities

Question 31

Prokaryotic DNA Organization

Answer 31

- Double stranded circular DNA molecules associated with small amounts of protein - DNA is supercoiled and found in the nucleoid

Question 32

Eukaryotic DNA Organization

Answer 32

- Linear DNA molecules associated with large amounts of protein

Question 33

What is a nucleosome?

Answer 33

A unit of DNA storage made up of 8 histones

Question 34

What is a histone?

Answer 34

Structural Protein