DNA Structure and Function

Question 1

What does DNA stand for?

Answer 1

Deoxyribonucleic Acid

Question 2

DNA is a polymer of ________, which are held together by ________ bonds.

Answer 2

nucleotides; phosphodiester

Question 3

Label the 5’ end and the 3’ end of this single DNA strand.

Answer 3

The 3’ end carbon is attached to an -OH group and the 5’ end carbon is attached to a phosphate group.

Question 4

Define:

the antiparallel nature of DNA.

Answer 4

The two strands of DNA that make up the double helix run in opposite directions, one strand with a 5’ -> 3’ orientation and the other with a 3’ -> 5’ orientation.

Question 5

What are the three main parts of a nucleotide?

Answer 5

a phosphate group, a 5-carbon sugar, and a nitrogenous base

Question 6

Name the purines and pyrimidines.

Answer 6

The purines are adenine and guanine. The pyrimidines are cytosine and thymine.

Question 7

What is the difference in structure between purines and pyrimidines?

Answer 7

Purines are two ring structures while pyrimidines are single ring structures.

Question 8

Which nitrogenous base forms hydrogen bonds with adenine?

Answer 8

thymine

Question 9

Which nitrogenous base forms hydrogen bonds with guanine?

Answer 9

cytosine

Question 10

Which type of bond forms between the nitrogenous bases of two complementary DNA strands?

Answer 10

hydrogen bond

Question 11

How many hydrogen bonds form between adenine and thymine?

Answer 11

two hydrogen bonds

Question 12

How many hydrogen bonds form between guanine and cytosine?

Answer 12

three hydrogen bonds

Question 13

What is the central dogma of molecular biology?

Answer 13

DNA is transcribed to RNA which is translated to amino acids that make up a protein.

Question 14

Define:

DNA helicase

Answer 14

an enzyme responsible for separating the two strands of a DNA double helix needed for initiation of DNA replication

Question 15

What is the name of the enzyme responsible for adding deoxyribonucleotides to a newly created DNA strand during replication?

Answer 15

DNA polymerase

Question 16

What does DNA polymerase require to get started?

Answer 16

DNA polymerase cannot begin adding nucleotides by itself. An RNA primer of approximately 10 ribonucleotides is required to which DNA polymerase can begin adding nucleotides.

Question 17

In what direction does DNA polymerase read the parental strand?

Answer 17

3’ -> 5’

Question 18

In what direction is the new complementary strand created by DNA polymerase?

Answer 18

5’ -> 3’

Question 19

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

Answer 19

The leading strand is the newly synthesized strand of DNA being replicated continuously due to the complementary parental strand’s 3’ -> 5’ direction towards the replication fork. The lagging strand is the newly synthesized strand of DNA that is replicated in a series of fragments (Okazaki fragments) due to the complementary parental strand’s 5’ -> 3’ direction towards the replication fork.

Question 20

Define:

**semiconservative **
in terms of DNA replication.

Answer 20

The semiconservative nature of replication means that when a new double helix is created, it contains one strand from the original DNA, and one newly synthesized strand.

Question 21

Which enzyme is responsible for making repairs during DNA replication?

Answer 21

DNA polymerase proofreads as it adds nucleotides to new DNA strands. When a mismatched nucleotide is detected, DNA polymerase re replaces it with the correct nucleotide.

Question 22

Define:

recombinant DNA

Answer 22

DNA whose two DNA strands have been artificially recombined.

Question 23

A __________ enzyme cuts a DNA strand at a specific nucleotide sequence that is usually palindromic.

Answer 23

restriction

Question 24

Define:

sticky ends

Answer 24

Sticky ends are complementary single stranded ends created by a restriction enzyme cut. A restriction enzyme will often cut a strand unevenly, creating sticky ends that can form base pairs with any DNA molecule that has a complementary sticky end.

Question 25

_________ ends are those caused by a restriction enzyme that cuts a DNA strand straight across, leaving no uneven ends that can hybridize.

Answer 25

Blunt

Question 26

Define:

hybridization

Answer 26

Hybridization is the process by which separated strands of DNA will spontaneously bond with either their original complementary partner or any other complementary strand.

Question 27

Which three kinds of double stranded combinations can be made from hybridization?

Answer 27

• DNA-DNA
• DNA-RNA
• RNA-RNA

Question 28

Describe the process of:

gene cloning

Answer 28

1. Cut human DNA and plasmid DNA with the same restriction enzyme.
2. Insert human DNA restriction fragment into plasmid by mixing them together.
3. Seal with DNA ligase.
4. Insert plasmid into bacteria, where replication occurs.

Question 29

What use does an antibiotic resistant gene have during gene cloning?

Answer 29

Since the cloning process is not perfect, some bacteria will not have the desired plasmid. To get rid of this bacteria, an antibiotic resistant gene is necessary in desired plasmids. Bacteria that do not have the appropriate plasmid will be killed upon contact with the antibiotic, leaving only desired clones.

Question 30

Which two specific genes must a bacterial plasmid contain to eliminate undesirable bacteria in the gene cloning process?

Answer 30

The lacZ gene and an antibiotic resistance gene

Question 31

When active, what does the lacZ gene do?

Answer 31

An active lacZ gene allows bacteria to break down the sugar X-gal. When placed on a medium with X-gal, the active lacZ gene is indicated by blue.

Question 32

What purpose does an inactivated lacZ gene have in the gene cloning process?

Answer 32

An inactivated lacZ gene containing the desired DNA fragment cannot break down the sugar X-gal. When the cloned bacteria is put on a medium with X-gal, the inactive lacZ gene does not change color (like active lacZ gene would).

Question 33

The ________ gene allows for detection of desired DNA fragments while an _________ ____________ gene allows for detection of desired vectors.

Answer 33

lacZ; antibiotic resistance

Question 34

What does PCR stand for?

Answer 34

Polymerase Chain Reaction

Question 35

Why is PCR more beneficial than simply gene cloning?

Answer 35

PCR is a much faster method of cloning.

Question 36

Describe the process of:

PCR

Answer 36

1. Target DNA is denatured to separate the double stranded DNA template.
2. Many copies of two complementary DNA primers are mixed.
3. The solution is cooled so primers can hybridize with the single stranded templates.
4. Heat resistance polymerase is added to extend the primers.

Question 37

Which three items must be mixed for PCR to take place?

Answer 37

target DNA, two RNA primers, and a heat resistance polymerase