Unit 1.2 Structure & replication of DNA

Question 1

The structure of DNA

Answer 1

Double stranded helix

Question 2

What does DNA carry

Answer 2

The genetic information for making proteins

Question 3

What are the four bases that make up the genetic code

Answer 3

Adenine, cytosine, guanine, & thymine

Question 4

What is the complementary base pair rule

Answer 4

Adenine always pairs with Thymine, Cytosine always pairs with Guanine

Question 5

What does each molecule of DNA consist of

Answer 5

2 strands, where each strand is made up of repeating units called nucleotides

Question 6

What does each DNA nucleotide consist of

Answer 6

Deoxyribose sugar, phosphate & a base

Question 7

What type of bond forms between the phosphate of one nucleotide & the deoxyribose sugar of the next nucleotide. What does this create

Answer 7

Strong chemical bonds that are not easily broken, this creates the sugar-phosphate backbone

Question 8

How many different types of nucleotides are there and why

Answer 8

4 as there are 4 different types of bases

Question 9

What are the base pairs joined together by

Answer 9

Weak hydrogen bonds that are easily broken

Question 10

What is it called when the 2 strands of DNA run in opposite directions

Answer 10

Anti-parallel

Question 11

Why is DNA unique

Answer 11

It is able to direct its own replication & reproduce itself exactly

Question 12

Why is it important that DNA replication takes place before a cell undergoes mitosis

Answer 12

It ensures each new cell has the correct chromosome complement

Question 13

What are the 7 stages of DNA replication

Answer 13

1- DNA double helix unwinds
2- Weak hydrogen bonds between the bases are broken to form 2 template strands
3- To initiate replication, a primer binds to each template strand at the 3’ end
4- DNA polymerase adds DNA nucleotides (using complementary base pairing) to the 3’ end of the new DNA strand that is forming
5- As nucleotides are added, weak hydrogen bonds form between the base pairs
6- Strong chemical bonds form between the nucleotides of the new strand (forming a sugar-phosphate backbone)
7- Newly formed daughter DNA fold back to double helix

Question 14

What is each DNA molecule known as after replication

Answer 14

Semi-conservative

Question 15

What does semi-conservative mean

Answer 15

Each DNA molecule contains one strand from the original parent & one newly synthesised strand

Question 16

What is the only direction DNA polymerase can add DNA nucleotides

Answer 16

They can only be added to the 3’ end

Question 17

What DNA strand is replicated continuously

Answer 17

The leading strand

Question 18

What DNA strand is replicated in fragments

Answer 18

The lagging strand

Question 19

What enzyme joins the fragments of the lagging strand together

Answer 19

Ligase

Question 20

What are the 5 requirements for DNA replication

Answer 20

• DNA
• Primers
• DNA nucleotides
• Enzymes
• ATP

Question 21

What chemical group is found at the 5’ end of the DNA strand

Answer 21

Phosphate

Question 22

What is required when studying the genome

Answer 22

Millions of identical fragments of DNA need to be created

Question 23

How are millions of identical fragments of DNA created

Answer 23

Through the process of PCR

Question 24

What does PCR produce

Answer 24

Many copies of a specific section of DNA

Question 25

What does in vitro mean

Answer 25

In the lab

Question 26

What does PCR use to amplify DNA

Answer 26

Complementary primers for specific target sequences

Question 27

What are primers in PCR

Answer 27

Short strands of nucleotides which are complementary to specific target sequences at the 2 ends of the region of DNA to be amplified

Question 28

First stage of PCR

Answer 28

Melting: DNA is heated (92-98°C) to break the hydrogen bonds, allowing the original DNA strands to be separated

Question 29

Second stage of PCR

Answer 29

Annealing: Sample is cooled (50-65°C). Allows complementary primers to bind to target sequences at the start of each strand

Question 30

Third stage of PCR

Answer 30

Extension: Sample is heated (70-80°C) for heat-tolerant DNA polymerase to replicate the region of DNA & adds DNA nucleotides to the 3’ end of the new strands

Question 31

How many identical copies of DNA are made after the first cycle of PCR

Answer 31

Two

Question 32

What are the 6 requirements for PCR

Answer 32

1- Original DNA sample/template
2- A stock of each of the 4 DNA nucleotides
3- DNA primers
4- Heat-tolerant DNA polymerase (enzyme)
5- Buffer solutions
6- A thermal cycler

Question 33

What do buffer solutions do

Answer 33

maintain optimum pH of the enzyme

Question 34

What is a thermal cycler

Answer 34

An automated reaction vessel

Question 35

What can PCR be useful for

Answer 35

Solving crimes, settling paternity disputes & diagnosing genetic disorders

Question 36

What does amplification mean

Answer 36

The number of original molecules has doubled

Question 37

What/ whose DNA samples do forensic scientists take to solve crime

Answer 37

DNA samples from the crime scene, the suspect(s) and the victim

Question 38

What then happens to the DNA samples once taken (solving crimes)

Answer 38

The components of the samples are separated using gel electrophoresis & compared to identify the criminal

Question 39

What is gel electrophoresis

Answer 39

A technique used to separate macromolecules such as DNA

Question 40

Describe how gel electrophoresis works

Answer 40

DNA samples are placed in wells of a gel.
An electric current is applied to the gel & since DNA molecules are negatively charged they move towards the positive end of the gel.
As the DNA fragments are different sized the smaller particles move further in the gel thus separating out the DNA fragments

Question 41

How much DNA does an individual inherit from each of their parents

Answer 41

50%