Unit 1: Human cells: 1.2 Structure and Function of DNA

Question 1

What is DNA a molecule of?

Answer 1

DNA is the molecule of inheritance and stores genetic information in its sequence of bases

Question 2

What does the sequence of bases on DNA determine in an organism?

Answer 2

The sequence determines the organisms genotype and the structure of its proteins

Question 3

What does DNA consist of?

Answer 3

Units called nucleotides

Question 4

What are nucleotides?

Answer 4

DNA consists of two strands composed of repeating units called nucleotides

Question 5

What are nucleotides made of?

Answer 5

Each nucleotide consists of a molecule of DEOXYRIBOSE SUGAR joined to a PHOSPHATE group and an organic BASE

Question 6

What forms the genetic code?

Answer 6

The base sequence

Question 7

What holds each strand of DNA together?

Answer 7

A chemical BOND forms between the PHOSPHATE group of one nucleotide and the DEOXYRIBOSE SUGAR of another nucleotide

Question 8

How are two strands of DNA joined together?

Answer 8

Two strands of nucleotides are joined together

by HYDROGEN BONDS forming between COMPLIMENTARY BASES

Question 9

What is the use of weak hydrogen bonds between strands?

Answer 9

The strands can become easily separated (for replication)

Question 10

What is the base pair rule?

Answer 10

Each base can only join with one other type of base: Adenine(A) always bonds with Thymine(T) and Guanine(G) always bonds with Cytosine(C)

Question 11

What does the term anti parallel describe?

Answer 11

Anti parallel is used to describe the structure of the two DNA strands as they run in opposite directions to each other

Question 12

What is at the 5’end of a DNA strand?

Answer 12

Phosphate

Question 13

What is at the 3’end of a DNA strand?

Answer 13

Deoxyribose sugar

Question 14

What are histones?

Answer 14

Bundles of protein that molecules of DNA become tightly coiled and packaged around

Question 15

What are the uses of histones?

Answer 15

They help in the STORAGE of the long structures (DNA) and they unwind again when required to do so

Question 16

Why is DNA a unique molecule?

Answer 16

DNA is a unique molecule as it is able to direct its OWN REPLICATION and produce an EXACT COPY of itself

Question 17

What is essential prior to cell division and why?

Answer 17

DNA REPLICATION is essential prior to cell division so that each daughter cell contains the EXACT SAME genetic information as the original parent cell

Question 18

For DNA replication to take place what must the nucleus contain? Name 5

Answer 18

DNA(to act as a template)
Primers(short sequence of nucleotides)
A supply of the four types of DNA nucleotides (ATGC)
Enzymes(DNA polymerase and ligase)
ATP

Question 19

Describe the first stage of the process of DNA replication

Answer 19

A starting point on the DNA molecule is recognised and the DNA unwinds and the weak hydrogen bonds between bases break

This means the tow strands separate at a “replication fork” to form two template strands

Question 20

Describe the second stage of the process of DNA replication

Answer 20

A primer binds to the 3’end of the template strands. This acts as a starting point for replication as this is where the nucleotides are added to

Question 21

Which strand is replicated in fragments?

Answer 21

Lagging strand

Question 22

Which strand is replicated continuously?

Answer 22

Leading strand

Question 23

What is the name of the strand with the free 3’end?

Answer 23

Leading strand

Question 24

What is the name of the strand with the free 5’end?

Answer 24

Lagging strand

Question 25

Describe the third stage of DNA replication

Answer 25

Once the primers are in place the enzyme DNA polymerase is able to add complementary DNA nucleotides( through base pairing) from deoxyribose 3'end of the new DNA strand which is forming

Question 26

Describe the fourth stage of DNA replication

Answer 26

As DNA can only add nucleotides in one direction the leading strand is replicated continuously and the lagging strand replicated in fragments

Question 27

Describe the fifth stage of DNA replication

Answer 27

On the lagging strand many primers bind along the other strand as the replication fork opens the fragments of DNA are then joined together with the help of an enzyme called ligase

Question 28

What is ligase and what does it do?

Answer 28

Ligase is an enzyme which allows fragments of DNA to join together on the 5'end strand

Question 29

What is PCR and what does it involve?

Answer 29

Polymerase chain reaction(PCR) is used AMPLIFY target sequences of DNA(copy it in the lab) PCR involves repeated cycles of heating and cooling

Question 30

What does PCR use?

Answer 30

Primers

Question 31

What does PCR use primers for?

Answer 31

PCR uses primers which are short strands of DNA nucleotides which are complimentary to specific target sequences at the two ends of the region of the DNA to be amplified

Question 32

Describe is the first stage of PCR

Answer 32

DNA is heated to between 92 and 98 degrees to separate the two strands(by breaking the hydrogen bonds between bases)

Question 33

Describe the second stage of PCR

Answer 33

It (DNA) is heated to between 50 and 60 degrees to allow primers to bind/anneal

Question 34

Describe the third stage of PCR

Answer 34

It (DNA) is then heated to between 70 and 80 degrees for heat tolerant DNA polymerase to replicate the region of DNA

Question 35

Describe the stages of PCR

Answer 35

1. DNA is heated to between 92 and 98 degrees to separate the two strands(by breaking the hydrogen bonds between bases) 2. It is heated to between 50 and 60 degrees to allow primers to bind/anneal 3. It is then heated to between 70 and 80 degrees for heat tolerant DNA polymerase to replicate the region of DNA

Question 36

What is the end product of PCR and how many times is the process repeated?

Answer 36

The product is two identical copies of DNA at the end of the first cycle. It is repeated many times (20-30) with each cycle doubling the quantity of DNA

Question 37

State the uses of PCR and an example for each

Answer 37

MEDICAL- diagnose a disease - estimate the risk of disease onset FORENSIC- help solve crimes PATERNITY DISPUTES - confirm genetic relationships between individuals

Question 38

What experiment allows DNA fragments to be assessed according to size?

Answer 38

Gel electrophoresis separates mixtures of DNA fragments according to size

Question 39

On paternity diagrams can DNA come from the mother or father?

Answer 39

Yes