Introduction to DNA

Question 1

How many chromosomes are there in each human cell?

Answer 1

46

Question 2

Describe the relationship between DNA, Chromosomes and Genes

Answer 2

• Chromosomes are made of genes

- Genes are made of DNA

Question 3

Describe DNA packaging (‘beads on a string’)

Answer 3

• DNA is wrapped around HISTONE cores forming a NUCLEOSOME

Question 4

What is the name for a tightly packed sequence of nucleosomes?

Answer 4

Solenoid

Question 5

What kind of chromatin has expressed genes and appears white on a slide?

Answer 5

Euchromatin

Question 6

What form of chromatin has unexpressed genes and appears black on a slide?

Answer 6

Heterochromatin

Question 7

What is a genome?

Answer 7

An entire DNA sequence of a species

Question 8

What is the difference between the structure of a Nucleoside and a Nucleotide?

Answer 8

• Both have a base and a sugar

- A nucleotide also contains a phosphate group

Question 9

Name two types of Nucleic Acids

Answer 9

DNA and RNA

Question 10

Name the two types of Nitrogenous Base and how many carbon rings does each have?

Answer 10

Pyrimidine - 1 carbon ring

Purine - 2 carbon rings

Question 11

Which two bases are Purines?

Answer 11

• Adenine

- Guanine

Question 12

What are the 3 Pyrimidine bases?

Answer 12

• Cytosine
• Uracil
• Thymine

Question 13

Which bases differ between RNA and DNA?

Answer 13

• Uracil in RNA

- Thymine in DNA

Question 14

How are Nucleotides joined?

Answer 14

Phosphodiester bonds

Question 15

What are the two chain ends of DNA strands?

Answer 15

5’P (phosphate group on 5th carbon in ring)

3’OH (OH group on 3rd carbon in ring)

Question 16

What kind of bonds join DNA base pairs?

Answer 16

Hydrogen bonds

Question 17

Which way are DNA ends written and read?

Answer 17

5’ to 3’

Question 18

What is the function of DNA Polymerase in DNA replication?

Answer 18

• It catalysed the process

- It elongates each existing DNA strand by one nucleotide

Question 19

What are the three stages of DNA replication?

Answer 19

• Initiation
• Elongation
• Termination

Question 20

What happens in the Initiation phase of DNA replication?

Answer 20

• Helicase breaks the hydrogen bonds forming the Replication Fork
• Primase kick-starts the process

Question 21

Which strand is coded continuously by DNA Polymerase and why?

Answer 21

• 3’ to 5’

- Anti-Parallel strand is being made (5’ to 3’)

Question 22

Which strand is coded in bits and what are these bits called?

Answer 22

• Lagging strand

- Okazaki fragments

Question 23

What chemical joins Okazaki fragments?

Answer 23

DNA ligase

Question 24

What happens in the termination stage of DNA replication?

Answer 24

Two facing replication forks meet and DNA ligase joins the fragments

Question 25

How many DNA molecules does a chromosome contain?

Answer 25

Can be one DNA molecule or two DNA molecules joined by a centromere