John Barrow

Question 1

Which two experiments prove that DNA stores genetic information?

Answer 1

Avery-MacLeod-McCarty
&
Hershey-Chase

Question 2

The Avery-MacLeod-McCarty experiment had 5 different controls; in how many of these controls, did the mouse die?

What were the controls?

Answer 2

3/5 controls resulted in the mouse dying.

1. Live, encapsulated, virulent bacteria
2. Live, non-encapsulated, non-virulent // heat-killed virulent mix
3. Live, non-virulent // DNA of heat-killed virulent bacteria that was TRANSFORMED and encapsulated

Question 3

What are the structural components of a nucleoside?

Answer 3

base + pentose sugar

Question 4

What are the structural components of a nucleotide?

Answer 4

base + pentose sugar + phosphate

Question 5

Cytosine, Thymine & Uracil have what in common?

Answer 5

They are all pyrimidines; their nucleotide structures are all 1 ringed.

Question 6

Adenine & Guanine have what in common?

Answer 6

They are both purines; their nucleotide structures are both 2 ringed.

Question 7

How do nucleotides polymerise?

Answer 7

via a phosphodiester linkage

Question 8

Why is RNA less stable than DNA?

Answer 8

The -OH group is more open to degradation

Question 9

What is Chargaff’s 4th rule?

What assumptions can we make from this?

Answer 9

(i) Adenine = Thymine & Guanine = Cytosine

(ii) Sum of purine residues = sum of pyrimidine residues
& Adenine + Guanine = Thymine + Cytosine

Question 10

Give examples of 4 different unusual DNA structures.

Answer 10

• Palindrome
• Mirror repeat
• Hairpin
• Cruciform

Question 11

Name the three ways in which RNA is structurally different to DNA

Answer 11

• Single polymer chain
• The sugar contains and OH group
• Thymine is replaced with Uracil

Question 12

Give 3 examples of DNA damaging agents that can cause non-enzymatic transformations.

Answer 12

• UV light (& other types of radiation)
• Chemicals in the environment
• Oxidative damage (Hydrogen peroxide// hydroxyl radicals)

Question 13

What are the main components of a chromsome?

Answer 13

Genes + Intergenic DNA

Question 14

What is meant by “genes”?

Answer 14

Genetic data; coding for RNA and proteins

Question 15

What is meant by “intergenic DNA”?

Answer 15

Regulatory sequences:

• for transcription of genes;
• DNA replication;
• Packing of genes

Question 16

What are the two types of DNA supercoiling?

Answer 16

• Plectonemic

- Solenoidal

Question 17

What catalyses the changes in the supercoiling of DNA

Answer 17

Topoisomerases

Question 18

What is a nucleosome?

Answer 18

The fundamental organisational units of chromatin

Question 19

What are the fundamental rules of DNA replication?

Answer 19

1. DNA replication is semi-conservative
2. Replication begins at an origin and usually proceeds bidirectionally
3. DNA synthesis proceeds in a 5’–> 3’ direction and is semi-discontinuous

Question 20

What can mutations alter?

Answer 20

• Protein-coding sequences to generate mutant proteins

- Sequences that regulate DNA replication, transcription or translation

Question 21

What is DNA damage repaired by?

Answer 21

• Base excision repair enzymes

- Nucleotide excision repair enzymes

Question 22

Briefly describe base & nucleotide excision repair

Answer 22

1. Recognising damage within the DNA double helix
2. Cleaving the damaged DNA strand with endonucleases to remove the damaged section
3. Using DNA polymerase and the undamaged complementary DNA strand, the gap is filled.

Question 23

Briefly describe the 5 general procedures of DNA cloning

Answer 23

1. Cutting DNA at precise locations
2. Selecting cloning vectors
3. Covalently linking DNA fragments to form recombinant DNA
4. Moving recombinant DNA from the test tube to a host cell
5. Selecting or identifying host cells that contain recombinant DNA

Question 24

What kind of sequences do type II restriction enzymes usually recognise?
Briefly describe the different kinds of cuts.

Answer 24

(i) 4 or 6 base pair palindromic sequences

(ii) Usually symmetrical although;
- Cuts can generate blunt ends
- Cuts can be staggered

Question 25

What does it mean for two restriction fragment ends to be compatible?

Answer 25

They must be able to hydrogen bond

Question 26

Why are nucleic acids negatively charged?

Answer 26

Due to the acidic phosphate groups in the backbone

Question 27

Cloning plasmids allow amplification of inserted DNA fragments, but what do they require?

Answer 27

• Origin of replication

- Selectable marker(s)

Question 28

What is ddNTP analogue?

Answer 28

dideoxynucleotide

Question 29

Briefly describe genetically modified organisms

Answer 29

• Can use recombination to introduce specific DNA sequences into the genome of an organism

Question 30

Briefly describe the two kinds of recombination

Answer 30

• Directed (homologous); incoming DNA recombines at a specific site in the genome.
• Random (non-homologous) ; incoming DNA inserted at random in genome. This could inactive important/essential genes.

Question 31

What is the term given when a bacteria naturally takes up DNA from its environment?

Answer 31

Transformation

Question 32

What are the two methods used to modify animal genomes?

Answer 32

• Pronuclear injection of DNA

- Gene targeting using embryonic stem (ES) cells