DNA

Question 1

What is a eukaryotic cell?

Answer 1

This is a cell that has a nucleus

Question 2

What is a prokaryotic cell?

Answer 2

This is a cell that does not have a nucleus

Question 3

How are the parts of the cell compartmentalised?

Answer 3

They are contained within organelles

Question 4

What is the central dogma?

Answer 4

1) DNA replication
2) DNA is transcribed into RNA
3) the RNA is translated into a protein

Question 5

What is the transforming principle?

Answer 5

S cells contain a chemical that is fatal
R cells do not contain this chemical
The chemical in dead S cell bacteria could be transformed into living bacteria to make them deadly- Living R cells are changed to S cells

Question 6

What is a bacteriophage?

Answer 6

This is a virus that infects bacteria by sticking to bacteria surface and injecting its own genetic material

Question 7

Which experiment established DNA as genetic material?

Answer 7

Hershey and Chase: 1952
35S proteins
1) protein coats of phages are radioactively labelled
2) phages infect bacteria with GM
3) no radioactivity enters the cell
32P DNA
1) DNA of phases is radioactively labelled
2) phages infect bacteria with GM
3) radioactivity enters the cell

Question 8

What makes up a nucleotide?

Answer 8

DNA backbone- phosphates and their esters (phosphate)
Carbohydrates- ribose and deoxyribose (sugar)
Organic bases (nucleoside bases)- AGTC (unit)

Question 9

What is a nucleotide?

Answer 9

Nucleotides form the basic structural unit of nucleic acids such as DNA

Question 10

What are the bases and are they purines or pyramidines?

Answer 10

Adenine
Guanine
(Purines)

Uracil
Thymine
Cytosine
(Pyramidines)

Question 11

What is the difference between ribose and deoxyribose?

Answer 11

Deoxyribose contains one less OH group than ribose

Question 12

At which parts of DNA does it assemble?

Answer 12

DNA is assembled 5’ to 3’ direction

Question 13

Describe the structure of the double helix of DNA

Answer 13

Phosphates are on the outside
Bases and hydrogen bonding is on the inside
It contains 2 strands which are antiparallel

Question 14

Are nucleic acids acidic?

Answer 14

No nucleic acids are not acidic
At pH 7, only one in 1000 will have a proton to donate
The phosphate normally exists as an anion

Question 15

Are DNA bases basic?

Answer 15

No they are not

Bases at pH 7 are neutral

Question 16

Why does DNA have an overall negative charge?

Answer 16

Phosphates on the backbone will be negatively charged and so DNA has an overall negative charge

Question 17

What are the difference between DNA and RNA?

Answer 17

1) DNA has thymine as a base whereas RNA has uracil
2) DNA has 2’ deoxyribose
On a macro molecular level, DNA is double stranded whereas RNA is single stranded
But RNA can still bind to DNA
RNA is short lived

Question 18

Why does DNA have thymine instead of uracil?

Answer 18

Cytosine can easily lose an NH3 and become uracil
This means that if this happens, the dUTpase can recognise this as a mistake and replace it whereas if uracil was a natural base of DNA, adenine would be paired with it which would lead to incorrect replication

Question 19

How is cytosine converted into uracil?

Answer 19

Water attacks and NH3 leaves

Question 20

What is the difference between thymine and uracil?

Answer 20

There is one methyl group difference

Question 21

How is cytosine converted to uracil

Answer 21

Water is added and NH3 leaves
Slow rate
(See mechanism

Question 22

What is the role of DUTpase?

Answer 22

DUTpase seeks out mutated uracil (from cytosine)

Even though uracil has a similar structure to thymine, it does not affect thymine as the methyl group on thymine is differentiating

Question 23

Is DNA or RNA more stable?

Answer 23

DNA is more stable than RNA (RNA is short lived)
RNA is more chemically reactive
DNA has a phosphate ester backbone
RNA has a reactive 2’ OH group

Question 24

What happens when DNA mutates?

Answer 24

It is passed onto future generations due to DNA replication

Question 25

Where can RNA be attacked?

Answer 25

RNA can be attacked by a base at the 2' OH group (RNA is removed) ( see mechanism) This reaction is catalysed by RNAse which is shed by human skin

Question 26

Why do A-T and C-G pair together?

Answer 26

They have complementary H bonding stabilisation A-T has 2 hydrogen bonds C-G has 3 hydrogen bonds and so is more stable

Question 27

What is pi- pi stacking?

Answer 27

Interactions and attraction between aromatic rings when close in space, this makes a stack This causes stabilisation in the double helix Flat and aromatic which means drugs can fit in the spaces

Question 28

What is the role of DNA polymerase?

Answer 28

DNA polymerase extends the DNA chain in the 5' to 3' directions Catalysed the bond formation between 3' (See mechanism)

Question 29

How is DNA sequences?

Answer 29

1) heat DNA to break 2) primer reanneals 3) DNA polymerase adds free bases to primer (complementary) 4) dideoxy nucleotide terminates the chain- leads to fragments with different lengths (fluorescent chain terminators) 5) capillary electrophoresis- size dependent, small leave first 6) laser reads fluorescent ends

Question 30

What do you require for DNA sequencing?

Answer 30

Template strand- primer bonds to small parts of strand DNA polymerase Free DNA bases Dideoxy nucleotides (fluoresently labelled)

Question 31

Describe the fidelity of DNA polymerase in humans and viruses

Answer 31

Fidelity is the accuracy of the polymerase Human has a high fidelity and so few errors Viral polymerase works faster but less meticulous as it competes with the host

Question 32

What will viral polymerase accept?

Answer 32

It will accept bases that lack 3' OH dideoxynucleotides | Accept variations to bases- fluorescent bases

Question 33

How does capillary electrophoresis work?

Answer 33

It separated based on charge and size | Electrosmotic flow- migration of positive ions to the negative cathode

Question 34

What happens when thymine is exposed to UV radiation?

Answer 34

UV radiation damage The excited state leads to dimers of thymine

Question 35

What is DNA photolase?

Answer 35

DNA repair enzyme. It binds to UV-damaged DNA containing pyrimidine dimers and breaks the cyclobutane ring joining the two pyrimidines of the dimer.

Question 36

How do cells repair DNA?

Answer 36

Prevents mistakes before the double helix (in replication) 1) two enzymes detect that the bases don't match 2) a third enzyme detects the correct DNA strand 3) the defective strand is replaced

Question 37

What is base exclusion repair?

Answer 37

1) cytosine can lose an amino group forming uracil 2) enzymes cut out the defect and then damaged nucleotide 3) DNA fills in the gap

Question 38

When is DNA damage a good thing?

Answer 38

DNA damage is only lethal to cells engaged in the cell cycle In mitosis, cell death is triggered if there is not enough DNA (apoptosis)

Question 39

How can apoptosis be triggered?

Answer 39

If you can stop the S phase in cell division (synthesis of DNA) , you can trigger apoptosis Block the synthesis of thymine, if there is not enough DNA, (convert to uracil) cell death is triggered at check point

Question 40

How is uracil converted to thymine?

Answer 40

2) removal of 2'OH 2) removal of phosphate 3) addition of CH3 You need 2'OH and proton- recognised by ribonucleotide reductase (See mechanism)