Nucleic Acids

Question 1

What are the monomers for DNA and RNA?

Answer 1

Nucleotides

Question 2

What is the structure of a nucleotide?

Answer 2

• A phosphate group
• A pentose sugar (ribose/deoxyribose)
• Nitrogenous base (1 of 5 organic bases)

Question 3

Which 4 nitrogenous bases does DNA contain?

Answer 3

• Adenine
• Thymine
• Guanine
• Cytosine

Question 4

Which 4 nitrogenous bases does RNA contain?

Answer 4

• Adenine
• Uracil (replaces thymine)
• Cytosine
• Guanine

Question 5

How many polynucleotide chains does DNA have?

Answer 5

2 anti-parallel polynucleotide chains

Question 6

How many polynucleotide chains does RNA have?

Answer 6

1 polynucleotide chain

Question 7

What protein is associated with DNA?

Answer 7

Histones

Question 8

What is the function of DNA?

Answer 8

• Codes for proteins (amino acid sequences)
• DNA replication for cell division

Question 9

What’s the function of RNA?

Answer 9

Transfers genetic information from DNA to ribosomes

Question 10

What are pyrimidines?

Answer 10

They have a single ring structure
(Cytosine, Thymine Uracil)

Question 11

What is a purine?

Answer 11

A two/double ring structure
(Adenine, Guanine)

Question 12

What bond forms between neighbouring nucleotides?

Answer 12

Phosphodiester bonds form between a pentose sugar and phosphate group (in a condensation reaction)

Question 13

What forms when many nucleotides are joined together (through phosphodiester bonds)?

Answer 13

Sugar-Phosphate backbone

Question 14

What type of bond forms between complementary base pairs?

Answer 14

Hydrogen bonds

Question 15

How many hydrogen bonds form between Adenine and Thymine (Uracil)?

Answer 15

2 hydrogen bonds

Question 16

How many hydrogen bonds form between cytosine and guanine?

Answer 16

3 hydrogen bonds
Therefore More stable

Question 17

What function does being a long and large molecule give DNA?

Answer 17

So it can store a lot of genetic information

Question 18

What function does being a coiled helix give DNA?

Answer 18

So it’s compact

Question 19

What function does having a sugar-phosphate backbone give DNA?

Answer 19

The bases in the double helix (middle) are protected

Question 20

Why does DNA have bases arranged in specific sequences?

Answer 20

So it can code for specific amino acids

Question 21

Why is DNA double stranded?

Answer 21

So it can be separated and unwound to act as a template for accurate replication using complementary base pairing

Question 22

DNA has weak hydrogen bonds between the bases on each strand - how does this make it better for its function?

Answer 22

So the DNA helicase can easily be separated when it replicates

Question 23

Which two enzymes are involved in DNA replication?

Answer 23

DNA Helicase
DNA Polymerase

Question 24

Describe the process of DNA replication?

Answer 24

• The enzyme DNA helicase causes the DNA double helix to unwind and separate into two strands by breaking the hydrogen bonds between the complementary base pairs exposing the bases
• Both strands then act as a template for DNA replication
• Free activated DNA nucleotide (in the nucleoplasm) are attracted and hydrogen bond to complementary bases on the exposed templates strands by complementary base pairing
• The newly added nucleotides are then joined by DNA polymerase in a condensation reaction to form phosphodiester bonds between adjacent nucleotides
• This results in two identical FNA molecules being produced each of which contain one original DNA strand and one newly synthesised strand (Semi-Conservative)

Question 25

What does DNA helicase do?

Answer 25

Unwinds and separates the double helix (by breaking the hydrogen bonds)

Question 26

How is DNA replicated?

Answer 26

Semi-conservatively

Question 27

Describe what is meant by semi-conservative replication?

Answer 27

The two identical DNA molecules produced contain one original DNA strand and one newly synthesised strand

Question 28

What happens when the hydrogen bonds between the complementary base pairs are broken?

Answer 28

The base pairs on the strand are exposed to act as a template

Question 29

What molecules are attracted and hydrogen bond to their complementary bases?

Answer 29

Free Activated DNA nucleotides

Question 30

How do free activated DNA nucleotides bonds to the template strands?

Answer 30

They hydrogen bond to their complementary base pairs

Question 31

Which enzyme joins the newly added nucleotides together?

Answer 31

DNA polymerase

Question 32

What type of bond forms between adjacent nucleotides?

Answer 32

Phosphodiester bond (during condensation reaction)

Question 33

How is chromatin formed?

Answer 33

DNA is wound around histone proteins

Question 34

What is chromatin?

Answer 34

A more spread out form of DNA (which forms fibres)

Question 35

What is a chromosome?

Answer 35

Most condensed form of DNA (formed from chromatin)

Question 36

What are the two main stages of cell division?

Answer 36

Nuclear división (mitosis/meiosis) - nucleus divides Cytokinesis - whole cell (cytoplasm) divides into daughter cells

Question 37

What must happen before a nucleus can divide?

Answer 37

DNA replication

Question 38

What’s a replication fork?

Answer 38

When DNA helicase and polymerase are working simultaneously so the bases aren’t exposed for too long

Question 39

Why does DNA polymerase only add nucleotides in a 5’ to 3’ direction?

Answer 39

DNA polymerase has a complementary active site to the 3’ end

Question 40

What were the 3 proposed DNA replication models?

Answer 40

- Conservative - Dispersive - Semi-conservative

Question 41

What does the conservative model suggest about DNA replication?

Answer 41

One completely newly synthesised molecule is made and the original molecule is conserved

Question 42

What does the dispersive model suggest about DNA replication ?

Answer 42

Fragments of DNA molecules are copied and dispersed in the structure

Question 43

Which two scientist tried to validate Watson and Cricks model of semi-conservative replication ?

Answer 43

Meselson and Stahl

Question 44

What three facts did Meselson and Stahl base their work on?

Answer 44

- All DNA contains nitrogen - Nitrogen has an isotopes - When bacteria grows in a medium they will absorb any nitrogen from the growth medium and incorporate it into any new DNA formed

Question 45

What are the stages of Meselson and Stahl’s experiment?

Answer 45

1. Bacteria are grown for several generations in a growth medium containing heavy nitrogen (N15) 2. DNA is the extracted and spun in a centrifuge solution of caesium chloride. This forms a band near the bottom of the test tube 3. The bacteria from the end of stage 1 is transferred and grown for 1 generation in a growth medium containing light nitrogen (N14) 4. The DNA is extracted and spun in a centrifuge and a intermediate band is formed (due to one heavy and one light strand per DNA molecule) 5. The bacteria from the end of stage 2 is grown for a second generation in the light nitrogen before the DNA is extracted and spun in a centrifuge (a light and intermediate band forms)

Question 46

When spun in a centrifuge what happens to DNA?

Answer 46

Based on density/mass DNA will settle in the test tube - Heaviest/most dense towards the bottom - Lightest/least dense towards the top

Question 47

At the end of the 5th stage of the experiment (DNA) why do we have one light and one intermediate strand?

Answer 47

2 DNA molecules are made from completely newly synthesised light nitrogen 2 DNA molecules have one light and one heavy strand

Question 48

How can we disprove the conservative model?

Answer 48

After the first generation in the light nitrogen we would have seen one denser band and one less dense band but an intermediate strand was observed

Question 49

How can we disprove the dispersive model for DNA replication ?

Answer 49

After the second generation in light nitrogen the band in the test tube would still be intermediate because there are still heavy DNA fragments in the molecule (although more light fragments have been joined/added)