Nucleic Acids

Question 1

What is a nucleotide?

Answer 1

The monomer of nucleic acids, made up of a phosphate group, organic nitrogenous base and a pentose sugar.

Question 2

What is the structure of a DNA nucleotide?

Answer 2

• A phosphate
• A deoxyribose sugar
• A base (ATCG)

Question 3

Why are phosphate ions important in DNA?

Answer 3

They help create strong sugar phosphate backbones along with the deoxyribose sugar

Question 4

How are polynucleotides formed?

Answer 4

A condensation reaction between the phosphate of one nucleotide and the pentose sugar of another. This forms phosphodiester bonds between the two nucleotides.

Question 5

What are the 4 bases in DNA?

Answer 5

• Thymine
• Adenine
• Cytosine
• Guanine

Question 6

Which bases bind together in DNA?

Answer 6

Cytosine to Guanine
Thymine to Adenine

Question 7

What bond is between two complimentary bases?

Answer 7

Hydrogen bonds

Question 8

How does DNA’s double helix structure relate to its function?

Answer 8

• Provides strength and stability for passing through generations

Question 9

How does DNA’s large structure relate to its function?

Answer 9

Can store lots of information

Question 10

How does DNA’s coiled structure relate to its function?

Answer 10

Compact so can store a lot of info in a small space

Question 11

How does DNA’s base sequence structure relate to its function?

Answer 11

Gives triplets that code for amino acids

Question 12

How does DNA’s double stranded structure relate to its function?

Answer 12

Allows for semiconservative replication where both strands act as a template

Question 13

How does DNA’s hydrogen bonds between bases structure relate to its function?

Answer 13

Many hydrogen bonds so stable

Question 14

What is the structure of an RNA nucelotide?

Answer 14

• A phosphate
• A ribose sugar
• A base (AUGC)

Question 15

What are the three types of RNA?

Answer 15

tRNA - transfer RNA
mRNA - messenger RNA
rRNA - ribosomal RNA

Question 16

Is RNA polynucleotides single or double stranded?

Answer 16

Single

Question 17

What is the general role of RNA?

Answer 17

Responsible for the copying of DNA inside and outside the nucleus so that DNA soes not have to leave the nucleus, protecting it from damages

Question 18

How is DNA replicated?

Answer 18

Semi-conservatively

Question 19

What is semi-conservative replication?

Answer 19

Before a cell divides, it needs to copy the DNA so that identical cells are made.
When a new cell in made, one of the DNA strands is from the mother cell and one is new.

Question 20

Why is semi-conservative replication important?

Answer 20

To ensure there is genetic continuity between generations and to make sure we can replace cells regularly

Question 21

What enzymes are involved in the semi-conservative replication of DNA?

Answer 21

• DNA helicase
• DNA polymerase
• DNA ligase

Question 22

I belive in you

Answer 22

Youll get better

Question 23

What are the stages in the process of DNA replication?

Answer 23

1. DNA helicase breaks hydrogen bonds so DNA unwinds
2. Each strand used as a template which free floating nucleotides attach to (via complimentary base pairs)
3. DNA polymerase catalyses the formation of phosphodiester bonds between nucleotides
4. Two new daughter DNA strands have one parental DNA strand and one new

Question 24

What is the leading strand in DNA?

Answer 24

As DNA is unzipped from the 3’ end to the 5’ end, DNA polymerase will attach to the 3’ end and move towards the replication fork.
DNA polymerase synthesises the leading strand continuously.

Question 25

What is the lagging strand?

Answer 25

When DNA polymerase moves away from the replication form, so can only synthesise the lagging strand in segments. DNA ligase is then used to join the segments together.

Question 26

True or false: Complimentary bases have the same frequency as each other.

Answer 26

True So if 13% of bases in a DNA sample are thymine, 13% of them will be adenine

Question 27

What is the Meselson and Stahl model? How was it done?

Answer 27

The model that proved DNA replicated semi-conservatively (theorised by Watson and Crick). 1. Bacteria with heavy nitrogen DNA is centrifuged to show DNA is at the bottom of tube 2. Bacteria is allowed to use lighter nitrogen in replication If semi-conservative: DNA now containing one of each type of nitrogen sits in the middle of centrifuge If conservative: Two lines in centrifuge as two different weights present

Question 28

What is the structure of ATP?

Answer 28

A ribose sugar Three phosphates An adenine base

Question 29

What are the features of ATP?

Answer 29

- **Small but useful amount of energy** prevents wastage - **Stable** so doesn't breakdown without enzyme, prevents wastage - **Recyclable** so can be reused - **Quick hydrolysis** so allows cell to respond to sudden changes - **Soluble** so can be transported to where energy is needed

Question 30

What is the use of ATP?

Answer 30

The primary carrier of energy in cells, produced in aerobic respiration. ''The universal energy currency''

Question 31

ATP is useful in many biological processes. Explain why. (4)

Answer 31

1. Releases energy in small /manageable amounts; (there is very little energy lost as heat - so there is little danger of thermal death of cells) 2. Releases energy instantaneously because it is broken down in a one-step reaction (a single bond is broken) 3. Phosphorylates other compounds, making them more reactive; 4. Can be rapidly reformed/resynthesized; 5. Cannot leave cells, so is not lost

Question 32

Describe how DNA is replicated. (6)

Answer 32

1. Strands separate / H-bonds break; 2. DNA helicase (involved); 3. Both strands/each strand act(s) as (a) template(s); 4. (Free) nucleotides attach; 5. Complementary/specific base pairing / AT and GC; 6. DNA polymerase joins nucleotides (on new strand); 7. H-bonds reform; 8. Semi-conservative replication / new DNA molecules contain one old strand and one new strand;

Question 33

Explain why new nucleotides can only be added in a 5' to 3' direction. (4)

Answer 33

1. Reference to DNA polymerase; 2. (Which is) specific; 3. Only complementary with / binds to 5' end (of strand); Reject hydrogen bonds / base pairing 4. Shapes of 5' end and 3' end are different / description of how different;

Question 34

Explain how the structure of DNA is related to its functions. (6)

Answer 34

1. sugar-phosphate backbone gives strength; (coiling gives) compact shape; 2. sequence of bases allows information to be stored; 3. long molecule stores large amount of information; 4. information can be replicated / complementary base pairing; 5. (double helix protects) weak hydrogen bonds / double helix makes molecule stable prevents code being corrupted; 6. chains held together by weak hydrogen bonds; chains can split for replication / transcription