Nucleic Acids

Question 1

What bonds are present between bases?

Answer 1

Hydrogen bonds

Question 2

What bonds are present between the sugar and phosphate group?

Answer 2

Phosphodiester bonds

Question 3

What does a nucleotide consist of?

Answer 3

A nitrogenous base
A pentode sugar
A phosphate group

Question 4

What does the backbone of a DNA molecule consist of?

Answer 4

A phosphate group

A deoxyribose sugar

Question 5

How are phosphodiester bonds broken?

Answer 5

Hydrolysis

Question 6

What is the structure of ATP?

Answer 6

Composed of an adenine base, a ribose sugar and 3 phosphate groups
ATP + H20 -> ADP + Pi + energy (hydrolysis)
Properties = small and water soluble

Question 7

Give 4 reasons why ATP is useful

Answer 7

1- Releases energy in small amounts
2- Broken down in a single reaction, releasing energy quickly
3- Adds phosphate to other molecules, makes them more reactive
4- Easily resynthesised

Question 8

What are pyrimidines?

Answer 8

Contain single carbon ring structures (hexagon)
Made up of carbon and nitrogen
Thymine and Cytosine

Question 9

What are purines?

Answer 9

Contain double carbon ring structures (hexagon and pentagon)
Made up of carbon and nitrogen
Adenine and Guanine

Question 10

How many hydrogen bonds are between adenine and thymine?

Answer 10

2 h bonds

Complementary base pairing

Question 11

How many hydrogen bonds are between cytosine and guanine?

Answer 11

3 h bonds

Complementary base pairing

Question 12

Base pairing

Answer 12

• Adenine and Thymine (2 h bonds)
  Cytosine and Guanine (3 h bonds)
• Small pyrimidine bases always bind to larger purine bases (parallel)
• Means that DNA always has equal amounts of all bases

Question 13

What is a gene?

Answer 13

A section of DNA that contains the complete sequence of DNA to code for an entire protein

Question 14

How is the genetic code degenerate?

Answer 14

There are more possible codes than there are amino acids (20)
Same amino acid can be coded for by more than one triplet

Question 15

How is the genetic code universal?

Answer 15

• Codes for the same a.a in all living organisms

All organisms use this same code - all life on earth has common ancestory

Question 16

How is the genetic code non-overlapping?

Answer 16

Each DNA triplet and gene is separate from each other

Question 17

Describe semi conservative DNA replication

Answer 17

• DNA helicase unwinds DNA by breaking H bonds
• Both strands act as templates
• Free DNA nucleotides attach by complementary base pairing
• DNA polymerase joins nucleotides, forming phosphodiester bonds
• H bonds reform
• DNA replication is semi conservative (new DNA contains one old strand and one new strand)

Question 18

What is the function of DNA helicase?

Answer 18

Unwinds DNA by breaking H to bonds

Question 19

What is the function of DNA polymerase

Answer 19

It catalyses the condensation reaction between the nucleotides in a DNA strand
It forms phosphodiester bonds between adjacent nucleotides

Question 20

What is the function of DNA Ligase?

Answer 20

Seals up the fragments in the sugar-phosphate backbone to form continuous DNA

Question 21

What does primase do?

Answer 21

Makes a small piece of RNA called a primer

Question 21

Describe Meselsohn-Stahl experiment

Answer 21

• population cultured in a growth medium containing heavy nitrogen (15N) only
• When centrifuged, only 1 heavy band is observed
• Cells transferred to a medium with only light nitrogen (14N)
• After 1 replication the DNA band was intermediate (twice the thickness)
• After 2 replications, intermediate and light bands were observed

Question 22

Where does transcription take place?

Answer 22

Nucleus

Question 24

Why is transcription important?

Answer 24

Makes a shorter mRNA molecule so that it can leave the nucleus and travel to the ribosomes

Question 25

What is the process of transcription?

Answer 25

• DNA helicase unwinds strands by breaking H bonds
• Free RNA nucleotides attach to template strand
• Complementary base pairing
• RNA polymerase joins nucleotides together
• H bonds reform
• Once the mRNA strand is formed, it can move out of the nucleus and travel to the ribosomes (either free or those on the RER)

Question 26

What are introns?

Answer 26

Non-coding sections of DNA

Question 27

What is splicing?

Answer 27

Removing introns

Question 29

What is the process of translation?

Answer 29

• Ribosome binds onto the mRNA at a start codon
• Codon is matched to an anticodon by complementary base pairing
• Ribosome holds tRNA in place
• Amino acids are joined together with a peptide bond
• Only 2 tRNA molecules can do this at a time
• Once the bond is formed, it moves onto the next 2 until it has a chain of amino acids (primary structure of a protein/polypeptide)

Question 30

Where does translation take place?

Answer 30

Cytoplasm

Question 36

Describe the method of purifying DNA by precipitation

Answer 36

1- Break open cells, e.g. blender
2- Mix: washing up detergent (break down nuclear membrane), table salt (Clump together pieces of DNA) and distilled water
3- Mix in cell mixture and wait 10 mins
4- Keep ice cold (stop enzymes breaking down DNA)
5- Filter mixture
6- Slowly pour cold ethanol to form a layer on top
7- Wait 10 mins
8- DNA forms a white precipitate
9- Remove DNA (tweezers/centrifuge)

Question 37

What is a codon?

Answer 37

Triplet of bases on mRNA that codes for a specific amino acid

Question 38

What is an anticodon?

Answer 38

Triplet of bases that is complementary to codon on mRNA

Question 39

Describe tRNA

Answer 39

• Polynucleotide
• Folded by H bonds
• Anticodon is specific to amino acid that it carries

Question 40

What is the DNA antisense strand?

Answer 40

• Template stand
• Acts as the template for mRNA
• Complementary to genes on sense strand

Question 41

What is the DNA sense strand?

Answer 41

• Contains the genes

- Doesn’t act as the template for mRNA

Question 42

What is the primary mRNA?

Answer 42

Same as DNA sense strand except U replaces T

Question 43

What is the locus?

Answer 43

Location of gene on a chromosome