Nucleotides and nucleic acids

Question 1

2.1.3 a)

What is a monomer?

Answer 1

• Molecule that when repeated makes up a polymer

Question 2

2.1.3 a)

What is a nucleotide?

Answer 2

• Biological molecule (contain elements H, C, O, N, P) consisting of:
  
  • five-carbon sugar
    
    • ribose (RNA) or deoxyribose (DNA)
  • phosphate group (PO₄^2-)
  • inorganic molecule that is acidic and negatively charged
    
    • attached to either C₃ or C₅ of sugar
  • nitrogenous base e.g. A,C,G,T,U
  • complex, organic, containing nitrogen, and containing one or two carbon rings
    
    • attached to C₁ of sugar
• participate in nearly all biochemical processes

Question 3

2.1.3 a)

What does the nitrogenous base A stand for?

Answer 3

Question 4

2.1.3 a)

What does the nitrogenous base C stand for?

Answer 4

Question 5

2.1.3 a)

What does the nitrogenous base T stand for?

Answer 5

Question 6

2.1.3 a)

What does the nitrogenous base G stand for?

Answer 6

Question 7

2.1.3 a)

What does the nitrogenous base U stand for?

Answer 7

Question 8

2.1.3 a)

What is the difference between RNA and DNA nucleotides?

Answer 8

• DNA has the pentose monosaccharide deoxyribose (one less oxygen)
• RNA has the pentose monosaccharide ribose
• DNA has nitrogenous bases A,C,G,T
• RNA has nitrogenous bases A,C,G,U

Question 9

2.1.3 a)

What is a pyrimidine?

Answer 9

• the smaller bases e.g. T and C
• containing one carbon ring structure

Question 10

2.1.3 a)

What is a purine?

Answer 10

• larger bases e.g. A, G
• containing two carbon ring structures

Question 11

2.1.3 d) i)

What base is complementary to A?

Answer 11

• A is purine, T is pyrimidine
• T (in DNA), U (in RNA)
• 2 hydrogen bonds are formed

Question 12

2.1.3 d) i)

What base is complementary to T?

Answer 12

• A is purine, T is pyrimidine
• A
• 2 hydrogen bonds are formed

Question 13

2.1.3 d) i)

What base is complementary to C?

Answer 13

• G is purine, C is pyrimidine
• G
• 3 hydrogen bonds are formed

Question 14

2.1.3 d) i)

What base is complementary to G?

Answer 14

• G is purine, C is pyrimidine
• C
• 3 hydrogen bonds are formed

Question 15

2.1.3 b)

What is a polynucleotide?

Answer 15

• A large molecule formed by condensation reaction of many nucleotides
• Phosphate group of C₅ covalently bonds by condensation with the hydroxyl (OH) group at C₃ of the nucleotide above
• This bond is called a phosphodiester bond
• forms a long strong, strong, sugar phosphate backbone with a base attached to each sugar

Question 16

2.1.3 a)

How is a nucleotide formed?

Answer 16

• phosphate and pentose sugar form a covalent bond by condensation reaction
• nitrogenous base and pentose sugar form a covalent bond by condensation reaction

Question 17

2.1.3 b)

How is a polynucleotide broken down?

Answer 17

• Hydrolysis reactions (gaining water)
  
  • opposite of condensation reaction
• releasing individual nucleotides

Question 18

2.1.3 c)

What does ADP stand for?

Answer 18

• adenosine diphosphate

Question 19

2.1.3 c)

What does AMP stand for?

Answer 19

• adenosine monophosphate

Question 20

2.1.3 c)

What does ATP stand for?

Answer 20

• adenosine triphosphate

Question 21

2.1.3 c)

When does a nucleotide form a phosphorylated nucleotide?

Answer 21

• when the nucleotide has more than one phosphate group
  
  • e.g. ATP and ADP

Question 22

2.1.3 c)

What is ATP?

Answer 22

• adenosine triphoshphate
• energy-rich end-product of most energy releasing biochemical pathways (reactions)
• used to drive most energy requiring metabolic processes in cells
• ATP, AMP and ADP all help to regulate metabolic pathways

Question 23

2.1.3 d) i)

Where is DNA found?

Answer 23

• Nuclei of all eukaryotic cells
  
  • Each large molecule of DNA is wound around special histone proteins into a chromosome
  • Each chromosome = one DNA molecule
  • in eukaryotic cells, there is a loop of DNA without histone proteins, inside mitochondria and chloroplasts
• Cytoplasm of prokaryotic cells
  
  • not enclosed in a nucleus and not wound around histone proteins (naked)
• In some viruses
  
  • viruses that have DNA, dont have histone proteins or a nucleus, similar to prokaryotic cells, the DNA in the viruses that have DNA is naked

Question 24

2.1.3 d) i)

What is DNA?

Answer 24

• DNA is a hereditary material
• carries coded instructions used in development and function of all living organisms
• DNA is an important macromolecule
  
  • makes up structure of living organism
  • other important macromolecules that make up structure include, proteins, lipids, carbohydrates

Question 25

2.1.3 d) i)

Describe the structure of DNA?

Answer 25

• DNA is a polymer
• One DNA molecule has two polynucleotide strands
  
  • run in opposite directions (antiparallel)
• DNA = long
  
  • therefore can carry lots of coded information
• hydrogen bonds formed between complementary base pairs
  
  • purine always bonds with pyrimidine
    
    • forming equal length ladder like rungs
    • twisted (coiled) into a double helix structure, for molecules stability and integrity of the coded information within the double helix is protected

Question 26

2.1.3 d) i)

What does antiparallel mean?

Answer 26

• DNA - two polynucleotide strands are antiparallel
• arranged so that they run in opposite directions
  
  • opposite directions - refers to the direction that the third and fifth carbon of the pentose sugar are facing

Question 27

2.1.3 d) i)

When was the DNA structure determined?

Answer 27

• 1953
• by Watson and Crick

Question 28

2.1.3 d) i)

If a double strand of DNA has 14% Guanine, what percentage of the other nucleotides does the double strand contain?

Answer 28

• 14% Cytosine
• 100 - 2(14)
• 100 - 28 = 72
• 72/2 = 36
• 36% Thymine
• 36% Adenine
  
  • Because of complementary base pairing, DNA always has equal amounts of adenine and thymine, as well as equal amounts of guanine and cytosine
  • this was known before Watson and Crick determined the structure of DNA

Question 29

2.1.3 e)

What were the three theories in the 1950s of how DNA was a self-replicating molecule?

Answer 29

• conservative replication
  
  • the original molecule acts as a template and a new molecule is made
• dispersive replication
  
  • the orginal molecule breaks up into nucleotides, each one joins to a complementary nucleotide, and the base pairs join up again
• semi-conservative replication
  
  • the new molecule consists of one original strand and one newly formed strand

Question 30

2.1.3 e)

Why do living organisms need DNA replication to happen?

Answer 30

• DNA within a cell (genome) carries the coded instructions for an organism
• DNA replication happens for cell division
  
  • more cells need to be produced for growth and repair

Question 31

2.1.3 e)

When does DNA replication take place?

Answer 31

• DNA replication takes place during interphase before the cell divides
• (each chromosome makes a copy of itself)
  
  • first chromosomes are joined by centromere
  • two sister chromatids are formed
• DNA in mitochondria and chloroplasts also needs to be replicated before the cell divides

Question 32

2.1.3 e)

What is semi-conservative replication?

Answer 32

• Double helix unwinds
  
  • by gyrase enzyme
• Polynucleotide strands are unzipped, hydrogen bonds between the nucleotide bases are broken
  
  • catalysed by DNA helicase
  • results in two single strands of DNA with exposed nucleotide bases
• free nucleotides in the nucleoplasm in the nucleus are bonded to the exposed bases, by complementary base pairing (A and T), (C and G)
  
  • addition of new nucleotides is catalysed by the enzyme DNA polymerase, in the 5’ to 3’ direction, to the single strands of DNA
    
    • each unzipped DNA strand is used as a template
• leading strand