Nucleotides And Nucleic Acids

Question 1

Draw the structure of a nucleotide

Answer 1

Phosphate group to 5 carbon sugar (pentose) to a nitrogenous base

Question 2

Name the pentose sugars in DNA and RNA.

Answer 2

DNA: deoxyribose
RNA: ribose

Question 3

Describe how polynucleotide strands are formed and broken down.

Answer 3

Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone). Hydrolysis reactions use a molecule of water to break these bonds.
Enzymes catalyse these reactions.

Question 4

Describe the structure of DNA.

Answer 4

Molecule twists to form double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate backbones).
H-bonds form between complementary base pairs (AT & GC) on strands that run antiparallel.

Question 5

Name the purine bases and describe their structure.

Answer 5

adenine C5H5N5

guanine C5H5N5O

Question 6

Name the pyrimidine bases and describe their structure.

Answer 6

thymine C5H6N2O2
cytosine C4H5N3O
uracil C4H4N2O2

Question 7

Name the complementary base pairs in DNA and RNA.

Answer 7

DNA: 2 H-bonds between adenine (A) + thymine (T)

RNA: 2 H-bonds between adenine (A) + uracil (U)

Both have 3 H-bonds between guanine (G) + cytosine (C)

Question 8

Why is DNA replication described as semiconservative?

Answer 8

Semi conservative replication is the method in which DNA replicates, creating two molecules of DNA that consist of one original DNA strand and one newly synthesised DNA strand.

Question 9

Explain the role of DNA helicase in semiconservative replication.

Answer 9

Breaks H-bonds between base pairs to form 2 single strands, each of which can act as a template.

Question 10

How is a new strand formed during semiconservative replication?

Answer 10

1. Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing.
2. DNA polymerase catalyses condensation reactions to join adjacent nucleotides form phosphodiester bonds.
3. H-bonds reform.

Question 11

Identify features of the genetic code.

Answer 11

● Non-overlapping: each triplet is only read once.
● Degenerate: more than one triplet codes for the
same amino acid (64 possible triplets for 20
amino acids).
● Universal: same bases and sequences used by
all species.

Question 12

How does a gene determine the sequence of amino acids in a protein?

Answer 12

Consists of base triplets that code for a specific amino acids.

Question 13

Describe how DNA can be purified by precipitation.

Answer 13

Add ethanol & a salt to aqueous solution. Nucleic acids precipitate out of solution.
Centrifuge to obtain pellet of nucleic acid. Wash pellet with ethanol & centrifuge again.

Question 14

What does transcription produce and where does it occur?

Answer 14

produces mRNA occurs in nucleus

Question 15

Outline the process of transcription.

Answer 15

1. RNA polymerase binds to promoter region on a gene.
2. Section of DNA uncoils into 2 strands with exposed
   bases. Antisense strand acts as template.
3. Free nucleotides are attracted to their complementary
   bases.
4. RNA polymerase joins adjacent nucleotides to form
   phosphodiester bonds.

Question 16

What happens after a strand of mRNA is transcribed?

Answer 16

● RNA polymerase detaches at terminator region.
● H-bonds reform & DNA rewinds.
● splicing removes introns from pre-mRNA in
eukaryotic cells.
● mRNA moves out of nucleus via nuclear pore &
attaches to ribosome.

Question 17

What does translation produce and where does it occur?

Answer 17

Produces proteins
Occurs in cytoplasm on ribosomes
(which are made of protein + rRNA)

Question 18

Outline the process of translation.

Answer 18

1. Ribosome moves along mRNA until ‘start’ codon.
2. tRNA anticodon attaches to complementary bases on mRNA.
3. Condensation reactions between amino acids on tRNA
   form peptide bonds. Requires energy from ATP
   hydrolysis.
4. Process continues to form polypeptide chain until ‘stop’
   codon is reached.

Question 19

Describe the structure of adenosine triphosphate (ATP) and adenosine diphosphate (ADP).

Answer 19

nucleotide derivative of adenine
ATP has 3 inorganic phosphate groups
ADP has 2

Question 20

What is a mutation?

Answer 20

An alteration to the DNA base sequence. Mutations often arise spontaneously during DNA replication.

Question 21

Structure of RNA

Answer 21

• single strand
• relatively short
• ribose is its pentose sugar

Question 22

function of RNA

Answer 22

transfers genetic information and forms ribosomes with proteins

Question 23

structure of ATP

Answer 23

• 3 phosphate groups
• adenine
• ribose

Question 24

what is the reaction that happens from ATP -> ADP

Answer 24

hydrolysis reaction

Question 25

what is the reaction that happens from ADP -> ATP

Answer 25

condensation reaction

Question 26

enzymes involved in hydrolysis of ATP

Answer 26

ATP hydrolase

Question 27

enzymes involved in condensation of ADP

Answer 27

ATP synthase

Question 28

what is the energy profile for hydrolysis

Answer 28

releases energy

Question 29

what is the energy profile for condensation

Answer 29

requires energy

Question 30

what is transcription

Answer 30

Transcription is the process of making messenger RNA

from a DNA template

Question 31

what is translation

Answer 31

Translation is the process of making proteins by forming a specific sequence of amino acids based on coded instructions in mRNA.