A1CC1 Chapter 5 - Nucleic Acids and Their Functions

Question 1

What are the monomers of nucleic acids?

Answer 1

Nucleotides

Question 2

State the three components of nucleotides.

Answer 2

Pentose Sugar
Organic Base
Phosphate Group

Question 3

How does the structure of a nucleotide look?

Answer 3

Phosphate group – 5 Carbon Sugar – Nitrogenous Base

Question 4

What are the two types of organic base?

Answer 4

Purine and Pyramidine

Question 5

What is a purine?

Answer 5

• A class of organic structures
• Has a double ring structure
• Includes Adenine and Guanine

Question 6

What is a pyramidine?

Answer 6

• A class of organic bases
• Single ring structure
• Includes Thymine, Cytosine and Uracil

Question 7

Describe the sturcture of a DNA nucleotide.

Answer 7

• Deoxyribose sugar
• Organic Base (A,T,C,G)
• Phosphate Group

Question 8

Describe the structure of an RNA nucleotide.

Answer 8

• Ribose sugar
• Organic base (A,T,C,G)
• Phosphate Group

Question 9

Describe the structure of an ATP nucleotide.

Answer 9

• Ribose sugar
• Adenine
• Three phosphate groups

Question 10

What is an endergonic reaction?

Answer 10

A non-spontaneous reaction that requires an input of energy, Eg: ATP formation.

Question 11

What is an exergonic reaction?

Answer 11

A spontaneous reaction that overall releases energy, eg: ATP Hydrolysis

Question 12

Describe the role of ATP.

Answer 12

The universal energy currency. Hydrolysed to release energy.

ATP + Water <–> ADP + Pi + Energy

Question 13

What is complementary base pairing?

Answer 13

Describes how hydrogen bonds form between complimentary purine and pyramidine bases.
Two bonds between A and T (or U)
Three bonds between C and G

Question 14

Describe the structure of DNA. (4)

Answer 14

1. Double stranded polymer of nucleotides twisted to form a double helix.
2. Nucleotides joined together by phosphodiester bonds
3. Hydrogen bonds form between complementary base pairs, A and T, C and G.
4. Antiparallel Strands

Question 15

Why are the strands of a DNA double helix described as ‘antiparallel’?

Answer 15

The complimentary strands run parallel but in opposite directions. 5’ to 3’ and 3’ to 5’.

Question 16

Describe the structure of RNA. (3)

Answer 16

1. Single stranded polymer of nucleotides
2. Nucleotides joined together by phosphodiester bonds
3. Hydrogen bonds form between complementary base pairs, A and U, C and G.

Question 17

Compare and contrast DNA and RNA.

Answer 17

DNA vs RNA:
1. Double Stranded vs Single Stranded
2. Long Chain of Nucleotides vs Shorter chain of nucleotides
3. Contains deoxyribose sugar vs Contains ribose sugar
4. Contains bases A,T,C and G vs Contains bases A,U,C, and G
5. Storage of genetic information vs Role in protein synthesis
6. Phosphodiester bonds join nucleotides vs Phosphodiester bonds join nucleotides.

Question 18

Name the three types of RNA found in cells.

Answer 18

1. tRNA = Transfer RNA
2. mRNA = Messenger RNA
3. rRNA = Ribosomal RNA

Question 19

What is the function of tRNA?

Answer 19

It carries specific amino acids to the ribosomes.

Question 20

Describe the structure of tRNA. (4)

Answer 20

80 nucleotides
Single helix
Clover leaf shape
Anticodon on one end, amino acid binding site on the other

Question 21

What is the function of mRNA?

Answer 21

Carries genetic information from the nucleus to the ribosomes for protein synthesis.

Question 22

Describe the structure of mRNA.

Answer 22

2000 nucleotides
Single helix
Unstable

Question 23

What is the function of rRNA?

Answer 23

Associates with proteins in the cytoplasm to form ribosomes.

Question 24

Describe the structure of rRNA.

Answer 24

1800 - 5000 nucleotides
Two subunits: One large, One small

Question 25

What is semiconservative replication?

Answer 25

The replication of DNA to produce two new DNA molecules which both contain one new strand and one old strand from the original DNA molecule.

Question 26

What is the role of DNA Helicase in semiconservative replication?

Answer 26

Catalyses the unzipping of double-stranded DNA into two single strands, each of which acts as a template.

Question 27

What is the role of DNA Polymerase in semiconservative replication?

Answer 27

It catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand.

Question 28

What is the genetic code? (collection of exons)

Answer 28

The rules where triplets in a DNA base sequence code for the sequence of amino acids in a polypeptide chain. The genetic code is known as degenerate, universal and non-overlapping.

Question 29

Why is the genetic code described as degenerate?

Answer 29

More than one triplet can code for a particular amino acid.

Question 30

Why is the genetic code described as universal?

Answer 30

The same codons code for the same amino acids in almost all organisms.

Question 31

What is meant by 'non-overlapping'?

Answer 31

Each base in a sequence is read once and is only part of one triplet.

Question 32

Describe the 'triplet code' for amino acids.

Answer 32

A specific sequence of three nucleotides (known as codon) on a molecule of DNA or RNA coding for a particular amino acid in protein synthesis.

Question 33

What is an exon?

Answer 33

A region of DNA that CODES for an amino acid sequence.

Question 34

What is an intron?

Answer 34

A non-coding sequence of DNA that is found between exons.

Question 35

Compare eukaryotic and prokaryotic genes.

Answer 35

Eukaryotic genes are discontinuous with non-coding introns and coding exons. Prokaryotic genes are continuous with coding sequences only.

Question 36

What is protein synthesis?

Answer 36

The formation of protein from amino acids. There are two stages, transcription and translation.

Question 37

Define transcription.

Answer 37

- The first stage of protein synthesis - The formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA.

Question 38

Outline the process of transcription.

Answer 38

1. DNA helicase unwinds section of DNA, breaking hydrogen bonds between DNA strands. Antisense strand acts as a template. 2. RNA Polymerase binds to the promoter region of a gene 3. Free RNA Nucleotides align next to their complimentary bases. 4. RNA Polymerase joins adjacent RNA nucleotides, forming phosphodiester bonds. 5. RNA Polymerase reaches stop codon and detaches. mRNA is complete.

Question 39

Describe post-transcriptional modification.

Answer 39

Splicing removes introns from pre-mRNA in eukaryotic cells.

Question 40

Define translation.

Answer 40

- The second stage of protein synthesis - Takes place in ribosomes - mRNA used as a template for attachment of rRNA molcuiles with complementary anticodons. Amino acids carried on the adjacent tRNA molecules are joined to form a polypeptide chain.

Question 41

Outline the process of translation.

Answer 41

1. mRNA attaches to groove between subunits of ribosome. 2. Ribosome moves along mRNA until 'start codon' reached. 3. Amino acid-tRNA complex anticodon attaches to the complementary mRNA codon via hydrogen bonding. Another complex binds. 4. Peptide bond forms between adjacent amino acids in the complex. 5. Ribosome moves along one codon and releases the empty tRNA. Process continues to form polypeptide chain until 'stop' codon is reached.

Question 42

What is the 'one gene - one polypeptide' hypothesis?

Answer 42

The theory that each gene encodes a single protein.

Question 43

What happens to the polypeptide after translation?

Answer 43

It is further modified by adding carbohydrates, lipids or phosphates. Different polypeptides may be combined.

Question 44

Describe how DNA can be purified by precipitation.

Answer 44

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