Chapter 5 - Nucleic acids and their functions

Question 1

What are the 3 components of a nucleotide?

Answer 1

A phosphate group.
A pentose sugar.
An organic (nitrogenous) base.

Question 2

What are the two groups of organic bases and what bases are in these groups?

Answer 2

Pyridamines - Uracil, Thymine and Cytosine.

Purines - Adenine and Guanine.

Question 3

What is the molecule that makes energy available when it is needed?

Answer 3

ATP - Adenosine Triphosphate.

Question 4

What is the structure of ATP?

Answer 4

It is a nucleotide so it contains the base Adenine, the sugar ribose and 3 phosphate groups.

Question 5

What is the ATP molecule hydrolysed into when energy is needed?

Answer 5

Adenosine Diphosphate and an inorganic phosphate ion.

Question 6

What is the addition of phosphate to ADP called?

Answer 6

Phosphorylation.

Question 7

What are the advantages to using ATP as an intermediate instead of glucose directly?

Answer 7

• ATP to ADP involves a single reaction that releases energy immediately.
• Only one enzyme is needed to release energy from ATP.
• ATP releases energy in small amounts, when and where it’s needed.
• It provides a common source of energy for many different chemical reactions.

Question 8

What processes does ATP provide energy for?

Answer 8

• Metabolic processes - to build large complex molecules.
• Active transport - Allow molecules to be moves against a concentration gradient.
• Movement - muscle contraction.
• Nerve transmission.
• Secretion - packaging and transport.

Question 9

What is the structure of DNA?

Answer 9

Two polynucleotide strands wound around each other in a double helix. Sugar-phosphate backbone running anti-parallel to each other.

Question 10

What are the 4 bases in DNA and which is complementary to which? What holds the bases together?

Answer 10

Adenine, Thymine, Guanine and Cytosine.
Adenine pairs with Thymine and Cytosine pairs with Guanine.
Hydrogen bonds hold them together C-G has 3 and A-T has 2.

Question 11

How is DNA suited to its functions?

Answer 11

• Very stable molecule and its information passes essentially unchanged between generations.
• Very large so carries a large amount of genetic information.
• Two strands are easily separated.
• The sugar-phosphate backbone protects the genetic information.

Question 12

What is the structure of RNA?

Answer 12

• A single stranded polynucleotide.
• Contains the pentose sugar ribose.
• Contains Cytosine, Adenine, Guanine but Uracil instead of Thymine.

Question 13

What are the 3 types of RNA involved in the process of protein synthesis?

Answer 13

Messenger RNA.
Ribosomal RNA.
Transfer RNA.

Question 14

Who proposed the molecular structure of DNA ?

Answer 14

Watson and Crick.

Question 15

What are the 2 main roles of DNA?

Answer 15

Replication and Protein synthesis.

Question 16

What were the 3 possibilities thought of for the replication of DNA?

Answer 16

Conservative replication.
Semi-conservative replication.
Dispersive replication.

Question 17

What is the Meselson-Stahl experiment?

Answer 17

• Culture E. Coli. in 15N until it was incorporated into their DNA.
• Then washed, and transferred into 14N and allowed to divide for one generation.
• This was then centrifuged and this had a mid point density which ruled out conservative replication.
• Allowed to divide once more and then centrifuged again, proved theory of Semi-conservative as it settled at mid point and high point in the tube.

Question 18

How many bases code for an amino acid?

Answer 18

3 (Triplet code).

Question 19

Why does the RNA need to be processed before it can be used to synthesised the polypeptide?

Answer 19

Because it contains sequences of bases that have to be removed (Introns).

Question 20

What is an exon?

Answer 20

Nucleotide sequence in DNA and pre-mRNA that remains present in the final mature mRNA , after introns have been removed.

Question 21

What is the process of protein synthesis?

Answer 21

• DNA.
• Transcription in the nucleus.
• mRNA.
• Translation at ribosomes.
• Polypeptide.

Question 22

What is the difference between Transcription and Translation?

Answer 22

Transcription - One strand of DNA acts as a template for the production of mRNA.
Translation - mRNA acts of a template to which tRNA molecules attach, and the amino acids they carry are linked to form a polypeptide.

Question 23

What are the 3 enzymes involved in ‘unzipping’ DNA?

Answer 23

• DNA helicase; breaks the hydrogen bonds between the bases.
• DNA Polymerase.
• DNA Ligase.

Question 24

What are the steps in Transcription?

Answer 24

• DNA helicase breaks the H bonds between bases.
• RNA Polymerase binds to the beginning of the template strand.
• Free nucleotides align opposite the template strand.
• RNA Polymerase moves along and forms bonds adding RNA nucleotides.
• Polymerase separates from the template strand when ‘Stop’ signal is reached.

Question 25

What are the steps in Translation?

Answer 25

• A ribosome attaches to a ‘Start’ codon.
• A tRNA with a complementary anticodon attaches to the ribosome.
• Another tRNA attaches to the other attachment site.
• The two amino acids are close enough for a ribosomal enzyme to catalyse the formation of a peptide bond between them.
• The 1st tRNA leaves the ribosome and the ribosome moves one codon along.
• The next tRNA binds until a ‘Stop’ codon is reached.