1.5 Nucleic Acids

Question 1

What is a gene?

Answer 1

Sequence if DNA bases that codes for a specific polypeptide chain. Found on chromosomes in the DNA

Question 2

What are the two types of nucleic acids?

Answer 2

1. DNA (deoxyribonucleic acid)
2. RNA (ribonucleic acid)

Question 3

What do the sequence of bases in DNA code for?

Answer 3

Codes for the sequence of amino acids in a protein

Question 4

What does protein do in DNA?

Answer 4

Determines all the characteristics of an organism

Question 5

What are RNA molecules used in?

Answer 5

Used in protein synthesis

Question 6

What are the monomers that make up nucleic acids? What are they made up of?

Answer 6

Nucleotides
Made up of:
1. Phosphate group - found in DNA AND RNA
2. Pentose (5C) carbon sugar
• DNA contains deoxyribose
• RNA contains ribose
3. Nitrogenous base
• DNA contains A,T,C,G
• RNA contains A,U,C,G

Question 7

What is the complementary base pair rule?

Answer 7

Adenine is able to base pair through hydrogen bonds with Thymine (Uracil in RNA)

Guanine is able to base pair through hydrogen bonds with Cytosine

Question 8

How do nucleic acids form?

Answer 8

• Nucleotides link together to form polynucleotides, through condensation reactions.
• a phosphodiester covalent bond is formed between carbon 3 of one nucleotide and the phosphate of the adjacent nucleotide
• this bonding forms a sugar phosphate backbone

Question 9

What is difference deoxyribose and ribose?

Answer 9

Question 10

What is the structure and function of DNA?

Answer 10

1. Two anti-parallel polynucleotide chains joined together through hydrogen bonds between complementary base pairs (chains twist around each other to form a double helix)
2. Stable molecule - allows genetic information to Beto be passed from generation to generation without change unless through mutation
3. DNA is a large molecule which allows it to carry a large quantity of genetic information
4. quantities of A=T and quantities of C=G as they pair together
5. Weak hydrogen bonds join the two strands - allows easy separation during DNA replication and protein synthesis
6. There are 2 hydrogen bonds between A&T and 3 hydrogen bonds between C&G
7. Strong phosphodiester bonds - protect the nitrogenous bases which form the code in the centre of the molecule

Question 11

What is the structure of RNA?

Answer 11

1. Short, single polynucleotide chain
2. Pentose sugar is a ribose
3. Contains adenine, uracil, guanine and cytosine

Question 12

What are the 3 types of RNA and what is there function?

Answer 12

• mRNA - messenger RNA - transfers the genetic information from DNA to the ribosome
• rRNA - ribosomal DNA - together with proteins makes up the ribosome
• tRNA - transfer RNA - transfers specific amino acids to the ribosome for protein synthesis

Question 13

Explain the process of semi conservative DNA replication

Answer 13

1. Double helix is untwisted
2. Enzyme DNA helicase breaks the hydrogen bonds between the complementary nitrogenous bases allowing the two strands to separate and expose the unpaired nucleotide bases
3. Both strands act as a template
4. Free complementary nucleotide bases hydrogen bind to the exposed bases according to the complementary base pairing rule
5. Phosphodiester covalent bonds are formed by a condemnation reaction between the nucleotides (NOT BASES)
6. The enzyme DNA polymerase joins the sugar phosphate backbone
7. Each DNA molecule consists of one ‘old’ strand and one newly built strand

Question 14

Why is it called semi- conservative replication?

Answer 14

Each DNA molecule consists of one conserved ‘old’ strand and one newly built strand

Question 15

Why can DNA polymerase only add new nucleotides to the new strand at the 3’ end of the deoxyribose?

Answer 15

The active site of DNA polymerase is only complementary to the 3’ end of the deoxyribose
The strands in the double helix are anti parallel, because DNA polymerase working on one of the template strands works in the opposite direction to the DNA polymerase working on the other template strand

Question 16

Who carried out the semi-conservative replication experiment?

Answer 16

Meselson and Stahl

Question 17

What did meselson and stahl do in there experiment?

Answer 17

• grew Escherichia coli bacteria for many generations in a medium in which the only source of nitrogen was the heavy isotope 15^N - heavy nitrogen
• the DNA in the offspring of these bacteria was denser than usual because the bases contained heavy nitrogen
• the bacteria containing heavy nitrogen were transferred to a medium containing only 14^N (light nitrogen) and allowed to replicate for several generations.
• samples of bacteria were taken after each generation, their DNA extracted and centrifuged. The DNA formed visible bands in the tube
• centrifugation separates the DNA on the basis of mass - the DNA with the heaviest mass will be the lowest down the tube

Question 18

What were the other models of DNA replication disproved by the Meselson-Stahl experiment?

Answer 18

Conservative and dispersive

Question 19

What was the conservative model?

Answer 19

Each replication results in one DNA molecule that consists of both original strands of DNA, and one DNA molecule that consists of two completely new strands of DNA

Question 20

What is the dispersive model?

Answer 20

Each replication results in two DNA molecules that are combinations of original and new DNA