Topic 7 - Nucleic Acids

Question 1

List the functions of a nucleotide

Answer 1

Energy for metabolism (ATP) Enzyme cofactors (NAD+) Signal Transduction (cAMP)

Question 2

List the functions of nucleic acid

Answer 2

Storage of genetic info (DNA) Transmission of genetic info (mRNA) Processing genetic info (ribozymes) Protein synthesis (tRNA & rRNA)

Question 3

What is a gene?

Answer 3

segment of DNA that encodes a protein

Question 4

Name the two types of nucleic acid

Answer 4

DNA (deoxyribonucleic acid) RNA (ribonucleic acid)

Question 5

What is the function of DNA?

Answer 5

Storage and transmission of biological info

Question 6

What is the function of mRNA?

Answer 6

Messenger RNA: intermediates, carry genetic info from genes to ribosomes

Question 7

What is the function of tRNA?

Answer 7

Transfer RNA: adapter molecules, transfer specific aa’s to proteins at ribosomes

Question 8

What is the function of rRNA?

Answer 8

Ribosomal RNA: protein synthesis

Question 9

Name the 3 components of a nucleotide, and where some of these are attached

Answer 9

Nitrogenous base (N containing) attached at 1’

Pentose (5-membered sugar)

Phosphate attached at 5’

Question 10

Describe the structural difference b/w DNA & RNA

Answer 10

If only H attached would be deoxyribose

If OH attached is ribose

Picture below shows a ribose

Question 11

Phosphate group is negatively charged at a neutral pH, and are attached to the 5’ position.

T or F?

Answer 11

True

Question 12

Name the nucleotides that make up DNA & RNA

Answer 12

Adenine triphosphate (ATP)

Guanine triphosphate (GTP)

**Thymine triphosphate (TTP)

Cytosine triphosphate (CTP)

**Uracil triphosphate (UTP)

**RNA does not have TTP. Has UTP instead, which binds w/ ATP.

Question 13

Name the two types of pentose (5-membered sugar)

Answer 13

ribose (OH) group

deoxyribose (H) group

Question 14

Name the two types of nitrogenous bases, what type of structure they are and their components

Answer 14

Purines (adenine & guanine) => lrg, bicyclic

Pyrimidines (cytosine, thymine & uracil) =>sml, monocyclic

Question 15

Draw the basic structure of a purine

Answer 15

Question 16

Draw the basic structure of a pyrimidine and give some info

Answer 16

All NH groups are attached to sugar

Amino group (HN) wants to give up its H

Carbonyl group (C=O) wants to H bond

Question 17

Just some general info to read on structure!

Answer 17

• 5’-phosphate of one nucleotide is linked w/ 3’-hydroxyl group of next nucleotide
• Back bone of nucleic acids consist of alternating phosphate & sugar
• Bases are regarded as side groups, hydrophobic
• Ribo-phosphate backbone is hydrophilic and -ve charged

Question 18

What direction are gene sequences written in?

Answer 18

5’ to 3’ direction

Question 19

If purine on one strand, other strand must have a pyrimidine & vice versa.

(view pic in answer)

Answer 19

broken line indicates H bonding

Question 20

Properties of nucleotide bases affect nucleic acid structure.
T or F?

Answer 20

True

Question 21

Describe Chargaff’s rule

Answer 21

ratio of pyrimidine to purine is 1:1

i.e. amount of guanine is equal to cytosine

amount of adenine is equal to thymine

Question 22

What is it about nitrogenous bases that allows them to absorb UV light?

Answer 22

aromatic nature (cyclic structure)

Question 23

Describe the structure of the double helix

Answer 23

• two antiparallel complementary helical chains
• hydrophilic backbone (sugar & phosphate) are on outside
• purine and pyrimidine bases are stacked inside helix
• Major & minor groove
• Main forces that stabilise helix are: H bonding & base stacking

Question 24

DNA replication is semiconservative. Why?

Answer 24

Each DNA strand acts as a template for synthesis of a new strand

-progeny DNA consists of one parent and one newly synthesised strand

Question 25

Describe the basis of DNA replication

Answer 25

Always occurs in the 5'-3' direction - one strand is complement of the other - separate two strands - synthesise completely new strand using existing strand as template - occurs are replication fork - leading and lagging strand

Question 26

Name the enzymes & their functions involved in DNA replication in *E.Coli*

Answer 26

**DNA polymerase III** =\> catalyses reaction, proof reading **DNA helicase** =\> unwinds double stranded DNA to allow access by polymerase **Topisomerases **=\> relieve topological 'super coal' stress as helix is unwound **Primase **=\> synthesis short pieces of RNA to allow DNA Pol. to initiate replication **single stranded binding proteins** (not enzymatic)

Question 27

Describe the central dogma of flow of info from DNA to translation

Answer 27

**DNA**=\>(transcription)=\>**RNA**=\>(translation)=\>**PROTEIN**

Question 28

describe process of DNA transcription and what it requires

Answer 28

very selective RNA is synthesised by RNA polymerases, which require: * DNA template, * all 4 ribonucleotides (A,G,C,U) * Mg2+ * Zn2+ Enzyme elongates RNA by adding ribonuc. to 3' end Each nucleotide inserted is selected by base pairing - Does not require a primer for initiation; init. occurs when RNA polymerase binds promotor region - DNA unwound to form bubble; involves only limited segments of DNA - RNA polymerase lacks proof reading ability

Question 29

3 nucleotides encode each aa. What are these 3 nucleotides called?

Answer 29

Codons

Question 30

Reading frames & genetic code -see pic in answer

Answer 30

Question 31

Genetic code & degeneracy -see pic in answer

Answer 31

Question 32

Genetic code and codon function -see pic in answer

Answer 32