Nucleic Acids & DNA replication🧬

Question 1

What is the structure of a nucleotide?

Answer 1

• Pentose sugar
• Nitrogenous base
• Phosphate group

Question 2

Structure of DNA

Answer 2

•Deoxyribose sugar
•Phosphates bonded to pentoses by covalent bonds (condensation)
•Nitrogenous base 
•Double stranded
•Sugar phosphate backbones are anti-parallel 
-form a double helix
•Contains pyrimidines: C and T
•Contains purines: A and G

Question 3

Structure of RNA

Answer 3

• Ribose sugar
• Phosphates groups
• Single stranded
• Contains pyrimidines: C and U
• Contains purines: A and G
• Tend to be short lived

Question 4

What is a pyrimidine?

Answer 4

• A base with a single ring structure
• Cytosine
• Thymine
• Uracil

Question 5

What is a purine?

Answer 5

• A base with a double ring structure
• Adenine
• Guanine

Question 6

How are polynucleotides formed?

Answer 6

• One nucleotide can join to another by a condensation reaction
• Takes place between the sugar and phosphate groups
• Many nucleotides joining up this way form a polynucleotide chain

Question 7

What is a nucleoside?

Answer 7

• Organic base + pentose sugar but no phosphate
• Nucleoside monophosphate (1p)
• Nucleoside diphosphate (2p)
• Nucleoside triphosphate (3p)
• Phosphorylated nucleoside (2/3p)

Question 8

What is the structure of ATP?

Answer 8

• Adenine nitrogenous base
• Ribose
• 3 phosphate groups
• Forms a phosphorylated nucleotide

Question 9

What are the similarities and differences between ATP, RNA & DNA?

Answer 9

•All made of a pentose sugar
-containing a phosphate group
•Made of different pentose sugars
•Contain different number of phosphate groups

Question 10

Hydrolysis of ATP

Answer 10

ATP + water
(Hydrolysis)—>
(Condensation)

Question 11

What is an exergonic reaction?

Answer 11

A reaction that releases energy

E.g. ATP hydrolysis

Question 12

What are the advantages of ATP as a supplier of energy?

Answer 12

•Hydrolysis involves a single reaction that releases energy immediately - glucose takes longer
•Only one enzyme is needed to release energy from ATP compared to many in glucose
•ATP releases energy in small amounts, when & where it is needed, so no energy is wasted
-glucose releases large amounts of energy all at once
•ATP is a universal source of energy
•Readily available as the phosphate group is transferred on demand

Question 13

What is ATP synthase?

Answer 13

• Catalyses condensation reaction to produce ATP

* During respiration or photosynthesis

Question 14

What are the roles of ATP?

Answer 14

•Metabolic processes
-building large, complex molecules 
•Active transport
-change shape of carrier proteins and allow molecules/ions to move against a conc gradient
•Movement 
-for muscle contraction
•Nerve transmissions
-sodium-potassium pumps
•Secretions
-packaging into vesicles
•Homeostasis
-energy lost as heat from ATP hydrolysis 
•Adding phosphate groups to proteins

Question 15

What is the complimentary base pairing rule?

Answer 15

• Adenine must always pair with Thymine (or Uracil in RNA)

* Cytosine must always pair with Guanine

Question 16

What are the two main functions of DNA?

Answer 16

• DNA replication

* Protein synthesis

Question 17

What is the process of DNA replication?

Answer 17

• Helicase enzyme breaks hydrogen bonds between complementary strands
• Both strands are used as templates
• Free nucleotides pair with complementary bases now exposed
• Hydrogen bonds form between the bases
• DNA polymerase joins adjacent nucleotides by condensation reactions, forming phosphodiester bonds
• 2 identical DNA molecules are produced

Question 18

What is the semi-conservative idea?

Answer 18

Each new DNA molecule contains one original strand and one newly formed strand

Question 19

Describe Meselson and Stahl’s experiment

Answer 19

• Grew E.coli in a medium containing amino acids with the isotope 15N (heavy nitrogen)
• Bacterium’s DNA contains 15N
• Centrifuged DNA in caesium chloride solution
• DNA settles depending on mass
• 15N bacteria transferred to a growth medium containing 14N (light)
• Bactria divided
• 1st gen 50% 15N (og), 50% 14N (new)
• 2nd gen 25% 15N, 75% 14N

Question 20

Explain Meselson and Stahl’s experiment

Answer 20

• At succeeding generation times, the DNA extracts were found to have a lower proportion of 15N
• More 14N was incorporated into the bacterial DNA
• Due to semi-conservative theory

Question 21

What is a nucleic acid?

Answer 21

A polymer of nucleotides

Question 22

What is a sugar-phosphate backbone?

Answer 22

The deoxyribose of one nucleotide forms a bond with the phosphate of another nucleotide to form a sugar-phosphate backbone

Question 23

What bonds hold the two strands of double helix together?

Answer 23

Hydrogen bonds between a pair of nitrogenous bases

Question 24

What does the complementary base pairing rule ensure?

Answer 24

• DNA replicates correctly

* Same proportion of A/T and C/G

Question 25

What does anti parallel mean?

Answer 25

* 5’ end to 3’ end | * 3’ end to 5’ end

Question 26

What is genetic code?

Answer 26

The way in which information about the sequence of amino acids in a protein is coded by the bases on a molecule of DNA

Question 27

What does genetic stability rely on?

Answer 27

The genetic code being passed on to daughter cells without changes or errors

Question 28

What is conservative replication?

Answer 28

* Original double stranded DNA molecule remained | * Totally new double stranded molecule was produced

Question 29

What is dispersive replication?

Answer 29

Both strands consist of sections of new and old DNA

Question 30

Why might testing a DNA enzyme on synthetic DNA not provide a valid conclusion in using it for humans? OWTTE (could be on exam)

Answer 30

* Enzyme may be less effective against human DNA * The synthetic DNA may be single stranded whereas human is double * May not have been tested on a live sample * Could damage healthy cells * Could have side effects

Question 31

What is the function of DNA helicase?

Answer 31

Unwinds and unzips DNA molecule for replication

Question 32

What is the function of DNA polymerase?

Answer 32

Forms phosphodiester bonds between adjacent nucleotides during replication