Nucleotides

Question 1

What are some of the roles of nucleotides?

Answer 1

• Structural components for DNA, RNA
• Energy (ie ATP, NADH etc)
• Synthesis and protection
  Centre point of metabolism (acetyl coA)
• Signal transduction (cAMP etc)

Question 2

What are the 3 main components of a nucleotide?

Answer 2

Nitrogenous base (purine or pyrimidine)
Pentose sugar (either ribose or deoxyribose)
Phosphate group

Question 3

What are purine and pyrimidine bases? Name some examples.

Answer 3

Purine bases have a 2 carbon-nitrogen ring structure (adenine & guanine)
Pyrimidine bases have a single carbon-nitrogen ring structure (cytosine, thymine, and uracil)

Question 4

What nucleotides are used to store and carry chemical energy in cells

Answer 4

ATP & ADP

Question 5

What is a phosphorylated nucleotide?

Answer 5

When one or more phosphate groups are added to a nucleotide (ie ATP & ADP)

Question 6

What kind of bond holds phosphate groups together?

Answer 6

Phosphoanhydride bonds

Question 7

What happens in glycolysis (substrate level phosphorylation)

Answer 7

Pyruvate is formed from glucose. First glucose is phosphorylated by adding to phosphate groups from 2 ATP molecules. This forms a molecule of hexose bisphosphate and 2 molecules of ADP. Hexose bisphosphate is the split into 2 triose phosphate molecules. Triose phosphate is the oxidised forming 2 molecules of pyruvate and 2 reduced NAD molecules.

Question 8

Where does glycolysis take place?

Answer 8

Cytoplasm of cells

Question 9

What happens in oxidative phosphorylation? And where does it happen?

Answer 9

Takes place in the mitochondria (inner mitochondrial membrane).
H+ atoms are released from reduced NAD and FAD as they are oxidised to produce NAD & FAD. H atoms then split into protons and electrons.
Electrons move along electron transport chain, losing energy. Energy is used by carriers to pump protons from mitochondrial matrix to intermembrane space. Forming an electrochemical gradient. Protons move down gradient back into matrix via ATP synthase. This movement drives synthesis of ATP from ADP & Pi.

Question 10

Adenine nucleotides are components of many ……….

Answer 10

Enzyme cofactors

Question 11

……. ATP molecules are made from each reduced NAD
…….ATP molecules are made from each reduced FAD

Answer 11

2.5 ATP molecules
1.5 ATP molecules
So, a cell can make 32 ATP molecules from 1 molecule of glucose in aerobic respiration.

Question 12

What happens in the link reaction?

Answer 12

Happens in the matrix of the mitochondria
Pyruvate is decarboxylated (C atom is removed and forms CO2) and NAD is reduced to NADH forming acetate. Acetate is then combined with coenzyme A to form Acetyl coenzyme A.

Question 13

What happens in the Krebs cycle?

Answer 13

Acetyl coenzyme combines with oxaloacetate to form citrate and CoA. Citrate is then converted into a 5-carbon compound, a molecule of CO2 and reduced NAD is also produced. 5-carbon compound is then converted back onto oxaloacetate. A molecule of CO2, a molecule of ATP, 2 molecules of reduced NAD and 2 molecules of reduced FAD are also produced.
Cycle happens twice for every glucose molecule.

Question 14

What is lactate fermentation?

Answer 14

Is a type of anaerobic respiration occurring in mammals and produces lactate. Glycolysis occurs first and then the pyruvate is converted into lactate (lactic acid) and a molecule of NAD is also produced.

Question 15

What is the difference between NADP+ (NADPH) and NAD+ (NADH)

Answer 15

the only difference is a phosphate on the hydroxyl group of the 2’C

Question 16

What are some of the roles of NADP+ (NADPH)

Answer 16

Reductive biosynthesis - synthesis of fatty acids and cholesterol.
Phagocytosis
Drug metabolism
Nitric oxide synthesis

Question 17

Cellular Respiration

Answer 17

The process in which cells consume O2 & produce CO2

Question 18

What are the 3 methods of producing Acetyl coenzyme A

Answer 18

1) Glucose converted to pyruvate in glycolysis
Remove a C (CO2)
2 C left converted to acetyl - CoA

2)Fatty acids are metabolised via B-oxidation
Removes 2 Cs at a time
2 C converted to acetyl-CoA

3)Removal of amino group
Ammonia converted to urea (in mammals)
Ammonia converted to uric acid (in birds and reptiles)
Remainder of amino acid is the carbon skeleton - many of which can be converted to acetyl - CoA

Question 19

cyclic AMP is a common …….. ………. produced in response to hormones & other chemical signals

Answer 19

Second messenger

Question 20

How is cAMP formed?

Answer 20

Formed from ATP in a reaction catalysed by adenylate cyclase (AC)