Carbohydrate Metabolism (Lec 3)

Question 1

Carbohydrate Nomenclature

Answer 1

Number of carbon atoms in the carbohydrate + -ose
–	Three carbons 	= triose
–	Four carbon 		= tetrose
–	Five carbon 		= pentose
–	Six carbon 		= hexose

Question 2

Carbohydrate Formula

Answer 2

Cn(H2O)n

Question 3

Glycosidic Bond

Answer 3

The bond that joins 2 sugar molecules together

Question 4

Disaccharides

Answer 4

2 sugar molecules joined via glycosidic bonding

Question 5

Polysaccharides

Answer 5

Natural carbohydrates usually found as polymers
– Homopolysaccharides (one monomer unit)
– Heteropolysaccharides (multiple monomer units)
– Linear (one type of glycosidic bond)
– Branched (multiple types of glycosidic bonds)

Question 6

Glycogen

Answer 6

A branched homopolysaccharide of glucose. Glucose monomers form (α1 → 4) linked chains. There are branch points with (α1 → 6) linkers every 8–12 residues.

Question 7

Laws of Thermodynamics

Answer 7

1. Living organisms cannot create energy from nothing
2. Living organisms cannot destroy energy into nothing
3. Living organisms may transform energy from one form to another

Question 8

Free Energy (Equilibrium Constant)

Answer 8

K'eq  = Equilibrium constant 
ΔG'˚=  Gibbs free energy

• When K’eq is at >1, ΔG’˚ is negative and reaction proceeds forwards
• When K’eq is at 1, ΔG’˚ is neutral and reaction is at equilibrium
• When K’eq is at <1, ΔG’˚ is positive and reaction proceeds backwards

Question 9

Key Energy Carriers in the Cell

Answer 9

ATP, NADH, NADPH, FADH2

Question 10

Glycolysis: Preparatory Phase

Answer 10

Energy Investment Phase:

• Costs 2ATP
• Hexokinase, Phosphofructokinase

Question 11

Glycolysis: Pay-Off Phase

Answer 11

Energy Generation Phase:

• Produces 4ATP (2 per pyruvate)
• Pyruvate Kinase

Question 12

Fates of Pyruvate

Answer 12

Aerobic: Acetyl-CoA (Citric Acid Cycle)
Aaerobic: Ethanol (fermentation in yeast), Lactate (exercise, contracting muscles)

Question 13

Glycolysis vs. Gluconeogenesis

Answer 13

Opposing pathways that are both thermodynamically favourable. Glycolysis occurs mainly in the muscle and brain, Gluconeogenesis mainly in the liver

Question 14

Gluconeogenesis (GNG)

Answer 14

2 Pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ + 4 H2O

–> Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+

Question 15

Gluconeogenesis: Enzymes

Answer 15

1. Pyruvate Carobxylase
2. Phosphoenol-pyruvate (PEP) Carboxykinase
3. Frustose 1,6 biphosphatase
4. Glucose 6 phosphatase

Question 16

Pentose Phosphate Pathway

Answer 16

Main products: NADPH (electron donor) and Ribose 5-phosphate (biosynthetic precursor of nucleotides)

Question 17

Factors that Determine Enzyme Activity

Answer 17

1. Extracellular signals
2. Transcription of specific gene(s)
3. mRNA degredation
4. mRNA translation on ribosome
5. Protein degredation
6. Enzyme sequestered in subcellular organelle
7. Enzyme binds substrate
8. Enzyme binds ligand (allosteric effector)
9. Enzyme undergoes phosphorylation/dephosphorylation
10. Enzyme combines with regulatory protein