Energy: Carbohydrate 1

Question 1

Polymers

Answer 1

Disaccharides (2 units) 
- maltose (glucose & glucose) 
- lactose (galactose & glucose) 
- sucrose (fructose & glucose) 
Oliosaccharides (3-12 units) 
- dextrins 
Polysaccharide (10-1000 units) 
- glycogen, starch, cellulose 
- all polymers of glucose

Question 2

Disaccharides

Answer 2

Condensation of 2 monosaccharides
H20 eliminated
O-glycosidic bonds

Question 3

Glycogen

Answer 3

• main storage polysaccharide in mammals (liver and skeletal muscle)
• alpha 1-4 and 1-6 linked (branched)
• polymer of glucose

Question 4

Starch

Answer 4

• polymer of glucose in plants
• mixture of amylose (alpha 1-4) and amylopectin (alpha 1,4 and alpha 1,6)
• enzymes release glucose and maltose

Question 5

Cellulose

Answer 5

• structural polymer of glucose in plants
• beta 1-4 linkages
• no human enzymes to digest beta 1-4 linkages
• an important for GI function

Question 6

Enzymes to digest carbohydrates

Answer 6

Saliva 
- amylase STARCH AND GLYCOGEN TO DEXTRINS
Pancreas 
- amylase DEXTRINS TO MONOSACCHARIDES
Small intestine 
- disaccharides attached to brush boarder membrane of epithelial cells on the lumen
- lactase
- sucrase 
- pancreatic amylase 
- isomaltase

Question 7

Absorption of monosaccharides

Answer 7

• actively transported into intestinal epithelial cells to blood supply to target tissues (glucose level in cells higher than that in lumen)
• uptake into cells via facilitated diffusing using transport proteins (GLUT1-GLUT5)
  GLUTs have different tissue distributions and affinities, can be hormonally controlled

Question 8

Tissue requirement of glucose

Answer 8

• major sugar in blood
• all tissues can metabolise glucose
• blood glucose regulated ~5mM
• RBC, WBC, kidney medulla, lens of eye) have an absolute requirement and uptake by these tissues
• CNS (brain) prefers glucose
• some tissues need it for specialised functions (liver, adipose)

Question 9

Glycolysis

can be controlled - unidirectional

Answer 9

Cytosolic 
- oxidise glucose/NADH production 
- synthesis of ATP from ADP 
- produces C6 and C3 intermediates 
Exergonic, oxidative 
No loss of CO2 
can operate anaerobically with the addition of one enzyme

Question 10

Phase 1 of Glycolysis

reactions 1-3

Answer 10

• phosphorylation of glucose to glycose-6-phosphate (G6P)
• glucose negatively charged (anionic)
• prevents passage back across the plasma membrane
  increases the reactivity of glucose to permit subsequent steps after the initial investment of energy
• reaction 1 and 3 have large negative delta G values - so are irreversible
  Step three is the committing step - first step that commits glucose to metabolism via glycolysis

Question 11

Carbohydrates

CHO

Answer 11

General formula: (CH2O)n
Contains aldehyde or keto group
Multiple -OH groups
Hydrophilic - attracts water, water soluble, cannot pass across cell membranes without help
Partially oxidised - needs less oxygen than fatty acids for complete oxidisation
D-Glucose is the naturally occurring form

Question 12

Phase 2 Glycolysis

reactions 4-10

Answer 12

Reaction 4
- cleavage of C6 into two C3 units
Reaction 6 
- small amount of reducing power NADH captured 
reactions 7 and 10 ATP SYNTHESIS - SUBSTRATE LEVEL PHOSPHORYLATION 
- 1,3-BPG and PEP 
- transfer PI to ADP to give ATP 
Reaction 10 
- large -ve delta G so irreversible

Question 13

ATP synthesis during Glycolysis

Answer 13

• 2 moles ATP invested
• 4 moles of ATP produced
• net of 2 moles of ATP produced per 1 mole of glucose by SUBSTRATE LEVEL PHOSPHORYLATION