Lecture 23 - Glucose as a fuel molecule #1 Flashcards
What is glucose?
A hexose simple sugar monosaccharide
What is hexose?
6 Carbons
What are the 3 types of drawn conformations of glucose?
Ring, Open, Chair
What is the chemical structure of glucose?
C6H12O6
What is a carbohydrate?
A large macromolecule / polysaccharide
What are sources of glucose from carbohydrates?
Starch from plants and glycogen from meat
What is starch?
A polymer made up of up to 1 million glucose units joined by glycosidic bonds
What are the two forms of starch?
Amylose and amylopectin
What is the structure of amylose?
A linear polymer of glucose units
What is the structure of amylopectin?
A branched polymer of glucose units
What is glycogen?
A branched polymer of glucose units
What is a disaccharide?
Two monosaccharides joined by a glycosidic bond
What are some examples of disaccharides?
Sucrose, lactose, maltose
What is the structure of sucrose?
A glucose bound to a fructose by a glycosidic bond
Where are disaccharides found in the diet?
Fruit and raw sugar
What enzyme cleaves glycosidic bonds from polysaccharides to disaccharides?
Amylase through hydrolysis
What enzymes cleave the glycosidic bonds from disaccharides to monosaccharides?
Specific enzymes e.g. sucrase for sucrose
What is the end result of digestion of carbohydrates?
Glucose in the GI tract
Are sugars polar or non polar?
Highly polar
Are sugars water or lipid soluble?
Water
How do glucose molecules cross the lipid membrane?
through specific transporter proteins anchored in the membrane
What are the two types of transport?
Active and facilitated transport
What is active transport?
The movement molecules against a concentration gradient, requiring energy input
What is facilitated transport?
The movement of molecules down a concentration gradient, not requiring energy input
What transporter protein transports glucose via active transport across the apical membrane in the GI tract?
The sodium-glucose linked transporter (SGLT)
(facilitative)
What moves down their concentration gradient through the SGLT?
Na+ (into cell from GIT)
What moves up their concentration gradient through the SGLT?
Glucose (into cell from GIT)
What transporter protein, found on the baso-lateral membrane transports glucose via facilitated transport across the membrane into the interstitial fluid?
GLUT2
(facilitative)
What transporter protein, located on the baso-lateral membrane, creates the low concentration gradient without the cell?
Na+/K+ ATPase
- Na+ pumped out of cell
- K+ pumped into cell
(Active) - energy from ATP hydrolysis
What happens to the K+ that was pumped into the cell via the Na+/K+ ATPase?
returns to interstitial fluid, down concentration gradient, through a channel protein to be used by the Na+/K+ ATPase pump again.
How is glucose used as a fuel molecule?
It is oxidised in glycolysis (in all organisms) which usually occurs in the cytoplasm in eukaryotes
Why is glucose essential as fuel for red blood cells?
RBCS do not have mitochondria and can therefore not utilise other pathways
What is the energy requirement in the brain?
120g of glucose per day
Do brain cells have mitochondria?
Yes
What is the traditional view on why the brain favours glucose?
Glucose easily crosses the blood-brain barrier and fats do not
What is the modern hypothesis as to why the brain prefers glucose?
It is safer, providing a quicker source of ATP without the risk of damage
Why is glucose favoured as a energy molecule in the eye cells?
High amounts of blood vessels and mitochondria would refract the light, so these are limited and glucose does not require either
Which muscle cells use fats as fuel?
Red muscle cells, for endurance
Which muscle cells use glucose as fuel?
White muscle cells, for sprinting
What is this molecule?
Glucose
What are the two main polysaccarides are sources of glucose in human diet?
Starch from plants (amylose, amylopectin)
Glycogen from meat
