Carbohydrates Flashcards
Give some characteristics of Carbohydrates
Highly oxidisable
Can store potential energy
Provide structure and protection (animal extra cellular matrix)
Cell communication
3 example of monosaccharides and 3 examples of 3 disaccharides
Mono = glucose (glc), galactose (gal), fructose (fru)
Di = maltose, lactose, sucrose
Describe formation + function of disaccharides
Formed by monomers linked by glycosidic bonds
Hydroxyl group of monosaccharides react with anomeric carbon of another monosaccharide to form disaccharide.
What is an anomeric carbon?
Different carbon anomers are mirror images of eachother (left and right handed forms)
It is carbon #1 on the glucose residue
Stabilises glucose structure
Only residue that can be oxidised
What are polysaccharides?
Polymers of medium-high molecular weight
Can be distinguished from eachother by:
- length of chains
- the type of reoccurring monosaccharide units
- types of bonds linking monosaccharide units
- Amount of branching
They can be branched or unbranched
Difference between homo+heteropolysaccharides?
Homopolysaccharides = single monomeric species.
Heteropolysaccharides = have two or more monomer species
What are some of the main carbohydrates in our diets?
• Sucrose
• Lactose
• Maltose
• Starch
• Glycogen
• Cellulose and Hemicellulose
• Oligosaccharides containing linked galactose
• Glucose
• Fructose
Describe the synthesis of glycogen
Process begins by glycogenin covalently binding Glc from Uracildiphosphate (UDP) glucose to form chains of approx 8 Glc residues.
Then glycogen synthase takes over and extends the Glc chains.
These chains are the broken by glycogen-branching enzyme and re attached via 1-6 bonds to give branch points.
Describe the degradation of glycogen
Glc residues removed by glycogen phosphorylase to release G1P.
Glc near the branch is removed in 2step process by de branching enzymes.
Transferase de branching enzyme removes set of 3 Glc residues and attaches them to nearest non reducing end via 1-4 bond.
Glucosidase the removes final Glc by breaking 1-6 linkage,realessing free Glc.
Unbranvhed chain is left which can be further degraded or built upon as needed.
Functions of glycogen
Liver : acting to replenish blood glucose when fasting
Skeletal Muscle: catabolism produces ATP for contraction
The ratio of where the glycogen is used varies throughout the day.
What is the fate of blood lactate?
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What are the fates of absorbed galactose + fructose
Fructose: binds to gluts channel protein.it men moves down its conc gradient (high in lumen, lowin blood)
Galactose: ATP driven Na pump maintains low Nat so can move into epithelial cells utilising gradients to facilitate its transport
What are the precursors ofgluconeogenesis?
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What is the function of glycolysis?
Glycolysis precedes lactic acid fermentation; the pyruvate made in the former process serves as the prerequisite for the lactate made in the latter process. Lactic acid fermentation is the primary source of ATP in animal tissues with low metabolic requirements and little to no mitochondria. In erythrocytes, lactic acid fermentation is the sole source of ATP, as they lack mitochondria and mature red blood cells have little demand for ATP
Describe the functions and actions of hexokinase and glucokinase
Both catalyse phosphorylation of glucose.
Glucokinase = high Km and high Vmax so it can therefore phosphorylase all the glc quickly this most absorbed Glc is trapped in the liver
Hexokinase = low Km and low Vmax means that even at low {Glc} tissues hexokinase can gran Glc effectively.
