Carbohydrates Flashcards
What is the general structure of a carbohydrate?
(CH2O)n - aldehyde or ketone group and multiple hydroxyl groups
What are monosaccharides? Give examples.
Singular units of sugar - glucose, fructose, galactose
What are disaccharides? Give examples.
Sugars with two subunits - maltose (2 x glucose), sucrose (glucose + fructose), lactose (glucose + galactose)
What are oligosaccharides?
Sugars with 3-10 subunits - e.g. dextrins
What are dextrins?
Smaller carbohydrates of up to 10 subunits. Formed when polysaccharides are cleaved by enzymes in digestion
What are polysaccharides? Give examples.
10’s - 1000’s of subunits - starch, glycogen, cellulose
What is the function of carbohydrates?
They are metabolised to produce energy and provide useful intermediates for use in other biochemical pathways. Required for formation of glycoproteins, glycolipids, etc.
What is the first step in the digestion of carbohydrates?
Amylase in the salivary glands breaks down polysaccharides like starch and glycogen into dextrins
Where does salivary amylase stop working?
In the stomach due to the acidic conditions
What is the role of the pancreas in the digestion of carbohydrates?
It releases bicarbonate into the duodenum to neutralise stomach acid which creates an environment for pancreatic amylase (and other pancreatic enzymes) to work in
What is the role of disaccharidases and where are they located?
They break down remaining disaccharides into monosaccharides and are found on the membrane of the small intestine
How is glucose absorbed into the blood?
- Via secondary active transport
- Sodium potassium pump - pumps out 3 Na+ and pumps in 2 K+ which creates a conc. grad.
- Less Na+ in epithelial cell that in lumen of SI
- Na+ moves down conc. gradient co-transporting glucose in via protein carrier
- blood flow maintains a conc. gradient of higher glucose in cell than in blood so glucose moves into blood via F.D.
What does phase 1 of catabolism involve?
The breakdown of molecules into building blocks. It is extracellular
Why isn’t cellulose digested in the human GI tract?
Cellulose contains BETA 1,4 linkages that result in a more rigid and elongated shape of molecule than ALPHA 1,4 linkages. This means it doesn’t fit the shape of the active sites of the enzymes that break down the alpha 1,4 linkages in starch and glycogen.
IMPORTANT = ALPHA AND BETA GLYCOSIDIC BONDS ARE DIFFERENT
What causes lactose intolerance?
Lactase deficiency
Why is lactase deficiency normal in some populations?
When being BF, we have lots of lactase but as weaned off it, lactase levels drop. This is normal as there is less lactose in the diet so high lactase levels unnecessary
Why can people in many populations continue to consume lactose after being weaned off breast milk?
We continue to consume lactose in higher quantities so have developed a lactase persistence phenotype, preventing the drop off
What is primary lactase deficiency?
Where there is an absence of lactase persistence allele. It occurs in adults and is common in Northwest Europe
What is secondary lactase deficiency?
Where there is damage to the GI tract so lactase enzyme in membrane of SI not effective. This is reversible as the damaged area recovers and can be seen in infants and adults. It is caused by gastroenteritis, Crohn’s, UC, Coeliac disease