Carbohydrates 2 Flashcards
Where can we get glycogen from in our diet?
Meat
Can we digest cellulose?
No
Where in our diet can we get oligosaccharides?
Contains linked galactose, found in peas beans and lentils
What does salivary amylase hydrolyse?
The 1,4 glycosidic bonds in starch
Are carbohydrates digested in the stomach?
no
Where and what is the duodenum?
It is the shortest part of the small intestine where most chemical digestion takes place. It precedes the jejunum.
What enzyme works in the duodenum to break down carbohydrates?
Pancreatic amylase - hydrolyses 1,4 bonds as in mouth
What happens in the jejunum?
Final digestion by mucosal cell surface enzymes
What enzymes are contained within the jejunum and what are their functions?
Isomaltase - hydrolyses the 1,6 bonds
Glucoamylase - releases glucose from non-reducing ends
Sucrase - Hydrolyses sucrose
Lactase - Hydrolyses lactose
What is the function of high sodium levels in glucose transport within the intestinal lumen?
Glucose symporter - High sodium levels drive glucose across the membrane
How does the glucose leave the epithelial cell into the blood?
Through a glucose uniporter - facillitates downhill eflux (diffusion)
Which other monosaccharide uses other gradients to facilitate its transport?
Galactose
Which sugar binds to the channel protein GLUT 5 and simply moves down its concentration gradient?
Fructose
What is the function of cellulose within the gut?
Increases faecal bulk and decreases transit time
What are cellulose polymers broken down by gut bacteria to produce?
CH4 and H2
What can cause disaccharidase deficiencies?
Genetic condition Severe intestinal infection Other inflammation of the gut lining Drugs injuring the gut wall Surgical removal of the tissue Characterised by abdominal distension and cramps
How would you diagnose disaccharidase deficiencies?
Enzyme tests of intestinal secretions - checking for lactase maltase and sucrase activity low levels of enzymes might reflect low levels of disaccharide?
What reasons are behind high lactase activity in western white adults?
High cattle domestication
What happens when lactase is deficient?
Causes disaccharide deficiency symptoms - Gas build up and irritant acids - caused by undigested lactose being broken down by gut bacteria
Diarrhoea
Why does lactase deficiency cause diarrhoea?
Lactose is osmotically active - drawing water from the gut in to the intestinal lumen
How can lactose intolerance symptoms be avoided?
Avoiding milk products
Using milk products treated with fungal lactase
Supplementing diet with lactase
What happens to glucose after it is absorbed by the intestinal epithelium cells?
Enters hepatic portal vein and travels to the liver
What is the effect of hepatocytes on absorbed glucose?
They immediately phospohorylate them to into glucose-6 phosphate
Why can’t glucose 6 phosphate leave the cell?
GLUT transporters won’t recognise it - traps glucose within the cell
What are the catalysts involved with glucose phosphorylation?
Glucokinase (liver) and hexokinase (other cells)
When is most glucose trapped in the liver?
After a meal, glucokinase phosphorylates all the glucose quickly.
When is glucokinase turned on?
Turned on at high glucose levels
Why is hexokinase able to grab glucose effectively?
It has a low KMax
Why isn’t hexokinase able to continuously grab glucose?
It is easily satisfied because of its low vmax
What are the potential products of g 6 p?
ATP, Glycogen, NADPH
Where can you find 90% of the glycogen in the body?
Skeletal muscles and the liver
What happens to glycogen when blood glucose levels fall?
Glucose 6 phosphatase converts the GP to glucose
What happens to glycogen that is trapped in the muscle?when blood glucose is low
There is no glucose 6 phosphate
Glycogen —> Glucose 6 Phosphate —-> Lactate
How does glycogenin begin the process of glycogen synthesis?
Binds the glucose from uracil-diphosphate-glucose to form chains of approximately 8 glucose residues. It’s a polymer, binding the first few molecules of glucose.
What enzyme takes over after glucogenin?
Glycogen synthase
How are chains foromed in glycogen?
Glycogen branching enzyme breaks the chains formed by glycogen synthase and then reattach these chains via alpha 1-6 bonds to give branch points
How are glucose monomers removed from the end of glycogen chains?
They are removed one by one from the non-reducing ends as G-1-P
What enzyme releases G-1-P from glycogen?
Glycogen phosphorylase
What is the result of the transferase activity of the de-branching enzyme?
It removes three glucose residues and connects them to the nearest non-reducing end via 1,4 glycosidic bonds
What is the result of the glucosidase activity of the debranching enzyme on the last glucose residue?
Breaks the 1,6 glycosidic bond to release a free glucose monomer.
What is happens to glucose 6 phosphate that enters the liver?
It is de-phosphorylated to form glucose
What happens to G6P that enters the muscle?
Substrate phosphorylation of ADP forming atp, glycolysis forming lactate.
What is von gierkes disease characterised by?
Liver glucose-6-phosphatase deficiency
What are the symptoms of von gierkes disease?
High liver glycogen levels
Low blood glucose concentrations
High blood lactate - Lacticacidaemia
Why is there a high level of lactate in von gierkes disease?
Lactate produced by the skeletal muscle cannot be reconverted into glucose by the liver - a process which requires glucose - 6 - phosphatase
What is the treatment for von gierkes disease?
Carbohydrate feeding
What is McCardle’s disease characterised by?
Skeletal muscle phosphorylase deficiency results in high glycogen levels and no increase in blood glucose levels after exercise. Glycogen phosphorylase is responsible for removing glucose 6 phosphate groups from glycogen
What are the symptoms of McCardle’s disease?
Weakness and cramps after exercise
