Carbohydrates And The Pentose Phosphate Pathway Flashcards
What enzyme in the saliva and the pancreas helps to break down carbohydrates?
Amylase
What substances in the small intestine break down dissaccharides to monosaccharides? Give an example.
Dissacharidases.
Lactase breaks down lactose.
Sucrose breaks down sucrose.
What is secondary lactose intolerance?
Injury to the small intestine following an illness e.g. Coeliac disease, Crohn’s disease - usually reversible.
What are the three types of lactose tolerance?
Primary - lactase deficiency
Secondary - after injury
Congenital - very rare, autosomal recessive
What are some symptoms of lactose intolerance?
Cramping, vomiting, bloating, diarrhoea.
What two transporter pumps do monosaccharides have to pass through the meet the bloodstream? How do they work?
To pass through intestinal epithelium - Sodium Dependent Glucose Transporter 1 (SGLT1). 2 sodiums exchanged for 1 glucose. ACTIVE TRANSPORT.
To pass from epithelium to bloodstream - GLUT2 pump - uses transport proteins to pass through (GLU1-GLU5).
Where are GLU2 proteins used?
In pancreatic beta cells.
Where are GLU4 proteins used?
In adipose tissue, striated muscle - is insulin regulated.
Name four areas/cells of the body where glucose is an absolute requirement.
RBC - no mitochondria
Neutrophils - Mitochondria is only used to destroy bacteria
Innermost cells of kidney medulla
Lens of eye - no capillaries, poor oxygen supply.
What is the CNS’s preferred fuel?
Glucose.
What is glycolysis?
The breakdown of glucose by enzymes, releasing energy and pyruvic acid.
What is the net gain of ATP during glycolysis?
2
2 are invested for 2 return
During glycolysis there is no loss of carbons, how are these carbons distributed by the end?
Glucose - 6 carbons
X2 Pyruvate - 3 carbons each
Where does glycolysis occur?
In the cytosol of cells.
How many NADH molecules are produced in glycolysis?
2 (2 per glucose molecule).
In what two steps of glycolysis are ATPs invested?
Stage 1 (glucose to glucose-6-p) and stage 3 (Fructose-6-p and fructose 1,6-bids-p).
What product represents the first ‘committing step’ of glycolysis, where the chain reaction is irreversible? Why is this?
Fructose 1,6-bis-p
Large negative Gibbs Free Energy - reaction cannot be turned.
At what stage in glycolysis does the cleavage of the 6 glucose carbons to 3 pyruvate carbons occur?
Stage 4 - conversion from Fructose 1,6-bid-P to DHAP
How many irreversible steps int the glycolysis pathway are there?
3
What the name of the production of ATP is stages 7 and 10?
Substrate Level phosphorylation
What is Glycerol Phosphate an important intermediate for?
Triglyceride and Phospholipid biosynthesis.
What enzyme produces glycerol phosphate and what co-enzyme is used?
Enzyme - Glycerol 3-phosphate dehydrogenase
Co-enzyme - NADH (NAD+ to NADH)
Where is glycerol phosphate produced?
In the liver and adipose tissue.
Where is 2,3-bisphoglycerate found?
In the RBC
What does 2,3-bisphosphoglycerate regulate?
Haemoglobin oxygen affinity
What effect would an increase in 2,3-bids phosphoglycerate have on oxygen affinity? What effect would this have in the body?
It would decrease it.
High levels of 2,3-DPG at tissues - encourage oxygen release.
The rate of glycolysis is X times more in cancer.
X = 200
Key regulator phosphofructokinase (PFK) is present at which stage of glycolysis?
Stage 3
From fructose-6-phosphate to fructose 1,6-bisphosphate
Phosphofructokinase (PFK) is an allosteric muscle regulator. What effect does the varying levels of ATP have on its activity?
Inhibited by high levels of ATP
Stimulated by low levels of AMP.
This is because if ATP in the cell is high, there is no need to produce more, therefore glycolysis is unnecessary.
PFK (phosphofructokinase) is also a hormonal tissue regulator. What effect do the levels of insulin and glucagon have on its activity?
Stimulated by insulin.
Inhibited by glucagon.
After a meal, there is lots of glucose in the body, so insulin is released, and PFK helps to break it down in glycolysis.
Glucagon is released by the liver when the body has a low blood sugar level, so PFK is reduced to ensure glycolysis doesnt break down the little glucose there is in the body.
How does Hexokinase help regulate step one of the glycolysis pathway (glucose to glucose-6-p)?
A high amount of product slows down the reaction.
So if there are high amounts of glucose-6-p, hexokinase is reduced to ensure no backlog of product.
Would high levels of NADH is step 6 of the glycolysis pathway speed up or slow down the reaction?
Slow down
NAD+ is converted to NADH here.
If there are high levels of NADH (product), reaction needs to slow down to ensure there is no backlog.
Equally, low amount of NAD+ stimulates the reaction.
What is pyruvate kinase inhibited and stimulated by in the glycolysis pathway?
Stimulated by insulin (lots of glucose to break down).
Inhibited by glucagon (no glucose to breaks down).
At what stage in the glycolysis pathway does lactate dehydrogenase (LDH) take place and why?
Stage 4.
In aerobic conditions, NAD+ is regenerated from NADH and the pathway continually.
However oxygen is needed to do this, so in anaerobic conditions (e.g. Exercising muscles), NAD+ regeneration is done via LDH.
What is the equation of lactate dehydrogenase?
NADH + H+ + pyruvate = NAD+ + lactate
In anaerobic conditions, pyruvate is converted to X instead of age 4 metabolism.
X = lactate
What plasma concentration range of lactic acid is considered hyperlactaemia?
2-5 mM
What plasma concentration range of lactic acid is considered lactic acidosis? Why is this so dangerous?
Above 5mM
Low ph
Kidneys cannot dispose of lactic acid in time.
What is the average safe amount of lactic acid concentration in the body?
Under 1mM
What food is galactose found in?
Milk
What three enzyme deficiencies could result is galactosaemia?
Galactokinase
Uridyl transferase
UDP-galactose epimerase
What do you call of galactose intolerance?
Galactosaemia
Where is fructose metabolised?
In the liver
What is fructosuria?
Where the enzyme fructokinase is missing in the body.
No symptoms - just high fructose level in urine.
What enzyme is missing in patients with fructose intolerance and what can it lead to?
Missing aldokinase
Leads to a build up of fructose-1p (no aldokinase to use it up) - can lead to liver damage.
Treatment: no fruit
