Carbohydrates Flashcards
What are the advantages to carbohydrates being hydrophilic?
water soluble
attract water
cannot pass easily across membranes
already partially oxidised so take less oxygen than fatty acids for complete oxidation
Name the 3 disaccharides
lactose, maltose, sucrose
What are oligosaccharides?
Carbohydrates that are 3-12 units in length
Where is glycogen stored in the body?
Liver and muscle
Which enzymes are attached to the brush border of epithelial cells in the small intestine?
lactase, sucrase, amylase, isomaltase
How do monosaccharides enter cells?
Via facilitated diffusion using transport proteins (GLUT1-GLUT5)
Which tissues can metabolise glucose?
All tissues
What is the normal blood glucose concentration?
5mM
Which tissues have an absolute requirement for glucose?
red blood cells white blood cells kidney medulla lens of eye brain
What is the net ATP production of glycolysis?
2 ATP molecules (net) per glucose
Why are there so many steps in glycolysis?
the chemistry is easier in smaller stages
allows for efficient energy conservation
gives versatility (interconnections to other pathways)
can be controlled
What is different about glycolysis in cancer?
The rate of glycolysis can be up to 200 times faster
What is DHAP and what can it be converted to?
DHAP is an intermediate of glycolysis (one of the C3 molecules produced after cleavage)
DHAP can be converted to glycerol phosphate
Where and for what is glycerol phosphate used?
adipose tissue and liver
important for triglyceride and phospholipid biosynthesis
What is the role of 2,3-bisphosphoglycerate?
important regulator of oxygen affinity of haemoglobin present in RBCs
What are allosteric effectors?
Activators or inhibitors that bind to enzymes at a different site to the active site
What product inhibits hexokinase in glycolysis?
glucose-6-phosphate
Under what conditions is phosphofructokinase-1 increased in activity?
high AMP levels
high insulin levels
Does a high insulin level increase or decrease the activity of pyruvate kinase?
It increases the activity (dephosphorylation so that ADP can be phosphorylated)
Why can’t RBCs perform oxidative phosphorylation?
They don’t have any mitochondria
Which enzyme converts pyruvate to lactate?
Lactate dehydrogenase
Where is lactate normally metabolised?
In the liver and heart
Define lactic acidosis
A high concentration of lactate in the blood (>5mM) which lowers the pH of the blood.
Where is fructose metabolised?
In the liver
What is the pathway for fructose metabolism and what are the enzymes that catalyse each stage?
Fructose -> Fructose-1-P (Fructokinase)
Fructose-1-P -> 2-Glyceraldehyde-3-P (Aldolase)
What disease do we have if fructokinase is missing and how would we spot it?
essential fructosuria
fructose in the urine
What disease do we have is aldolase missing and what does this lead to?
Fructose intolerance
Fructose-1-P accumulates in the liver and causes liver damage
Where is galactose metabolised?
In the liver
What 3 enzymes are involved in galactose metabolism?
galactokinase
galactose-1-P uridyl transferase
UDP-galactose 4’-epimerase
Which enzymes can be deficient to cause galactosaemia?
galactokinase deficiency (rare) transferase deficiency (common)
In people with galactosaemia, what pathway does galactose enter?
galactose -> galactitol (aldose reductase)
NADPH reoxidised to NADP+
Which organs are affected by the accumulation of galactose-1-P?
liver
kidney
brain
Why is it a bad thing that the NADPH levels are depleted in galactosaemia?
lowered NADPH prevents the maintenance of free sulphdryl groups so inappropriate disulphide bonds are formed
this causes loss of structural and functional integrity in some proteins
Also more susceptible to oxidative damage as cannot reduced GSSG back to GSH as efficiently
Which enzyme catalyses the conversion of glucose-6-P to a five carbon sugar?
glucose-6-P dehydrogenase
What are the functions of the pentose phosphate pathway?
produce NADPH in the cytoplasm
produce five carbon sugars for nucleotides
What is the general formula of a carbohydrate?
(CH2O)n
What does pyruvate dehydrogenase deficiency lead to?
Lactic acidosis
Because the pyruvate is converted into lactate instead
How many oxidative steps does the TCA cycle have and how many of those steps release CO2?
4 oxidative steps
2 of them release CO2
How are Krebs cycle enzymes inhibited?
Allosterically
Does the Krebs cycle function in the absence of oxygen?
No
NADH and FAD2H will build up and allosterically inhibit the action of the enzymes
At the electron transport chain the majority of the electrons’ energy is…
released as heat
Which hydrogen carrier has a higher energy yield?
NADH
What do uncouplers do?
Increase the permeability of the inner mitochondrial membrane to protons
the protons no longer need to pass through ATP synthase to move down their electrochemical gradient
Give 2 examples of electron transport inhibitors
cyanide
carbon monoxide
Give 3 examples of uncouplers
dinitrophenol
fatty acids
dinitrocresol
Which protein is most significant in brown adipose tissue and what does it do?
Thermogenin (UCP-1)
It is a natural uncoupling protein that is used when the body requires extra heat generation
How many molecules of ATP are synthesised from glucose in normal aerobic respiration?
32 moles ATP per glucose
