Carbohydrates Flashcards
General formula of carbohydrates
(CH2O)n
How can carbohydrates be modified?
Addition of amino, sulphate and phosphate functional groups
What are monomers of carbohydrates called?
Monosaccharides
Three ways carbohydrate can be divided?
> no. of carbohydrate they contain (triose, pentose)
Shape - linear or ring
Size (mono, di, poly - saccharides)
Characteristics of glucose
> C6H12O6
Hexose
Most abundant sugar in the body and cellular fuel
Levels controlled by hormones (insulin, glucagon)
Digestion & absorption of glucose in the body
Polysaccharides -> dextrins & maltose (via salivary amylase) -> disaccharides (via pancreatic amylase) -> monosaccharides (via intestinal disaccharidases)
Transported via portal blood to the liver and stored as glycogen
Irregular blood sugars names
Hypoglycaemia - low
Hyperglycaemia - high
What might hyperglycaemia indicate?
Type 1, Type 2 or gestational diabetes
Irregularities may highlight deficiencies in insulin production or inability of insulin to act as it should
Homeostatic control of blood glucose levels
Hyperglycaemia - beta cells of pancreas increase insulin production - released into blood - facilitate cellular uptake of glucose & cause liver to convert glucose to glycogen - blood glucose levels decline to healthy amount
Hypoglycaemia - alpha cells in pancreas stimulated to increase production of glucagon and released into blood - liver breaks down glycogen into glucose and released into blood - blood glucose levels increase to a healthy level
Glucose specimen requirements
Plasma sample with sodium fluoride to prevent glycolysis (citrate buffer can also be used)
Fasting serum can be used for some tests when transported on slurry ice and serum separated fast to avoid glycolysis
Whole blood can be used for some tests within 30 minutes
The Reactions in the Folin-Wu Copper Reduction Method
Glucose + Cu^2+ = Cu2O (hot alkaline conditions)
Cu2O + phosphomolybic acid = Molybdenum Blue
Explain the Folin-Wu Copper Reduction Method
> Glucose under alkaline conditions reduces the cupric ions of the copper reagent to cuprous ions. Cuprous oxides react with phosphomolybdic acid to form molybdenum blue.
Intensity of molybdenum blue is directly proportional to concentration of glucose - spectrophotometer @ 420nm
Uric acid, creatinine, & sulphydryl compounds may cause positive interference - also reduce cupric ions
Explain the Folin-Wu Copper Reduction Method
> Glucose under alkaline conditions reduces the cupric ions of the copper reagent to cuprous ions. Cuprous oxides react with phosphomolybdic acid to form molybdenum blue.
Intensity of molybdenum blue is directly proportional to concentration of glucose - spectrophotometer @ 420nm
Uric acid, creatinine, & sulphydryl compounds may cause positive interference - also reduce cupric ions
Name a redox method of testing glucose?
Folin-Wu Copper Reduction Method
Name 2 enzymatic reactions used to measure glucose concentration
Hexokinase method and glucose oxidase method
What reactions are involved in the hexokinase method?
Glucose + hexokinase + ATP = ADP + glucose-6-phosphate
Glucose-6-phosphate + NAD+ + G6PD = 6-glucose phosphate ester + NADH
Principles and limitations of the HK method
NADH produced is directly proportional to the glucose concentration - spectrophotometer @ 340nm
>Phosphate esters and enzymes released from RBCs might alter NAD+ concentration - haemolysed specimens cannot be used
Reactions that take place in the Glucose Oxidase method
Glucose + H2O + O2 (glucose oxidase) = gluconic acid + H2O2
O-dianisidine + H2O2 (peroxidase) = oxidised o-dianisidine + H20
Principles of the GOD-POD Method
Enzyme glucose oxidase catalyses oxidation of glucose to gluconic acid & hydrogen peroxide - hydrogen peroxide used as a substrate using the peroxidase enzyme and Q chromogenic oxygen acceptor - brown colour forms - spectrophotometer @ 500nm
Limitations of the GOD-POD Method
> highly specific to the beta form of glucose - exists 36% alpha and 64% beta in solution
Standard solution from dry glucose should be left to sit for 2 hours - reach equilibrium
Peroxidase step not specific - uric acid, ascorbic acid, bilirubin, haemoglobin, tetracycline, glutathione compete with chromogen for H2O2
Explain the HbA1c method to test glucose concentration
> HbA1c= glycosylated haemoglobin - measure amount of glucose attached to RBCs
Higher the HbA1c = more glucose attached to RBCs
Does not change rapidly - RBCs stay in circulation for 120 days - indicates 2-3 months of blood-glucose levels
Types of Diabetes Mellitus
Type 1, Type 2, gestational diabetes, MODY, LADA, and neonatal diabetes
What might hyperglycaemia indicate?
Diabetes Mellitus - relative lack of insulin and/or insulin resistance
Explain Type 1 DM
> 5-10% of diabetes
Usually develops in youth (9-14) but can develop later (stress, illness)
Absolute lack of insulin due to autoimmune destruction of beta cells
Presence of islet cell antibodies in serum predicts Type 1 DM development
Explain T2 DM
> 90%
Any age - (common 40-80)
Resistance of peripheral tissue to actions of insulin level - insulin level normal/high
Obesity is common
Explain gestational diabetes?
> Pregnant women - mother isn’t able to produce enough insulin
High blood sugar pass via placenta to baby - health problems
2nd 1/2 of pregnancy and stops after birth
Explain MODY
Mature Onset Diabetes of the Young
>Hereditary differs from T1 & T2
>Mutation in single gene - if a parent has it 50% chance child has it
>Develop MODY before 25 irrespective of weight, lifestyle
Explain LADA
Latent Autoimmune Diabetes of Diabetes
>T1 DM development in adults
Explain neonatal diabetes?
> Diagnosed before 6 months
Not autoimmune
Change in gene which affects insulin production - blood glucose levels rise quickly
Transient & permanent types
Explain hypoglycaemia
> RAPID Sweating, trembling, weakness, & anxiety
SLOW headache, irritability, & lethargy
Fasting glucose <2.5mmol/L
Insulin intake of diabetics, not eating enough, & malnutrition
Fasting glucose reference range
3.9mmol/L - 5.6mmol/L
