Homeostasis: control of blood glucose concentration

Name the factors that affect blood glucose concentration

• Amount of carbohydrate digested from diet

• Rate of glycogenolysis

• Rate of gluconeogenesis

Define glycogenesis , glycogenolysis and gluconeogenesis

• Glycogenesis: liver converts glucose into the storage polymer glycogen

• Glycogenolysis: liver hydrolyses glycogen into glucose which can diffuse into the blood

• Gluconeogenesis: liver converts glycerol and amino acids into glucose

Outline the role of glucagon when blood glucose concentration decreases

1. Glucagon binds to liver cell membrane receptors

2. G protein is activated which activates the enzyme adenylyl cyclase by changing its shape

3. Active adenylyl cyclase converts ATP to cyclic AMP (cAMP)

4. cAMP is the second messenger and initiates protein kinases

5. Protein kinase enzymes activate a cascade which catalyses the breakdown of glycogen to glucose (glycogenolysis)

Outline the role of adrenaline when blood glucose concentration decreases

1. Adrenaline binds to different receptors on the liver cells to glucagon

2. This causes the enzyme adenylyl cyclase to change shape and become activated

3. Active adenylyl cyclase catalyses the conversion of ATP to the second messenger cAMP

4. cAMP is the second messenger and initiates protein kinases

5. Protein kinase enzymes activate a cascade which catalyses the breakdown of glycogen to glucose

Outline what happens when blood glucose concentration increases

1. Beta cels in Islets of Langerhans in pancreas detect increase and secrete insulin into bloodstream Glucagon

2. Insulin binds to surface receptors on target cells to:

3. a) increase cellular glucose uptake b) activate enzymes for glycogenesis (liver and muscles) c)stimulate adipose tissue to synthesise fat

Describe how insulin leads to a decrease in blood glucose concentration

• Increases permeability of cells to glucose

• Increases glucose concentration gradient

• Triggers inhibition of enzymes for glycogenolysis

How does insulin increase permeability of cells to glucose

• Increases number of glucose carrier proteins

• Triggers conformational change which opens glucose carrier proteins

How does insulin increase the glucose concentration gradient

• Activates enzymes for glycogenesis in liver and muscles

• Stimulates fat synthesis in adipose tissue

Explain the causes of Type 1 diabetes and how it can be controlled

• Body cannot produce insulin e.g due to autoimmune response which attacks beta cells of islets of langerhans

Explain the causes of type 2 diabetes and how it can be controlled

Glycoprotein receptors are damaged or become less responsive to insulin

Strong positive correlation with poor diet/ obesity

Treat by controlling diet and exercise

Name some signs and symptoms of diabetes

• Glucose in the urine

• Blurred vision

• Sudden weight loss

Suggest how a student could produce a desired concentration of glucose solution from a stock solution

• Volume of stock solution= required concentration x final volume needed / concentration of stock solution

• Volume of distilled water=final volume needed- volume of stock solution

Outline how colorimetry could be used to identify the glucose concentration in a sample

1. Benedict’s test on solutions of known glucose concentration. Use colorimeter to record absorbance.

2. Plot calibration curve: absorbance (Y), glucose concentration (X)

3. Benedict’s test on unknown sample. Use calibration curve to read glucose concentration at its absorbance value