Blood Sugar Levels

AQA A-Level Biology

Pancreas

• Involved in controlling blood sugar levels

• Made up of groups of cells called islets of Langerhans

• Alpha cells make glucagon

• Beta cells make insulin

Blood Glucose too High

1. Insulin binds to glycoprotein receptor (GLUT 4) on target cell (on liver), changing the tertiary structure

2. Leads to more transport proteins for glucose becoming active by opening them

3. More glucose enters cells from blood, lowering concentration in the blood

4. Insulin causes increase in activity of enzymes that convert glucose to glycogen (glycogenesis)

5. Also causes vesicles containing glucose transporters to fuse with cell membrane by exocytosis, allowing facilitated diffusion of glucose

Blood Glucose too Low

Glucagon released and attaches to receptors on target cells, activating enzymes to:

• Convert stored glycogen to glucose (glycogenolysis) using second messenger model. Liver has lots of glucagon receptors as it is where glycogen is stored.

• Convert glycerol, amino acids and fatty acids into glucose (gluconeogenesis)

Glycogenolysis

Breakdown of glycogen into glucose

Gluconeogenesis

Making new glucose e.g. from glycerol and amino acids by liver

Glycogenesis

Converting glucose into glycogen

Second Messenger Model

• Glucagon / adrenaline bind to receptor site and activate the enzyme adenylate cyclase by changing shape of protein

• Enzyme makes cyclic AMP from ATP (acts as second messenger)

• cAMP binds to protein kinase enzyme, changing its shape and activating it

• Leads to glycogenolysis (glycogen → glucose), which increases blood sugar levels.

Type 1 Diabetes

Person makes no insulin and tend to be younger

Type 2 Diabetes

Receptors don’t respond to insulin - diet and lack of exercise may be triggers.

Metformin

• Treatment for type 2 diabetes

• Increases cell’s sensitivity to insulin

• More insulin binds to GLUT 4 receptors, stimulating uptake of glucose by transport proteins

• Activates enzymes which convert glucose to glycogen

Metformin and Inhibition of Adenylate Cyclase

• Less ATP converted into cAMP

• Less cAMP binding to protein kinase

• Less protein kinase activated

• Less glycogenolysis occurring