Glucose Metabolism and Insulin Action

Explain what diabetes type is shown in the diagram and what the effects are on metabolism (2 marks).

Answer explanation

Model Answer: Explain what diabetes type is shown in the diagram and what the effects are on metabolism (2 marks).

 

Part 1 Explanation – should include what type 1 diabetes is (brief description) and also justify your choice by providing examples from the diagram that support your choice (1 mark).

(0.5 marks) Type 1 diabetes is characterised by the body’s inability to produce insulin due the destruction of the beta islets.

 

(0.5 marks) This is shown by the cross at number 1, that indicates the pancreas cannot secrete insulin.

 

Part 2 Explanation – should describe the metabolic effects that result (there are quite a few but you don’t need to go overboard, so stick to an overall effect here use the image and the number of marks as a guide)

 

(0.5 marks) In untreated T1 diabetes, muscle and adipocytes are unable to access blood sugar due their GLUT4 transporters not present on the plasma membrane

 

(0.5 marks) The cells act like they are in a starvation state and fat cells will mobilise fats as an alternate fuel for energy.

Fill in the blank: Which glucose transporters are affected by insulin secretion (a)   . Options: A) GLUT4 B) GLUT2 C) GLUT1 D) GLUT3

• GLUT4
• GLUT2

• GLUT1

• GLUT3

• GLUT4 and GLUT2

Explain the role of glucose in this cell type (ie what pathways does it directly feed into) (2 marks).

Answer explanation

Explanation – should include what metabolic pathways glucose feeds into and explain what their purpose is.

 

(0.5 marks) when glucose enters the cell it is phosphorylated to G-6-P in glycolysis pathway and can be used for energy production

 

(0.5 marks) The product pyruvate enters the mitochondria and is converted to acetyl-CoA before entering the citric acid cycle, the electron carriers produced are converted to ATP by ox-phos

 

(0.5 marks) excess glucose can be stored as glycogen (glycogenesis pathway)

 

(0.5 marks) Intermediate, G-6-P can enter the pentose phosphate pathway to produce NADPH for fatty acid synthesis and ribose sugar for nucleic acids

Fill in the blank: Pyruvate is oxidized via the (a)   .

• Glycolysis

• PDH complex
• Pentose phosphate pathway

• Insulin receptor

• Citric acid cycle

Describe the function of the insulin receptor, using this image as a guide (2 marks)

Answer explanation

Description – should include the general mechanism of insulin receptor activation and the cellular effects shown in the diagram.

 

(0.5 marks) Insulin receptors are tyrosine kinases, that translate a message from outside the cell to the inside

(0.5 marks) when the ligand (insulin) binds it leads to the autophosphorylation of tyrosine residues on the cytoplasmic domains of the receptor.

 

(0.5 marks) The signalling cascade that results from this, leads to the activation of kinase enzymes such as PKB that activates the translocation of vesicles containing GLUT4 transporters to the plasma membrane

 

(0.5 marks) other metabolic pathways are also activated or inhibited, eg glycogenolysis is inhibited.

Explain what cell type is shown in this diagram and what metabolic role it plays in health compared to diabetes (shown in the image) (1.5 marks).

Answer explanation

Explanation part 1 – should include reasons from the image to support your answer of the chosen cell type.

 

(0.5 marks) The image is of a fat cell, as it contains glut4 receptors that are not found in liver cells. Both liver and fats cells contain TAGs.

 

 

Explanation part 2 – should describe what main role fat cells play in metabolism

(0.5 marks) fat cells synthesis and store fatty acids and TAGs in feasting state which are mobilised when sugar levels are low (fasting state)

 

Explanation part 3 – should describe what happens to the metabolic pathways in T1 diabetes.

 

(0.5 marks) In T1 DM, fat cells are unable to access glucose from the blood, it enters a starvation state mobilising TAGs even in the feasting state.