Insulin Basics

by Thad Wilson, PhD

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    00:01 Let’s have a look at insulin synthesis.

    00:04 Insulin is synthesized as a 110 amino acid long preproinsulin, composed of a signal peptide, depicted in orange, a B-chain in blue, the connecting peptide in yellow, which is a C-peptide to be exact and lastly the red part, which is the A-chain.

    00:23 The signal peptide is later cleaved off, resulting in the formation of proinsulin.

    00:29 Within the endoplasmic reticulum, three disulfide bonds are formed between cysteine residues.

    00:36 Proinsulin is then transported to the Golgi apparatus, where the C-peptide is cleaved off. This process converts proinsulin into mature insulin, which consists of the B and A chains only.

    00:51 Keep in mind that C-peptide is only produced during endogenous insulin production. Therefore, in the case of exogenous insulin, which is taken by diabetics, no C-peptide will be found in the blood.

    01:06 Exogenous insulin is typically manufactured in recombinant DNA technology using Escherichia coli.

    01:13 This type of insulin does not contain C-peptide, this allows the differentiation between true endogenous and false exogenously produced hypoglycemia.

    01:25 Insulin.

    01:28 Insulin forms usually of what glucagon is.

    01:33 It's formed also in the islet and specifically in the beta cells.

    01:38 It is also a peptide hormone similar to glucagon.

    01:43 It is clear about 50% by the first path.

    01:48 This is an important process because again it's going to mean that insulin is not around in the circulation very long.

    01:56 In fact it's half life is only 3 to 8 minutes.

    02:03 Importantly what we have produced at the same time as the peptide hormone insulin is something called C-peptide.

    02:14 Don't get this mixed up with C reactive peptide.

    02:17 This is just C-peptide.

    02:20 C-peptide is when passed through this first pass system in a slower time frame.

    02:29 Therefore, it has a longer half life.

    02:32 About 35 minutes.

    02:35 If you compare 35 minutes half life versus a 3 to 8 minute half life, you can see that C-peptide stays in the circulation longer.

    02:45 How is that useful for you clinically.

    02:47 How useful is that, you can use C-peptide if you measured in the blood as an index for how much insulin is being secreted.

    02:59 Because insulin is not going to be around long enough to really measure it's concentrations.

    03:04 But if you measure C-peptide, you know it's produced in a 1 to 1 ratio.

    03:09 Therefore, if C-peptides goes up, insulin has to go up and vice versa.

    03:16 You can see how this break down of this process works.

    03:19 If you see this polypeptide being formed.

    03:22 And there's a cleave that happens, that forms C-peptide and insulin.

    03:28 So they'll be making this preformed proinsulin peptide.

    03:34 You cleave a certain spot, leaving C-peptide and insulin as your two different secretory substrates.

    About the Lecture

    The lecture Insulin Basics by Thad Wilson, PhD is from the course Endocrine Physiology.

    Included Quiz Questions

    1. Insulin
    2. Glucagon
    3. Somatostatin
    4. Pancreatic polypeptide
    1. 3-8 min
    2. 15-20 min
    3. 20-45 min
    4. 12-14 min
    5. 16-19 min

    Author of lecture Insulin Basics

     Thad Wilson, PhD

    Thad Wilson, PhD

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