Aromatic Family: Tryptophan

by Kevin Ahern, PhD

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    00:02 The aromatic family is next stem we will consider, the synthesis of.

    00:06 These include the amino acids: tryptophan, phenylalanine and tyrosine.

    00:12 Each of these amino acids is derived from some very simple precursors.

    00:17 Phosphoenolpyruvate which is an intermediate in the glycolysis pathway and erythrose-4-phosphate which is an intermediate from the pentose phosphate, phosphate pathway.

    00:27 The synthesis pathways are complex.

    00:29 And again, I'm not going to go into individual reactions other than to show you the schematic that we see here.

    00:35 Each of the synthetic pathways involves the production of shikimic acid and chorismic acid.

    00:40 We can see the chorismate or the chorismic acid in the schematic here.

    00:44 Phenylalanine and tyrosine pathways overlap because tyrosine can be produced directly from phenylalanine.

    00:51 It can also be produced independently of it as well.

    00:55 Hormones and neurotransmitters are made from each of these amino acids.

    00:59 So this aromatic family has a lot of connections to other things that cells need.

    01:05 Now the synthesis of tryptophan is interesting.

    01:07 Its regulated synthesis and bacteria has a very interesting mechanism known as attenuation.

    01:14 Attenuation is a way of controlling an entire operon.

    01:17 Now an operon is a set of five genes.

    01:20 Making five genes takes a lot of energy.

    01:23 So cells only want to be synthesizing those five genes to make tryptophan when tryptophan is itself needed.

    01:29 If tryptophan is available, making those genes waste energy.

    01:34 So they have involved a way of controlling whether or not those five genes are made or not made depending upon whether tryptophan is present or not present.

    01:43 When tryptophan concentration is high, then the transcription of the operon to make those five genes actually aborts.

    01:50 It starts, but it aborts.

    01:53 That prevents these five genes from being made and saves energy because tryptophan is available.

    01:59 When tryptophan supply is slow, that aborted process does not occur.

    02:04 The entire transcription of the entire operon occurs.

    02:07 So this process is attenuation.

    02:09 Very interesting way of controlling synthesis of a set of genes.

    02:15 The molecules made from tryptophan are shown in the screen here.

    02:18 They include melatonin.

    02:19 And melatonin is important for circadian rhythm sensing.

    02:24 It affects our mood, it affects our sleep, affects our blood pressure.

    02:28 Melatonin is used in some sleeping treatments actually.

    02:33 The production of melatonin, we know now, is affected by blue light.

    02:38 And the more blue light we have, especially later in the evening, the less melatonin we produce.

    02:44 The less melatonin we produce, the more sleeping difficulty we have.

    02:48 So one suggestion people have is not to use your computer monitor too much at night or to use a computer program that actually reduces the amount of blue light being produced by your computer screen.

    03:00 Serotonin is what people refer to as the happy hormone.

    03:03 It's a neurotransmitter.

    03:04 It causes vasoconstriction, which actually increases blood pressure, and then enhances memory, learning and it's a contributor to happy feelings.

    03:13 When you're feeling well, feeling happy, you're probably producing serotonin.

    03:19 Niacin we can see is one of our vitamins.

    03:21 It's known as vitamin B3.

    03:24 It's important component of nicotinamide.

    03:27 And nicotinamide is used to make NAD, NADH, NADP, and NADPH.

    03:33 A deficiency of vitamin B3 is very severe and leads to the disease known as an pellagra.

    03:40 The last of the molecules made from tryptophan is that the auxins.

    03:43 There are families of molecules and indole-3-acetic acid is the most important and the most common one.

    03:49 It is a plant hormone and was in fact the first plant hormone that was discovered.

    03:54 It's used in plants to stimulate cell division and causes rooting in the plants.

    About the Lecture

    The lecture Aromatic Family: Tryptophan by Kevin Ahern, PhD is from the course Amino Acid Metabolism.

    Included Quiz Questions

    1. It is synthesized from phosphoenolpyruvate (PEP) and erythrose-4-phosphate
    2. It includes phenylalanine, tyrosine, and threonine
    3. It is made primarily from neurotransmitters
    4. All of the answers are true
    5. None of the answers are true
    1. All of the answers are correct
    2. It is partly regulated by attenuation in bacteria
    3. It is a precursor of plant hormones
    4. It is a precursor of a vitamin
    5. None of the answers are true

    Author of lecture Aromatic Family: Tryptophan

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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