Q: About Vitamins and NTD

 

Nutrition Question N-05

 

 

                                   

 

 

A very anxious 30 year-old female patient go to your office because she is late 7 days. Pregnancy tests confirm pregnancy. The patient tells you that in a former pregnancy, she had a fetus with anencephaly. Which of the following vitamins you indicate to the patient that she should begin to take immediately for avoiding a Neural Tube Defect?

 

a)     Ascorbic acid

 

b)     Folic Acid

 

c)      Lipoic acid

 

d)     Nicotinic acid

 

e)     Panthotenic acid

 

 

 

 

About the metabolic fate of the carbon skeleton of amino acids

 

Answer to Biochemistry Question AM-02 about Amino acid Metabolism.

 

Answer: (b) Ketogenic (Since the question only make reference to acetoacetyl CoA, we assume that it is the final product of the catabolism of this amino acid and no glucogenic metabolites are produced.)

 

 

                                                

 

 

Amino acids are used for different purposes in our body. Most of the metabolic pool of amino acids is used as building blocks of proteins, and a smaller proportion is used to synthesize specialized nitrogenated molecules as epinephrine and norepinephrine, neurotransmitters and the precursors of purines and pyrimidines.

 

Since amino acids can not be stored in the body for later use, any amino acid not required for immediate biosynthetic needs is deaminated and the carbon skeleton is used as metabolic fuel (10-20 % in normal conditions) or converted into fatty acids via acetyl CoA.

 

The main products of the catabolism of the carbon skeleton of the amino acids are pyruvate, oxalacetate, a-ketoglutarate, succinyl CoA, fumarate, acetyl CoA and acetoacetyl CoA.

 

When carbohydrates are not available (starvation, fasting) -or cannot be used properly, as in diabetes mellitus, amino acids can become a primary source of energy by oxidation of their carbon skeleton, but also by becoming an important source of glucose for those tissues that only can use this sugar as metabolic fuel.

 

The formation of glucose from amino acids (gluconeogenesis) in liver and kidney is intensified during starvation and this process becomes the most important source of glucose for the brain, RBC and other tissues.

 

Amino acids in skeletal proteins can be used, in a situation of prolonged starvation as an “emergency” energy store that can yield 25000 kcal.

 

Amino acids can be classified according to the metabolic fate of the carbon skeleton in:

 

-         ketogenic,

 

-         glucogenic

 

-         ketogenic and glucogenic

 

Ketogenics: Amino acids that yield acetyl CoA or acetoacetyl CoA ( e.g. they do not produce metabolites that can be converted in glucose).  

Lysine and Leucine are the only amino acids that are exclusively ketogenics.

 

Glucogenic: Amino acids whose catabolism yields to the formation of Pyruvate or Krebs Cycle metabolites, that can be converted in glucose through gluconeogenesis (Remember the pathway: pyruvate-àoxalacetate-à (P) enol pyruvate…etc.).

Glucogenic amino acids  are: Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glycine, Histidine, Methionine, Proline, Serine, and Valine

 

Glucogenic and ketogenic: Amino acids that yield some products that can become glucose and others that yields acetyl CoA or Acetoacetyl CoA.

Amino acids of this kind are Isoleucine, Phenylalanine, Tryptophan, Tyrosine and Threonine.

 

 

 

G Protein-Phospholipase C Signal System

Answer to Question about Hormones H-05:

 

(g) Ca⁺⁺, Diacylglycerol and Inositol 1,4,5 triphosphate

 

 

As was discussed in the answer to H-04, some hormones that can not penetrate the plasma membrane, interact with receptors in membrane that are linked to a G-protein. As a result of the interaction hormone-receptor, the a subunit of the G-protein binds to GTP and separates from the bg subunit. The a subunit-GTP complex activates an specific effector protein, depending on the kind of a subunit. In case the a subunit is Gas,  it activates Adenylate Cyclase, increasing the production of cAMP.

 

If the Hormone-receptor complex interacts with a Gaq/11 kind of G protein, then the activated enzyme is Phospholipase C.

 

Hormones that bind to receptors related to this Protein Gaq/11-Phospholipase C system include:

 

-Angiotensine II

 

-Catecholamines (alpha-receptors)

 

-Godatrophin Releasing Hormone GnRH)

 

-Growth Hormone Relaeasing Hormone

 

-Oxytocin

 

-Thyroid-releasing Hormone

 

-Vasopresin

 

Phospholipase C catalyze the hydrolysis of Phosphatidyl inositol 4,5 biphosphate that is forming part of the plasma membrane.

 

 

 

                                  

   

The action of the enzyme on this substrate produces IP3 (Inositol triphosphate) and diacylglycerol.

 

IP3 difuses into the cytosol and binds to its receptor in the sarcoplasmic reticulum and opens a Calcium channel

 

Diacylglycerol remains close to the membrane and, with the participation of Ca⁺⁺ released by IP3, activates Protein Kinase C, that phosphorylates other proteins, modifying its function (for the general action of Kinases, see related post)

 

 

 

       

 

Ca⁺⁺ binds to Calmodulin, Troponin C and other Ca++ binding proteins provoking activation of some enzymes, actin myosine interaction, promotes exocytosis, synthesis of NO, and other effects.

 

Recommended sites:

 

http://www3.us.elsevierhealth.com/promo/Guyton/ch74.pdf),

 

http://mcb.berkeley.edu/courses/mcb136/topic/Endocrine_Autonomic/SlideSet1/endo1.pdf

 

An excellent animation here!