Question

1.

A) Nitrogen metabolism brings together a lot of different chemical entities within the many pathways covered in order to generate the chemical transformations that are needed. Please list 5 chemical entities and the general type of chemical transformation(s) they are needed for.

B)

Hormones are chemically diverse. Why is it that hormones that bind to a nuclear receptor can cross the cell membrane whereas other hormones require a cellular protein to pass the signal to the the interior of the cell?

C) List 2 peptide/protein hormones and 2 non-peptide hormones and indicate if any of them are recognized by nuclear receptors. What do they signal?

Answer 1

A) Amino acids are oeganic compounds, having aminom gropu (-NH2) and carboxylic group (-COOH) attached to the same carbon i.e., the -carbon. Nitrogen is the constituent part of the amino acid. The chain of amino acid forms up the polypeptide chain or proteins. And proteins form up the major metabolism activities of the body. Nitrogen metabolism or urea cycle lead to production of important nitrogen constitutes.

1) Alanine - It is a free amino acid which is required during translation process for synthesis of different proteins.

2) Glutamate - It act as in neurotransmitter pathways inside the brain.

3) Glutamine - It is also a free amino acid used up in translation for protein synthesis, lipid systhesis and energy production.

4) NADPH + H+ - Produced during nitrogen metabolism is used as electron donor in a number of pathway. It is used up in ETS for the generation of energy.

5) Oxaloacetate - It is used in the pathways of glyconeogenesis.

B) and C)

The hormones which interact with the membrane-bound receptors normally do not enter the target cell but generate second messengers. Peptide, polypeptide, protein hormones and catecholamines act through this mechanisms. Example,

1) Growth hormone which regulates the growth of the body by promoting protein anabolism, intestinal absorption of calcium, conservation of glucose, growth of long bones etc.

2) Insulin which regulates the glucose homeostatis by acting mainly on adipocyctes, hepatocyctes and muscle cells and enhances cellular uptake and utilization of glucose.

The hormones that cross the plasma membrane and hence they move inside the target cell without any difficulty. After entering the cells i.e., the cytoplasm they attach with their specific intracellular receptors. Steroid hormones and iodothyronines come in this category. There main receptors are usually on the nucleus or chromosomes because they regulate the gene expression or chromosome function. Example,

1) Estrogen which is required during the puberty for full growth, development and function of female secondary sexual organs.

2) Testosterone which helps in the development and maintance of male sexual characteristics such as beard, moustache and low-pitch voice.

Some hormones cross the plasma membrane and will some don't because the plasma membrane is a phospholipid bi-layer and only allow the entry of fat or lipid soluble compounds through it. Due to which protein hormone find it difficult to cross the plasma membrane while steriod hormones are lipid soluble which are able to cross the plasma membrane.

Mechanisms of action of peptide hormonesMechanisms of action of steroid hormones