Monday, September 19, 2016

Cartoon about lipids and carbohydrates


Thursday, September 15, 2016

Glycogenin

The glycogenin is a protein whose main function is to be the initiator molecule of glycogen synthesis (glycogenesis), a process that allows the storage of glucose residues in the form of a polysaccharide. Glucose residues are added to glycogenin through α-1,4 bonds. The first step in the glycogen synthesis is indeed the synthesis of this protein. Each glycogen molecule is linked to a glycogenin by a glycosidic linkage which involves the first glucose residue of the chain and a tyrosine residue of glycogenin. The glycogenin designation stems from the fact that this protein is involved in the genesis of glycogen, by functioning as a primer in the formation of a new glycogen molecule.The glycogenin through its glucosyltransferase activity, binds covalently to itself a glucose molecule (from UDP-glucose - the active form of glucose). Then, the glycogenin forms a compact complex with glycogen synthase, the enzyme responsible for glycogen synthesis. After the addition of up to 7 more glucose residues (from UDP-glucose) mediated again by the activity of glucosyltransferase of glycogenin. Finally, glycogen synthase and branching enzyme enter in action, being glycogenin covalently linked to the unique reducing end of the glycogen molecule.
In humans there are two isoforms of glycogenin which can be expressed as glycogenin-1, having a molecular weight of 37 kD, and encoded by the GYG gene that is expressed mainly in muscle, or as glycogenin-2 having a molecular weight of 66 kDae encoded by GYG2 gene which is expressed mainly in the liver, cardiac muscle and other types of tissues except skeletal muscle

Disability glycogenin-1 (GYG1) - Mutation of the gene GYG1
A glycogenin-1 deficiency was detected in its gene, GYG1, which revealed a nonsense mutation in one allele and a missense mutation in another allele. A missense mutation results from inactivation of the autoglycosilation of glycogenin-1, which is required for the initiation of glycogen synthesis in muscle. The glycogenin-1 autoglycosilation occurs at Tyr195 by the action of glucose-1-O-tyrosine. A missense mutation of this residue results in inactivation of the autoglycosilation. However, it was also demonstrated that missense mutations affecting other residues of glycogenin 1-cause problems on autoglycosilation.
Phenotypic characteristics of skeletal muscle in a patient with this disorder are muscle glycogen depletion, mitochondrial proliferation and marked predominance of slow twitch amd oxidized muscle fibers. Mutations in glycogenin-1 gene GYG1 are also causes of cardiomyopathy and arrhythmia.

Text written by:
Daniela Marinheiro

Carla Marty

Maria Rocha

Marta Rodrigues

Rita Osório
.

Tuesday, September 6, 2016

Enolase

Enolase is an enzyme, more particularly, an active metalloenzyme. This enzyme belongs to the family of lyases, the hydro-lyases, breaking the carbon-oxygen bonds, and is present in all tissues and organisms involved in glycolysis or fermentation. The optimal pH of this enzyme is 6.5 in humans.Its main function is to intervene in the 9th step of glycolysis (the penultimate step in this metabolic pathway), a step in which occurs the dehydration of 2-phosphoglycerate (2-PG) in phosphoenolpyruvate (PEP), a product that will be used in the next and final step for the production of energy (ATP).
Enolase has three different isoforms: the ENO1 or alpha-enolase (in muscle tissue); ENO2 or gamma-enolase or neuro specific enolase (in neurons); ENO3 or beta-enolase (in skeletal muscle cells). Enolase has a molecular weight of about 100000 Daltons (depending on the isoform). In humans, the α-enolase has two antiparallel subunits, which have two domains that establish hydrophobic interactions. The subunits interact via salt bridges, involving arginine and glutamate.
The specific enolase to neurons is released in a wide variety of diseases, such as multiple sclerosis or stroke, or myocardial infarction.
In several medical experiments, it was employed enolase concentrations in samples in an attempt to diagnose certain conditions and its severity. Several studies demonstrated that different levels of enolase may also be associated with tumor growth or with the occurrence of myocardial infarction or stroke, so it was inferred that the levels of enolase serve as an indicative of the prognostic evaluation of victims of cardiac arrest.
Enolase inhibitors have been utilized in health care for the treatment and prevention various diseases, such as anti-trypanosome drugs and more recently as anticancer agents. Enolase can be inhibited by fluoride ion (F-). The fluoride forms a complex with magnesium and phosphate, which binds to the active center of the enzyme rather than the substrate 2-PG, preventing the conversion of 2-PG into PEP, decreasing the production of PEP and, consequently, ATP.
Intake of fluoride-containing water inhibits the catalytic activity of enolase of bacteria present in oral cavity (highly dependent on glycolysis due to the anaerobic environment), interrupting glycolysis and, thus, bacterial fermentation (decreased acid production), preventing the formation of dental caries.


Text written by:
Inês Carvalho
Junjie Lin
Maria Alves
Susana Pinto
.

Sunday, August 28, 2016

Carbohydrates (main functions)



Carbohydrates play a variety of functions in nature. Because of this, they are indispensable elements for living beings. The main functions of carbohydrates are:

- Metabolic fuel – various monosaccharides may be used as a source of chemical energy through its catabolism. Logically, the main carbohydrate used as metabolic fuel is glucose. However, there are several other monosaccharides that can also be used as metabolic fuel (more information on this subject here), such as fructose, mannose or galactose;


 
- Nucleotide components– this function is performed by two different pentose, ribose and deoxyribose. Actually, only one of these carbohydrates is a “pure” monosaccharide (ribose), the other is a derivative of monosaccharide (deoxyribose). Soon, I will write a post about this... Both ribose and deoxyribose are pentoses, that means, they are monosaccharides with 5 carbons. Ribose enters in the composition of ribonucleotides (and consequently RNA) while deoxyribose takes part of the composition of deoxyribonucleotides (and hence the DNA);


- Metabolic fuel reserve - some polysaccharides play the function of metabolic fuel reserve. In this context, there are two molecules that deserve a highlight: starch and glycogen. Both are composed of a single type of monosaccharide, glucose. Starch is the reserve polysaccharide of glucose in plant cells, while glycogen is the reserve polysaccharide in animal cells;

 





- Structural function - some polysaccharides play structural functions, including cellulose and peptidoglycan. The first is the main component of cell walls of plant cells, while the latter is the main component of the cell wall of prokaryotes;

 





- Protection - some polysaccharides play a protective function, such as chitin, which is the main component of the exoskeleton of insects;









- Lubrication and hydration - due to their rich composition in hydrophilic functional groups, carbohydrates have the ability to interact with a large number of water molecules. Because of this feature, various polysaccharides form viscous and highly hydrated mixtures. These polysaccharides are referred to as glycosaminoglycans and are essential for the skin, joints, etc.

 

- Recognition and cell adhesion - there are several molecules involved in cell adhesion and recognition. These molecules are found on the cell surface and have carbohydrate components, being called glycoproteins or glycolipids.
.