Cell Biology

               


                                                           Gaucher disease

The most common lysomal storage disease (LSD) in the world which affects all ethnic groups. It is present in approximately 1 in 20,000 live births.

It is an autosomal recessive disorder, both parents must carry the Gaucher gene in order to pass it on to their children.

Gaucher disease, also known as glucocerebrosidase deficiency, occurs when a lipid called glucosylceramide accumulates in the bone marrow, lungs, spleen, liver and sometimes the brain. Gaucher disease is caused by mutations in a gene called GBA. Changes in the GBA gene cause low levels of glucocerebrosidase.

Despite the fact that the disease consists of a phenotype, with varying degrees of severity, it has been sub-divided in three subtypes according to the presence or absence of neurological involvement. Depending on the type, Gaucher disease symptoms can include fatigue, anemia, easy bruising and bleeding, severe bone pain and easily broken bones, distended stomach due to an enlarged spleen and more.

Treatment:

Enzyme replacement therapy 

Substrate replacement therapy

 Bone Marrow Transplant

Microbiology

 
                                                Nuclear waste eating bacteria

                                                   Deinococcus radiodurans

Extremophilic bacterium, most radition-resistant organism known.

It can survive in acid, dehydration, vacuum and cold condition: polyextremophile

It has been listed as the world's toughest bacterium in the Guinness book of world records.

D. radiodurans is large, spherical bacterium. Four cells stick together, forming a tetrad.

Colonies are smooth, convex, and pink to red in color. The cells stain is Gram-Positive.

D. radiodurans does not form endospore and is nonmotile. It is an obligate aerobic chemoorganoheterotroph. It uses oxygen to make energy from organic compounds in its environment. It is often found in habitats rich in organic materials, such as soil, feces, meat, or sewage, but has also been isolated from dried foods, room dust, medical instruments and textiles.

It is extremely resistant to ionizing radiation, desiccation, oxidizing and electrophilic agents.

Deinococcus make its resistance to radiation by having multiple copies of its genome and rapid DNA repair mechanisms. It usually repairs breaks in its chromosomes within 12–24 hours through a 2-step process. First, D. radiodurans reconnects some chromosome fragments through a process called single-stranded annealing. In the second step, multiple proteins mend double-strand breaks through homologous recombination. This process does not introduce any more mutations than a normal round of replication would.

Scanning electron microscopy analysis has shown that DNA in D. radiodurans is organized into tightly packed toroids, which may facilitate DNA repair.

D. radiodurans is capable of genetic transformation, a process by which DNA derived from one cell can be taken up by another cell and integrated into the recipient genome by homologous recombination. When DNA damages (e.g. pyrimidine dimers) are introduced into donor DNA by UV irradiation, the recipient cells efficiently repair the damages in the transforming DNA as they do in cellular DNA when the cells themselves are irradiated.

           

Microbiology

               Pharyngitis

Pharyngitis is inflammation of the pharynx in the back of the throat. This can cause a sore throat, as well as scratchiness in the throat and difficulty swallowing.

Viruses are the most common cause of sore throats, but some sore throats are caused by bacterial infections.

Viral Infection

Pharyngitis is most commonly caused by viral infections such as the common cold, influenza, or mononucleosis. Viral infections do not respond to antibiotics, and treatment is only necessary to help relieve symptoms.

Bacterial Infection

Less commonly, pharyngitis is caused by a bacterial infection. Bacterial infections do require antibiotics. The most common bacterial infection of the throat is strep throat, which is caused by streptococcus A. Rare causes of bacterial pharyngitis include gonorrhea, chlamydia, and corynebacterium.

Symptoms :

sneezing
runny nose
headache
cough
fatigue
body aches
chills
fever

Cell Biology

                               HAT Coactivator

A coactivator is a protein that increases gene expression by binding to an activator or transcription factor which contains a DNA binding domain. The coactivator is unable to bind DNA by itself.

The coactivator can enhance transcription initiation by stabilizing the formation of the RNA polymerase holoenzyme enabling faster clearance of the promoter. Coactivators also control elongation, RNA splicing, and termination and degradation of the coactivator-activator complex.

Some coactivators possess intrinsic histone acetyltransferase (HAT) activity, which acetylates histones and causes chromatin to relax in a limited region allowing increased access to the DNA. CBP and p300 are examples of coactivators with HAT activity. Coactivators work in high molecular weight complexes of 6-10 coactivator and coactivator-associated proteins.

Histone deacetylase 2 

Histone deacetylase 2 is an enzyme that in humans is encoded by the HDAC2 gene. This gene product belongs to the Histone deacetylase family. Histone deacetylases act via the formation of large multiprotein complexes and are responsible for the deacetylation of lysine residues on the N-terminal region of the core histones (H2A, H2B, H3 and H4). This protein also forms transcriptional repressor complexes by associating with many different proteins, including YY1, a mammalian zinc-finger transcription factor. Thus it plays an important role in transcriptional regulation, cell cycle progression and developmental events.

RNA-induced transcriptional silencing (RITS)

RNA-induced transcriptional silencing (RITS) is a form of RNA interference by which short RNA molecule such as a small interfering RNA (siRNA) trigger the downregulation of transcription of a particular gene or genomic region. This is usually accomplished by posttranslational modification of histon tails (methylation of lysine 9 of histone H3) which target the genomic region for heterochromatin formation. The protein complex that binds to siRNAs and interacts with the methylated lysine 9 residue of histones H3 is the RITS complex.

http://en.wikipedia.org/wiki/Histone_acetylation_and_deacetylation

http://archives.focus.hms.harvard.edu/2004/Feb20_2004/cell_biology.html

Cell Biology

                                                  Double stranded RNA 

                 Double stranded ribonucleic acid (RNA) is a unique form of RNA that appears with two complementary strands, instead of a single strand that is more common for this genetic material. RNA plays an important role in living organisms.

               Double stranded RNA (dsRNA), usually shows up in viruses and is somewhat unusual. In viruses, it is a unique characteristic, and only a small number of viral families exhibit this trait.

                 Single stranded forms can have a very complex structure because they fold on each other and create elaborate three dimensional forms. Double stranded RNA can become even more complex, as the two chains of genetic material will also fold and twist to accomplish different functions.

               Imaging RNA is challenging because of the extremely small size. Very sensitive and powerful imaging systems are necessary to see RNA in a lab setting.

              One the most important function of double stranded RNA is interference or silencing. The strands can change the way a gene expresses or turn it off altogether. For dsRNA viruses, this confers a distinct advantage. The virus can enter a cell and turn genes off to protect itself, and hijack the cell to produce more copies of the virus. Viruses in this group can be difficult to treat, as they may become a moving target in the body and can fight the medications a doctor might prescribe to treat them.

          Also,Double-stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates.

http://genesdev.cshlp.org/content/13/2/139.full