Elzu's micro notes

Aim To prepare antibiotic discs economically and to determine   the resistance pattern of   antibiotics against common pathogens. Principle Antibiotics are   defined as   antimicrobial substances which inhibit the growth of pathogenic bacteria. It is widely used in treatment of many diseases. Penicillin was the first antibiotic, discovered by Alexander Fleming in1928. Antimicrobial susceptibility testing can be studied   by different methods such as disk diffusion method, dilution method, E test   method. The  disk -diffusion agar methods assess the effectiveness of  antibiotics  on a specific microorganism. Each disc is a standard size and is impregnated with a standard volume and concentration of the antibiotic. Impregnated   disc with a known concentration of an antimicrobial compound is placed on Mueller-Hinton (MH) agar which is swabbed with test organism .After incubation, t he absence of growth around the antibiotic disks indicates the respected organism is susceptible to

Protein Sorting in the cell In prokaryotes and eukaryotes, some of proteins produced are placed in different cell compartments, such as the nucleus, mitochondrion, chloroplast and lysosome. The sorting of proteins to appropriate compartments is under genetic control. The specific “signal” or “leader” sequences on the proteins direct them to the correct organelles.  In 1975, Gunther Blobel ,B. Dobberstein and colleagues found that secreted proteins and other protein sorted by the Golgi initially contain extra amino acid at the amino terminal end. This work  has led to the  signal hypothesis , which states that proteins sorted by the Golgi bind to the ER by an hydrophobic amino terminal extension to the membrane that is subsequently removed and degraded. Gunther Blobel won the noble prize for his work in physiology or medicine in 1999. The signal sequence   of a protein designed for ER consist of about 15-to-30 N-terminal amino acids. When the signal sequence is translated and expose

Translation in eukaryotes Translation process in eukaryotes also includes 3 steps which is almost similar to prokaryotic translation. The steps are: Initiation, Elongation and termination. The major difference in eukaryotic translation   are 1.       The initiator methionine is unmodified although a special initiator tRNA brings it to the ribosome. 2.       Shine Dalgarno sequences are not found in eukaryotic mRNA .In eukaryotes, AUG is embedded in Kozak sequence. Inorder to bind AUG initiation codon, 1. Eukaryotic initiator factor eIF-4F-( a multimer of eIF-4E,Cap binding protein(CBP ))binds to 5’ end of mRNA. 2. Scanning process of   initiator AUG codon, by a complex of 40S ribosomal subunit with initiator Met-tRNA and several proteins along with GTP and other   eIF along the mRNA. This process is called the scanning model for initiation. 3.Once,40S subunit binds to AUG ,60S subunit binds to it and releases all other   eIF except, eIF-4F   producing 80S initiation comp