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 in...

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 sequ...

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...

  Pulsed Electric Fields   Pulsed electric fields PEF is a non-thermal method of food preservation that uses short pulses of electricity for microbial inactivation and causes minimal damaging effect on food qualities. PEF technology aims to offer consumers high-quality foods. High Intensity Pulsed Electric Field (PEF) Processing involves the application of pulses of high voltage (typically 20-80 kV/cm) to foods placed between 2 electrodes . PEF may be applied in the form of exponentially decaying, square wave, bipolar, or oscillatory pulses and at ambient, sub-ambient, or slightly above ambient temperature for less than 1s. Energy loss due to heating of foods is minimized, reducing the detrimental changes of the sensory and physical properties of foods. PEF treatments showed effects on the microbial inactivation in milk, milk products, egg products, juice and other liquid foods Some important aspects in pulsed electric field technology are the generation of high e...

The three basic stages of protein synthesis are initiation, elongation, termination. These process is almost similar in prokaryotes and eukaryotes. Initiation in prokaryotes This involves mRNA molecule, a ribosome, a specific initiator tRNA, Initiation factors(proteins) GTP and magnesium ions. Steps involved: ·         Binding of 30Ssmall ribosomal unit to the region of the mRNA with AUG initiation codon. Actually it binds to a sequence upstream of AUG which is known as Ribosome binding site(RBS). Most of RBS are 8 to 12 nucleotides upstream from initiation codon.   This is a purine rich region almost similar to AGGAG and complementary to a pyrimidine rich region (UCCUCC) at 3’ end of 16SrRNA. RBS   was evident from work of John Shine and Lynn Dalgarno.   So this region is also known as Shine- Dalgarno sequence . Mutation occur to Shine- Dalgarno sequence or sequence complementary to it, mRNA translation will be abolished. ·   ...

Characteristics of Genetic code Triplet code A single base cannot be codes because there are 20aminoacids and only 4 bases. Pairs of bases also cannot serve   as codons because there are only   4 2 = 16 possible pairs   of 4 bases .Triplets of bases are possible because there are 4 3   =   64. triplets which is more than adequate . Ø   Triplet code is minimum required to code for 20 amino acid . There are certain trends for patters of genetic codes . Ø   Aspartic acid codons are similar ( GAU , GAC ) to   glutamic acid codons(GAA,GAG) the difference only exhibited in the third base . Ø   Codes for aromatic acids phenylalanine ( UUU , UU C ) and tyrosine (UAU,UAC) and tryptophan UGG    all begins with uracil First two bases are assigned to 5 amino acids GC –Alanine GG- Glycine CC-Proline AC-Threonine GU- Valine All codons with A in the second position specify the changed amino acid except arginine. All t...

GENITIC CODE How do nucleotides in mRNA  molecules specify the AA the segment in proteins ? With 4 different nucleoids ( A , C G , U ) a three letter code generate 64 possible codes. Genetic code : collections of basic sequences that respond to each  amino acid and stop signals  for translate . 1960- Francis Crick , Leslie Barnett , Sidney Berner , Watts Tobin There are several ways in which a codes could be read from a mRNA  molecule . Two most important ways are : Ø   Overlapping codes Ø   Non overlapping codes   In overlapping model Each base serves as  first base of some codon . After the first amino acid  in a protein is coded the next two and for that matters the remaining amino acids in the protein are particularly pre determined . Non overlapping model Mutation allow change in one base single mutagenic base change could after as many as 3 amino acids .  If mRNA  strand  ...