Elzu's micro notes

Molecular  Chaperones are diverse group of protein molecules that  control conformational changes in native protein to make it as biologically functional protein . Main role of molecular  chaperones  Prevent protein degradation Protein folding assistance Prevent aggregation of proteins Prevent prion formation Assistance of translocation of other molecules Types of Chaperones 1.HSP(Heat shock proteins) Proteins which help to assist stressful conditions (elevated temperature, toxic chemical, radiation)in cell. Eg: Eukaryotes                                         Prokaryotes: HSP-10                                                               GroES HSP-40              ...

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...

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  ...

Wobble hypothesis This hypothesis was proposed by Francis Crick in 1965 According to this hypothesis, the complete set of 61 sense codons can be read by fewer than 61 distinct tRNAs because pairing properties of the bases in the anticodon. Specifically , the base at the 5’end of the anticodon complementary to the 3’ end of the codon is not constrained three dimensionally as the other 2 bases. This feature allows for less exact base pairing ,so that the base at 5’end of the anticodon can pair with more than one type of base at the 3’end of the codon or it can wobble. No single tRNA molecule can recognize 4 different codons .But if the tRNA molecule contains the modified purine inosine(I) at the 5’end of the anticodon ,then that tRNA can recognize 3 different codons (A,U,C) G Nucleoside at 5’ end of anticodon    can pair with U or C C Nucleoside at 5’ end of anticodon    can pair with G A Nucleoside at 5’ end of anticodon    can pair with U U ...

Protein synthesis take place on ribosomes, where the genetic message encoded in mRNA is translated .The mRNA is translated in the 5’ to3’ direction and the polypeptide is made in the N terminal to C terminal direction. Aminoacids are bought to the ribosome bound to tRNA   molecules. The correct amino acid sequence is achieved because of The binding of each   aminoacid to its own specific tRNA The binding between the codon of the mRNA and the complementary anticodon in the tRNA mRNA recognizes tRNA codon was proved by G Von Ehrenstein, B Weisblum and S Benzer.T hey concluded that specificity of codon recognition lies in the tRNA molecule not in the amino acid it carries. Adding an amino acid to tRNA The correct amino acid is attached to the tRNA by enzyme aminoacyl –tRNA synthetase.The process is called aminoacylation or charging and it produces aminoacyl tNA or charged tRNA. Amino acylation uses energy from ATP hydrolysis. Since there are20 different amino acids,...

Central dogma of molecular genetics, postulates the genetic information flows from nuclei acid to protein. Concept was put forward by H C Crick in 1958. It is a 3 step process ·         Replication ·         Transcription ·         Translation   DNA    Transcription    RNA     Translation    Protein   Translation: Genetic message coded in mRNA is translated into proteins with a specific sequence of amino acids   Ribosomes: Site of protein synthesis. First   identified by Paul Zamecnik in 1950 Ribosomes in prokaryotes Ribosomes in prokaryotes seen in cytoplasmic matrix   and also bound to plasma membrane of the cell. Ribosomes in cytoplasmic matrix produce proteins within the cell where as   ribosomes bound to plasma membrane make proteins for transport to the outside. Size –small I...