central dogma of molecular biology

• rRna - 3rd type of RNA
• rRna is the decoding unit of the cell
• ribosomes have 2 binding sites for tRNA and mRNA , an assemblage of rRNA and protein
• tRNA has an anticodon that matches with codons on mRNA
• mRNA carries genetic information from DNA to ribosome
• reading the message : mRNA molecule attach to the ribosome, as the ribosome moves the codon is exposed one at a time, tRNA bonds w/ mRNA, ribosomes positions the molecules, tRNA brings amino acids to the site of peptide synthesis
• elongation : as the the new amino acids are brought to thr ribosome, the peptide chain will attach to the new amino acid by a peptide bond, it will continue until it reach a stop codon, a single mRNA can read repetedlty to make more copies of polypeptide, as the trna gives it amino acid, it will back to the cytoplasm to bind to its another specific amino acid
• Initiation : the leader sequence at the 5' end of mRNA will bond to the small ribosomal subunit, usually, the first mRNA codon is AUG, wich attracts a tRNA that carries methionine, methionine signifies the start of the polypeptide,the large subunit will attach to the small subunit
• the trna carrying the second amino acid will bind to the second codon, the amino acids are connected by a covalent bond called peptide bond. with the protein called elongation factors, the polypeptide grows one aminio acid at a time
• elongation halts at a stop codon
• no trna corresponds to the stop codons, only proteins called release factors bind and prompts them to release the last trna
• ribosomal subunits separates and recycled, and the new polypeptide chain is released
• protein synthesis can be speedy, a plasma cell in immune system van make 2000 antibody proteins per second. dozens of ribosomes may attach to a single mrna
• errors in protein folding : alzheimer's associated with a protein called amyloidthat forms abnormal mass in brain. mad cow disaease and other is caused by abnormal clumps of misfolded proteins called prions in nerve cells
• some proteins must altered in other ways before it becomes functional
• insulin is 51 amino acids long but it is originally 80 a.a. long proinsulin, enzymes cut proinsulin to insulin
• another modification is when polypeptide joins to form larger protein molecules. hemoglobin is consists of 4 polypeptide chains( 2 alpha and 2 beta) encoded by a separate gene
• some poisons inhibits protein synthesis, cells that can't make proteins die
• amanatin: is a toxin in a death cup mushroom that inhibits rna polymerase so the transcription will not occur
• diphtheria toxin secretes bacteria called corynebacterium diphtheriae that secretes toxins that causes respiratory illnesses
• antibiotics - binds to bacterial ribosomes
• ricin - derived from the seed of a castor bean plant that consists of 2 parts, the 1st one binds to the cell and the other one enters the cell that inhibits protein synthesis
• trichothecenes - fungi that produce toxins, interferes ribosome