Amino Acid Becoming A Membrane Transporter free essay sample

Biology Oxford Presentation A. Entering the epithelia cell of the small intestine, until being loaded onto the proper tRNA. Amino acid present in the lumen of the small intestine The goal is to cross through the epithelial cell membrane to enter into the epithelial cell’s cytoplasm – its charged cuz of side chains To get through the membrane the amino acid must cross the Simple columnar epithelial cells lining the apical surface of the small intestinal tract. These cells are impermeable to any harmful bacteria that may be ingested by the body, but permeable to necessary ions. Absorption of amino acids occurs through a process known as facilitated diffusion through membrane transporters (carrier protein) by means of active transport OR The type of transporter which an animo acids is transported through the epithelial membrane through depends on the R-group attacked to the particular amino acid (structure and combosition) These transporters bind amino acids only once they have bound sodium ions – this is known as coupled transport This coupled transport is through a symport transporter protein which works by transporting the amino acid across the cell membrane only in the presence of a sodium ion (sodium is co-transported) Once the amino acid is released from the transporter protein into the cytoplasm of the epithelial cell the amino acids collect in pools until they are pick-up by tRNA that is floating throughout the cytoplasm The enzyme aminoacyl tRNA synthetase for that specific amino acid binds ATP and the amoni acid to the active site ATP is hydrolyzed inot AMP which then minds to the amino acid in the active site The tRNA for the specific amino acid comes into contact with the specific aminoacyl tRNA synthetase to collect the activated amino acid The amino acid uses the energy from the bonded AMP to transfer to the tRNA B. Initiation of translation, until incorporated into a folded protein Once the mature mRNA reaches the cytoplasm it will bind to the small subunit of the ribosome (ribosomes are organelles within the cell either free floating or attached to the ER, and are made of rRNA and proteins) Translation Initiation: Then the first tRNA lines up its anit-codon sequence to the corresponding codon sequence on the mRNA, which are specific to each amino acid, at the ‘p-site’ on the ribosome (the initiating tRNA will most likely be carrying the amino acid methionine) Initiation of translation is completed with the large subunit of the ribosome binds to the small unit Elongation: The next tRNA (with the correct aintcodon and carrying a specific amino acid) moves in a parks at the A-site A peptide bond forms between the two amino acids   The ribosome moves down the mRNA by one reading frame, which puts the first amino acid in the E-site (where the tRNA will exit, and the second amino acid moves into the P-site Now another tRNA can move into the empty A-site of the ribosome, and a new peptide bond forms between the new amino acid on the tRNA in the A-site, there by adding to the amino acid chain The ribosome moves over one frame, one amino acid exits, another enters, and another amino acid is added to the chain (the cycle continues) until I reaches a ‘stop’ When the ribosome reaches a reading frame that reads for the ‘stop’ sequence (one of three termination codons) which then signals to the ribosome that it is finished reading the mRNA strand Termination: The large and small subunits of the ribosome disengage from the mRNA strand, and release the amino acid sequence that will then go onto form its proper shape The folding of the protein has been taking place turning translation, before termination Folding takes place as a result of the hydrogen bonding and chemical interactions of the R-groups attached to the amino acids – this folding c=occurs spontaneously (no energy required) Molecular chaperones may assist in the protein folding (some chaperones bind to the ribosome near the ‘tunnel’ where growing peptide exits As a result of the H-bonding, and chemical iteraction of the R-groups – aided by chaperones; the protein will fold into its correct specific shape C. Post translation modifications, until installation on the plasma membrane All protein syntheses takes place on free ribosomes Post translation modifications are chemical modifications of the protein structure (of the amino acids) which generally involves the addition of functional groups/ small molecules which increases protein diversity Some types of post-translational modifications Glycosylation – addition of carbohydrate Lipoylation addition of lipid groups Phosphorylation addition of phosphate groups Ubiquitination – addition of ubiquitin Methylation – addition of methyl group Acetylation- addition of acetyl group Proteolysis- cleavage of peptide bonds †¦Ã¢â‚¬ ¦over 30 different types of PTMs Once the protein has been modified the signal sequence, a stretch of amino acids, will direct the protein to particular organelles All protein transport requires energy The protein contains a signal sequence which makes the protein bound for the ER The signal recognition particle on the signal sequence binds to SRP receptor in the ER membrane- the SRP is displaced and recycled The soluble protein travels through the translocation channel into the ER lumen where it is covalently modified to stabilize the protein (disulfide bonds), leaving the signal sequence in the ER membrane The protein is kept in the ER until it is properly folded and helps to direct it to the proper organelle The properly folded protein the then packed in a budding transport vesicle and sent to the golgi apparatus The golgi apparatus accepts the protein on the cis-golgi network (modifications and removal of the CHO groups from ER and addition of new ones) and and is then sent through the apparatus until it reaches the trans golgi network- where is is packaged and secreted from the organelle The trans golgi network secrets the secretary vesicle (membrane bound vesicle filled with protein) through constructive secretion The  vesicle travels to the cell membrane, and through unregulated membrane fusion, fusses to become apart of the plasma membrane, bringing with it the newly synthesized proteins that become apart of the plasma membrane