Translation Protein Biosynthesis Central Dogma DNA transcription RNA

Translation Protein Biosynthesis

Central Dogma DNA transcription RNA translation protein

m. RNAs are exported for translation ¡ Through nuclear pore complex l Recognizes and transports ONLY completed m. RNA

Translation ¡ ¡ Process by which the sequence of nucleotides in an m. RNA directs the incorporation of amino acids into a protein Necessary Components for Translation l l l ¡ m. RNA t. RNAs covalently linked to amino acids Ribosome Three phases of Translation l l l Initiation Elongation Termination

The m. RNA strand is “read” and amino acids are linked together to make a protein by the ribosome

m. RNA Carries the genetic information from the chromosomes to the ribosomes ¡ How is the language of nucleic acid sequences translated into the amino acid language of proteins? ¡ m. RNA is decoded in sets of three nucleotides = codons ¡

Genetic Code ¡ ¡ ¡ Each codon specifies either an amino acid or stop signal to translation There are only 20 amino acids and there are 64 possible codons The genetic code is degenerate - i. e. there are "synonyms" (multiple codons) for some amino acids Three codons (UAG, UGA, and UAA) encode translation "stop" signals rather than amino acids m. RNA must be read in the correct reading frame to be decoded into the protein

Redundancy or degenerate coding Reference page 367

Amino acids ¡ ¡ ¡ Organic molecule containing both an amino group and a carboxyl group Building blocks of proteins Are added to the C-terminal end of a growing polypeptide chain by the formation of a peptide bond Peptide bonds – between the carboxyl group at the end of growing chain and a free amino group of incoming amino acid Proteins are synthesized from its Nterminus to its C-terminus

t. RNA ¡ ¡ Adapter molecule that mediates recognition of the codon sequence in m. RNA and allows its translation into the appropriate amino acid. ~ 80 nucleotides long Folds into 3 D structure It has sites for amino-acid attachment and codon recognition l l The codon recognition is different for each t. RNA and is determined by the anticodon region, which contains the complementary bases to the ones encountered on the m. RNA. Each t. RNA molecule binds only one type of amino acid, but because the genetic code is degenerate, more than one codon exists for each amino acid.

Ribosomes ¡ ¡ ¡ Small and Large subunits The site of translation Helps to maintain the correct reading frame and to ensure accuracy Complex catalytic machine made up of 50 different proteins and several RNA molecules (r. RNAs) Produced in nucleolus Millions exist in cell

t. RNA structure t. RNA Molecule

Aminoacyl t. RNA Synthetase

In Eukaryotes Unique synthetase for each amino acid ¡ Proper Amino Acid by affinity or fit

Corrected by Hydrolytic editing

The Ribosome m. RNA binding • two subunits, a large and a small • the m. RNA binds to the small subunit • there are three sites of activity and t. RNA binding within the large subunit E P A

How do Ribosomes work? Via 4 binding sites for RNA molecules

The ribosome attaches to the RNA and scans for AUG, the start codon The ribosome reads the m. RNA three nucleotides at a time Each group of three nucleotides is a single codon Each codon specifies an particular amino acid codon C G codon A U C A A U G C G codon A U C A A codon U A C Start codon TRANSLATION INITIATION

Initiation Translation begins with the codon AUG ¡ A special t. RNA is required to initiate translation ¡ Initiator t. RNA always carries the amino acid methionine ¡ Initiator t. RNA is loaded onto the small subunit of the ribosome with the aid of additional proteins (e. IFs) which are attached to GTPs ¡

Initiation, cont. ¡ ¡ ¡ Initiator t. RNA binds small ribosomal subunit Small subunit then binds to 5’ end of an m. RNA molecule (recognized by 5’ cap) The small subunit then moves along m. RNA (5’-3’) searching for the first AUG e. IF 2 hydrolyzes GTP to GDP and detaches Large Subunit then assembles and elongation can begin Bacteria use Shine-Dalgarno sequences to initiate translation at any point on the m. RNA.

Shine Dalgarno sequence Ribosome docking sequences ¡ Upstream of AUG consensus sequence

Once the ribosome recognizes the start codon, protein synthesis begins The ribosome promotes a chemical reaction to occur that joins two amino acids with a peptide bond ¡ Amino acids are transferred to the ribosomes by t. RNA molecules ¡ t. RNAs have an anticodon on one end an amino acid on the other ¡ The anticodon is a sequence of three nucleotides that complement a codon ¡

Cont. ¡ ¡ ¡ The anticodon determines which amino acid it carries to the ribosome EF-Tu (EF-1) helps the fidelity of the process. Each of the twenty amino acids pairs up with between 1 and 4 anticodons The process continues, the ribosome moves along the m. RNA to the next codon with the help of EF-G (EF-2) A new t. RNA recognizes the next codon.

• This continues until the ribosome reaches a STOP codon, which indicates the end of the gene • The ribosome & last t. RNA fall off the m. RNA & the amino acid chain is complete! U C A G U A A U G U C A G C A A G A C Anti-codon t. RNA Amino acid Met TRANSLATION ELONGATION

Elongation

Termination One of the three STOP codons mark the end of translation ¡ The stop codons are recognized by proteins known as release factors that do not specify any amino acids ¡ The release factor triggers an addition of water to the end of the polypeptide chain the release of the new protein. ¡

Protein Folding Begins while Protein is still being synthesized ¡ Guided by and made more efficient by molecular chaperones ¡

Every protein has a unique order of amino acids The amino acid chain folds up into a 3 -dimensional structure dictated by the order of the amino acids. This unique structure gives the protein its unique function and allows it to do its work

Proteins have many functions

Protein example: Antibiotics Some antibiotics are peptides, others glycopeptides, others are amino acid derivatives ¡ Inhibitors of prokaryotic translation, allowing for discrimination between prokaryotic and eukaryotic cells ¡ Examples: Tetracycline, Streptomycin, Chloramphenicol, Erythromycin ¡