Ribosomes and Protein Synthesis

Amino acid structure

a carboxyl group, amine group, and R group, linked to a central alpha codon

r group

a functional group that defines a particular amino acid and gives it special properties.

peptide bond

The chemical bond that forms between the carboxyl group of one amino acid and the amino group of another amino acid

ribosomal subunits

subunits of ribosomes that unite for translation, the large subunit binds the tRNAs and the small subunit binds the mRNA template

N terminus

the end of a polypeptide or protein that has a free amino group where amino acids are added

c terminus

the end of a polypeptide or protein that has a free carboxyl group

polysome

A complex formed when multiple ribosomes are translating the same mRNA into proteins.

Protein Synthesis: tRNAs

tRNAs carry an amino acids to the polysome coded for by the mRNA codon, starting with AUG. multiple tRNAs will add amino acids to growing polypeptide chains, and once a tRNA gives its amino acid, it leaves the ribosome empty

aminoacyl tRNA synthases

An enzyme that joins each amino acid to the appropriate tRNA, which hydrolyzes ATP to get a AMP molecule and 2 phosphates, which creates a high energy bond that attracts an AA to a tRNA molecule

Protein Synthesis: Initiation

the small ribosomal subunit and initiator tRNA bond to the start amino acid MET bind to the 5' cap, this complex then scans the mRNA template to find the start codon, which attaches the large ribosomal subunit forming the initiation complex

initiation complex

a complex of protein factors, mRNA, met-tRNA, and the small and large ribosomal subunit which is required to start translation

Prokaryote Protein Synthesis: Initiation

the small ribosomal subunit connected to fMET attaches to a nucleotide sequence right before the start codon called the Shine-Dalgarno sequence, which then binds to the large subunit

fMET

another way to say initiator tRNA, the modified first amino acid of prokaryotic translated proteins

large ribosomal subunit sites

areas inside the large ribosomal subunit where tRNAs and their amino acids partake in protein synthesis with the energy provided by the aminoacyl tRNA synthases

A site

where the tRNAs and their amino acids enter

P site (think polypeptide)

where amino acids are linked to other amino acids in the Polypeptide

E site (think exit)

the exit point for tRNAs without their amino acids

Protein Synthesis: Translation Elongation

once the first tRNA molecule and its amino acid MET are translated, other tRNAs begin to enter the A site with complementary anticodons and their respective amino acids, with said amino acids binding to the polypeptide chain using the bonds created by peptidyle transferase. As this occurs, the tRNAs move from the A site to the P site, and then out the E site with the energy provided by GTP hydolysis

peptidyle transferase

enzyme that forms the peptide bonds between amino acids during translation

GTP hydrolysis

water being added to GTP ( guanosin triphosphate) to form GDP and a phosphate, releasing the energy tRNA needs to move within the ribosome

Protein Synthesis: Translation Termination

Once a stop codon reaches the P site, a release factor recognizes it and starts the termination process, which changes the shape of peptidyle transferase(turns it to water via GTP hydrolisis) so that it cannot make more peptide bonds and separates the small and large ribosomal subunits

Protein Synthesis: Protein Folding

signal sequences provide the instruction for where the newly made protein goes, more often than not to the cisterna of the Rough ER for folding with assitance of chaperones

chaperones

Proteins that assist in protein folding during posttranslational processing

Protein Folding steps

primary(linear chain of amino acids), secondary(alpha helix or beta pleated sheet structure), tertiary(3D shape), quaternary(2 alpha helixes or 2 beta pleated sheets)

Protein Synthesis: Rough ER

while in the cytosol, a signal recognition particle binds to the signal peptide on the end of the polypeptide and directs said polypeptide to a pore in Rough ER where translation resumes, until a rough ER enzyme cleaves the polypeptide into the cisterna, where chaperones fold the protein