1. Translation
Translation is the process of building a protein from the mRNA transcript. The protein is built as transfer RNA (tRNA) bring amino acids (AA), one at a time, to the ribosomal unit holding the mRNA.

2. tRNA
3D structure has an attachment site for an AA on one side and the anticodon on the other
anticodon is the complimentary sequence to the mRNA codon
if the mRNA is AAA the tRNA is UUU the AA attached is phe (phenylalanine)
is "L" shaped with a 3' attachment site for an AA and a loop on the other side that carries the anticodon
each tRNA is specific for the AA it attaches to
45 different versions in the cytoplasm at all times that correspond to the different AAs
should be 61 for the different codons
a few can bind to multiple codons due to a loosely attached 3' site - wobble

3. tRNA are joined to the correct AA by the enzyme aminoacyl-tRNA synthetase
each synthetase fits ONLY the tRNA and AA it is specific for
20 different versions in the cytoplasm at all times
catalyzes the attachment of the AA to the tRNA with the use of ATP
the released tRNA/AA complex is called an activated tRNA or aminoacyl tRNA
the activated tRNA delivers its AA to the growing polypeptide chain

4. Ribosomes
Ribosomes facilitate the binding of the tRNA to the mRNA by aligning the active sites and holding them in place.
Structure
ribosomes are made of mostly ribosomal RNA (rRNA) that is made from DNA that resides in the nucleolus
consists of a large unit and a small unit
each is made of rRNA and proteins imported from the cytoplasm
once assembled the 2 units are exported to the cytoplasm via membrane pores in the nuclear envelope
has 3 binding sites
A - site binds next tRNA with AA atached
P - site binds the tRNA whose AA is being attached to the growing chain
E - site binds the leaving tRNA minus the AA (already attached to the growing chain)

5. Initiation of translation
Small ribosomal subunit binds with the mRNA and searches for the start codon (AUG)
initiation tRNA (Met) binds to the P-site of the small unit
union of the mRNA & tRNA establishing the reading frame
large unit attaches after the union is made completing the initiation complex - translation begins
proteins called initiation factors bring the units together
energy from GTP is used in the formation of the unit

6. Elongation of Growing Polypeptide
requires several proteins called elongation factors
3 GTP are required for each translocation steps (APE)
mRNA moves from 5' to 3'
AAs are added N-terminus to C-terminus with new AAs added to the carboxyl end
elongation ends when a stop is reached - UAG, UAA, UGA
do not code for an AA but binds to a release factor that binds to the adjacent A-site
the release factor binds a water molecule to the end of the polypeptide hydrolyzing the chain
the ribosomal unit comes apart
may be translated by many ribosomes at the same time - ployribosomal unit

7. Post Translation Modifications
proteins begin to spontaneously fold as they are synthesized
some will require additional proteins (chaperonins)
free ribosomes make proteins destined for the cytosol
bound ribosomes make proteins for the membrane systems of the cell
(Nuc Env, ER, Golgi, Lysosomes, Vacuoles, Plasma membrane) as well as secreted proteins (Insulin)
ALL start as free ribosomes and bind to the ER if a signal peptide is present
about 20 peptides that form the signal-recognition particle (SRP) which attaches to the ER
after attachment the SRP is removed by enzymes and translation of the membrane protein continues
each membrane system has its own unique SRP - much like a zip code