7.3 Translation [HY] Flashcards
How does mRNA transcript leave the nucleus after its created and processed?
- Nuclear Pores
Translation
- a complex process that requires mRNA, tRNA, ribosomes, amino acids, and energy in the form of GTP.
Ribosome
- composed of proteins and
rRNA. In both prokaryotes and eukaryotes, there are large and small subunits; the subunits only bind together during protein synthesis.
What are the 3 binding sites in the ribosome for tRNA?
- the A site (aminoacyl), P site (peptidyl), and E site (exit)
What is replication and the direction?
DNA → DNA = replication: new DNA synthesized in 5′ → 3′ direction
What is transcription and the direction?
DNA → RNA = transcription: new RNA synthesized in 5′ → 3′ direction (template is read 3′ → 5′)
What is translation and direction?
RNA → protein = translation: mRNA read in 5′ → 3′ direction
What’re the ribosomal subunits?
- ribosomal subunits created are the 60S and 40S subunits; these subunits join during protein synthesis to form the whole 80S ribosome.
3 stages of translation?
- initiation, elongation, and
termination
Initiation
- The small ribosomal subunit binds to the mRNA
- In prokaryotes, the small
subunit binds to the Shine–Dalgarno sequence in the 5′ untranslated region of the mRNA - In eukaryotes, the small subunit binds to the 5′ cap structure.
- The charged initiator tRNA binds to the AUG start codon through base pairing with its anticodon within the P site of the ribosome
- The large subunit then binds to the small subunit, forming the completed
initiation complex. This is assisted by initiation factors (IF) that are not permanently associated with the ribosome.
Elongation
- During elongation, the ribosome moves in the 5′ to 3′ direction along the mRNA, synthesizing the protein from its amino (N-) to carboxyl (C-) terminus.
Peptide bond
- formed as the polypeptide is passed from the tRNA in the P site to the tRNA in the A site
- requires peptidyl transferase, an enzyme that is part of the
large subunit. - GTP is used for energy during the formation of this bond
Elongation factors (EF)
- assist by locating and recruiting aminoacyl-tRNA along with GTP, while helping to remove GDP once the energy has been used.
How are secreted peptides such as hormones and digestive enzymes moved?
a signal sequence directs the ribosome to move to the endoplasmic reticulum (ER),
so that the protein can be translated directly into the lumen of the rough ER
Termination
- When any of the three stop codons moves into the A site, a protein called release factor (RF) binds to the termination codon, causing a water molecule to be added to the polypeptide chain. The addition of this water molecule allows peptidyl transferase and termination factors to hydrolyze the completed polypeptide chain from the final tRNA. The polypeptide
chain will then be released from the tRNA in the P site, and the two ribosomal subunits will dissociate.