Protein Synthesis Flashcards
Introduction Part Two
-rapid process of 20 amino acids beginning added
-turnover of cell Is fast and it required many ribosomes
-ribosomes are made from two subunits- 40s subunit and 60s subunit
This collectively forms the 80S subunit
The ribosomes consists of the three compartments: rRNA, tRNA and mRNA
The 80s subunit contains three different subunits: peptidyl binding site, exit site and aminoacyl tRNA
Protein synthesis has three different stages
Introduction Part One
- complex multistep process
- DNA encodes for the production of the amino acids
- carried out ribonucleocomplex called ribosomes
- ribosomes are made from RNA and proteins
- there are two population of ribosomes:endoplamsic reticulum and the cytosol
initiation Part One
mRNA is associated with different proteins.
EIF4 + EIF5 bind to the cap structure
Poly A binding protein- binds to the poly A tail
These initiation factors give the mRNA a circularised shape
The translation of mRNA begins with the codon AUG.
initiator tRNA (met-tRNAi) carries methionine which can start translation.
The initiator tRNA recognised by the initiation factors different nucletide sequence other aminoacyl tRNA which normally carry the methionine
Initiation tRNA methionine complex and the eukaryotic
initiation factor will bind to the small ribosome subunit.
initiation Part Two
EIF2, GTP and met- tRNA will be added to the P site.
EIF3: binds to the 40s subunit this will start initiation and prevent the 40s and 60s subunit from binding together.
The small ribosome will then bind to the the 5 end of the mRNA which will be recognised by the 5 CAP.
The small subunit will move along the mRNA in the 5 to 3 direction to find the first AUG. Through the process of scanning.
Initiation Part Three
The energy for scanning will be provided through the hydrolysis of the ATP.
Every single nucleotide which the ribosome translocates uses up one molecule of ATP.
Once the first AUG is found translation begins.
First AUG found will result in the dissociation of some transcription factors
The large ribosomal subunit will now be associated with the small ribosomal subunit.
Initiator tRNA will be leaving the A site free
When the met-tRNA recognises the start codon there is a point where there is a pause.
Elongation Part One
Charged tRNA with an approate amino acid. The aminoacyl tRNA will bind with the ATP with the help of the aminoacyl tRNA synthase.
From this reaction you will form AMP and the pyrophosphate.
This charged tRNA will be able to enter the cleft of the ribosome.
Once the charged tRNA has entered the cleft and it will now bind to the A site binds to A site with the help of elongation factor one.
Elongation Part Two
The amino acid on the P site will bind the amino acid on the A site.
You have the formation of a peptide bond helped by the enzyme peptidyl transferase.
Translocase will allow the translocation of ribosome along the RNA.
Translocation of ribosome along the RNA is energy consuming which means that EF2 and GTP hydrolysis is required.
At this point you have the occupation of the E and the P site but the A site is free.
Termination
The termination occurs when the ribosome encounters a stop codon UAG.
Instead of another amino acid binding you have the binding of a release factor.
The release factor and the stop codon will bind at the A site. This binding would require the hydrolysis of GTP.
The hydrolysis of the GTP would produce a GDP and a pyrophosphates.
The GTP will also provide the energy for the release of the release factor, tRNA and cleavage between tRNA and amino acid chain.
Finally the dissociation of the ribosomal subunits and this would release the mRNA,
Transport Introduction:
Newly synthesised proteins are transported to the rough endoplasmic reticulum where they can attach to the ribosomes, nucleus, mitochondria and peroxisomes.
Traveling to is to is determined by the SIGNAL sequences.
SIGNAL sequences are amino acids which are found at the N terminal of the protein.
SIGNAL sequences will be recognised by enzyme systems within the cell that transport the protein to the correct destination.
Transport introduction Part Two:
Route pathway when it goes to the rough endoplasmic reticulum begins at the ribosomes.
starts at the ribosomes, rough endoplasmic reticulum, smooth endoplasmic reticulum, golgi.
Golgi then three different destinations: lysosomes, secretions or travelling to the cell surface.
SRP cycle
it will follow a four step cycle.
SRP cycle explains the transport from the ribosomes to the rough endoplasmic reticulum.
Ribosomes are able to recognise the signal peptide on the signal sequence.
Knows that the protein needs to be transported to the rough endoplasmic reticulum.
Result is the binding of the SRP to the signal sequences of the ribosomes
causes translation to the paused -this means that elongation will stop at around 70 amino acids long.
pause will allow times for the secreted protein to be targeted the endoplasmic reticulum.
SRP forms a big complex: ribosomes, mRNA and the signal recognition particle
The complex will then bind to SRP receptor which can be found on the cytosolic face of the membrane and the seci 61 translocation channel.
Sec 61 translocation channel is the gateway to get from the cytoplasm to the ER lumen.
SRP complex binding to the SRP receptor will require on e molecule of GTP.
This binding will allow elongation to continue.
The complex bound in proximity to the complex to the sec 61 translocation channel.
Ribosome will bind to sec61 and the growing polypeptide will enter the lumen.
The hydrolysis of GTP molecule causes the dissociation of the SRP complex from the receptor.
Transport to the golgi
Transport of the protein from the rough endoplasmic reticulum to the Golgi apparatus.
Help of the vesicles
Single membrane compartment-involved in sorting and packaging proteins.
Four to eight stacked layers of thin flat enclosed vesicles which are called cisternae.
Golgi apparatus: made of thee networks
1. cis -close to the nucleus
2. medial structure- close to cell
3. trans- positioned closer to the cell membrane
Transport to the Golgi apparatus part two
Three different types of vesicular routes in the cell:
1. Golgi apparatus, lysosomes and then the plasma membrane
2. Plasma membrane to the lysosomes
3. Endosomes to the cell membrane
Protein which are tranported from the endoplasmic reticulum to the Golgi apparatus.
COAT proteins need to be wrapped around the vesicles
COAT proteins are parts of the COPS family proteins.
Once the transport vesicles- formed and released from endoplasmic reticulum- removal of the COAT proteins.
Removal of the COAT proteins will cause the SNARE proteins to be more visible.
Vesicular transport
Transport vesicles will have V snare on the cell surface.
V snares is called synaptobrevin (VAMP) interact with the TT snares which are on the Golgi apparatus.
V snare synaptobrevin bind with two T snares which are syntaxin one and SNAP 25.
V snare and T snares pull the vesicles tight to the membrane causing the formation of the SNARE pin.
Calcium binds with another T snare called synaptotagmin
This will stabilise the SNARE pin and this will cause a KINK in the membrane.
The kink will result in the membrane pore opening releasing proteins to the golgi apparatus.
The vesicle degraded and it is recycled again.
Mannose phosphate pathway
Proteins transported from the endoplasmic reticulum to the lysosomes through the mannose phosphate pathway.
Lysosomal hydrolase precursors delivered from the ER to the golgi apparatus.
Lysosomal enzyme will react with carbohydrate molecules which is called mannose.
Complex is phosphorlyated and p-GIcNAc added and you will now have a mannose phosphate molecule bound to the hydrolase enzyme.
Mannose phosphate signal will be identified the mannose 6 phosphate receptor and the mannose 6.
