Intracellular Processes Flashcards
What are intracellular processes?
Processes that take place within a cell.
Each cellular process involves 1000s of chemical reaction however many are incompatible.
What are the two major strategies to segregate molecules for correct chemical reactions in the cell?
- Multicomponent complexes
2. Compartmentalisation into membrane-bound organelles
What is an organelle?
A cellular structure (subunit) that performs a specific function in a cell.
what do the specific proteins in the membrane of an organelle require?
- need to be replenished and maintained
- transferred from cytosol (where they are made) to the compartment where they are used (organelle)
What is protein sorting?
proteins are transferred from cytosol (where they are made) to the compartment where they are used (organelle)
What are the three steps to proteins getting to the right place in the cell?
- proteins need to be synthesised
- proteins are dispatched to different locations in the cell
- Once at correct address proteins enter the organelle
How are proteins synthesised?
- Process starts in the Cytosol (on Ribosomes = multicomponent complex of RNA and proteins)
How are proteins sent to different locations in the cell?
Done according to the specific ‘address labels’ contained in their amino acid sequence.
What are the stages of protein synthesis: translation?
Translation takes place at the ribosomes.
Ribosome = proteins + ribsoomal RNA and two subunits.
Ribosomes = 80S
The TRNA attaches to the MRNA creating a amino acid chain and eventually becoming polypeptide (protein)
Why are ribosomes the main target for antibiotic of a bacterial cell?
Because the Ribosome is whre protein synthesis takes place and therefore it prevents the polypeptide chain elongating and
spreading.
what are the 3 mechanisms of proteins getting into organelles?
- Nuclear pores - selective gates for nuclear proteins
- Protein translocators - for proteins moving from cytosol into ER, mitochondria, peroxisomes
- Transport vesicles - for proteins moving from ER onwards.
Why is it a challenge for proteins to get into organelles?
Hydrophilic (water-loving) proteins need to get across the hydrophobic (water-hating membrane) of organelle
What is the final destination of DNA polymerase?
Nucleus
What is the final destination of Epidermal growth factor?
Extracellular
What is the final destination of Keratin?
Cytosol
What is the final destination of melanin?
Melanosomes
What is the difference between smooth and rough ER?
Rough has ribosomes
How do ribosomes know to go to the ER?
The signal peptide on the protein being made.
What is a signal peptide?
A specific sequence on the N-terminal amino acid
What is the N-terminal of an amino acid?
It is the start of the polypeptide (protein). The free group.
How is the signal peptide guided to the ER membrane?
- Signal-recognition particle (SRP)
- SRP receptor
What is the SRP?
in the cytosol and binds to the ER signal peptide when it is exposed on the ribosome
Where is the SRP receptor?
Embedded on the ER membrane.
What happens in the translocan of the ER membrane?
polypeptide created is threaded through the in the ER membrane.
What is the golgi apparatus?
The sorting organelle of the cell.
Why is the golgi apparatus the post office of the cell?
Because it recieves proteins from one location and targets them for delivery to a second location.
What are the three components of the golgi apparatus?
- Cis Cisterna
- Medial and Trans Cisternae
- Trans golgi network
How are proteins sent from the ER to the golgi apparatus?
Carried in vesicles that fuse to become the cis cisternae
What occurs to the proteins according to the Cis maturation model?
They move through the golgi stack and as they do they undergo enzymatic modification, which labels them for a specific destination.
How does transport from the ER to the golgi and golgi to other compartments occur?
Continual budding and fusion of transport vesicles.
What are the two pathways for the transport vesicles after they budded of from golgi apparatus?
- Exoctyosis
- Endocytosis
What occurs in exocytosis?
proteins remain anchored to ER membrane
vesicles from the ER fuse with the plasma membrane
stop translocation signal causes this.
What occurs in Endocytosis ?
- occurs due to specific address label added in golgi apparatus for lysosomal (specific sugar chain), mannose-6-phosphate
- proeins labelled with M6P bind to specfic receptor in golgi membrane
- intial destination = endosome which matures to become lysosome
What are post-transitional modifications?
as proteins are transported along the pathway they undergo modifications.
What are proteoglycans?
proteins that are extensively glycosylated
What are glycoproteins?
Proteins with small sugar component.
What does the post-transitional modifcation phosphorylation do?
Adds a phosphate group.
Alters activity of protein.
What does the post-transitional modifcation acetylation do?
Adds Acetyl group.
In histones - regulation of gene expression
What does the post-transitional modifcation Farnesylation do?
Adds Farnesyl group.
Targets proteins to cytoplasmic face of plasma membrane.
What does the post-transitional modifcation Ubiquitination do?
adds upiquitin chain.
Targets protein for degradation.
What is protein degradation used for?
- required for proteins past their sell by date.
- proteins that are faulty
- proteins that are foreign to the cell
What are two mechanisms for protein degradation?
- lysosomal degradation
2. Proteasomal degradation
What are the characteristics of lysosomal degradation?
- long half life protein (>20 hours) = auophagy
- carried out by lysosomal enzymes.
used for: - proteins with a long half life
- membrane proteins brought into cell via endocytosis
- extracellular proteins brought into cell via receptor-mediated endocytosis.
- pathogenic proteins brought into the cell via phagocytosis.
What are the characteristics of proteasomal degradation?
- short half life. (seconds or minutes)
- takes place in the cytosol of proteasomes
- Proteins with specific PEST sequence
- proteins tagged with ubiquitin
How does proteasomal degradation occur in the proeasomes?
- in the cytosol
- walls formed by an proease enzyme - the active site is inside cylinder
- protein stoppers at either end have to open to allow protein that is going to be degraded to get in
- ATP-dependent.
