Week 1 - Intracellular Processes Flashcards
What are ribosomes composed of
Protein and rRNA
In what 2 ways does the cell act to segregate molecules
Through multicomponent complexes (such as the two subunits of the ribosome)
Through compartmentalisation into membrane-bound organelles
What do the membranes around organelles provide
A closed compartment in which sets of enzymes can operate without interference
Proteins in the membrane of organelles need to be what?
Replenished and maintained
Through production in cytosol where they are made and then to the organelle where they are used
Name the process by which synthesised proteins target their eventual location
Protein sorting
Where are proteins initially synthesised
Ribosomes in the cytosol
Where is the information that tells a protein where to end up
Specific signal peptides ‘address labels’ contained in the amino acid sequence
The ribosome is made up of how many subunits
2
Clinically used antibiotics target which sites on the ribosome?
Decoding site (small subunit)
Peptidyl-transferase centre (large subunit)
Name 3 ways in which proteins can get into organelles and give an example of when this happens
Nuclear pores
(proteins going into nucleus)
Protein translocators
(proteins moving from cytosol into ER)
Transport vesicles
(proteins moving from the ER onwards)
Why do some ribosomes know to go to the ER
The presence of a signal peptide on the protein being made (called the N-terminal amino acids at the start of the protein)
What is the C-terminal of the protein
The end of the protein
The signal peptide is guided to the ER by what?
The signal-recognition particle ( which detects the presence of signal peptide) and the SRP receptor (which is on the ER membrane
What is the name of the protein channel in the ER membrane
The translocon
Which enzyme cleaves the signal peptide once the protein is within the ER
Peptidase
What happens after the signal peptide has been cleaved by peptidase
The protein in the ER lumen is encapsulated into a transport vesicle that buds off and is secreted from the ER
Analogy of signalling to the ER FIX THIS WHEN SOBER
New protein = letter
Signal peptide = address label
Signal recognition particle = postman
SRP receptor in ER membrane = Postman
SRP receptor in ER membrane = Name-plate on door
Translocon (pore/channel in ER) = Letterbox
Once proteins are transported by vesicles to the Golgi apparatus, what is this called?
The cis cisterna
What happens as the proteins move through the Golgi stack
The proteins undergo enzymatic modification which labels them for a specific cell destination
What allows the transport from ER to Golgi apparatus and Golgi apparatus to other compartments
The continual budding and fusion of transport vesicles
Which side of the golgi apparatus is closest to the ER
Cis
Which side of the Golgi apparatus is furthest away from the ER
Trans
What happens at the trans end of the Golgi apparatus
Proteins are sorted into groups with the same target sequence as these are destined for the same location
What happens once proteins have been sorted into groups at the trans side of the golgi apparatus
The proteins migrate via vesicles to their eventual location
What directs proteins to the lysosome instead of the plasma membrane
What are the two processes that can occur after the golgi apparatus
Exocytosis
Endocytosis
Which signal ensures that the protein takes the exocytosis pathway
The stop translocation signal
What causes a protein to take the alternative pathway towards the lysosome
An ‘address label’ added in the Golgi apparatus such as the side chain ‘mannose-6-phosphate’ (M6P)
What happens to a protein that is labelled with M6P
It binds to a specific receptor in the golgi membrane
Protein will then bind with an endosome via vesicle transport which matures to become a lysosome
What do endosomes often contain
A pathogen which has been endocytosed by the cell previously for it to be destroyed by the protein has been targeted in the first place (example hydrolase)
Names of different sides of golgi apparatus
Cis cisterna (first side reached
Trans Golgi Cisternae
What is glycosylation
Addition of sugar (such as M6P) to protein (happens in Golgi apparatus(
What are proteins called that are extensively glycosylated
Proteoglycans
What are proteins that are composed of little sugar content
Glycoproteins
What is a hallmark of several neurodegenerative disorders
Hyperphosphorylation of the protein Tau
Describe phosphorylation
Addition of a phosphate group which alters the activity of a protein
Describe acetylation
Addition of an acetyl group which in histones regulates gene expression
Describe Farnesylation
Addition of a farnesyl group which targets proteins to the cytoplasmic face of the plasma membrane
Describe Ubiquitination
Addition of a ubiquitin chain which targets proteins for degradation
What causes a protein to move to the ER and subsequently the Golgi
The presence of a signal peptide
By default what will happen to the protein if there exists nothing other than a signal peptide
It will be secreted out of the cell
What happens to protein that has the ‘stop translocation’ peptide
It will end up in the plasma membrane
What will happen to a protein that has had a M6P sugar side chain added in the golgi apparatus
It will end up in the lysosomes
What happens to a protein that lacks a signal protein
It will remain in the cytosol
What happens to a protein that has a nuclear localisation signal in the protein sequence
It will end up in the nucleus
What will happen to a protein that has a mitochondrial import sequence
It will end up in the mitochondira
What will happen to proteins that have a c-terminal tripeptide?
They will end up in the peroxisomes
What is protein degradation required for (3)
Proteins that have passed their ‘sell by’ date
Proteins that are faulty
Proteins that are foreign to the cell i.e pathogens
What are the two mechanisms that can cause degradation
Lysosomal degradation
Proteasomal degradation
Name 3 lysosomal enzymes
Lipases, nucleases and proteases/proteolytic enzymes
How are lysosomal enzymes activated
By the acidic environment (pH 4.8) inside the lysosome
Which types of proteins is lysosomal degradation used for (4)
Proteins with a long half life (>20 hours) (autophagy)
Membrane proteins brought into the cell via endocytosis
Extracellular proteins brought into the cell via receptor-mediated endocytosis
Pathogenic proteins brought into the cell via phagocytosis
Where does proteasomal degradation occur
At the proteasomes
Describe the structure of proteasomes
Cylindrical protein complexes which consist of protease enzymes (the active site is inside the cylinder)
What controls the entry of proteins about to be degraded into the proteasome
Protein ‘stoppers’
What are proteosomes dependant on for their function
ATP
What is proteasomal degradation used for
Proteins that have a short half life and hence need to be removed quickly (seconds or minutes)
Proteins with a short half life generally are rich in which specific sequence
Key metabolic enzymes and proteins that need to gotten rid of
Proteins that have been covalently tagged with ubiquitin
PEST (P) proline, (E) glutamic acid (S) Serine and (T) threonine
Describe the 4 steps relating to proteasomal degradation of proteins that have been covalently tagged with ubiquitin
Shuttling proteins take ubiquitinated protein to proteasome
Tagged proteins are recognised, unfolded and translocated
Ubiquitinated proteins are degraded inside proteasome to give peptides
Peptides are extruded and digested by cytosolic peptidases
