Revision Lect Sem 1 Flashcards
What are the stages of protein post translational modification
Targeting
- -> moving a protein to its final cellular destination
- -> many possible locations within a cell
- -> depends on the presence of specific amino acid sequences within the translated protein
Modification
–> addition of further functional chemical groups etc
Degradation
–> unwanted or damaged proteins have to be removed
What is the endoplasmic reticulum
General structure is membrane enclosed flattened tubules
Rough ER
Roles –> protein synthesis, protein folding, modification of proteins, quality control of proteins and processing of proteins
Smooth ER
Roles –> chemically modifies proteins from RER, synthesis of lipids and steroids, detox of small molecules, site of glycogen degradation, stores calcium ions when released can trigger responses (muscle contraction)
What is the structural difference between the RER and the SER
RER –> a greatly convoluted flattish sealed sac, partly continuous with the nuclear envelope, have ribosomes for the protein synthesis
SER –> no ribosomes and more tubular than RER
How is the cellular fate of proteins depicted
Signal peptide sequence
What is a signal sequence
Proteins targeted for membranes or cellular organelles have a 20-30 amino acid sequence at the n terminus
The signal sequence is recognised by what complex, what kind of complex is this and when does this occur
Complex –> signal recognition particle SRP
What –> ribonucleoprotein
When –> shortly after translation
What does the signal recognition particle do
Binds to the sequnce and stops translation
After the SRP has binded to the signal sequence what happens to it
Targeted to the ribosome - signal recognition particle receptor SRPR on the endoplasmic reticulum
What happens to the SRP complex after it has arrived at the receptor on the ER
Signal sequence inserted into ER
SRP dissociates and translation continues
Protein made go to Golgi and to destination
Signal sequence may or may not be recovered
Where are the target proteins taken to
Lysosomes
Secretory vesicles
Plasma membrane
According to 3D shape and amino acid sequence
What are lysosomes
Contain digestive enzymes responsible for breaking down proteins, polysaccharides, nucleic acids and lipids
What are the cis- and trans- faces of the Golgi
Cis- face of Golgi receives vesicles form the ER
Trans- face of Golgi sends different set of vesicles to target sites
What are the organelles that play a central role in protein trafficking
Golgi and ER
What are types of protein modification
Glycosylation Proteolytic cleavage Formation of disulphides bonds Phosphorylation Addition of fatty acids (acylation) Acetylation Ubiquination
What is glycosylation
Addition of oligosaccharides to either asparagine, threonine or serine residue in a protein
MAJOR type of post translational modification of tissue proteins
What may glycosylation proteins do
Assist folding
Enhance solubility
Stabilise against denaturation
Protect against Proteolytic degradation
Target the protein to specific sub cellular locations
Act as a recognition signal for carbohydrate- binding proteins (lectins)
When may glycosylation occur
Co-translationally or post-translationally
Where does glycosylation occur
Within the lumen of the ER and Golgi
What can the oligosaccharides link to the protein through
Asparagine - n linked using amide side
Threonine - o linked using hydroxyl side
Serine - o linked using hydroxyl side
Where does n linkage occur
Occurs in ER and can continue to Golgi (mem and secretory proteins )
Where does o linkage occur
Only in the golgi (glycoproteins mem and sec proteins )
In N linked glycosylation how are the sugars activated and what is the enzyme involved called
Sugars activated first by adding UTP or GTP
Enzyme involved –> GLYCOTRANSFERASES
What is dolichol Phosphate
A specialised lipid molecule located in ER where large oligosaccharides destined for attachment to asparagine are assembled
What are the 3 main groups of glycoproteins
Glycoproteins - the protein component is the largest constituent by Weight
Proteoglycans - the carbohydrate component is the largest constituent by weight, the protein is conjugated to a glycosaminoglycan
Mucins - predominantly carbohydrates
What us the structure of glycoproteins
Have short highly branched polysaccharides Chains of up to 20 sugars
Have amino acids
Neutral sugars
Acidic sugar
Components of cell membranes and secreted proteins
What is an example of a neutral sugar and an acidic acid
D-galactose
D-mannose
L-fructose
Sialic acid
What su the structure of proteoglycans
Sugar chains are long and unbranched
Made up of repeating disaccharide units
Found in extra cellular matrix
What the LOW DENSITY LIPOPROTEIN RECEPTOR
Eg glycoprotein
Has both N and O linked oligosaccharides
2 N linked oligosaccharides help with protein folding in ER
The O inked oligosaccharide prevent receptor folding back on itself
What is ERYTHROPOIETIN
Glycoprotein
1-serine and 3-asparagine residues which increases its stability
Recombinant EPO can be Used to to treat anaemia as stimulate erythrocyte production
EPO and recombinant can be differentiated as glycosylation pattern is different
What is common between blood groups
All have common oligosaccharide called O antigen (H antigen)
How do A and B antigens differ
By addition of an additional monosaccharides
Which are
A –> has N - acetyl galactosamine
B –> has galactose
What is an antigen
Something that can trigger an immune response
What are antigens dependent on the presence of
Specific GLYCOTRANSFERASES
What is the Rare inherited disorder which has something to do with errors in glycosylation
I-cell disease
Describe what difference I-cell disease has
Deficiency in enzyme which phosphorylates the mannose which causes 8 essential enzymes to be mis-targeted and secreted form the cells and not delivered to the lysosomes
There is a build up of macromolecules, mucopolysaccharides and mucolipids in affected cells
Causes severe psychomotor retardation and skeletal deformities
What is the normal pathway of an enzyme delivery to a lysosomes
Mannose - 6- Phosphate component of n linked oligosaccharide added to enzymes for the lysosomes acts as a targeting signal
M6P is recognised by a specific receptor which binds to it and delivers the enzyme to the pre-lysosomal compartment via a transport vesicle
What are mucins
Family of highly glycosylated proteins lots of carbohydrate
Protein core rich in threonine, serine = post translationally O glycosylation
What dos O glycosylation do to mucins
Makes then resist Proteolysis and able to hold water giving gel like properties found mucosal barriers
What are mucins associated with
Membranes and may serve as receptor like Ligands for carbohydrates binding molecules
Where are mucins synthesised
In specialised cells in the
RESP tract
GI tract
Genitourinary tract
Where are mucins abundant
Saliva
What are some other functions of mucins
Adhere to epithelial cells and hydrate underlying cells
Protect cells from stomach acids, bacterial infection and inhaled chemicals
Have roles in fertilisation, immune repsonse and cell adhesion
Over expressed in bronchitis and cystic fibrosis
Characteristic of adenovracunomas
Where is insulin synthesised and secreted form and also what is the larger precursor molecule
Pancreatic beta cells
Preproinsulin - single polypeptide Chain
What happens to preproinsulin to get to insulin
Is post translationally processed in ER
- signal sequnce removed -> pro insulin
- disulphide bonds formed between cysteine groups
Transported to Golgi then
- endopeptidases remove part of polypeptide chain
What do molecular gchaperones do
Assist proteins to fold correctly inhibiting aggregation and stimulating folding
What kind of environment does the ER supply and what does this aid
Provides an oxidising environment aiding formation of disulphide bonds with the aid catalyst - protein disulphide isomerase
What is phosphorylation
Addison of phosphate group to serine, threonine, tyrosine residues
Very imp in cell signalling and cell cycle
What is acylation
Covalent modification of proteins with fatty acids
Lipid attachments plays an important role in protein localisation and function
Lipid attachment mediates membrane association of soluble proteins protein to proteins interactions, protein trafficking…..
Most common is palmitoylation - attachment of a palmitic acid molecule to the sulphydryl group of the cysteine group
What is acetylation
Most commonly at the n terminus of the protein or lysine residues
Important in histone packaging, Nucleosome stability and DNS accessibility
Removes positive charge
What is ubiquitin
Is a protein tag that attaches to a protein that targets it for degradation
Highly conserved molecule
Structure - extended Carboxyl terminus that is activated and linked to other proteins
Lysine 48 - major site for lining additional ubiquitin molecules
What is ubiquitination
Protein turnover tightly reg and requires complex enzyme systems
Pretend to be degredated are linked to a ubiquitin in a reaction using ATP hydrolysis for energy
Enzymes E1,2,3 responsible for adding ubiquitin to lysine
Protea some which requires ATP to function digests ubiquitinated proteins
Ubiquitin recycled
What can defective E3 enzymes lead to
Accumulation of proteins and diseases such as Parkinson’s and angelman syndrome
What does HPV activate
Specific E3 which ubiquitinates the tumour suppressor protein p53 and targets for degradation
What is bortezomid
Potent inhibitor of the protea some and is used in therapy for multiple myeloma cancer In bone marrow promote cell apoptosis
What is used for s target for drug design
Mycobacterium tuberculosis similar protea some to humans
One control of gene expression occurs at the level of…
Uproots in degradation
Proteins are turned over
Regularly
What happens to a protein which has an error
Turned over quickly
What restructs degradation pathways
Lysosomes
Protea somes
What are the processes regulated by protein degradation
Gene transcription Cell cycle progression Organ formation Inflammatory responses Tumour suppression Cholestrol metabolism Antigen processing
What is a human proteome
Proteome –> entire set of proteins expressed by a cell, tissue or organism at a certain time under defined conditions
