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Revision Lect Sem 1 Flashcards

1
Q

What are the stages of protein post translational modification

A

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

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2
Q

What is the endoplasmic reticulum

A

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)

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3
Q

What is the structural difference between the RER and the SER

A

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

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4
Q

How is the cellular fate of proteins depicted

A

Signal peptide sequence

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5
Q

What is a signal sequence

A

Proteins targeted for membranes or cellular organelles have a 20-30 amino acid sequence at the n terminus

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6
Q

The signal sequence is recognised by what complex, what kind of complex is this and when does this occur

A

Complex –> signal recognition particle SRP
What –> ribonucleoprotein
When –> shortly after translation

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7
Q

What does the signal recognition particle do

A

Binds to the sequnce and stops translation

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8
Q

After the SRP has binded to the signal sequence what happens to it

A

Targeted to the ribosome - signal recognition particle receptor SRPR on the endoplasmic reticulum

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9
Q

What happens to the SRP complex after it has arrived at the receptor on the ER

A

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

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10
Q

Where are the target proteins taken to

A

Lysosomes
Secretory vesicles
Plasma membrane

According to 3D shape and amino acid sequence

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11
Q

What are lysosomes

A

Contain digestive enzymes responsible for breaking down proteins, polysaccharides, nucleic acids and lipids

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12
Q

What are the cis- and trans- faces of the Golgi

A

Cis- face of Golgi receives vesicles form the ER

Trans- face of Golgi sends different set of vesicles to target sites

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13
Q

What are the organelles that play a central role in protein trafficking

A

Golgi and ER

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14
Q

What are types of protein modification

A 
Glycosylation
Proteolytic cleavage 
Formation of disulphides bonds 
Phosphorylation 
Addition of fatty acids (acylation)
Acetylation
Ubiquination
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15
Q

What is glycosylation

A

Addition of oligosaccharides to either asparagine, threonine or serine residue in a protein
MAJOR type of post translational modification of tissue proteins

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16
Q

What may glycosylation proteins do

A

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)

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17
Q

When may glycosylation occur

A

Co-translationally or post-translationally

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18
Q

Where does glycosylation occur

A

Within the lumen of the ER and Golgi

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19
Q

What can the oligosaccharides link to the protein through

A

Asparagine - n linked using amide side
Threonine - o linked using hydroxyl side
Serine - o linked using hydroxyl side

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20
Q

Where does n linkage occur

A

Occurs in ER and can continue to Golgi (mem and secretory proteins )

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21
Q

Where does o linkage occur

A

Only in the golgi (glycoproteins mem and sec proteins )

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22
Q

In N linked glycosylation how are the sugars activated and what is the enzyme involved called

A

Sugars activated first by adding UTP or GTP

Enzyme involved –> GLYCOTRANSFERASES

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23
Q

What is dolichol Phosphate

A

A specialised lipid molecule located in ER where large oligosaccharides destined for attachment to asparagine are assembled

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24
Q

What are the 3 main groups of glycoproteins

A

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

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25
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
26
What is an example of a neutral sugar and an acidic acid
D-galactose D-mannose L-fructose Sialic acid
27
What su the structure of proteoglycans
Sugar chains are long and unbranched Made up of repeating disaccharide units Found in extra cellular matrix
28
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
29
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
30
What is common between blood groups
All have common oligosaccharide called O antigen (H antigen)
31
How do A and B antigens differ
By addition of an additional monosaccharides Which are A --> has N - acetyl galactosamine B --> has galactose
32
What is an antigen
Something that can trigger an immune response
33
What are antigens dependent on the presence of
Specific GLYCOTRANSFERASES
34
What is the Rare inherited disorder which has something to do with errors in glycosylation
I-cell disease
35
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
36
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
37
What are mucins
Family of highly glycosylated proteins lots of carbohydrate | Protein core rich in threonine, serine = post translationally O glycosylation
38
What dos O glycosylation do to mucins
Makes then resist Proteolysis and able to hold water giving gel like properties found mucosal barriers
39
What are mucins associated with
Membranes and may serve as receptor like Ligands for carbohydrates binding molecules
40
Where are mucins synthesised
In specialised cells in the RESP tract GI tract Genitourinary tract
41
Where are mucins abundant
Saliva
42
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
43
Where is insulin synthesised and secreted form and also what is the larger precursor molecule
Pancreatic beta cells | Preproinsulin - single polypeptide Chain
44
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
45
What do molecular gchaperones do
Assist proteins to fold correctly inhibiting aggregation and stimulating folding
46
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
47
What is phosphorylation
Addison of phosphate group to serine, threonine, tyrosine residues Very imp in cell signalling and cell cycle
48
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
49
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
50
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
51
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
52
What can defective E3 enzymes lead to
Accumulation of proteins and diseases such as Parkinson's and angelman syndrome
53
What does HPV activate
Specific E3 which ubiquitinates the tumour suppressor protein p53 and targets for degradation
54
What is bortezomid
Potent inhibitor of the protea some and is used in therapy for multiple myeloma cancer In bone marrow promote cell apoptosis
55
What is used for s target for drug design
Mycobacterium tuberculosis similar protea some to humans
56
One control of gene expression occurs at the level of...
Uproots in degradation
57
Proteins are turned over
Regularly
58
What happens to a protein which has an error
Turned over quickly
59
What restructs degradation pathways
Lysosomes | Protea somes
60
What are the processes regulated by protein degradation
``` Gene transcription Cell cycle progression Organ formation Inflammatory responses Tumour suppression Cholestrol metabolism Antigen processing ```
61
What is a human proteome
Proteome --> entire set of proteins expressed by a cell, tissue or organism at a certain time under defined conditions

Biochemistry (13 decks)

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