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Biochemistry > Revision Lect Sem 1 > Flashcards

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
Q

What us the structure of glycoproteins

A

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
Q

What is an example of a neutral sugar and an acidic acid

A

D-galactose
D-mannose
L-fructose

Sialic acid

27
Q

What su the structure of proteoglycans

A

Sugar chains are long and unbranched
Made up of repeating disaccharide units
Found in extra cellular matrix

28
Q

What the LOW DENSITY LIPOPROTEIN RECEPTOR

A

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
Q

What is ERYTHROPOIETIN

A

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
Q

What is common between blood groups

A

All have common oligosaccharide called O antigen (H antigen)

31
Q

How do A and B antigens differ

A

By addition of an additional monosaccharides
Which are
A –> has N - acetyl galactosamine
B –> has galactose

32
Q

What is an antigen

A

Something that can trigger an immune response

33
Q

What are antigens dependent on the presence of

A

Specific GLYCOTRANSFERASES

34
Q

What is the Rare inherited disorder which has something to do with errors in glycosylation

A

I-cell disease

35
Q

Describe what difference I-cell disease has

A

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
Q

What is the normal pathway of an enzyme delivery to a lysosomes

A

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
Q

What are mucins

A

Family of highly glycosylated proteins lots of carbohydrate

Protein core rich in threonine, serine = post translationally O glycosylation

38
Q

What dos O glycosylation do to mucins

A

Makes then resist Proteolysis and able to hold water giving gel like properties found mucosal barriers

39
Q

What are mucins associated with

A

Membranes and may serve as receptor like Ligands for carbohydrates binding molecules

40
Q

Where are mucins synthesised

A

In specialised cells in the
RESP tract
GI tract
Genitourinary tract

41
Q

Where are mucins abundant

A

Saliva

42
Q

What are some other functions of mucins

A

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
Q

Where is insulin synthesised and secreted form and also what is the larger precursor molecule

A

Pancreatic beta cells

Preproinsulin - single polypeptide Chain

44
Q

What happens to preproinsulin to get to insulin

A

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
Q

What do molecular gchaperones do

A

Assist proteins to fold correctly inhibiting aggregation and stimulating folding

46
Q

What kind of environment does the ER supply and what does this aid

A

Provides an oxidising environment aiding formation of disulphide bonds with the aid catalyst - protein disulphide isomerase

47
Q

What is phosphorylation

A

Addison of phosphate group to serine, threonine, tyrosine residues
Very imp in cell signalling and cell cycle

48
Q

What is acylation

A

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
Q

What is acetylation

A

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
Q

What is ubiquitin

A

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
Q

What is ubiquitination

A

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
Q

What can defective E3 enzymes lead to

A

Accumulation of proteins and diseases such as Parkinson’s and angelman syndrome

53
Q

What does HPV activate

A

Specific E3 which ubiquitinates the tumour suppressor protein p53 and targets for degradation

54
Q

What is bortezomid

A

Potent inhibitor of the protea some and is used in therapy for multiple myeloma cancer In bone marrow promote cell apoptosis

55
Q

What is used for s target for drug design

A

Mycobacterium tuberculosis similar protea some to humans

56
Q

One control of gene expression occurs at the level of…

A

Uproots in degradation

57
Q

Proteins are turned over

A

Regularly

58
Q

What happens to a protein which has an error

A

Turned over quickly

59
Q

What restructs degradation pathways

A

Lysosomes

Protea somes

60
Q

What are the processes regulated by protein degradation

A 
Gene transcription 
Cell cycle progression
Organ formation 
Inflammatory responses 
Tumour suppression
Cholestrol metabolism 
Antigen processing
61
Q

What is a human proteome

A

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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