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People and Illness > Week 4 > Flashcards

Week 4 Flashcards

1
Q

With what essential amino acid is transcription always started?

A

Methionine

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2
Q

What are the 2 pathways for protein degradation?

A

Lysosomal - long half-life, membrane proteins, extracellular proteins
Proteosomal - short half-life, key metabolic enzymes, defective proteins

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3
Q

What are the stages of protein folding?

A

Primary (aa sequence) → secondary (local folding - α helices and β pleated sheets) → tertiary (long-range folding) → quarternary (multimeric organisation) → supramolecular (large scale assemblies) → function

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4
Q

What is proteostasis?

A

Protein homeostasis

Synthesis, folding, processing, assembly, trafficking, localisation, degradation

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5
Q

What are the components of an amino acid?

A 
Amino group 
Carbon chain 
Hydrogen 
R-group 
Carboxyl group
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6
Q

How are α helices formed?

A

H bond forms between carbonyl oxygen atom of each peptide bond and amide H atom from an amino acid 4 positions towards the C-terminus

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7
Q

What are the main features of α helices?

A

Periodic spiral
Directionality
R groups face outwards

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8
Q

How many amino acids are in a single turn of an α helix?

A

3.6

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9
Q

How are β pleated sheets formed?

A

Each strand is 5-8 aa residues

Hydrogen bonding between strands of polypeptide form the planar sheet

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10
Q

What are the main features β pleated sheets?

A

Directionality is parallel anti-parallel

R groups project from both faces of the sheet

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11
Q

What types of bonding are present in tertiary protein structures?

A 
Hydrophobic bonds (non-polar R groups)
Hydrogen bonds (polar R groups)
Disulfide bonds
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12
Q

What is protein conformation determined by?

A

Primary structure

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13
Q

Why is there a tendency for proteins to aggregate?

A

Cellular environment is crowded (300-400 g/l)

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14
Q

What is a molecular chaperone?

A

Any protein that interacts with, stabilises or helps another protein to acquire its functionally active conformation, without being present in its final structure
Selectively bind to short stretches of hydrophobic amino acids
E.g. chaperonin

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15
Q

What percentage of newly synthesised proteins are misfolded?

A

30%

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16
Q

What enzyme is responsible for deciding if a protein is misfolded and how does it do this?

A

Glucosyltransferase

Detection of stretches of hydrophobicity on the outside (will encourage aggregation which is detrimental)

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17
Q

Outline the process of quality control in the ER

A

Newly synthesised protein → glycosylated in ER (chain of specialised sugar groups on the end) → glucosidase I and II will cleave all sugar groups except 1 → binds to chaperone (e.g. calnexin/calreticulin) which aids folding → glucosidase II cleaves the final sugar group → correctly folded proteins leave; incorrectly folded proteins will be refolded )

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18
Q

What happens when the same protein is misfolded several times?

A

Sent to proteasome for degradation

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19
Q

What is the structure of a proteasome?

A

Hollow, cylindrical structures
CAP
α-subunits (non-enzymatic, structural)
β-subunits (proteolytic activity, destroy protein)

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20
Q

Outline the process by which proteins are labelled for destruction and destroyed

A

Polyubiquitination (labelling) → label recognised by CAP of proteasome → label removed and protein unfolded → protein threaded through proteasome and proteolysis occurs

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21
Q

What are proteinopathies?

A

Protein folding diseases

Accumulation of misfolded proteins resulting in aggregates, thereby gaining toxic activity or losing the normal function

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22
Q

What types of protein are aggregated in amyloidosis?

A

Aβ - Alzheimer’s
ABri - familial British dementia
ADan - familial Danish dementia
PrP - Creutzfeldt-Jakob disease (prionopathy)

23
Q

What types of protein are aggregated in tauopathy?

A

Hyperphosphorylated Tau - Alzheimer’s, fronto-temporal lobar degeneration etc.

24
Q

What types of protein are aggregated in synucleopathy?

A

α-synuclein - Parkinson’s, Lewy Body dementia

25
Q

What is Alzheimer’s and what does it affect?

A

Most common form of dementia

Progressive and fatal - language, memory, vision, emotion, personality

26
Q

What are the 2 genetic types of Alzheimer’s disease and what are they caused by?

A

Early onset familial - mutation of amyloid precursor protein (APP), presenilin-1 or presenilin-2
Sporadic - mutation of APOE4 allele

27
Q

What are the 2 abnormal structures found in the brains of people with Alzheimer’s and what do they have in common?

A 
Amyloid plaques (extracellular space)
Neurofibrillary tangles (cytoplasm) 
Both due to misfolded proteins
28
Q

How is amyloid precursor protein involved in Alzheimer’s pathology?

A

Altered APP processing gives rise to amyloid β-peptide (Aβ)

29
Q

What is the function of APP?

A

Specific function unknown

Involved in synaptic plasticity and neuronal development

30
Q

How long is APP compared to Aβ peptide?

A

APP - 770 amino acids

Aβ peptide - 40/42 amino acids

31
Q

How are the 2 types of protein in the non-amyloidogenic state formed?

A

Transmembrane protein is cleaved by α-secretase to soluble molecule sAPPα

32
Q

How are the 3 types of protein in the amyloidogenic state formed?

A

Transmembrane protein is cleaved by β-secretase to soluble sAPPβ and then further cleaved by γ-secretase to Aβ peptide

33
Q

What is γ-secretase?

A

Protease made up of other protease components including presenilins (associated with early Alzheimer’s)

34
Q

What is the amyloid hypothesis?

A

Amyloid β-peptide (Aβ) undergoes a secondary structure changes – α-helix rich to β-sheet rich

35
Q

Outline the process by which neurofibrillary tangles are formed

A

Aβ secondary structure change → oligomer aggregation → fibrils and plaques → inflammatory response → tau aggregation and tangles → synaptic and neuronal loss → inflammatory response → cognitive decline and disability

36
Q

What are the main components of neurofibrillary tangles?

A

Paired helical filaments - long fibrous proteins braided together consisting of the microtubule-associated protein tau

37
Q

What is the normal role of tau?

A

Binds to microtubules to stabilise them and keep them intact; removal of tau by phosphorylation destabilises the microtuble and allows changes

38
Q

What is the consequence of overphosphorylation of tau?

A

Filament formation/neuronal fibrillary tangles
Microtubule dysfunction
Cell death

39
Q

What are the possible causes of tau aggregation?

A

Phosphorylation by kinases (e.g. Cdk5, GSK3β) is upregulated and dephosphorylation by phosphatases is downregulated

40
Q

What are the features of dementia with Lewy bodies?

A

Shares symptoms with Alzheimer’s and Parkinson’s diseases

Presence of cortical Lewy bodies - α-synuclein aggregates

41
Q

How are Lewy bodies formed?

A

α-synuclein misfolded into β-pleated sheets which aggregates into higher-order insoluble fibrils which are the building blocks for Lewy bodies

42
Q

Where does α-synuclein aggregate?

A

In neuronal or glial cells

43
Q

What are prion diseases?

A

Family of rare, progressive and fatal neurodegenerative disorders caused by infective prion proteins causing loss of motor coordination and behavioural changes
Can be inherited, sporadic or acquired and have long incubation periods

44
Q

What are prion diseases also known as?

A

Transmissible spongiform encephalopathies

45
Q

What changes are characteristic of prion diseases?

A

Spongiform changes associated with neuronal loss and a failure to induce an inflammatory response

46
Q

How are sporadic, iatrogenic, familial and variant Creutzfeld-Jakob disease transmitted?

A

Sporadic - unknown
Iatrogenic - exposure to contaminated hormones/tissues/blood products
Familial - genetic germline PRNP mutation
Variant - ingestion of contaminated food

47
Q

What prion diseases are genetic?

A

Familial CJD
Gerstmann-Straussler-Scheinkler syndrome
Fatal familial insomnia

48
Q

What prion disease is transmitted by ritualistic cannibalism?

A

Kuru

49
Q

What are the histological changes in prion disease?

A

Neuronal loss/vacuolation

Amyloid plaque surrounded by spongiform changes

50
Q

What is the normal cellular and pathological forms of prion protein?

A

PrPC - normal

PrPSc - pathological

51
Q

How are CJD and AD similar?

A

Fatal neurodegenerative diseases
Inherited and sporadic forms
Amyloid deposits
Increased β-pleated sheets

52
Q

How are CJD and AD different?

A 
Unrelated proteins (APP to Aβ peptide and PrPC to PrPSc)
PrPSc is infective
53
Q

Why are prion proteins termed infectious?

A

They can self-aggregate and propagate

People and Illness (4 decks)

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