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IMS- Strand 2 > Protein structure and function > Flashcards

Protein structure and function Flashcards

1
Q

What are amino acids?

A

small molecules that are building blocks of proteins
20 common natural amino acids

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2
Q

What do amino acids exist as at neutral pH?

A

zwitterions

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3
Q

How is property of amino acids determined?

A
  • side chain
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4
Q

What are peptides?

A

Two or more amino acids linked by a peptide bond

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5
Q

What are proteins?

A

Large biomolecules comprised of one or more long chains of amino acid residues
Polypeptide= protein
Each amino acid unit in polypeptide= residue

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6
Q

What is the primary structure of a protein?

A
  • Linear sequence of amino acids encoded by DNA
  • Defines how the protein will fold and function
  • Single change in amino acid structure can cause disease
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7
Q

What is the secondary structure?

A

Hydrogen bonds between aa form stable structural elements
Alpha helices
Beta pleated sheets

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8
Q

What influences the conformations of each polypeptide chain?

A

Limitations in bond length
Bond angle

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9
Q

What is an alpha helix?

A

Coiled structure stabilised by intrachain hydrogen bonds

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10
Q

What is Proline?

A

Helix breaker
Ring structure does not allow for 100 degree rotation
No H-bond donor

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11
Q

What are the 5 common amino acids (MARKL)

A

Methionine
Alanine
Arginine
Lysine
Leucine

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12
Q

What are beta sheets?

A

Are stabilised by hydrogen bonds between strands
Polypeptide chains can change direction by making reverse turns and loops

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13
Q

What is the tertiary and quaternary structure?

A

To function many proteins fold into a compact, globular shape= tertiary structure
When two or more polypeptide chains come together to give a functional molecule= quaternary structure

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14
Q

What holds together tertiary and quaternary structures?

A

H-bonds
Ionic interactions
Disulfide bonds
Van der waals
Hydrophobic interactions

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15
Q

What are hydrogen bonds?

A

between hydrogen atom (covalently bound to a proton donor) and a proton acceptor

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16
Q

What are ionic interactions?

A

between charged amino acids, often found surface exposed

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17
Q

What are disulfide bonds?

A

Between cysteine residues

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18
Q

What are van der waals interactions?

A

weak electrostatic forces

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19
Q

What are hydrophobic interactions?

A

between hydrophobic residues, often form on the inside of proteins

20
Q

What does protein diversity mean?

A

Diversity in protein structure means proteins can have a large number of functions in the cell

21
Q

What are 5 protein functions?

A

Structural
Regulatory
Carriers
Catalytic
Sensory

22
Q

What is protein trafficking?

A

the mechanism by which a cell transports proteins to the appropriate locations either inside or outside the cell

23
Q

Why is correct trafficking essential?

A

Incorrect= disease

24
Q

Where are proteins synthesised?

A

On ribosomes bound to ER or on free ribosomes

25
Q

What is the cytosolic pathway?

A

-By default, proteins synthesised on free ribosomes remain in cytosol
-For import into nucleus they have nuclear localisation signal (allows them to be recognised and transported through the nuclear pores)
- For import into mitochondria, have N-terminal mitochondrial import sequence

26
Q

What is the secretory pathway?

A

Proteins for secretory pathway have:
N-terminal signal sequence
8-10 hydrophobic amino acids
Proteins synthesised on ER-bound ribosomes will be secreted from the cell unless they contain addition localisation signals

27
Q

What happens when N-terminal signal sequence is translated?

A
  • Recognised by SRP (signal recognition particle), which binds to SRP receptor on ER and recruits ribosome to ER membrane
    Nascent polypeptide chain is then translocated into the ER lumen
28
Q

What happens to soluble proteins?

A

N-terminal signal cleaved
Secreted into vesicles

29
Q

What happens to proteins with more un-soluble regions?

A

Additional localisation signals allow membrane proteins to be folded into the ER or other membrane bound organelles (plasma membrane)
Uncleaved

30
Q

What are post- translational modifications (PTMs)?

A

A process of changing one or more amino acids in a protein after translation
50 types
Can alter function, cell location & viability

31
Q

What are the most commons PTMs?

A

Phosphorylation and dephosphorylation

32
Q

What is phosphorylation?

A

Addition of a phosphate group
At serine, threonine or tyrosine

33
Q

What can phosphorylation do?

A

Alter protein function and enable cell signalling
Occurs throughout the cell

34
Q

What is the PTM glycosylation?

A
  • Attach carbohydrate
  • O-linked at serine or threonine (simple)
  • N-linked at asparagine (complex_
  • Occurs in ER & Golgi
35
Q

What can glycosylation do?

A
  • Increase protein stability
  • Help protein folding
  • Modulate protein function, protein- ligand interactions
  • Aid in cell attachment to extracellular matrix
  • Block pathogens from attacking host cells
36
Q

What is the PTM UBIQUITINATION?

A

Three step enzymatic cascade involving E1, E2, E3 enzymes
Transfers ubiquitin, via its c-terminal glycine, onto the amino acid group of a lysine residue of the substrate

37
Q

What does ubiquitination cause?

A

Different forms code for different functions
Large role in targeting proteins for proteasomal degradation
Occurs in multiple locations in the cell

38
Q

What is protein misfolding?

A

Correct protein folding crucial for function
Incorrect can lead to disease
Misfolding can happen due to change in primary sequence or escape from the native folding pathway

39
Q

What is prion disease?

A

Fatal neurodegenerative diseases
Transmissible spongiform encephalopatjoes

40
Q

What is a prion?

A

Misfolded protein that induces misfolding in normal variants of the same protein
Leads to accumulation of prion protein aggregates and cell death

41
Q

How does prion disease originate?

A

Sporadically, by transmisson or in heritance

42
Q

What is amyloidosis?

A

misfolding of amyloid protein results in formation of fibrils with cross beta structure that cannot be degraded

43
Q

What is alzheimer’s disease?

A

Age related neurodegenerative disease, affects memory, thinking and behaviour

44
Q

What is alzheimers disease characterised by?

A
  • Extracellular accumlation of amyloid- beta peptides as amyloid plaques
  • Aggregation of abnomally- phosphorylated tau protein into intraneuronal neurofibrillary tangles
45
Q

What does Tau protein normally do?

A
  • Stabilises microtubules
  • Microtubules are essential for intercellular transport and neuronal structure
  • Excessive or abnormal phosphorylation of tau leads to oligomerisation and tangle formation= microtubule destabilisation

IMS- Strand 2 (4 decks)

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