BBOL- Proteins Flashcards
1
Q
What types of amino acids are there?
A
- Charged polar (acidic and basic)
- Uncharged polar (amide, hydroxyl and sulfhydryl groups)
- Non polar
2
Q
Give examples of different protein shapes
A
- Globular
- Fibrous
- Multiple polypeptides
- Single subunits
3
Q
What is X-ray crystallography?
A
Crystalline atoms in the protein would cause x-ray beams to diffract in specific ways, helps determine protein structure
4
Q
What are examples of disease that are caused by one amino acid change?
A
- Sickle cell anaemia
- Cystic fibrosis
5
Q
What are the features of primary protein structure?
A
- Conformation of the lowest energy
- Changes when other protein interacts with other molecules in the cell
- Proteins can fold on their own, in a living cell require chaperone proteins
6
Q
Why is protein folding constrained?
A
- Peptide bond is not fully flexible
- Partial double bond- electrons from O migrate to bond between C-N
- Restricted rotation about C-N
- Weak non-covalent bond (H bonds, ionic and van Der Waals attractions)
7
Q
What is the stability of the final shape of the protein determined by?
A
- Combined strength of many non-covalent bonds
8
Q
Why do proteins fold?
A
To minimise disruption to hydrogens bonds in water
- Non-polar hydrophobic side chains inside
- Polar hydrophilic side chains outside
- Folding determined by distribution of polar non-polar amino acids in polypeptide
9
Q
Describe the secondary structure of proteins
A
- Alpa helix or beta sheet
- Hydrogen bonding between N-H and C=O in polypeptide backbone
- Common structures because they don’t depend on amino acid sequence
10
Q
What are protein domains?
A
- Substructure produced by part of polypeptide that can old independently into a compact stable conformation
- Typically 40-350 amino acids are modular units
- Proteins often contain several different domains
11
Q
Describe domain shuffling in evolution
A
- Larger proteins have often evolved through combinations of different domains
- Often domains= exons
- Protein binding sites and active sites often found at domain junctions
12
Q
Describe quaternary structure
A
- Proteins containing more than one polypeptide
- Subunit describes the way subunits are arranged together and nature of their contacts
- Subunits associate by non-covalent interactions similar to those involved in tertiary
(hydrophobic interaction, H bonds, salt bridges/ion pairs) - Some complexes involve 1 type of subunit
- Others contain different types of subunit
13
Q
Give types of tertiary structure
A
- Fibrous proteins (structural, arranged in long strands, insoluble)
- Globular ( polypeptide chains folded into knot, dynamic functions)
14
Q
Describe fibrous proteins
A
- Simple elongated 3D structure
- Some intracellular (actin/myosin) or fibrin
- Many extracellular (collagen, keratin)
- Extracellular often contain disulphide bridges
( formed in ER before cell export, links two cysteine amino acids, can be intra or inter molecular)
15
Q
Describe globular proteins
A
- Enzymes, hormones, antibodies, transport proteins, binding proteins, membrane proteins
16
Q
Describe membrane proteins
A
- Often contain alpha helix, short regions of this span lipid membranes
- Hydrophilic peptide backbone is H bonded to itself in a- helix, shielded from hydrophobic lipid by non-polar side chains
- Proteins have many membrane spanning helices
17
Q
Describe the regulation of protein folding
A
- Usually co-translational (starts from n-terminal as soon as it exits ribosome while c-terminal end of polypeptides is still being synthesised)
- Molecular chaperones (help correct folding, heat shock as activated by heat that could damage folding
18
Q
What are the consequences of incorrect folding?
A
- Can cause disease
- Exposed hydrophobic regions cause aggregation and precipitation out of solution
- E.g. Alzheimer’s (amyloid plaques)
- E.g. Prion diseases- BSE
19
Q
How is protein transported?
A
- Synthesised in cytosol but often required in different cellular compartments, gated transport
- Regulated by complexes of proteins forming selective gate, e.g. transport through nuclear pores
- Transmembrane transport, protein translators move proteins across specific membranes, e.g. cytosol to ER or mitochondria
(relies on signal peptide to direct protein to correct cellular address) - Vesicular transport, vesicles budding off one compartments and fusing with another, e.g. ER to Golgi
20
Q
Describe localisation signals
A
- Protein localisation sequences direct proteins to specific organelles
- Can be signal peptides/patches- peptides usually cleaved by signal peptidase after transport
- Patch, amino acids brought together to form signal after folding
- Signal recognition particles guide proteins to correct translocators
- E.g. signal recognition particle guides new proteins to ER
21
Q
Describe post-translational modification
A
- Some proteins undergo this
- Proteolysis- cleavage into fragments often with different functions- preproinsulin- proinsulin- insulin
- Addition of carb (glycosylation)
- Addition of lipids (myristolisation)
- Phosphorylation, methylation, acetylation etc.
