Secondary Structure Flashcards
1
Q
Catalysis
A
- enzymes for biosynthesis, degredation, energy relations
2
Q
Structure
A
- proteins for support and protection (collagen, elastin and extensin)
3
Q
Transport
A
- carriers & membrane transporters (ATPases, antiporters, hemoglobin, lipoproteins).
4
Q
Regulation
A
- control of gene expression, growth & development (transcription factors, activators, hormones, receptors).
5
Q
Movement
A
- amoeboid movement, cytoplasmic streaming, chromosome separation, muscle contraction (e.g. tubulin, actin).
6
Q
Storage
A
- ovalbumin & casein (animals); zein, gluten, phaseolin (corn, wheat, bean).
7
Q
Defense
A
- keratin (skin), antibodies, fibrinogen & thrombin (clotting).
8
Q
Stress Response
A
- cytochrome P450, heat shock proteins, DNA repair enzymes.
9
Q
Fibrous Proteins
A
- rod-like or sheet-like proteins greatly enriched in a-helices or B-pleated sheets
10
Q
Globular proteins
A
- spherical, water soluble proteins with hydrophilic residues towards the surface
- most chemical work is done by them
- their polypeptide chains are folded into compact structures
11
Q
Membrane Proteins
A
- spherical/globular proteins embedded in membranes with hydrophobic residues towards the surface
- often “channel” proteins for conducting materials across membranes
12
Q
Primary Structure of proteins
A
- a portion of the amino acid sequence
- defined number and order of AAs
13
Q
How is protein sequence analysis complicated by multiple chains?
A
- it does not identify with post-translational modifications
- biosynthesis of insulin as a covalent interaction to create disulfide bonds to hold the chains together (insulin has two chains linked by disulfide bonds)
14
Q
Post translational modification: Insulin processing
A
- insulin synthesized as an inactive precursor (preproinsulin)
- undergoes enzymatic cleavage to proinsulin, followed by folding and a dsuisulfide bond
- followed by additional enzymatic proteolysis
- allows insulin to be stored as a inactive precursor ready for mobilization on demand
15
Q
Secondary Protein Structure
A
- the folding or coiling of polypeptide chains into small localized regions of having non-random organization
- two main types: alpha helix and beta pleated sheets
- both stabilized by H bonds between carbonyl and amino groups and all secondary structures MUST follow Paulings law
16
Q
Paulings rules for secondary structures
A
- Bond lengths and bond angles should be distorted as little as possible (from X-ray information)
- No two atoms should approach each other more closely than is allowed by their vdW radii
- The six atoms in the amide plane must remain coplanar with the alpha carbon
- Some kind non covalent bonding is necessary to stabilize protein folding
- preferred conformation of polypeptides must allow for max H bonding but satisfy rules 1-3
17
Q
Tertiary Protein Structure
A
- multiple beta sheets or alpha helices folded
- binds a heme
18
Q
Quaternary Protein Structure
A
- when 2 or more proteins folded in tertiary interact to form well defined complexes
- four separate protein subunits, two alpha subunits and two beta subunits
19
Q
Alpha Helix
A
- clockwise corkscrew (right handed)
- R groups extend outwards
- H bonds form between carbonyl and amino groups of every 4th residue
- plane of peptide bond parallel to axis of helix
20
Q
Polyproline helix (polypeptide helix)
A
- does not meet criteria of alpha helix
- it is left handed and commonly found in glycine
21
Q
Beta Pleated Sheets
A
- A multi-folded (pleated) sheet-like arrangement of amino acid that is obtained when segments of peptides line up side-by-side.
- perpendicular to AA chain
- lane of peptide bond is parallel to plane of pleat
- R groups alternate above and below the plane of the sheet
- H bonds between carbonyl and amino groups of adjacent chains
22
Q
Two forms of Beta Pleated Sheets
A
- Antiparallel configuration
2. Parallel configuration
23
Q
Antiparallel configuration of Beta Pleated Sheets
A
- shorter, stronger, more stable H bonds
24
Q
Parallel configuration of Beta Pleated Sheets
A
- longer, weaker, less stable H bond
25
Q
Beta turns
A
- facilitate peptide folding
- antiparallel b-structures have sharp turns in their peptide chains
- allow tight reversals in the direction of the peptide chains
- B turns are tighter than turns in alpha helices
- H bond between the 1st and 4th amino acid (1st and 3rd peptide bond) stabilizes turn
26
Q
a-keratins
A
- bundles of multiple, cpiled alpha helixes that form fibers
ex: hair, wool, outer skin, claws, scales, horns, hoofs
27
Q
B-keratins
A
- stacked, anti-parallel B-sheets embedded in a matrix of other protein structure (also known as fibroin).
ex: spider web silk, silkworm silk, bird feathers & beaks
28
Q
Collagen
A
- triple helix of polypeptides each having only “a-helix” coils of secondary structure
- most abundant protein in animals
- triple helix of tropocollagen
- quaternary structure of a cross linked collagen
- cross linking is via lysinorleucines derived from 2 lysines in diff polypeptides
ex: connective tissue in tendons, blood vessels, skin, bone.
29
Q
Cysteines residues form many _______ between polypeptides
A
- disulfide bridges
30
Q
What is the affect of disulfides in keratin?
A
- make keratin very rigid and insoluble (important for hair stry
31
Q
Structure of spider silk
A
- the beta sheet regions of fibroin have a high number of glycines
- beta sheets impart strength and a-helices impart flexibility to the strand
- stronger than steel
32
Q
Amino acid composition of collagen
A
- (Gly-Pro-X)n
- 1/3 Gly, 1/3 Pro
- X is often 5-hydroxylysine
- Pro is often hydroxylated
33
Q
Scurvy
A
- collagen related disease
- vitamin C deficiency
- Vit C is a cofactor for prolyl hydroxylase (hydroxylates proline and lysine)
- results in weakened collagen & connective tissue.
- symptoms include gum disease, poor healing of wounds, joint pain
34
Q
Lathyrism
A
- collagen related disease
- consumption of a common range sweet-pea plant (Lathyrus odoratus).
- Plant contains a toxin (B-aminopropionitrile) that inactivates lysyl oxidase.
- This enzyme facilitates lysine cross-linking in collagen. -
Lathyrism results in bone, joint & blood vessel abnormalities.
35
Q
Marfan’s syndrome
A
- collagen related disease
- a genetic disorder of connective tissue
- involves mutations in the fibrillin gene.
- Fibrillin helps maintain connective tissue integrity. -
Symptoms include excessively long limbs, fingers, toes & joint flexibility.
36
Q
Fibrillin
A
- one of three main proteins of connective tissue
- along with collagen and elastin
