Tertiary structure

Question 1

what are Fibrous proteins

Answer 1

• Scleroproteins
• 2° structures form long parallel fibres and sheets
• Usually insoluble

Question 2

what are the two types of fibrous proteins important for support and strength

Answer 2

• Collagen

* Keratins

Question 3

give example in where alpha and beta keratin are found

Answer 3

• α-keratins
• Mammalian hair and nails
• B-keratins
• Invertebrate silks, reptile claws, scales and shells
• Avian feathers, beaks and claws

Question 4

Collagen structure and properties

Answer 4

• Superhelices of glycine-rich α-helices
• Main protein of connective tissue
• Most abundant protein (25% of total protein)
• Strong and elastic

Question 5

α-Keratins: Hair and nails structures and properties

Answer 5

• Composed of coiled-coils of two α-helices that assemble together into larger fibres
• Strong and inextensible
• Insoluble and chemically inert
• Disulphide bridges cross link coiled coils

Question 6

beta-Keratins: Fibroin structures and properties

Answer 6

• Fibroin is found in silk cloth and spider webs
• Layers of anti-parallel β sheets rich in Ala and Gly residues
• Small side chains interdigitate and allow close packing of the sheets
• Great strength
• Sheets joined by amorphous stretches which confer elasticity

Question 7

what are Globular Proteins properties

Answer 7

• Mixture of irregularly folded secondary elements to form a compact 3-D spherical shape

• Usually soluble with inner hydrophobic core
• Transported easily in body fluids
• Important functions in cell chemistry

Question 8

examples of Globular Proteins?

Answer 8

• Myoglobin
• Haemoglobin
• Immunoglobins

Question 9

where is it found Myoglobin and what is its structure

Answer 9

oxygen
porphyrin and fe+2
histidine

Question 10

what are Quaternary Structure

Answer 10

• Assembly of subunits (separate polypeptide chains) of multimeric proteins
• Enabled by van der Waals interactions

Question 11

structure of Haemoglobin A

Answer 11

• Tetramer

• 4 chains/subunits (α2, beta-2)
• 4 haem molecules (porphyrin and Fe2+)

Question 12

how do these diseases arise

Answer 12

• Sickle Cell Anaemia
• beta-chain mutation (Glu to Val)
• Thalassaemia
• Underproduction of globin chains (genetic)
• beta-thalassaemia (beta-chains decrease )
• α-thalassaemia (α-chains decrease )

• Porphyria

• decreased Haem production (defects in synthetic pathway)
• Photosensitivity, hirsutism and discolouration

Question 13

what are Immunoglobulins

Answer 13

• Y-shaped proteins (antibodies) used by the immune system to identify and combat non-self

• 4 chains linked by disulphide bridges
• 2 large H (heavy) chains
• 2 short L (light) chains
• Chain tips have a variable structure
• Chain tips form specific binding sites for non-self targets (antigens)
• Antigen recognition by an antibody tags it for attack by other parts of the immune system

Question 14

Some proteins tend to aggregate into non-functional structures during assembly

what is a Chaperone proteins

Answer 14

• Chaperone proteins assist the non-covalent folding/unfolding of a protein

Question 15

Chaperone protein functions

Answer 15

• Prevent aggregation into non-functional units
• Repair misfolded/heat damaged units
• Require ATP for energy to assist folding
• Chaperonin is a type of chaperone

Question 16

why is preventing aggregation important?

Answer 16

• Aggregation can cause disease

* Prion and amyloid

Question 17

what occurs to proteins when pH changes

Answer 17

Low pH = high H+ concentration (acidic)

Adding H+ neutralises the COO- part of the ionic bond removing its charge

High pH = low H+ concentration (alkaline)

Removing H+ neutralises the NH3+ part of the ionic bond removing its charge

Question 18

how can Denaturation occur from extreme pH?

Answer 18

• Extreme pH changes
• Break ionic bonds
• Degrades tertiary structure
• Can produce insoluble secondary structures

Question 19

how can Denaturation occur from extreme heat?

Answer 19

• Vibrates and breaks hydrogen and ionic bonds

* Pyrexia

Question 20

Give examples of Denaturants

Answer 20

• Alcohol, acetone (solvents)