2.2.10 proteins 3: fibrous & globular proteins Flashcards
fibrous proteins
- relatively long, thin structure
- insoluble in water
- metabolically inactive
- often have structural role in organism
globular protein
- molecules of relatively spherical shape
- soluble in water
- often have metabolic roles in organism
prosthetic group
non-protein component that forms permanent part of functioning protein molecule
properties of fibrous proteins
- regular, repetitive sequences of amino acids
- usually insoluble in water
- features enable them to form fibres = structural function
properties of globular proteins
- roll into almost spherical shape
- hydrophobic R groups = inwards to centre of molecule
- hydrophilic R groups = outside & makes protein soluble in water so molecules cluster around
- often have very specific shapes & can take up roles incl. enzymes, hormones (eg. insulin) & haemoglobin
examples of fibrous proteins
- collagen/elastin (connective tissue)
- keratin (hair)
properties/functions of collagen (fibrous protein)
- function: provide mechanical strength
eg.
- artery walls = prevents bursting due to high pressure of blood
- tendons = connect muscle to bone which allows them to pull on bones
- bones = reinforced with calcium phosphate (makes them hard) but made of collagen
- cartilage/connective tissue
properties/functions of keratin (fibrous protein)
properties:
- rich in cysteine = disulfide bridges between polypeptide chains (alongside h bonds) makes molecule very strong
- found wherever needs to be hard/strong
- eg. finger nails, hair, hoofs, horns, scales, fur & feathers
functions:
- provides mechanical protection
- provides impermeable barrier to infection
- (as waterproof) prevents entry of water-borne pollutants
properties/functions of elastin (fibrous protein)
properties:
- cross-linking & coiling = strong & extensible
function:
- skin can stretch around bones/muscles
- lungs = allows inflation/deflation
- bladder = expand to hold urine
- helps blood vessels stretch/recoil as blood pumped through them & helps maintain pressure
structure of haemoglobin (globular protein)
quaternary structure:
- 4 polypeptides = 2 alpha-globin chains & 2 beta-globin chains
- each has own tertiary structure
= fitted together: 1 haemoglobin molecule
- interactions between polypeptides gives molecule specific shape
- at 1 position on outside of each chain, there’s space for a haem group (prosthetic group) = iron ion
function of haemoglobin (globular protein)
- in lungs
- carry oxygen from lungs to tissues
in lungs:
- oxygen molecule binds to iron in each haem group (4)
- haemoglobin turns from purple/red to bright red
- oxygen released by haemoglobin when reaches tissues
what’s a protein called when it’s associated with a haem group
conjugated protein
what’s a haem group
(prosthetic group)
essential part of molecule (couldn’t function without) but not made of amino acids
structure, properties & function of insulin (globular protein)
structure:
- 2 polypeptide chains
- A chain = begins with section of alpha-helix
- B chain = ends with section of beta-pleated sheet
- both fold into tertiary structure & joined by disulfide links
properties:
- amino acids w/ hydrophilic R group on outside of molecule = soluble in water
function:
- insulin binds to glycoprotein receptors on outside of muscle/fat cells = increase uptake of glucose from blood & rate of consumption of glucose
structure, function & properties of pepsin (globular protein)
= enzyme that digests protein in stomach
structure:
- single polypeptide chain (327 amino acids)
- folds into symmetrical tertiary structure
- held by hydrogen bonds & 2 disulfide bridges
properties/function:
- few amino acids with basic R groups (4) & many with acidic (43) = so stable in acidic environments
