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
- tend to roll up into almost spherical shape
- hydrophobic R groups = inwards to centre of molecule
- hydrophilic R groups = outside
^^ makes protein water soluble –> molecules easily cluster around & bind to them - 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:
- artery walls = layer of collagen prevents it bursting due to high pressure of blood
- tendons = made of collagen & connect muscle to bone - allowing them to pull on bones
- bones = made from collagen & reinforced with calcium phosphate (makes them hard)
- cartilage/connective tissue = made of collagen
properties/functions of keratin (fibrous protein)
properties
- rich in cysteine = lots of disulfide bridges between polypeptide chains –> (alongside h bonds) makes molecule very strong
- found wherever body part needs to be hard/strong
- found in 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
- found in living things where they need to stretch/adapt shape
function
- skin can stretch around bones/muscles due to elastin
- elastin in lungs = allows inflation/deflation
- elastin in bladder = expand to hold urine
- helps blood vessels stretch/recoil as blood pumped through them & helps maintain pressure
structure of haemoglobin (globular protein)
- quaternary:
–> 4 polypeptides = 2 alpha-globin chains & 2 beta-globin chains
–> each has own tertiary structure
^^ when 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)
- carry oxygen from lungs to tissues
- lungs: oxygen molecule binds to iron in each haem group (4)
- when binds = 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, function & properties 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/functions
- amino acids w/ hydrophilic R group = on outside of molecule
–> soluble in water
- 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 h bonds & 2 disulfide bridges
properties/function
- few amino acids with basic R groups (4) & many with acidic (43)
–> so stable in acidic environment (few basic groups to accept H+
ions) = little effect on enzyme structure
