fibrous and globular Flashcards
fibrous proteins
Long, insoluble molecules (do not fold)
High proportion of amino acids with small hydrophobic R-groups.
Long polypeptide chains run parallel to one another and hydrogen bonds form crosslinks between them.
Strong – provide strength
Structural role
Examples: keratin, elastin and collagen
keratin
found in hair, skin, horns, claws, scales, feathers, fur, hooves and nails.
Can be flexible (skin) or hard and tough (nails)
Large proportion of the sulfur-containing amino acid cysteine -strong disulfide bonds to form strong, inflexible and insoluble
materials.
Waterproof impermeable barrier.
The degree of disulfide bonds determines the flexibility – hair has fewer disulfide bonds than nails, making it more flexible.
elastin
made from stretchy molecules called tropoelastin, found in elastic fibres.
Cross-linking and coiling make elastin strong and extensible.
Elastic fibres are present in blood vessels, the alveoli in the lungs, bladder, stomach,
and skin.
Elastin allows blood vessels to withstand
the pressure of the blood travelling
through them.
collagen
Connective tissue found in skin, tendons, ligaments and the nervous system.
Bones are made from collagen and then reinforced with calcium phosphate.
provide mechanical strength and flexibility (does not stretch)
Made of three polypeptides wound together in a long, strong, rope-like structure.
Every third amino acid in the polypeptide is a glycine which allows the close packing of the helix.
Many hydrogen bonds form between the
polypeptides.
Globular proteins
spherical shape - tightly folded polypeptide
chains.
Hydrophobic groups are on the inside and the hydrophilic groups are on the outside
Hydrophilic groups associate with water molecules making many soluble in water.
Examples: hormones, enzymes, opsonins, plasma membrane carrier proteins, haemoglobin, insulin and pepsin.
Prosthetic groups
non-protein part
conjugated protein
chemically bonded to a non-protein part called a prosthetic group
haemoglobin
red, oxygen-carrying pigment in red blood cells.
Each of the 4 subunits contains a haem
prosthetic group that holds an iron ion.
The iron ions bind reversibly with oxygen, and this is how haemoglobin transports oxygen around the body.
When oxygen combines with iron the shape of the pigment changes and the protein is called oxyhaemoglobin.
insulin
Hormone
Regulation of blood glucose concentration.
Soluble (bloodstream)
Precise shape to fit into specific membrane receptors.
Insulin has two polypeptide chains that fold into a tertiary structure and are then joined together by disulphide bonds.
pepsin
enzyme that digests protein in the stomach
Some of pepsin’s amino acids have acidic R-groups which makes it stable in acidic environments.
The tertiary structure is also held together by H bonds and 2 disulfide bridges.
catalase
enzyme which interacts with hydrogen peroxide to speed up its breakdown into water and oxygen.
Catalase is a quaternary protein with
four haem prosthetic groups. There
are iron II ions in the prosthetic
groups which allow the interaction
with hydrogen peroxide.
Protein denaturation
Changes in pH, temperature and salt concentration
Fibrous proteins lose their structural strength when they denature, whereas globular proteins become insoluble and inactive
