Types of proteins 3.7 Flashcards
what are the characteristics of globular proteins
globular proteins are compact, water soluble and usually roughly spherical in shape
how are globular proteins formed
they form when proteins fold into their tertiary structures in such a way that the hydrophobic R-groups on the amino acids are kept away from the aqueous environment.
The hydrophilic R-groups are on the outside of the protein.
how does the structure of globular proteins effect its properties
due to the proteins structure they are soluble in water as the hydrophilic R-groups are on the outside
what protein type is insulin and what is its function
insulin is a globular protein, it is a hormone involved in the regulation of blood glucose concentration, hormones are transported by blood and so need to be soluble
hormones also have to fit into specific receptors on cell-surface membranes to have their effect and therefore need to have precise shapes
what are conjugated proteins
conjugated proteins are globular proteins that contain a non-protein component called a prosthetic group
what are proteins with no prosthetic group called
simple proteins
what is an example of a prosthetic group else where in biology
haem groups are examples of a prosthetic group. they contain an iron (II) ion (Fe2+)
catalase and haemoglobin both contain haem groups
what is catalase and what is its function
catalase is an enzyme
catalase is a quaternary protein containing 4 haem prosthetic groups.
The presence of the iron II ions in the prosthetic groups allow catalase to interact with hydrogen peroxide and speed up its breakdown
what are fibrous proteins
fibrous proteins are formed from long, insoluble molecules
what is the structure of fibrous protein
-high proportion of amino acids with the hydrophobic R-groups in their primary structures
-They contain a limited range of amino acids, usually with small R-groups
-The amino acid sequence in the primary structure is usually quite repetitive
what are some examples of fibrous proteins
Keratin, elastin and collagen are examples of fibrous proteins
where is keratin found in the body
keratin is a group of fibrous proteins present in hair, skin and nails.
what is the structure of keratin
It has a large proportion of the sulphur-containing amino acid (cysteine).
This results in many strong disulphide bonds (disulphide bridges) forming strong, inflexible and insoluble materials.
what does the number of disulfide bonds influence about a compound and give an example where this can be seen
The degree of disulfide bonds determines the flexibility - hair contains fewer bonds making it more flexible than nails, which contain more bonds
where is elastin found in the body
elastin is a fibrous protein found in elastic fibres (along with small protein fibres)
where are elastic fibres found
elastic fibres are present in the walls of blood vessels and in the alveoli of the lungs
what properties does elastic fibres give the structures its found in
they give these structures the flexibility to expand when needed, but also to return to their normal size
what is the structure of elastin and how it is stabilised
elastin is made by linking many soluble tropoelastin protein molecules to make very large, insoluble and stable, cross-linked structure
The structure is stabilised by cross-linking covalent bonds involving the amino acid lysine, but the polypeptide structure still has flexibility
what is collogen and where it is found
it is a connective tissue found in skin, tendons, ligaments and the nervous system
in some tissues multiple fibres of collagen aggregate into larger bundles. This is the structure found in ligaments and tendons. In skin, collagen fibres form a mesh that is resistant to tearing
what is the structure of collagen
Collagen molecules have 3 polypeptide chains wound around each other in a triple helix structure to from a tough, rope-like protein
Many hydrogen bonds form between the polypeptide chains forming long quaternary proteins with staggered ends. These allow the proteins to join end to end, forming long fibrils called tropocollagen
what is the function and features of tropoelastin
tropoelastin molecules are able to stretch and recoil without breaking, acting like small springs. They contain alternate hydrophobic and lysine-rich areas
How is elastin formed
elastin is formed when multiple tropoelastin molecules aggregate via interactions between the hydrophobic areas.
what is the function of elastin
elastin confers strength and elasticity to the skin and other tissues and organs in the body
whats the structure of the polypeptide chains involved in the structure of collagen
Every 3rd amino acid in the polypeptide chains is glycine, which is a small amino acid. Its small side allows the 3 protein molecules to form a closely packed triple helix.
How is collagen stabilised by its structure
collagen contains high proportions of the amino acid proline and hydroxyproline. The R-groups in these amino acids repel each other and this adds to the stability of collagen
