Types of proteins 3.7

Question 1

what are the characteristics of globular proteins

Answer 1

globular proteins are compact, water soluble and usually roughly spherical in shape

Question 2

how are globular proteins formed

Answer 2

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.

Question 3

how does the structure of globular proteins effect its properties

Answer 3

due to the proteins structure they are soluble in water as the hydrophilic R-groups are on the outside

Question 4

what protein type is insulin and what is its function

Answer 4

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

Question 5

what are conjugated proteins

Answer 5

conjugated proteins are globular proteins that contain a non-protein component called a prosthetic group

Question 6

what are proteins with no prosthetic group called

Answer 6

simple proteins

Question 7

what is an example of a prosthetic group else where in biology

Answer 7

haem groups are examples of a prosthetic group. they contain an iron (II) ion (Fe2+)
catalase and haemoglobin both contain haem groups

Question 8

what is catalase and what is its function

Answer 8

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

Question 9

what are fibrous proteins

Answer 9

fibrous proteins are formed from long, insoluble molecules

Question 10

what is the structure of fibrous protein

Answer 10

-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

Question 11

what are some examples of fibrous proteins

Answer 11

Keratin, elastin and collagen are examples of fibrous proteins

Question 12

where is keratin found in the body

Answer 12

keratin is a group of fibrous proteins present in hair, skin and nails.

Question 13

what is the structure of keratin

Answer 13

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.

Question 14

what does the number of disulfide bonds influence about a compound and give an example where this can be seen

Answer 14

The degree of disulfide bonds determines the flexibility - hair contains fewer bonds making it more flexible than nails, which contain more bonds

Question 15

where is elastin found in the body

Answer 15

elastin is a fibrous protein found in elastic fibres (along with small protein fibres)

Question 16

where are elastic fibres found

Answer 16

elastic fibres are present in the walls of blood vessels and in the alveoli of the lungs

Question 17

what properties does elastic fibres give the structures its found in

Answer 17

they give these structures the flexibility to expand when needed, but also to return to their normal size

Question 18

what is the structure of elastin and how it is stabilised

Answer 18

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

Question 19

what is collogen and where it is found

Answer 19

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

Question 20

what is the structure of collagen

Answer 20

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

Question 21

what is the function and features of tropoelastin

Answer 21

tropoelastin molecules are able to stretch and recoil without breaking, acting like small springs. They contain alternate hydrophobic and lysine-rich areas

Question 22

How is elastin formed

Answer 22

elastin is formed when multiple tropoelastin molecules aggregate via interactions between the hydrophobic areas.

Question 23

what is the function of elastin

Answer 23

elastin confers strength and elasticity to the skin and other tissues and organs in the body

Question 24

whats the structure of the polypeptide chains involved in the structure of collagen

Answer 24

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.

Question 25

How is collagen stabilised by its structure

Answer 25

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