3.7 Types of proteins Flashcards
What are the two main groups of proteins? (2 marks)
Globular and fibrous
Describe the tertiary structure of globular proteins. (1 mark)
The hydrophobic R-groups on the amino acids are kept away from the aqueous environment, and the hydrophilic R-groups are on the outside of the protein.
Are globular proteins soluble in water, why/why not? (2 marks)
Yes, globular proteins are soluble in water, due to the hydrophobic R-groups being kept on the inside of the molecule and the hydrophilic R-groups being kept on the outside.
State three main characteristics of globular proteins. (3 marks)
Compact
Roughly spherical shape
Water soluble
Give an example of a globular protein. (1 mark)
Insulin
Haemoglobin
Catalase
Why is it important that globular proteins are water soluble, use insulin as an example. (1 mark)
Hormones are transported in the blood, so need to be soluble.
What is a conjugated protein? (2 marks)
A globular protein that contains a prosthetic group.
What is a prosthetic group? (1 mark)
A non-protein component.
Give 2 examples of prosthetic groups. (2 marks)
Lipid
Carbohydrate
Metal ions
Why is haemoglobin a conjugated protein? (1 mark)
It contains haem prosthetic groups.
Describe the structure of haemoglobin. (2 marks)
2 alpha and 2 beta subunits
Each subunit contains a prosthetic haem group.
What prosthestic group does catalase contain? (1 mark)
Haem
What enables catalase to interact with hydrogen peroxide and speed up its breakdown. (1 mark)
The iron II ions in the haem prosthetic groups.
What does catalase speed up the breakdown of? (1 mark)
Hydrogen peroxide
What is a fibrous protein? (1 mark)
They are formed from long, insoluble molecules, that are string. They do not fold into complex 3D shapes.
Explain why the structure of fibrous proteins is long and organised. (3 marks)
There is a high proportion of amino acids with hydrophobic R-groups in their primary structures.
Contain a limited range of amino acids with small R-groups.
The amino acid sequence in the primary structure is repetitive.
Give 3 examples of fibrous proteins. (3 marks)
Keratin
Elastin
Collagen
Where us keratin found in the body? (1 mark)
Hair, skin, nails
Where is elastin found in the body? (1 mark)
Walls of blood vessels and in the alveoli in the lungs.
Where is collagen found in the body? (1 mark)
Connective tissue: skin, tendons, ligaments, nervous system
What makes keratin so strong? (2 marks)
Contains a large proportion of the sulfur containing amino acid, cysteine.
This results in strong disulfide bridges forming.
Why are nails less flexible than hair? (1 mark)
There are more disulfide bridges in the keratin in the nails.
Describe the structure of elastin. (3 marks)
Many stretchy molecules called tropoelastin are linked to form a large, insoluble, stable, cross-linked structure.
Why is elastin stretchy? (2 marks)
It is made up of many tropoelastin molecules that are able to stretch and recoil without breaking.
Describe the basic structure of collagen. (1 mark)
Three polypeptide chains wound around each other in a triple helix structure to form a tough, rope-like protein.
