Proteins (not full just draft for test)

Question 1

General structure of amino acid

Answer 1

• Carboxyl group -COOH and an amino group -NH2 attached to a carbon atom.
• The difference between different amino acids is the variable ‘R’ group they contain.

Question 2

What are proteins made from?

Answer 2

• The monomers are amino acids.
• Dipeptide is formed when 2 amino acids join.
• Polypeptide is formed when more than 2 A.A join
• Proteins are made of more than 1 polypeptide.

Question 3

Synthesis and breakdown of Dipeptides and Polypeptides by the formation and breakage of peptide bonds.

Answer 3

• Amino acids link by peptide bonds to form dipeptides and polypeptides.
• It is a condensation reaction and opposite is hydrolysis which breaks the peptide bond.
• Peptide bonds are -N

Question 4

Primary structure

Answer 4

• The sequence of amino acids in a polypeptide chain. Different proteins have a different sequence of A.A
• A change in 1 A.A = a change in the structure of the whole protein.
• Held together by peptide bonds.

Question 5

Secondary structure

Answer 5

• Polypeptide chains don’t remain flat and straight.
• H-Bonds form between the -NH and -CO groups of amino acids.
• This makes them curl to a alpha helix or fold to a beta pleated sheet.

Question 6

Tertiary structure

Answer 6

More bonds form between parts of the coiled and folded polypeptide chain

• Ionic bonds: Attractions between negatively charged R groups and positively charged R groups on different parts of the molecule.
• Disulfide bonds: When two molecules of amino acid named CYSTEINE come close together, a sulfur atom in 1 cysteine bonds to the other sulfur in the other cysteine- forming a disulphide bond.
• Hydrophobic and Hydrophilic interactions: Hydrophobic R groups clump together and force hydrophilic R groups on the outside which affects how the protein folds up.

Hydrogen bonds: Form between partially positive Hydrogen atoms form weak H-Bonds with partially negative charged atoms in other R groups.

Question 7

Quaternary structure

Answer 7

• This structure is the way these polypeptide chains are assembled together. Quaternary structure is determined by tertiary structure.

Question 8

Globular proteins

Answer 8

• Round and compact.
• In globular protein, the hydrophilic R groups are pushed on the outside. This is caused by hydrophobic hydrophilic interactions in the tertiary structure.
• This makes globular proteins soluble so they are easily transported.

Question 9

Haemoglobin

Answer 9

• Globular protein that carries oxygen around the body in red blood cells.
• It si a CONJUGATED protein. This means it is attached to a non protein group.
• The non protein part is called a PROSTHETIC group.
• Each of the 4 polypeptide chains in haemoglobin has a prosthetic group called Haem.
• A Haem group contains Iron which Oxygen binds to.

Question 10

Insulin and Amylase

Answer 10

Insulin

• Hormone secreted by pancreas. It helps regulate the blood glucose level.
• It is soluble so it can be transported to tissues.
• An insulin molecule has 2 polypeptide chains which are held together by disulphide bonds.
• When they are in the pancreas, 6 of these bind to form globular structures.

Amylase:

• Amylase is an enzyme that catalyses the breakdown of starch in the digestive system.
• Made from a single chain of amino acid and it’s secondary structure has BOTH alpha helix and beta pleated sheets.

Question 11

Fibrous proteins

Answer 11

• Fibrous proteins are touch and rope shaped. They are insoluble and strong.
• They’re structural proteins that are fairly unreactive.

Collagen:

• Found in animal connective tissue, such as bone, skin & muscle.
• Minerals can bind to the protein to increase rigidity.

Keratin:

• Found in many external structures of animals, such as skin, hair, nails, feathers and horns.
• It can either be flexible like hair or hard and tough like nails.

Elastin:

• Found in elastic connective tissue, such as skin, large blood vessels and some ligaments.
• It’s elastic so it allows tissues to return to original shape after being stretched.

Question 12

Biuret test for proteins

Answer 12

1. Test solutions needs to be alkaline, so add a few drops of sodium hydroxide solutions.
2. Then add some copper(ii) sulfate solution.

If protein is present, the solution turns purple.