Proteins

Question 1

Proteins : elements, monomer, function

Answer 1

CHON(S), Amino acids, structural fibres, enzymes, hormones, antibodies,

Question 2

Primary structure

Answer 2

A sequence of amino acids in a polypeptide chain held together by peptide chains. Different sequences of amino acids form different proteins in primary structure.

Question 3

Secondary structure

Answer 3

Hydrogen bonds that form between the NH and CO groups of the amino acids make the chain coil into an alpha helix or fold into a beta pleated sheet

Question 4

Tertiary structure

Answer 4

Coiled or folded chains are folded and coiled Further. more bonds are formed between parts of the polypeptide chains. Forming a 3-D structure.

Question 5

Ionic bonds in proteins

Answer 5

attractions between negatively charged R groups and positively charged R groups on different parts of the molecule

Question 6

Disulphide bonds in proteins

Answer 6

Whenever two molecules of the amino acid cysteine come close together the sulphur atom in one cysteine bonds to the other one

Question 7

Hydrophobic and hydrophilic interactions

Answer 7

When hydrophobic (Water repelling) our groups are close together in protein they tend to clump together inside the molecule away from water. This means that hydrophilic (water attracting) all groups are more likely to be pushed to the outside which affects how the protein folds up into its final structure

Question 8

Hydrogen bonds in protein

Answer 8

These weak bonds form between slightly positively charged hydrogen atoms in an R group and slightly negative charged atom in another R group of the polypeptide chain

Question 9

Quaternary structure

Answer 9

Made of several polypeptide chains held together by cross-link covalent bonds.

Question 10

Globular proteins

Answer 10

• are round and compact
• The hydrophilic R groups on the amino acids are pushed to outside of the molecules
• this makes globular protein soluble
• so they are easily transported in fluids
• metabolic function
• can be conjugated ( contains a non-protein group (prosthetic group)
• Irregular amino acid sequence To
• more sensitive to changes eg in heat or pH

Question 11

Fibrous proteins

Answer 11

• Tough and long and narrow rope shaped
• Strong and insoluble
• Are structural proteins so fairly unreactive
• few repetitive amino acid sequence
• Less sensitive to changes eg in heat or pH

Question 12

Globular protein examples

Answer 12

Haemoglobin, insulin, Amylase

Question 13

Fibrous protein examples

Answer 13

Collagen, keratin, elastin, actin

Question 14

Structure and function of Haemoglobin (globular)

Answer 14

• globular
• carries oxygen around the body in red blood cells.
• It is known as a conjugated protein (non-protein group attached (a prosthetic group))
• all four polypeptide chains in haemoglobin has a prosthetic group called haem
• it contains iron which oxygen binds to.
• it is soluble

Question 15

What is the function and structure of Insulin (globular)

Answer 15

-is a hormone that regulates the blood glucose level secreted by the pancreas.
- Its solubility is important. It means it can be transported in the blood to the tissue to act
- consist of two polypeptide chains which are held together by disulphide bonds
- when they’re in the pancreas, six of these molecules bind together to form large globular structure.

Question 16

Function and structure of Amylase (globular)

Answer 16

• Amylase is an enzyme that catalyses the
  Hydrolysis of starch in the digestive system.
• It is made of a single chain of amino acid
• in secondary structure contains both alpha and beta sheets
• are globular proteins.
• is soluble

Question 17

Function and structure of Collagen (fibrous)

Answer 17

• forms animal connective tissues such as bone skin and muscle.
• It is a very strong molecule so not soluble
• minerals can bind to the protein to increase its rigidity eg in bones.
• forms a triple helix then a fibre
• made mostly of glycine

Question 18

Function and structure of Keratin (fibrous)

Answer 18

• Found in many of the external structures of animals such as skin, hair, nails, feathers, and horns
• it can be flexible eg skin or hard and tough eg nails so not soluble

Question 19

Function and structure of Elastin (fibrous)

Answer 19

• Found in elastic connective tissue such as skin, large blood vessels and some ligaments
• It is elastic so allows tissues to recoil to their original shape after being stretched

Question 20

Explain how the globular structure of haemoglobin makes it suited to its function

Answer 20

The hydrophilic side chains are on the outside of the molecule meaning it is soluble in water which makes it a good transport for oxygen in the blood

Question 21

What is meant by glycoprotein?

Answer 21

A protein combined with a carbohydrate

Question 22

Explain how the structure of collagen contributes to its strength And how it suited to its function

Answer 22

Many hydrogen bonds and many strong covalent bonds which keep triple helix together, contains amino acids which form a tight coiled helix which form fibers. This means it can form strong rigid structures like bone

Question 23

State two properties of a globular protein that are different to those of a fibrous protein

Answer 23

Soluble and reactive

Question 24

Explain how the structure of insulin makes it soluble

Answer 24

The hydrophobic R groups on the amino acids of the insulin clump together causing the hydrophilic groups to be pushed to the outside of the molecule making it soluble

Question 25

How to test for a protein

Answer 25

Add a few drops of biuret Regent (Sodium hydroxide and copper sulphate) to the sample, a change from Blue to purple is a positive result

Question 26

Compare the bonding in secondary and tertiary structure of a protein

Answer 26

Secondary structure only has hydrogen bonds but tertiary structures also contain ionic sulphide hydrophobic and hydrophilic interactions