Proteins

Question 1

Draw and label a diagram of an amino acid.

Answer 1

Alpha carbon atom in the centre, with a carboxly group (COOH) and an amino group (NH2) off to the side, plus a hydrogen atom above or below the alpha the carbon. A variable R group also above or below the alpha carbon.

Question 2

Identify the part of an amino acid which is variable.

Answer 2

The R group

Question 3

State how many amino acids occur in life.

Answer 3

There are 20 variations of amino acids.

Question 4

Describe the different types of amino acid in life.

Answer 4

Unclear

Question 5

Draw a labelled diagram demonstrating the condensation of peptide bonds. (Explain and draw out)

Answer 5

A peptide bond connects amino acids together when the carboxyl group on one reacts with the amino group on another. The R groups are not involved at this point. The hydroxly from the carboxyl group and the hydrogen from the amino group react to form a dipeptide. Water is released. This is an example of a condensation reaction.

Question 6

Draw a labelled diagram demonstrating the hydrolysis of peptide bonds.

Answer 6

Breaking peptide bonds by addding a water molecule. The amino and carboxyl groups are reformed.

Question 7

Draw a dipeptide and label the peptide bond.

Answer 7

Two amino acids connected with a bond between the carbon atom and the nitrogen.

Question 8

Explain how the variety of amino acids leads to a wide range of dipeptides and very quickly to an incredible variety of polypeptide chains.

Answer 8

The R group of an amino acid is variable, so when they are sequenced together in a condensation reaction the resulting polypeptide chain is different each time.

Question 9

Define the term “polypeptide chain”

Answer 9

A molecule formed from more than two amino acids

Question 10

Define the term ‘‘protein’’

Answer 10

One or more polypeptide chains arranged as a complex macromolecule

Question 11

Describe how one end of a polypeptide chain differs from the other end

Answer 11

In a polypeptide the NH and the CO groups are polar. The H atom is slightly postive and the O atom is slightly negative (delta). So hydrogen bonding can form between them (they are polar)

Question 12

Define the term “primary structure” of a protein and describe how it is held together.

Answer 12

The primary structure is the sequence and number of amino acids in the polypeptide chain. Different proteins have different sequences as amino acids in its primary structure. The primary structure is held together by peptide bonds.

Question 13

Define the term “secondary structure” of a protein.

Answer 13

The folding of the polypeptide chain/primary structure into an alpha helix or a beta pleated sheet due to hydrogen bonds between N-H and C=O groups of amino acids in the same polypeptide chain.
No interactions between R-groups

Question 14

Describe the structure of an alpha helix coil.

Answer 14

Hydrogen bonds may form within the amino acid chain, pulling it into a coil shape.

Question 15

Describe the structure of a beta pleated sheet.

Answer 15

Different region on a long polypeptide chain can parallel to each other. Hydrogen bonds join these regions together, forming a sheet-like structure. The pattern formed by individual amino acids causes the structure to appear pleated.

Question 16

Define the term “tertiary structure” of a protein.

Answer 16

Further folding of the polypeptide chain/secondary structure due to bonds forming between R-groups on the same polypeptide chain, resulting in a 3D shape.

(The R-groups are brought close enough together to react when the protein coils or fold into the secondary structure.)

Question 17

State all the interactions that can occur in the tertiary structure.

Answer 17

• Hydrophobic and Hydrophilic interactions
• hydrogen bonds
• ionic bonds
• disulphide bonds

Question 18

Describe the hydrophobic and hydrophilic interactions in the tertiary structure.

Answer 18

When hydrophobic R groups are close together in the protein they tend to clump together. This means that hydrophilic R groups are more likely to be pushed to the outside which affects how the protein folds up into its final structure. `

Question 19

Describe the hydrogen bonds in the tertiary structure.

Answer 19

These weak bonds form between slightly negatively charged atoms in R-groups and slightly positively charged hydrogen atoms in other R-groups on the polypeptide chain.

Question 20

Describe the ionic bonds in the tertiary structure.

Answer 20

Much stronger than hydrogen bonds. They form between oppositely charged R-groups on different parts of the molecule.

Question 21

Describe the disulphide bonds in the tertiary structure.

Answer 21

These are covalent and the strongest of the bonds but only form between R-groups that contain sulfur atoms.

Question 22

Explain how the primary structure of a protein determines its tertiary structure.

Answer 22

The tertiary is structure is defined by R-group interactions. The primary structure sets the sequence of these R-groups as it is the order of the amino acids, therefore, the tertiary structure is reliant on the primary structure

Question 23

Define the term “quaternary structure” of a protein, and describe how it is held in place. Include all possible bonds.

Answer 23

Interactions between R-groups of more than one polypeptide chain.

• disulphide bridges
• hydrogen bonds
• hyrophobic/ hydrophilic interactions
• ionic bonds
• covalent bonds

Question 24

Define the term“globular protein”.

Answer 24

• Spherical, water soluble proteins.
• Form when proteins fold into their tertiary structure so that hydrophobic R-groups are folded up inside the protein (away from the aqueous environment) and the hydrophilic R-groups are on the outside.
• This makes them soluble and so easily transported.
• Normally have a metabolic role
  (any enzyme is a globular protein).

Question 25

Define the term fibrous protein.

Answer 25

• Strong, structural proteins.
• Form fibres, 2D shape
• Insoluble due to high proportion of hydrophobic R-groups in the primary structure.
• Limited range of amino acids so primary structure is quite repetitive.
• Normally have a structural role.

Question 26

Define the term prosthetic group

Answer 26

A non-protein component of a conjugated protein.

Question 27

Define the term conjugated protein.

Answer 27

A globular protein with a prosthetic group (non-protein component) attached.

Question 28

Describe haemoglobin.

Answer 28

• Globular protein with a quarternary structure
• Has four polypeptide chains (or subunits), 2 alpha and 2 beta.
• Conjugated protein because it has a prosthetic group (a haem group) on each of it’s polypeptide chains
• Haem groups contains iron which binds to oxygen for transportation.

Question 29

Describe Insulin.

Answer 29

• Globular protein with a quarternary structure
• Soluble so it can be transported in the blood to reach the place where it acts.
• Contains two polypeptide chains held together by disulphide bonds.
• Secreted by the pancreas to help regulate blood glucose levels.

Question 30

Describe Amylase.

Answer 30

• Globular protein, NO quarternary structure so made of a single chain of amino acids.
• Catalyses the breakdown of starch
• Its secondary structure has both beta pleated sheet and alpha helix sections.

Question 31

Describe Collagen.

Answer 31

• Fibrous protein
• Quaternary structure has three polpeptide chains wound around each other in a triple helix to form a tough rope-like protein.
• Made of mainly glycine amino acids
• Found in connective tissues such as bone, skin and muscle.
• Very strong, minerals can bind to it to increase its rigidity.

Question 32

Describe Keratin.

Answer 32

• Fibrous, structural protein
• Found in external structures of animals such as skin hair and nails.
• Can be flexible or hard and tough.

Question 33

Describe Elastin.

Answer 33

• Fibrous, quarternary protein
• Made from stretchy molecules called tropoelastin.
• Found in elastic connective tissue such as skin, large blood vessels and some ligaments.
• It’s elasticity allows elastic recoil of tissues.
• It confers strength and elasticity to the skin and other tissues and organs in the body.

Question 34

Compare globular and fibrous proteins

Answer 34

1) FIBROUS:
- structural proteins
- insoluble in water
- 2D shape, forms fibres
- fairly unreactive
2) Globular:
- Mostly involved in physiological, metabolic reactions
- Soluble
- 3D, spherical shape
- reactive

Question 35

What is a lipoprotein?

Answer 35

A conjugated protein that has a lipid component and a protein component.
They are soluble so that they can combine with and then transport fat and other lipids in the blood plasma.

Question 36

Why is cholesterol carried as a lipoprotein?

Answer 36

So that it can be dissolved into the blood and then transported in the blood between body cells and the liver.