Proteins - 1.6

Question 1

What are amino acids?

Answer 1

The basic monomer units which combine to make up a polymer called a polypeptide.

Question 2

What can polypeptides be combined to form?

Answer 2

Proteins

Question 3

What evidence do amino acids provide for evolution?

Answer 3

The fact that the same 20 amino acids occur naturally in all living organisms provide indirect evidence for evolution.

Question 4

What is the central atom of every amino acids?

Answer 4

Carbon

Question 5

What four chemical groups attach to the central carbon atom of an amino acid?

Answer 5

• Amino group (-NH2)
• Carboxyl group (-COOH)
• Hydrogen atom (-H)
• R (side) group

Question 6

What is the amino group of an amino acid?

Answer 6

A basic group from which the amino part of the name amino acid is derived.

Question 7

What is the carboxyl group of an amino acid?

Answer 7

An acidic group which gives the amino acid the acid part of its name.

Question 8

What is the R (side) group of an amino acid?

Answer 8

A variety of different chemical groups. Each amino acid has a different R group. These 20 naturally occurring amino acids differ only in their R (side) group.

Question 9

What can two amino acids combine to form?

Answer 9

A dipeptide.

Question 10

In what reaction are dipeptides and polypeptides formed?

Answer 10

Condensation reaction.

Question 11

How is the water produced in the condensation reaction of two amino acids?

Answer 11

By combining an -OH group from the carboxyl group of one amino acid with an -H from the amino group of another amino acid.

Question 12

What bond is formed when two amino acids are joined?

Answer 12

Peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.

Question 13

How can a peptide bond be broken?

Answer 13

Hydrolysis.

Question 14

In what process are many amino acid monomers joined together?

Answer 14

Polymerisation.

Question 15

What is a chain of hundreds of amino acids called?

Answer 15

Polypeptide.

Question 16

What does the sequence of amino acids in a polypeptide form?

Answer 16

The primary structure of any protein.

Question 17

How is the primary structure of a protein (amino acid sequence) determined?

Answer 17

By DNA

Question 18

Why is there an almost limitless of number of possible types of primary protein structure?

Answer 18

Polypeptides have many (usually hundreds) of the 20 naturally occurring amino acids joined in different sequences, so it follows that there is an almost limitless number of possible combinations, and therefore types, of primary protein structure.

Question 19

What does the primary structure of a protein determine?

Answer 19

The proteins shape and hence its function.

Question 20

What can a change in a single amino acid in a proteins primary structure lead to?

Answer 20

A change in the shape of the protein, so it may stop carrying out its function.

Question 21

What is the secondary structure of a protein?

Answer 21

when hydrogen bonds cause the long polypeptide chain to be twisted into 3D shape, such as alpha-helix or Beta pleated sheets.

Question 22

How are the hydrogen bonds formed in the secondary structure of a protein?

Answer 22

The linked amino acids that make up a polypeptide possess both -NH and -C=O groups on either side of every peptide bond. The hydrogen of the -NH group has an overall positive charge while the O of the -C=O group has an overall negative charge. These two groups therefore readily form weak bonds, called hydrogen bonds.

Question 23

What is the tertiary structure of proteins?

Answer 23

The alpha-helices of the secondary protein structure can be twisted and folded even more to give the complex, and often specific, 3D structure of each protein.

Question 24

How its the tertiary structure of a protein maintained?

Answer 24

By a number of bonds, such as disulphide bridges, ionic bonds and hydrogen bonds.

Question 25

What bonds are important in the tertiary structure of a protein?

Answer 25

• Disulphide bridges - which are fairly strong and therefore not easily broken.
• Ionic bonds - Which are formed between any carboxyl and amino groups that are not involved in forming peptide bonds. They are weaker than disulphide bond and are easily broken by changes in pH.
• Hydrogen bonds - which are numerous but easily broken.

Question 26

Why is the 3D structure of a protein important?

Answer 26

It is important when it comes to how it functions. It makes each protein distinctive and allows it to recognise, and be recognised by, other molecules. It can interact with them in a very specific way.

Question 27

What is the quaternary structure of a protein?

Answer 27

When large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. There may also be non-protein (prosthetic) groups associated with the molecules, such as the iron-containing haem group in haemoglobin.

Question 28

What is the test for proteins called?

Answer 28

The Biuret test

Question 29

What does the Biuret test detect?

Answer 29

Peptide bonds

Question 30

How is the Biuret test conducted?

Answer 30

• Place a sample of the sodium to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature.
• Add a few drops of very dilute (0.05%) copper (II) sulphate solution and mix gently.
• A purple colouration indicates the presence of peptide bonds and hence a protein. If no protein is present, the solution remains blue.

Question 31

What are the two basic types of molecular shapes of proteins?

Answer 31

• Fibrous proteins, such as collagen.

- Globular proteins, such as enzyme and haemoglobin.

Question 32

What function do fibrous proteins have?

Answer 32

Structural functions.

Question 33

What function do globular proteins have?

Answer 33

Metabolic functions.

Question 34

What is the molecular structure of fibrous proteins?

Answer 34

Primary - unbranched polypeptide chains.
Secondary - the polypeptide chain is very tightly wound. Lots of the amino acid glycine helps close packing.
Tertiary - The chain is twisted into a second helix.
Quaternary - made up of three such polypeptide chains wound together in the same way as individual fibre are wound together in a rope.

Question 35

Where is collagen found?

Answer 35

In tendons, which join muscles to bones. When a muscle contracts, the bone is pulled in the direction of the contraction.

Question 36

How are individual collagen polypeptide chains in the fibres held together?

Answer 36

By bonds between amino acids of adjacent chains.
The points where one collagen molecules ends and the next begins are spread throughout the fibre rather than all being in the same position along it.