3.1.4.1 Proteins - structure, function and biuret test

Question 1

What decides the amino acid sequence that determines the primary structure of a protein?

Answer 1

A DNA sequence

Question 2

Describe the ionic bonds that hold the tertiary structure of a protein in place.

Answer 2

Weaker than disulfide bonds

Easily broken by changes in pH

Form between free carboxyl and amino groups in the polypeptide chain

Question 3

What does Biuret reagent contain?

Answer 3

Concentrated Copper (II) sulfate solution

Question 4

Describe the disulfide bonds that hold the tertiary structure of a protein in place.

Answer 4

Strong

Not easily broken

Occur between two cysteine amino acids

Question 5

Name the bonds that hold the tertiary structure of a protein in place.

Answer 5

Disulfide Bonds

Hydrogen Bonds

Ionic Bonds

Question 6

What do the below instructions describe:

1. Place a 2cm3 of food in a test tube.
2. Add 2 cm3 of sodium hydroxide solution at room temperature.
3. Add a few drops of very dilute copper (II) sulfate solution (Biuret reagent)
4. Observe and record colour change.

Answer 6

The Biuret test for proteins.

Question 7

Identify the molecule

Answer 7

Amino acid

Question 8

Name 3 fibrous type proteins

Answer 8

Collagen

Keratin

Silk

Question 9

What is the monomer unit of a protein?

Answer 9

Amino acid

Question 10

What do we call 2 amino acids chemically joined together?

Answer 10

Dipeptide

Question 11

What is meant by a fibrous protein?

Answer 11

A protein made from many parallel polypeptide chains. These chains main form an α helix shape.

Fibrous proteins are usually insoluble in water.

Question 12

Which colour does Biuret solution turn in the presence of protein?

Answer 12

Biuret changes from blue to purple.

Question 13

Give 3 examples of enzymes

Answer 13

Amylase

Protease

Lipase

Question 14

Which colour does Biuret reagent turn in the absence of protein?

Answer 14

It remains a blue colour

Question 15

Identify the circled group

Answer 15

R group

Question 16

Idenitfy the circled group

Answer 16

Amine group

Question 17

What is meant by the tertiary structure of a protein?

Answer 17

When the α helix or β pleated sheets of the secondary protein structure are folded even more to give a complex, specific 3D structure.

Question 18

What colour is Biuret reagent?

Answer 18

Blue

Question 19

What is meant by a globular protein?

Answer 19

A protein made from few polypeptides, which form a spherical shape.

They are usually water soluble.

Question 20

Describe the hyodrogen bonds that hold the tertiary structure of a protein in place.

Answer 20

Individually weak and easily broken

Cumulatively provide some strength

Question 21

What is the polymer unit of a protein?

Answer 21

Polypeptide

Question 22

What is meant by the secondary structure of a protein?

Answer 22

When hydrogen bonds form between the C=O and -NH groups of the amino acids that form a polypeptide. This causes a polypeptide chain to fold into a 3D shape such as an α helix or β pleated sheet.

Question 23

How can a polypeptide be broken down into amino acids?

Answer 23

Hydrolysis

Question 24

What is meant by the primary structure of a protein?

Answer 24

The sequence of the amino acids in the polypeptide that forms the protein.

Question 25

How many naturally occurring amino acids are their?

Answer 25

20

Question 26

Name 3 globular type proteins

Answer 26

Enzymes Hormones Transport proteins

Question 27

What is the only difference between different amino acids?

Answer 27

the R-group

Question 28

What is the function of the protein keratin?

Answer 28

the main component of hard structures such as hair, nails, claws and hooves.

Question 29

Give an example of a transport protein

Answer 29

Haemoglobin in red blood cells Cell membrane transport protiens

Question 30

Which type of bond forms between two amino acids?

Answer 30

Peptide bond

Question 31

A change of just 1 amino acid in the primary structure of a protein can cause what to happen?

Answer 31

A change in the shape of the protein. The protein will stop working. The protein will stop working as well.

Question 32

Every protein has a very _________ 3D shape, which is why they can carry out very ________ functions

Answer 32

specific specific

Question 33

Name the 3 groups present on in an amino acids molecule.

Answer 33

Amino group (NH₂) Carboxyl group (COOH) R-group

Question 34

Give 2 examples of hormones

Answer 34

Insulin Oestrogen

Question 35

What is released when two amino acids chemically join together?

Answer 35

A water molecule (from condensation reaction)

Question 36

Identify the circled group

Answer 36

Carboxyl group

Question 37

How would you carry out the Biuret test for proteins?

Answer 37

1. Place a 2cm3 of food in a test tube. 2. Add 2 cm3 of sodium hydroxide solution at room temperature. 3. Add a few drops of very dilute copper (II) sulfate solution (Biuret reagent) 4. Observe and record colour change.

Question 38

Which type of reaction takes place during the polymerisation of amino acids?

Answer 38

Condensation reaction

Question 39

What is the function of the protein collagen?

Answer 39

the main component of connective tissue such as tendons and cartilage

Question 40

Which part of the amino acid structure is different in the 20 different amino acids.

Answer 40

The R group

Question 41

Give an example of a prosthetic group that is asociated with a quaternary protein structure.

Answer 41

The iron containing 'Haem' group in the haemoglobin protein.

Question 42

What is meant by the quaternary structure of a protein?

Answer 42

(Molecule contains) more than one polypeptide (chain); There may also be prosthetic (non protein) groups attached to these proteins.

Question 43

Describe the structure of proteins

Answer 43

1. Polymer of amino acids; 2. Joined by peptide bonds; 3. Formed by condensation; 4. Primary structure is order of amino acids; 5. Secondary structure is folding of polypeptide chain due to hydrogen bonding; 6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic/disulfide bonds; 7. Quaternary structure is two or more polypeptide chains;

Question 44

Describe how proteins are digested in the gut

Answer 44

1. Hydrolysis of peptide bonds; 2. Endopeptidases break polypeptides into smaller peptide chains; 3. Exopeptidases remove terminal amino acids; 4. Dipeptidases hydrolyse/break down dipeptides into amino acids;

Question 45

describe how a peptide bond is formed between 2 AA to form a dipeptide

Answer 45

condensation reaction/loss water between amine and carboxyl group

Question 46

describe how the secondary structure of a protein is produced

Answer 46

H bonds between NH and C=O forming beta pleat sheets or alpha helix

Question 47

2 proteins have same number and type of AA but different tertiary structire - why?

Answer 47

different sequence of AA therefore ionic/H/disulphide bonds form in different places