3.1.4.1 Proteins - structure, function and biuret test Flashcards Preview

SHHS - Science - NEW AQA A-Level Biology (Year 1) > 3.1.4.1 Proteins - structure, function and biuret test > Flashcards

Flashcards in 3.1.4.1 Proteins - structure, function and biuret test Deck (47):
1

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

A DNA sequence

2

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

Weaker than disulfide bonds

Easily broken by changes in pH

Form between free carboxyl and amino groups in the polypeptide chain

3

How would you carry out the Biuret test for proteins?

  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.

3

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

Biuret changes from blue to purple.

3

What does Biuret reagent contain?

Concentrated Copper (II) sulfate solution

4

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

Strong

Not easily broken

Occur between two cysteine amino acids

5

What do we call 2 amino acids chemically joined together?

Dipeptide

5

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

Disulfide Bonds

Hydrogen Bonds

Ionic Bonds

6

Name 3 fibrous type proteins

Collagen

Keratin

Silk

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.

The Biuret test for proteins.

7

Identify the molecule

Q image thumb

Amino acid

A image thumb
9

What is the monomer unit of a protein?

Amino acid

11

What is meant by a fibrous protein?

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

Fibrous proteins are usually insoluble in water.

13

Give 3 examples of enzymes

Amylase

Protease

Lipase

14

Give 2 examples of hormones

Insulin

Oestrogen

14

What is the function of the protein keratin?

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

14

What is meant by the primary structure of a protein?

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

14

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

It remains a blue colour

15

What is meant by the secondary structure of a protein?

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.

15

Identify the circled group

Q image thumb

R group

A image thumb
16

Idenitfy the circled group

Q image thumb

Amine group

A image thumb
17

What is meant by the tertiary structure of a protein?

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

18

What colour is Biuret reagent?

Blue

19

What is meant by a globular protein?

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

They are usually water soluble.

20

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

Individually weak and easily broken

Cumulatively provide some strength

21

What is the polymer unit of a protein?

Polypeptide

23

How can a polypeptide be broken down into amino acids?

Hydrolysis

25

How many naturally occurring amino acids are their?

20

26

Name 3 globular type proteins

Enzymes

Hormones

Transport proteins

27

What is the only difference between different amino acids?

the R-group

29

Give an example of a transport protein

Haemoglobin in red blood cells

Cell membrane transport protiens

30

Which type of bond forms between two amino acids?

Peptide bond

31

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

A change in the shape of the protein.

The protein will stop working.

The protein will stop working as well.

32

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

specific

specific

33

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

Amino group (NH2)

Carboxyl group (COOH)

R-group

35

What is released when two amino acids chemically join together?

A water molecule (from condensation reaction)

36

Identify the circled group

Q image thumb

Carboxyl group

A image thumb
38

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

Condensation reaction

39

What is the function of the protein collagen?

the main component of connective tissue such as tendons and cartilage

40

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

Q image thumb

The R group

A image thumb
41

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

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

42

What is meant by the quaternary structure of a protein?

(Molecule contains) more than one polypeptide (chain);

There may also be prosthetic (non protein) groups attached to these proteins.

43

Describe the structure of proteins

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;

44

Describe how proteins are digested in the gut

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;

45

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

condensation reaction/loss water

between amine and carboxyl group

46

describe how the secondary structure of a protein is produced

H bonds

between NH and C=O 

forming beta pleat sheets or alpha helix

47

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

different sequence of AA

therefore

ionic/H/disulphide bonds form in different places