3.1.4.1 Proteins - structure, function and biuret test Flashcards
What decides the amino acid sequence that determines the primary structure of a protein?
A DNA sequence
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
What does Biuret reagent contain?
Concentrated Copper (II) sulfate solution
Describe the disulfide bonds that hold the tertiary structure of a protein in place.
Strong
Not easily broken
Occur between two cysteine amino acids
Name the bonds that hold the tertiary structure of a protein in place.
Disulfide Bonds
Hydrogen Bonds
Ionic Bonds
What do the below instructions describe:
- Place a 2cm3 of food in a test tube.
- Add 2 cm3 of sodium hydroxide solution at room temperature.
- Add a few drops of very dilute copper (II) sulfate solution (Biuret reagent)
- Observe and record colour change.
The Biuret test for proteins.
Identify the molecule
Amino acid
Name 3 fibrous type proteins
Collagen
Keratin
Silk
What is the monomer unit of a protein?
Amino acid
What do we call 2 amino acids chemically joined together?
Dipeptide
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.
Which colour does Biuret solution turn in the presence of protein?
Biuret changes from blue to purple.
Give 3 examples of enzymes
Amylase
Protease
Lipase
Which colour does Biuret reagent turn in the absence of protein?
It remains a blue colour
Identify the circled group
R group
Idenitfy the circled group
Amine group
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.
What colour is Biuret reagent?
Blue
What is meant by a globular protein?
A protein made from few polypeptides, which form a spherical shape.
They are usually water soluble.
Describe the hyodrogen bonds that hold the tertiary structure of a protein in place.
Individually weak and easily broken
Cumulatively provide some strength
What is the polymer unit of a protein?
Polypeptide
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.
How can a polypeptide be broken down into amino acids?
Hydrolysis
What is meant by the primary structure of a protein?
The sequence of the amino acids in the polypeptide that forms the protein.
How many naturally occurring amino acids are their?
20
Name 3 globular type proteins
Enzymes
Hormones
Transport proteins
What is the only difference between different amino acids?
the R-group
What is the function of the protein keratin?
the main component of hard structures such as hair, nails, claws and hooves.
Give an example of a transport protein
Haemoglobin in red blood cells
Cell membrane transport protiens
Which type of bond forms between two amino acids?
Peptide bond
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.
Every protein has a very _________ 3D shape, which is why they can carry out very ________ functions
specific
specific
Name the 3 groups present on in an amino acids molecule.
Amino group (NH2)
Carboxyl group (COOH)
R-group
Give 2 examples of hormones
Insulin
Oestrogen
What is released when two amino acids chemically join together?
A water molecule (from condensation reaction)
Identify the circled group
Carboxyl group
How would you carry out the Biuret test for proteins?
- Place a 2cm3 of food in a test tube.
- Add 2 cm3 of sodium hydroxide solution at room temperature.
- Add a few drops of very dilute copper (II) sulfate solution (Biuret reagent)
- Observe and record colour change.
Which type of reaction takes place during the polymerisation of amino acids?
Condensation reaction
What is the function of the protein collagen?
the main component of connective tissue such as tendons and cartilage
Which part of the amino acid structure is different in the 20 different amino acids.
The R group
Give an example of a prosthetic group that is asociated with a quaternary protein structure.
The iron containing ‘Haem’ group in the haemoglobin protein.
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.
Describe the structure of proteins
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation;
- Primary structure is order of amino acids;
- Secondary structure is folding of polypeptide chain due to hydrogen bonding;
- Tertiary structure is 3-D folding due to hydrogen bonding and ionic/disulfide bonds;
- Quaternary structure is two or more polypeptide chains;
Describe how proteins are digested in the gut
- Hydrolysis of peptide bonds;
- Endopeptidases break polypeptides into smaller peptide chains;
- Exopeptidases remove terminal amino acids;
- Dipeptidases hydrolyse/break down dipeptides into amino acids;
describe how a peptide bond is formed between 2 AA to form a dipeptide
condensation reaction/loss water
between amine and carboxyl group
describe how the secondary structure of a protein is produced
H bonds
between NH and C=O
forming beta pleat sheets or alpha helix
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
