proteins Flashcards
biological molecules
what are the functions of proteins?
- structural: collagen (connective tissues), keratin (hair, nails, horns)
- signalling: hormone (insulin and FSH- matures egg)
- catalyst: enzymes that speeds up reactions
- transport: haemoglobin transports oxygen
what is the structure of amino acids
-there are 20 different amino acids
- all have the same general structure, only the ‘R’ changes
describe how amino acids join together
- condensation reaction
- removing a water molecule
- between carboxyl/COOH group of one and amine/ NH2 group of another
- forming a peptide bond
( amino acid is the only molecule that can lose a water molecule from a carboxyl group to undergo a condensation reaction)
what are dipeptides and polypeptides?
- dipeptide: 2 amino acids joined together
- polypeptide: many amino acids joined together
A functional protein may contain one or more polypeptides
describe the primary structure of a protein
- sequence of amino acids in a polypeptide chain, joined by peptide bonds
- this is determined by your genes
describe the secondary structure of a protein
- the initial folding (repeating patterns) of a polypeptide chain into an alpha helix or beta pleated sheet due to hydrogen bonding between amino acids
- between NH (group of one amino acid) and C=O (group)
describe the tertiary structure of a protein
-further folding of a polypeptide into a 3D shape held together by hydrogen bonds
-due to interactions between amino acid R groups (dependent on sequence of amino acids)
- forming hydrogen bonds, ionic bonds (occurs between C=O (carboxyl) and N-H (amine groups) and disulfide (strongest) bonds
describe the quaternary structure of a protein
more than one polypeptide chains bonded together e.g. haemoglobin and antibodies (hydrogen bonds, ionic bonds and disulfide bonds/bridges)
-There may also be prosthetic (non protein) groups attached to these proteins.
describe the test for proteins
- add biuret reagent (sodium hydroxide + copper (II) sulphate)
- positive result= blue to a purple/lilac colour (indicating presence of peptide bonds)
true or false : dipeptide has a primary structure
false: dipeptides is not a protein so doesn’t have a primary structure
true or false: all hydrogen bonds are between R groups
false: in the secondary structure, hydrogen bonds are between NH and C=O groups
true or false: all proteins have a quaternary structure
false: only proteins with more than one polypeptide chain possess a quaternary structure e.g. haemoglobin and antibodies
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
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 3 fibrous type proteins
-Collagen
-Keratin
-Silk
What is the monomer unit of a protein?
Amino acid
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.
What is meant by a globular protein? + examples
-A protein made from few polypeptides, which form a spherical shape.
-They are usually water soluble.
-Enzymes, Hormones, Transport proteins e.g. haemoglobin
Describe the hyodrogen bonds that hold the tertiary structure of a protein in place.
-Individually weak and easily broken
-Cumulatively provide some strength
How can a polypeptide be broken down into amino acids?
hydrolysis
Which type of bond forms between two amino acids?
peptide
A change of just 1 amino acid in the primary structure of a protein can cause what to happen?
the shape of the protein and will stop working as well
Name the 3 groups present on in an amino acids molecule
-Amino group (NH2)
-Carboxyl group (COOH)
-R-group
What is released when two amino acids chemically join together?
water molecules through condensation reaction
Give an example of a prosthetic group that is associated with a quaternary protein structure.
The iron containing ‘Haem’ group in the haemoglobin protein.
2 proteins have same number and type of AA but different tertiary structure - why?
-different sequence of AA
therefore ionic/H/disulphide bonds form in different places
what is the prosthetic group?
non-protein based molecule that aids function
