3.6 Structure of Proteins Flashcards
What is the monomer of proteins?
Amino acids
What bonds form when amino acids join?
Peptide bond
What elements are in proteins?
Carbon, hydrogen, oxygen, nitrogen
What is the role of proteins?
-Enzymes = used to break down and synthesise molecules
-Antibodies = immune response
-Transport = move molecules or ions across membranes
-Structural components = keratin, collagen used to create strong fibres
-Muscle contraction = muscles are made up of proteins
-Hormones = act as chemical messengers
What is the general structure of an amino acid?
-Central carbon atoms
-A amino group (NH2)
-A carboxyl group (COOH)
-A hydrogen atom
-An R group or a variable side group
What does the R group determine?
-Which amino acid it is, and its properties
-R groups are able to interact with each other forming different types of bond, leading to long chains of amino acids
How is a dipeptide formed?
-Condensation reaction of two amino acids
-The hydroxyl group (OH) of one amino acid reacts with the hydrogen (H) in the amino group of another amino acid
-Releases a water molecules
-Forms a peptide bond between the carbon of one amino acid and the nitrogen of another
How is a dipeptide broken down?
-Hydrolysis reaction
-Water molecule is added to dipeptide
-Peptide bond is broken
-Release two amine acids
What is the name of the molecules formed when more than two amino acids join?
Polypeptide
How are dipeptide and polypeptides broken down?
Hydrolysis
What are the 4 levels of protein structure?
Primary, Secondary, Tertiary, Quaternary
What is the name of test for proteins?
Biuret test
What does the Biuret test test for?
Presence of amino acids
What are the steps for the Biuret test?
- Place 4cm3 of food sample in a test tube
- Add an equal volume of Biuret solution (sodium hydroxide and copper sulfate)
- Shake and leave at room temperature
- If proteins are present, solution will turn from a blue solution to a purple precipitate
What is Biuret solution made from?
Sodium hydroxide and copper sulfate
What is the primary structure of a protein?
-The unique sequence in which amino acids are jointed
-Structure held together by peptide bonds
-Determines the 3D shape
-A change in just one of the amino acids can result in a change to the proteins structure and function
What bonds are in the primary structure of a protein?
Peptide
What is the secondary structure of a protein?
-Hydrogen bonds forming between amino acids in the chain
-Polypeptide chain coils/fold into either an α-helix or β-pleated sheet structure
-Many hydrogen bonds make the structure stable
-α-helix formed due to hydrogen bonds within the amino acids chain, pulling it into a coil shape
- β-pleated sheet structure formed by hydrogen bonds between parallel amino acids
What bonds are in the secondary structure of a protein?
Hydrogen bonds
What is the tertiary structure of a protein?
-3D shape of a polypeptide chain, caused by the folding and twisting of a protein
-Coiling and folding causes R-groups of different amino acids to become closer together, so they can interact
-Hydrophobic and hydrophilic interactions, weak interaction between polar and non-polar R groups
-Hydrogen bonds, weak individually but provide strength in large numbers
-Ionic bonds, form between oppositely charged R groups, stronger than hydrogen bonds
-Disulfide bridges, form between R groups that contain sulfur, covalent and the strongest of bonds
Where do ionic bonds form in the tertiary structure of a protein?
Between oppositely charged R-groups
Where do disulfide bridges form in the tertiary structure of a protein?
Between R groups that contain sulfur
Where do hydrophobic and hydrophilic interactions take place in the tertiary structure of a protein?
Between polar and non-polar R groups
What bonds are present in the tertiary structure of a protein?
Hydrophobic and hydrophilic interactions, Hydrogen bonds, Ionic bonds, Disulfide bridges
