General properties of proteins (3.1.4.1) Flashcards
what are amino acids?
the monomers from which proteins are made
what is the general structure of an amino acid?
C atom bonded to R, COOH, H and H2N
what does NH2 represent?
an amine group
what does COOH represent?
a carboxyl group
what does R represent?
a side chain - the twenty amino acids that are common in all organisms differ only in their side group.
what does a condensation reaction between two amino acids form?
a peptide bond
what is formed from the condensation of two amino acids?
a dipeptide
what is formed from the condensation of three or more amino acids?
a polypeptide
what may a functional protein contain?
one or more polypeptides
how does a polypeptide become a protein?
it folds into a complex, 3D structure which allows it to carry out its function
what are the four levels of protein structure?
primary, secondary, tertiary and quaternary
what is the primary structure of proteins?
the sequence of amino acids in a polypeptide chain
what is primary structure determined by?
the DNA sequence of the gene that encodes that polypeptide
why is primary structure important?
it determines the protein’s shape (tertiary structure) and therefore function, because if one amino acid is changed it will change the whole shape
what is the secondary structure of proteins?
hydrogen bonds form between amino acids so the protein twists and folds into a 3D shape eg. alpha helix, beta pleated sheet
how do the hydrogen bonds form in secondary structure?
the -NH group has an overall positive charge and the -C=O group has an overall negative charge so they form between them
what is the tertiary structure of proteins?
the overall 3D shape of a polypeptide chain - the secondary structure twists and folds to give a more complex structure
what is tertiary structure important for?
how the protein functions eg. the active site of an enzyme depends on it forming a specific tertiary structure and if this changes it can’t function properly
what is the quaternary structure of proteins?
when proteins consist of several polypeptide chains linked together to form a large molecule
what are prosthetic groups?
non-protein molecules which form part of the quaternary structure of proteins and help it to carry out its role eg. haem in haemoglobin
what is a conjugated protein?
a protein with a prosthetic group
what are subunits?
the individual polypeptide chains which make up the quarternary structure of a protein
what two thing does quaternary structure show?
- how individual subunits are arranged
- the position of any prosthetic groups
how do you carry out the test for proteins?
- place 3cm^3 of food solution into a test tube
- add 3cm^3 of dilute sodium hydroxide (alkali) solution and mix
- add 10 drops of dilute copper sulphate solution and mix
- positive test will show purple colour, negative will remain blue
what does the type of bonding in a protein depend on?
the specific amino acids present in the polypeptide (bonds form between R groups on amino acids)
when do hydrogen bonds form in a polypeptide chain?
when two amino acids have R groups containing a hydroxyl (OH) - forms due to slight positive and negative charges present on it
what are non-polar amino acids?
amino acids with uncharged R groups which are hydrophobic
what are hydrophobic interactions?
when non-polar amino acids cluster together, excluding water molecules (often found in centre of proteins)
where are hydrophilic amino acids usually found?
on the surface of proteins where they can interact with water molecules
where are ionic bonds found in proteins?
between amino acids with oppositely charged R groups
what is the role of an ionic bond?
to hold different parts of the polypeptide chain together, contributing to the protein’s overall structure
how do ionic bonds relate to the nature of enzymes?
ionic bonds break due to changes in pH, which is a reason for enzymes denaturing in alkaline/acidic conditions
what is a disulphide bond?
a covalent bond formed between two sulphur atoms in the R groups of two different amino acids
what are the different strengths of the bonds found in proteins?
hydrogen - weak
hydrophobic and hydrophilic interactions - weak
ionic - weak
disulphide - strong
when are the bonds in proteins involved in tertiary structure?
when they form between different amino acids on the same polypeptide chain
when are the bonds in proteins involved in quarternary structure?
when they form between different subunits
