topic 1 - proteins Flashcards
cgp (topic 1A) 8 - 9
what are proteins made from
long chains of amino acids
what is a monomer of proteins
amino acids
how is a dipeptide formed
when two amino acids join together by a peptide bond
what are protein made up of
one or more polypeptides
what is an amino acids general structure
a carboxyl group (-COOH)
an amine/ amino acid group (-NH²)
an R group/ variable side group
what is the only difference between the 20 amino acids
the R group
how are polypeptides formed
when more than two amino acids are joined together by peptide bonds
how do two amino acids become a dipeptide (detailed)
amino acids are linked together by condensation reactions to form a dipeptide - a molecule of water is released during the reaction - the bonds formed between amino acids are called peptide bonds
how many structural levels do proteins have
four
what are the proteins four structures
primary, secondary, tertiary, quaternary structures
what is the proteins primary structure
this is the sequence of amino acids in the polypeptide chain
what is the proteins secondary structure
the polypeptide chain doesn’t remain flat and straight - hydrogen bonds form between the amino acids in the chain, making it automatically coil into an alpha helix or fold into a beta pleated sheet
what is the tertiary structure
the coiled or folded chain of amino is often coiled and folded further - more bonds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds (attractions between negative and positive charges on different parts of the molecule)
disulphide bridges also form when two molecules of the amino acid cysteine come close together - the sulfur atom in one cysteine bond to the sulfur atom in the other
for proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure
what is the quaternary structure
some proteins are made of several different polypeptide chains held together by bonds
the quaternary structure is the way these polypeptide chains are assembled together
for proteins made from more than one polypeptide chain the quaternary structure is the protein’s final 3D structure
four examples of proteins
enzymes, antibodies, transport proteins, structural proteins
how do enzymes structure make them specialised to carry out its particular job
enzymes - soluble and often have roles in metabolism, some hep synthesize large molecules
structure: usually roughly spherical in shape due to the tight folding of the polypeptide chain
how do antibodies make them specialised to carry out its particular job
antibodies - involved in the immune response
structure: made of two light polypeptide chains and two heavy polypeptide chains bonded together
antibodies have variable regions - the amino acid sequences in these regions vary greatly
transport proteins make them specialised to carry out its particular job
transport protein - transport molecules and ions across membranes
structure: channel proteins are present in cell membranes - channel proteins contain hydrophobic and hydrophilic amino acids, causing the protein to fold up and firm a channel
structural protein make them specialised to carry out its particular job
structural proteins - physically strong
structure: consist of long polypeptide chains lying parallel to each other with cross links between them
include keratin and collagen
what test do you use for proteins
biuret test
what does a biuret test find out
if a substance contained protein
what are the two stages to a biuret test
(1) test solution needs to be alkaline, so you add a few drops of sodium hydroxide solution
(2) add copper (II) sulfate solution
- if protein is present the solution turns purple
- if no protein solution stays blue
