proteins Flashcards
(20 cards)
what elements do proteins contain?
proteins contain carbon, hydrogen, oxygen, nitrogen and sometimes sulphur
what are amino acids?
amino acids are the sub-units (monomers) from which proteins (polymers) are formed
how many different types of commonly occurring amino acids are there in living organisms?
there are 20 different commonly occurring amino acids in living organisms
what is the structure of amino acids?
all amino acids have an amino group and a carboxylic acid group but differ in the atomic group R. amino acids are joined together by peptide bonds (-CONH-) formed by condensation reactions.
two amino acids joined together form a _________.
many amino acids joined together in a chain form a ___________.
a protein may consist of ___ or ____ ____________.
two amino acids joined together form a dipeptide.
many amino acids joined together in a chain form a polypeptide.
a protein may consist of one or more polypeptides.
how are proteins hydrolysed?
proteins can be hydrolysed by heating with acid or by using enzymes (proteases) at their optimum temperature
how do proteins vary and how can they be classified?
proteins vary in the number, type and sequence of amino acids they contain. this produces a vast number of different protein molecules. they can be classified according to their structure.
what is the primary structure of a protein?
primary structure refers to the sequence of amino acids joined by peptide bonds in the polypeptide chain, this sequence determines the specific shape of the protein
what is the secondary structure of a protein?
the secondary structure represents the folding or coiling of the polypeptide chain as a result of hydrogen bonding between amino acids
what are two examples of secondary structures?
secondary structures include the alpha helix and the beta pleated sheet.
what is the tertiary structure of a protein?
the tertiary structure represents further folding and coiling of the secondary structure due to hydrogen bonds, ionic bonds and disulfide bridges
what does the tertiary structure determine in enzymes?
the tertiary structure of enzymes determines the shape of its active site and its precise function
what are globular and fibrous proteins? give examples
globular proteins consist of a highly folded and coiled polypeptide chain or chains to produce a compact, complex tertiary structure. they are soluble and have a specific tertiary structure.
fibrous proteins are typically long, thin and insoluble and usually have structural functions
give examples of globular and fibrous proteins?
globular proteins include enzymes and antibodies
fibrous proteins include keratin in hair and collagen in connective tissue
what is the quaternary structure of a protein?
the quaternary structure relates to highly complex proteins consisting of more than one polypeptide chain. the chains are held together by ionic bonds, hydrogen bonds, disulfide bridges and hydrophobic interactions.
what is an example of a protein with quaternary structure?
adult haemoglobin consists of four polypeptide chains
what is denaturation of a protein? what does this lead to?
denaturation is an alteration in the tertiary structure of a protein. this loss of the three dimensional shape of the protein is often irreversible and the protein is no longer functional.
what is denaturation usually caused by in proteins?
denaturation is usually caused by the breaking of hydrogen and ionic bonds. it can also be caused by high temperatures above the optimum, extreme changes in pH and by heavy metals.
what bonds are only broken by higher temperatures?
disulfide bonds are not broken at the temperatures which break hydrogen and ionic bonds
how do you test for proteins?
biuret test for proteins:
- adding biuret reagent
- a purple, lilac or mauve colour indicates protein is present
- if the solution remains blue, no protein is present
