Protein structure pt 2. Flashcards
What is the primary structure of a protein?
the sequence in which the amino acids are joined…
The particular amino acids will influence how the polypetide folds to give the proteins final shape…
This in turn determines its function… The only bonds involved in the primary structure of a protein are peptide bonds…
What is the secondary structure of a protein?
the O, H and N atoms of the basic, repeating structure of the amino acids (the R-groups are not involved in this stage) interact….
H-bonds may form within the amino acid chain, pulling it into a coil shape called an alpha helix…
. Secondary structure is the result of H-bonds and forms at regions along long protein molecules depending on the amino sequences….
What is beta pleated? In relation to ssecondary structure
Polypeptide chains can also lie parallel to one another, joined by H-bonds, forming sheet-like structures…
. The pattern formed by the individual amino acids causes the structure to appear pleated, hence the name beta pleated
What is tertiary structure?
This is the folding of a protein into its final shape….
It often includes sections of secondary structure…..
The coiling or folding bring the R-groups closer together so they are close enough to interact….
What are the interactions that form between R-groups?
hydrophobicity interactions - weak interactions between polar and non-polar R-groups…
. H-bonds - weakest of the bonds formed…
. ionic - form between oppositely charged R-groups..
. disulfide bond (aka bridges) - covalent and the strongest of the bond but only form between r-groups that contain sulfur atoms…..
What is the quaternary structure?
Results from the association of two or more individual proteins called subunits…..
The interactions between the subunits are the same as in the tertiary structure except that they are between different protein molecules rather than one within one molecule…..
The units can be identical or different, e.g. enzymes have two identical subunits whereas insulin has two different ones…..
How do hydrophillic/phobic interaction affect the shape in relation to the environment?
Proteins are assembled in a aqueous environment of the cytoplasm, so the way they fold will depend on whether the r-groups are hydrophillic or hydrophobic….
. Hydrophobic groups are on the inside of the molecule, shielded from the water in the cytoplasm……
How are peptides broken down?
proteases are enzymes thaat catalyse the reverse reaction…….
turning peptides back into their constituent amino acids….
.. a water molecule is used to break the peptide bond in a hydrolysis reaction, reforming the amine and carboxylic groups……
which are primary secondary tertiary quaternary
What is the test for proteins? What is the indication of a positive result? What causes the test?
- biuret test
- peptide bonds form violet coloured complexes with copper ions in alkaline solution
How is the test carried out?
- 3cm3 sample mixed with equal vol of 10% NaOH soln
- 1% copper sulfate soln added few drops at a time till sample turned blue
- mix soln and leave to stand
What is the biuret reagent>
- alkaline copper sulfate soln
- can be used instead of adding soln individually
