proteins Flashcards
how are polypeptides made?
amino acids are the basic monomer units that combine to make up a polymer called a polypeptide
what do polypeptides combine to form
proteins
what provides indirect evidence for evolution
the fact that the same 20 amino acids occur in a living organism provides indirect evidence for evolution
what does every amino acid have
a central carbon atom to which is attached to four different chemical groups
what are the four different chemical groups amino acids can be attached to
amino group NH2
Carboxyl group COOH
hydrogen atom H
R side group
define amino groups
a basic group from which the amino part of the name amino acid is derived
define carboxyl groups
an acidic group which gives the amino acid the acid part of its name
define the R (side) group
a variety of different chemical groups.
these 20 naturally occurring amino acids differ only in their R (side) group
draw the general structure of an amino acid
what do two amino acid monomers combine to form
a dipeptide
explain a condensation reaction between two amino monomers
the water is made by combining an OH from the carboxyl group of one amino acid with an H from the amino group of another amino acid
the two amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other
what breaks peptide bonds
a hydrolysis reaction
what do we call a chain with many amino acids
a polypeptide
define polymerisation in terms of amino acids
through a series of condensation reactions, many amino acid monomers can be joined together in a process called polymerisation
what forms the primary structure of any protein
and what is this determined by
the sequence of amino acids in a polypeptide chain.
this sequence is determined by DNA
what determines the shape and function of a protein
what does this mean
its primary structure
this means that a change in just a single amino acid in this primary sequence can lead to a change in just a single amino acid in the primary sequence that may stop it from carrying out its function
define hydrogen bonds
the hydrogen of the NH group has an overall positive charge while the O of the C=O group has an overall negative charge
these two groups therefore readily form weak bonds called hydrogen bonds
what do hydrogen bonds cause
the long polypeptide chain to be twisted into a 3d shape, such as the coil known as an a-helix
what can a-helices do
the a-helices of the secondary protein structure can be twisted and folded even more to give the complex, and often specific, 3-D structure of each protein
this is known as the tertiary structure
how are tertiary structures maintained
by a number of different bonds
where the bonds occur depends on the primary structure of the protein.
what bonds maintain the tertairy structure
disulfide bridges
ionic bonds
hydrogen bonds
describe disulfide bridges
they are fairly strong and therefore not easily broken
describe ionic bonds
they are formed between any carboxyl and amino groups that are not involved in forming peptide bonds.
they are groups that are not involved in forming peptide bonds.
they are weaker than disulfide bonds and are easily broken by changes in PH
describe hydrogen bonds
they are numerous but easily broken
explain why the 3-d shape of a protein is important
the 3-d shape of a protein is important when it comes to how it functions
it makes each protein distinctive and allows it to recognise, and be recognised by, other molecules.
it can then interact with them in a very specific way
describe the primary structure of a protein
the primary structure of a protein is the sequence of amino acids found in its polypeptide chains.
this sequence determines its properties and shape
following the elucidation of the amino acid sequence of the hormone insulin by Frederick sanger in 1954, the primary structure of many other proteins is now known
describe the secondary structure of a protein
the secondary structure is the shape that the polypeptide chain forms as a result of hydrogen bonding.
this is most often a spiral known as the a-helix, although other configurations occur
describe the tertiary structure of a protein
the tertiary structure is due to the bending and twisting of the polypeptide helix into a compact structure.
All three types of bond, disulfide, ionic and hydrogen, contribute to the maintenance of the tertiary structure
describe the quaternary structure of a protein
the quaternary structure arises from the combination of a number of different polypeptide chains and associated non-protein groups into a large, complex protein molecule
explain how we perform a test for proteins
place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
add a few drops of very dilute 0.05% copper(II) sulfate solution and mix gently
a purple coloration indicates the presence of peptide bonds and hence a protein.
if no protein is preset the solution remains blue
