Proteins - structure of proteins Flashcards
what is the primary structure of a protein
the specific sequence of amino acids in the polypeptide chains.
what do the sequence of amino acids influence
how the polypeptide chains folds to give the proteins final shape.
what do the shape of the proteins determine
the function
how many amino acids are there
20
what are the bonds involved in the primary structure
only peptide bonds
are the peptide bonds strong
yes
what is the secondary structure of a protein
the initial folding of the polypeptide chain due to hydrogen bonds
is the chain of amino acids straight
nope it twists
how does the secondary structure form
the oxygen, hydrogen, and nitrogen atoms of the basic repeating structure of the atoms interact
what bonds may form in the secondary structure
hydrogen bonds
where do the hydrogen bonds form in the secondary structure
between the -NH group of one amino acid and the -CO group of another
what is the shape called when the hydrogen bonds cause the chain to coil
alpha helix
what are beta pleated sheets
polypeptide chains can also lie parallel to one another joined by hydrogen bonds forming sheet like structures. the pattern formed by the individual amino acids causes the structure to appear pleated.
how are the beta pleated sheets held down
hydrogen bonds between the -NH group of one amino acid and the -CO of another further down hold the sheet together
how strong are the hydrogen bonds
they are relatively weak
what makes the alpha helix and the beta pleated sheet stable structures at optimal pH and temperature
they have lots of hydrogen bonds.
some chains dont adopt a regular structure and some chains have more than one secondary structure at different ends of the chain
what is the tertiary structure
the folding of the secondary protein structure into a specific 3D shape
what does the tertiary structure often include
sections of secondary structure
how do tertiary structures form
the coiling or folding of sections of proteins into their secondary structures brings R groups of different amino acids closer together so they are close enough to interact and further folding of these sections will occur.
what are the two types of tertiary structure
fibrous and globular
how are fibrous and globular proteins held in place
by bonding between R groups of amino acids
what do proteins bonds do
they hold the secondary, tertiary and quaternary structure together
what is the secondary structure held together by
hydrogen bonds
what is the tertiary and quaternary structure held by
hydrogen bonds and many more
what are hydrogen bonds
they form between hydrogen atoms with a slight positive charge and other atoms with a slightly negative charge,
where do hydrogen bonds form in amino acids
form between the amino group of one amino acid and the carboxyl group of another. they may also form between polar areas of the R groups of different amino acids.
what are the hydrogen bonds involved in
keeping the tertiary and quaternary structure of the protein in the correct shape.
what does the presence of multiple hydrogen bonds do
gives protein molecules a lot of strength.
how do ionic bonds form
between the carboxyl and amino groups that are part of R groups. these ionise into NH3+ and COO- groups. positive and negative groups are strongly attracted to eachother to form an ionic bond between oppositely charged R groups
how do disulfide links form
the R group of the amino acid cysteine contain sulfur. disulfide bridges between the R groups of two cysteines. these are strong covalent bonds.
how do hydrophobic and hydrophillic interactions occur
hydrophobic parts of the R groups tend to associate together in the centre of the polypeptide to avoid water. in the same way, hydrophillic parts are found at the edge of the water.
what do hydrophobic and hydrophillic interactions cause
twisting of the amino acid chain which changes the shape of the protein
why are hydrophobic and hydrophillic interactions an important influence
most proteins are found to be surrounded by water inside a living organism
what is the quaternary structure of a protein
3D protein comprised of two or more tertiary subunits
do all proteins have a quaternary structure
no
how do quaternary structures form
many proteins are made up of one or more polypeptide chains. quaternary structures describe how multiple polypeptide chains are arranged to make the complete protein molecule.
what can hold the quaternary structure together
the bonds from the tertiary structure
what are subunits
individual proteins which can be identical or different
