proteins Flashcards
what can proteins function as
- catalysts (for chemical reactions and carry out vital reactions in living systems as enzymes)
- transporters (channel proteins or more complex transmembrane proteins with multiple sub-units in impermeable lipid membranes)
- mechanical support
- immune protection
what do proteins control
- movement
- growth
- development
what proteins can transmit nerve impulses
signal receptors
what are proteins
- linear polymers built from monomer units called amino acids
- contain a wide range of functional groups (mostly governed by side chains of amino acids)
what do proteins interact with one another and with other biological molecules to form
complex assemblies
what types of structures can proteins display
- all different
- can be v rigid
- can display flexibility (ie structural proteins)
what are amino acids
building blocks of all proteins
20 proteinogenic amino acids (encoded as codons in the genetic code + linked together during translation to form a protein
what do the variable r side chain groups give amino acids
- different properties which influence folding
- 20 different r side chains = 20 different amino acids
what can happen to the amine and carboxyl groups of amino acids
can be protonated and deprotonated (work like acids and bases =
its why theyre called amino acids mostly bc of the carboxyl group)
what are the properties of the amine and carboxyl groups of amino acids at physiological (pH 7)
BOTH IONISED
- amine group = protonated ie +vely charged (-NH3^+)
- carboxyl group = deprotonated ie -vely charged (COO-)
- gives each amino acid a net charge of 0
- this is the zwitterionic form
- each amino acid has zwitterionic possibility in terms of their charge
what are the properties of amino acids at low pH
- protonated (as many H+/protons)
- amine group = protonated so +ve charge
- carboxyl group = protonated so no charge
- net charge = POSITIVE
what are the properties of amino acids moving towards neutral / physiological pH
- amount of zwitterionic (neutral) form is increasing
- amine group is protonated (+ve)
- carboxyl group deprotonated (-ve)
- net charge = 0
what are the properties of amino acids at high pH
- less H+/protons in solution
- moves to more basic environment
- amine group = deprotonated so no charge
- carboxyl group = deprotonated so -ve charge
- net charge = NEGATIVE
what does the asymmetric alpha carbon atom allow for
OPTICAL ISOMMERY
- 2 optical isomers of the molecule can be formed
- contain same atoms but the way the atoms are bound around the C-alpha atom differs
- 2 mirror images (or stereoisomers) that cant be superimposed
what can the optical/stereo isomers exist as in amino acids
what is the only one found in proteins in living systems
- L- or D- isomers
- the L-form
- ribosomes and tRNAs work as catalysts in terms of only incorporating the L forms of amino acids
how do side chains in amino acids and the backbone in the protein contribute to protein folding
- charge interaction
- hydrogen bonding
how does polarity occur in uncharged water molecules
because electrons between oxygen and hydrogen are differentially distributed and more skewed toward the oxygen atom
what does polarity mean in water molecules
- shift of overall electron distribution in the molecule is more towards the electronegative oxygen atom
- this moves -ve charge more towards the oxygen atom
- giving polarity (indicated by delta ie delta positive on H atoms and delta negative on O atom) which acts somewhat like a charge
what does polarity mean for water molecules
water forms hydrogen bonds with water molecules or other polar molecules
what do hydrogen bonds form between
- oxygen atom of 1 H2O
- hydrogen atom of 2nd
- demonstrated as small vertical lines between the two
what does polarity dictate
if a molecule is miscible w water / associates with it or NOT
- assume a molecule is miscible if it is considered polar + has a shift in its electron distribution
explain why methane is not easily miscible with water under normal conditions
- CH4
- no difference in electron charge distribution across the molecule = its APOLAR
- electron distribution is equal between all atoms
so why is it important to look at amino acid side chains?
what are all proteins in our bodies made up of
see if on inside or outside of the protein depending on their miscibility with h2o OR if they are hydrophilic or hydrophobic
the same 20 proteinogenic amino acids
what can side chain groups be grouped into
side chain types