Protein And Protein Structure Flashcards
What are some functions of proteins?
-enzymes
-storage
-structural
-transport
-defence (antibodies)
-regulatory
-receptors
-contractile
How many proteins are roughly in humans
100,000
what shapes can proteins appear in?
-globular
-fibrous (elongated)
-membrane spanning (need to be hydrophobic)
what are the different protein structures?
-primary - sequence of amino acids
-secondary - local regions formed into regular structures
-tertiary - folding of polypeptide into 3D conformation
-quaternary - multiple subunits
describe amino acids
-chiral molecules
-only 20 naturally occurring aa
-only L forms of the aa are used by cells (left-handed)
-consist of tetrahedral alpha carbon w amine and carboxyl groups and organic side chain
what is the ionisation state at different pHs?
-low pH -amide group is +ve
-high pH - carboxyl group is -ve
-neutral pH - both groups are charged
what are some drivers of the shape of proteins?
-amino acid sequence
-chaperones
-water (will cause hydrophilic R group amino acids to be on outside)
-disulfide bonds
-H bonds
-flexibility
what kind of buffer are aa?
weak buffer
What is the isoelectric point?
-the pH at which the molecule is electrically neutral
-avg of pK values on both side of neutral
describe peptide bonds
-rigid
-planar
-stable and covalent
-physiologically broken by proteases
-avg protein has 300 peptide bonds
what is post-translational modification?
-enzyme mediated modification of proteins after synthesis
-this changes properties of proteins
what are examples of post-translational modifications?
-glycosylation - addition of carb
-cleavage
-lipid addition
-oxidation, carboxylation, acetylation
-phosphorylation
what does phosphorylation of proteins do?
- changes shape
-changes charge
-activates protein
-switches kinases on
-switched phosphatases off
what does side chain (R group) affect?
-size
-charge
-shape
-reactivity
-H bonding
-Determines protein shape & function
how can aa be classified chemically?
-polar/non-polar
-acidic/basic
how can aa be classified structurally?
-aliphatic/aromatic
-sulphur containing
-charged
how can aa be classified structurally?
-aliphatic/aromatic
-sulphur containing
-charged
describe dentin phosphoryns
-made up of aspartic acid (35-45%) and serine (40-55%)
-highly negatively charge and acidic
-regulate bio-mineralisation
-binds to collagen I and Ca2+
how does aa structure relate to function?
Overall conformation gives protein its function
Binding specificity, flexibility, solubility, degradability
Position of amino acid side chains in 3D space
what are the different protein structures?
-primary - linear sequence of amino acids
-secondary - local regions formed into regular structures
-tertiary - folding of polypeptide into 3D conformation
-quaternary - multiple subunits
describe Secondary protein structure
Polypeptide chains can fold into regular structures
α helix
β pleated sheet
Structural motifs e.g. turns
Non regular coils & loops- more flexible e.g. hinges
Describe the alpha helix
-tightly coiled rod
-globular, DNA binding, membrane spanning proteins
-H bonds bw NH and CO groups
-some amino acids form alpha helices more than other e.g. met, ala, glu, lys
-major structural motif for haemoglobin
-two or more alpha helices can entwine to form a cable e.g. keratin
describe b pleated sheets
-H bonds form bw two parts of the protein that can be far apart
-H bonds are optimal when pleated
-can occur in same or opposite direction
describe Haemoglobin
α helices: major structural motif
Two or more α helices can entwine to form a cable eg keratin