Review
Review
• Hydrophobic (non polar)• Hydrophilic (polar)
Polar
• Have a charge to them• Molecules with a positive and negative side• Non-symmetrical • Amino acids: amine, alcohol, amide functional group
Nonpolar • No charge associated with a molecule• Electrons are evenly distributed creating no
electrical field (charges cancel out each other)• Symmetrical shape• In amino acids (benzene ring/alkyl functional
group)
Covalent bonds
–
–
H2 (hydrogen gas)H2 (hydrogen gas)
H — H
• Share a pair of electrons• Both atoms are holding onto electrons• Stable
Nonpolar covalent bond• Pair of electrons shared equally by 2 atoms– Methane (CH4)
H
H
Oxygen
Polar covalent bonds
+
+
––
––
• Pair of electrons shared unequally by 2 atoms
• Oxygen has higher electronegativity and will pull electrons more
Polar or Non-polar
NONPOLAR
POLAR
POLAR
NONPOLAR
A
B
C
D
Amino acid
Hydrophobic R groups
• Composed mostly of carbon and hydrogen, and tend to be repelled from water
• Glycine (Gly), alanine (Ala), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), phenylalanine (Phe), methionine (Met), and tryptophan (Trp).
Polar amino acids
• Side chains that are not charged
• Serine (Ser), threonine (Thr), cysteine (Cys), asparagine (Asn), glutamine (Gln), and tyrosine (Tyr)
Basic amino acids
• Arginine (Arg), lysine (Lys), and histidine (His)
• Their side chains contain nitrogen and resemble ammonia, which is a base
Acidic amino acids
• Acidic R groups
• Aspartate (Asp) and glutamic acid or glutamate (Glu)
Bonds
• Amino acids are linked together by peptide bonds
Primary (1°) structureOrder of amino acids in chain
amino acid sequence determined by gene (DNA)
slight change in amino acid sequence can affect protein’s structure & its functioneven just one amino acid change can
make all the difference!
lysozyme: enzyme in tears & mucus that kills bacteria
Secondary (2°) structure“Local folding”
folding along short sections of polypeptideinteractions between
adjacent amino acidsH bonds
weak bonds between R groups
forms sections of 3-D structure-helix-pleated sheet
Tertiary (3°) structure
“Whole molecule folding”interactions between distant amino acids
hydrophobic interactionscytoplasm is
water-basednonpolar amino
acids cluster away from water
H bonds & ionic bondsdisulfide bridges
covalent bonds between sulfurs in sulfhydryls (S–H)
anchors 3-D shape
Quaternary (4°) structure More than one polypeptide chain bonded together
only then does polypeptide become functional proteinhydrophobic interactions
collagen = skin & tendons hemoglobin
Protein structure (review)
amino acid sequencepeptide bonds
1°
determinedby DNA R groups
H bonds
R groupshydrophobic interactionsdisulfide bridges(H & ionic bonds)
3°multiple polypeptideshydrophobic interactions
4°
2°
Protein denaturation
Unfolding a proteinconditions that disrupt H bonds, ionic bonds,
disulfide bridgestemperaturepHsalinity
alter 2° & 3° structurealter 3-D shape
destroys functionalitysome proteins can return to their functional shape after
denaturation, many cannot
Enzymes
• Lock and key: The key (substrate) has a specific shape (arrangement of functional groups and other atoms) that allows it and no other key to fit into the lock (the enzyme).
Enzymes
• Induced fit: The substrate is distorted (atoms are shifted, bonds are stretched, and reactive groups are brought close together).
• Only molecules with the correct functional groups in the correct configurations are able to be induced to fit the active site of the enzyme.
Enzyme Inhibition