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