Proteins and enzymes

Proteins

Describe the central role of proteins in the activities of cells and justify the statement “Proteins do everything in cells”

Roles of proteins in the cells include:

Movement, e.g. actin, myosin

Communication between cells e.g. hormones

Recognition of self and foreign matter e.g. immunoglobulin

Receptors on membrane e.g. glycosylated membrane proteins

Biological catalysis e.g. majority of enzymes

Transport of matters e.g. membrane protein channels

Structural support e.g. mostly fibrous secondary proteins like keratin

Recognize a peptide bond (be able to circle it on a structure)

Recognize which side chains of amino acids would be polar, non-polar neutral, hydrophobic, or ionic

Polar: Glycine (Gly, G) Glutamine (Gln, Q), Asparagine (Asn, N), Serine (Ser, S), Threonine (Thr, T), Cysteine (Cys, C), Tyrosine (Tyr, Y)

Hydrophobic: Alanine (Ala, A), Valine (Val, V), Leucine (Leu, L), Isoleucine (Ile, I), Phenylalanine (Phe, F), Proline (Pro, P), Methionine (Met, M) and Tryptophan (Trp, W)

Ionic: Basic: histidine(His, H), lysine(Lys, K), arginine (Arg, R)

Acidic: aspartic acid/ aspartate (Asp, D), glutamic acid/ glutamate (Glu, E)

Describe the role of disulfide bonds

Disulfide bonds are formed between 2 cysteine residues.

They play an important role in forming covalent links between parts of a polypeptide molecule or different polypeptide chains. They interfere with chemical or enzymatic cleavage of the polypeptide

Predict where hydrophilic and hydrophobic amino acids would be in a protein

Hydrophilic: polar/ charged (hydro: water, -philic: like)

Hydrophobic: non-polar (-phobic: repel)

In a protein soluble in water, the hydrophobic residues are found inside while hydrophilic residues are found on the surface

In proteins embedded in the cell membrane (lipid bilayer), hydrophobic residues are found on the surface of the protein

Recognize the secondary structures α-helix and β-sheet

α-helix:

β-sheet