2.7 Proteins

Proteins

polymer of amino acids

Amino Acid - composed of central carbon atom linked to amino group, carboxyl group, hydrogen atom, and variable group of atoms called side chain or R-group

20 different amino acids synthesized by ribosomes

R group makes one amino acid different from another

There are 9 Essential Amino Acids - must get from diet

  • Series of amino acids link together to form a protein

  • Structure and function of protein are determined by sequence of amino acids and is coded for by genes

  • Amino acids are joined together through condensation reactions between a carboxyl group and amino group

  • Amino acids linked by covalent bond (peptide bond)

Primary Structure

linear sequence of aa’s in polypeptide chain

Amino acid sequence determines 3D shape of a protein and therefore its function

Secondary Structure

portions of repeated coils or folds caused by hydrogen bonding between adjacent amino acids

Polypeptide chain develops α-helix (delicate coil) or a β-pleated sheet (side by side alignment of aa chain - provides strength)

Tertiary Structure

  • 3D shape due to interaction of R-groups - ionic and H bonds, disulphide bridges, hydrophobic interactions

  • Disulfide bridge - S-S covalent bond - stabilize shape

Quaternary Structure

two or more polypeptides held together by same forces above or contains an inorganic prosthetic groups

Creates very specific 3D shape with unique surfaces and pockets

Denaturation

  • Proteins becomes denatured when shape gets deformed because hydrogen bonds are broken by heat or solubility is altered by pH changes

Changing structure usually results in loss of function

Proteome

  • totality of proteins expressed within a cell, tissue or organism at a certain time

  • Each individual has a unique proteome which is coded for by our genes

  • Proteome is always significantly larger than number of genes in an individual

Functions of Proteins

• Enzyme (catalyze reactions - Rubisco, catalase)

• Immunity (protection - antibodies, immunoglobulins)

• Hormones (chemical messengers - insulin, glucagon)

• Movement (contractile - actin, myosin)

• Sensation (receptors - rhodopsin)