Peptides to Proteins

What are PROTEINS? Proteins are large, complex molecules that serve diverse functional and structural roles within cells.

Proteins are the ACTION FORCE in the cell.

Defense Enzyme Support Transpor t Motion Regulation Proteins can be functionally classified. Hemoglobin AntibodyProtease Keratin Actin Insulin Carries O 2 Fights Viruses Degrades Protein Forms Hair and Nails Contracts Muscle Fibers Controls Blood Glucose

Proteins are chains of amino acids. C O OH N H H N H H Short chains of amino acids are called peptides. Proteins are polypeptide molecules that contain many peptide subunits.

Amino Acid 1 NH 2 R COOH C H Amino acids have an amino group, carboxyl group, R group and hydrogen.

Asparagine Glutamate Leucine Phenylalanine Cysteine Histidine Methionine Threonine Arginine Glutamine Isoleucine Tryptophan Alanine Glycine Proline Tyrosine Aspartate Lysine Serine Valine Each amino acid has unique chemical properties.

H2OH2O Amino Acid 2 N R COOH C H H H Amino Acid 1 NH 2 R C C H O OH Peptide bonds form by dehydration synthesis

Amino Acid 2 R COOH C H Amino Acid 1 NH 2 R C H Peptide Bond

 A protein is a linear sequence of amino acids linked together by peptide bonds. The peptide bond is a covalent bond between the -amino group of one amino acid and the -carboxyl group of another.  The peptide bond has partial double bond character and is nearly always in the trans configuration.  The backbone conformation of a polypeptide is specified by the rotation angles about the Cα–N bond (phi, φ) and Cα–C bond (psi, ψ) of each of its amino acid residues. Peptide bond

 The sterically allowed values of φ and ψ are visualized in a Ramachandran plot.  When two amino acids are joined by a peptide bond they form a dipeptide. Addition of further amino acids results in long chains called oligopeptides and polypeptides.

GAU AUGGCC UGG 5’ 3’ Gene Messenger Ribonucleic Acid (mRNA) Amino Acid- transfer RNA Ribosome tRNA Ala tRNA TrpMet tRNA Empty tRNA Met Empty tRNA Met Ala Nucleus Cytoplasm Large Subunit Small Subunit Met Ala Trp RibonucleotidesAUGC Codon 1AUG=Methionine CGCCodon 2=Alanine UGGCodon 3Tryptophan=UGCodon 4Stop=A is the synthesis of proteins in the cell.

PrimarySecondaryTertiar y Quaternary There are 4 basic

A V K R Y F I L H S T Q N P G E D M P C The primary structure is the sequence of amino acids.

Primary structure The linear sequence of amino acids joined together by peptide bonds is termed as the primary structure of the protein. The position of covalent disulfide bonds between cysteine residues is also included in the primary structure.

Alpha HelixBeta-Pleated Sheet The secondary structure is primarily composed of alpha helices and beta-pleated sheets. Primary Structure Folding Back and Coiling

Secondary structure Secondary structure in a protein refers to the regular folding of regions of the polypeptide chain. The two most common types of secondary structure are the -helix and the -pleated sheet. The -helix is a cylindrical, rod-like helical arrangement of the amino acids in the polypeptide chain which is maintained by hydrogen bonds parallel to the helix axis.

In a -pleated sheet, hydrogen bonds form between adjacent sections of polypeptides that are either running in the same direction (parallel -pleated sheet) or in the opposite direction (antiparallel -pleated sheet). Turns reverse the direction of the polypeptide chain and are often found connecting the ends of antiparallel - pleated sheets.

The tertiary structure is the protein’s 3D shape.

Tertiary structure in a protein refers to the three-dimensional arrangement of all the amino acids in the polypeptide chain. This biologically active, native conformation is maintained by multiple noncovalent bonds. Tertiary structure

The quaternary structure is the assembly of folded subunits.

Quaternary structure If a protein is made up of more than one polypeptide chain it is said to have quaternary structure. This refers to the spatial arrangement of the polypeptide subunits and the nature of the interactions between them.

Summary Proteins are biological workhorses that carry out most of the functions within the cell. Proteins are large biological molecules that serve diverse functional and structural roles within cells. Proteins are synthesized during the translation process.

Summary cont’d… Proteins are composed of amino acids that are covalently linked by peptide bonds. Proteins have four basic levels of structure. However, proteins must fold correctly in order to function properly.

The four levels of structure in proteins. (a) Primary structure (amino acid sequence), (b) secondary structure (-helix), (c) tertiary structure, (d) quaternary structure