Proteins Polypeptide chains in specific conformations Protein Graphic Design video

Proteins Monomer: Amino acids Functions: –Structural support –Transport – hemoglobin –Signaling – chemical messengers –Defense – antibodies –Catalysis - enzymes

20 amino acids each composed of Amino group – acts as weak base Carboxyl group – acts as weak acid Variable R group (radical) Properties of R group determine uniqueness of each amino acid

Variation in R groups What process is this?

Peptide bonds Between carboxyl group of one amino acid and amino group of another Dehydration synthesis N-C-C-N-C-C-N-C-C-

Formation of peptide bond

Function depends upon conformation Polypeptide like long piece of yarn, protein like a sweater knitted from yarn Structure enables protein to recognize and bind to another molecule Consequence of linear sequence of a.a. Stabilized by interactions between side chains

Four levels of Protein Structure Primary Secondary Tertiary Quaternary

Primary Unique sequence of amino acids Determined by genes Slight change can affect function and conformation Peptide bonds connect a.a’s Primary dictates secondary and tertiary

Sickle cell anemia-a.a. substitution in hemoglobin protein, abnormal hemoglobin crystallize, deforming some cells

Secondary Regular, repeated coiling and folding Stabilized by repeated hydrogen bonds between peptide linkages (between oxygen of one amino acid and amino group hydrogens on another amino acid) Two types: Alpha helix, Beta pleated sheet

1. Alpha helix coil In fibrous proteins: –Keratin and collagen ( inside hair, connective tissue)

Alpha helix

2. Beta pleated sheet 2 or more strands of the polypeptide chain lying side by side Connected by H-bonding between adjacent polypeptides Globular proteins Fibrous proteins –silk spider web B-keratin in feathers, hooves, claws, beaks, scales and horns

Beta sheet

3. Tertiary Structure Contortions due to bonding between side chains (R groups) Overall shape

Weak Interactions Stabilized by the cumulative effect of: H-bonding between polar side chains Ionic bonds between charged side chains Hydrophobic interactions cause nonpolar side chains to cluster in the center away from water, weak van der Waals interactions hold them together

Covalent Linkage Disulfide bridges –S-S- bond –Bonds between sulfur groups on Cysteine (an amino acid) –Rivets the protein together

Quaternary Structure Interaction between multiple polypeptide chains (2 separate proteins) Most enzymes Collagen – 3 helical polypeptides super coiled into a triple helix Connective tissue  strength Hemoglobin – 4 polypeptide chains, globular protein

Conformation determined by: primary structure Consequence of interactions responsible for secondary and tertiary Influenced by physical and chemical environment May be dynamic – alternating between several shapes

Denaturation – a process that alters protein’s conformation Excessive heat Change in pH Change in salt concentration Exposure to different chemicals Transfer to organic solvent

Nucleic acids Store and transmit hereditary info Monomer – nucleotide: –Phosphate –5C- sugar –Nitrogenous base

Two families of bases Pyrimidine – 1 ring (6 membered ring) Cytosine Thymine Uracil – only in RNA

Purine 2 rings 5 membered ring fused with a six membered ring Adenine guanine

Functions of nucleotides Monomers of nucleic acids Phosphodiester linkages between phosphate of one and sugar of another Transfer chemical energy in ATP Electron acceptors - NAD

DNA Double stranded helix Contains coded information for proteins Programs all cellular activity Can replicate itself Makes up genes Directs RNA to make proteins

RNA Single stranded Synthesis of proteins coded in DNA mRNA – copies code of DNA tRNA – transfers amino acids to ribosome rRNA – makes up ribosomes

Types of RNA