Post on 19-Jan-2016
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