Proteins Big Idea 4: Biological Systems Interact

Essential Knowledge Essential knowledge 4.B.1: Interactions between molecules affect their structure and function. a. Change in the structure of a molecular system may result in a change of the function of the system. b. The shape of enzymes, active sites, and interaction with specific molecules are essential for basic functioning of the enzyme.

Structural support, storage, transport, cellular communications, movement, and defense against foreigners Make up more than 50% of dry mass of cells Protein Functions!

Example: Hemoglobin Iron-containing protein found in red blood cells. Transports oxygen to body

Antibodies Defensive protein  fights bacteria and viruses Example: Antibodies

Example: Lactase, an Enzyme Enzyme that helps break down sugar lactose into galactose and glucose. Speeds up reactions rates: Lactose intolerant: Mutation of Chrom. 2. Cramps, bloating, flatulence

Hormonal protein: regulates sugar in blood (tells cells to take it in), pancreas Example: Insulin

Polypeptides Polymers built from same set of 20 amino acids A protein consists of one or more polypeptides

Amino Acid Monomers

Amino Acid Polymers Amino acids are linked by peptide bonds

Protein Structure and Function Consists of 1/more polypeptides twisted, folded, and coiled into a unique shape (determined by amino acid sequence)

Four Levels of Protein Structure Primary, Secondary, Tertiary, Quartenary! Watch Videos!

Hollow cylinder Cap Chaperonin (fully assembled) Polypeptide Steps of Chaperonin Action: An unfolded poly- peptide enters the cylinder from one end The cap attaches, causing the cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comes off, and the properly folded protein is released. Correctly folded protein Chaperonins are protein molecules that assist the proper folding of other proteins

Sickle-Cell Disease: A Change in Primary Structure A change in primary structure can affect a protein’s structure and ability to function Ex: Sickle-cell disease: results from a single amino acid substitution in protein hemoglobin

Fig. 5-22a Primary structure Secondary and tertiary structures Function Quaternary structure Molecules do not associate with one another; each carries oxygen. Normal hemoglobin (top view)  subunit Normal hemoglobin     GluValHis Leu ThrPro Glu

Fig. 5-22b Primary structure Secondary and tertiary structures Function Quaternary structure Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced. Sickle-cell hemoglobin  subunit Sickle-cell hemoglobin     Val HisLeuThrProGlu Exposed hydrophobic region

Fig. 5-22c Normal red blood cells are full of individual hemoglobin molecules, each carrying oxygen. Fibers of abnormal hemoglobin deform red blood cell into sickle shape. 10 µm

Messing Up Proteins? Alterations in pH, salt concentration, temp., or other environmental factors can cause a protein to unravel  denaturation  inactive protein

Acts as a catalyst to speed up chemical reactions Can perform functions repeatedly  workhorses! Enzyme Proteins!

Cofacto rs A non-protein chemical compound required for enzyme activity Ex: Fe “Helper Molecules" that assist in biochemical transformations.

Coenzy mes A protein chemical compound required for enzyme activity “Helper Molecules" that assist in biochemical transformations.

Cofactors and Coenzymes Work together to regulate enzyme function. Usually the interaction relates to a structural change that alters the activity rate of the enzyme

Competitive Inhibitors Binding of inhibitor molecule to active site of enzyme prevents binding of the substrate and vice versa.

Allosteric Competition Binding of inhibitor to another (allosteric) site of enzyme (rather than active site)  prevents binding of substrate

Model Interpretations The change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/ or presence of a competitive inhibitor.