Lesson 7 - The Proteins - Introduction, Demonstration, and Structure
Student Performance Objectives1. Explain the relationship between the genetic code and proteins found in human cells.2. List five body regions where proteins play an important role in that region's functioning.3. Define amino acid, dipeptide, tripeptide, polypeptide, essential amino acid, and non-essentialamino acid.4. Explain the difference between a protein's primary, secondary, tertiary and quarternary structure.5. Distinguish between the subtle changes in shape occurring when proteins interact normallywith other cellular molecules, and when a protein is denatured.6. List two factors that can denature proteins.Lesson OutlineA. Proteins are the macromolecules coded for by the genetic code 1. The genetic code is found in the sequence of bases in DNA. 2. Messenger RNA carries the genetic code to ribosomes where protein synthesis occurs. 3. The synthesis of proteins, and the replication of DNA, may be the most important functions of cells.B. DEMONSTRATION: Utilizing models and the human body, point out the importance of protein in obvious parts of the human body - skin (in the dermis, collagen for toughness and elastin for flexibility, and in the epidermis, keratin for waterproofing), hair (keratin in slender filaments of epidermal cells), nails (keratin in densely stacked epidermal cells), bones (~ 1/3 collagen), cartilage, e.g., ears, tip of nose, (collagen), saliva's slippery quality (10x more slippery than water) is due to mucin, a protein that becomes the familiar mucus when mixed with the water in saliva. [Note - mucus is spelled mucous when used in the context of a mucous membrane. It is spelled mucus when standing alone]. C. Composed of amino acids 1. Amino acids have two functional groups: an amino and an organic acid group both attached to the alpha carbon. See: http://www.chem4kids.com/files/bio_aminoacid.html For an animation of amino acid attachment to make proteins, see http://www.johnkyrk.com/aminoacid.html 2. The amino acid's "R" group determines acidic, basic and water solubility qualities of an amino acid. 3. Dipeptides, tripeptides, polypeptides. 4. About 22 different amino acids utilized in construction of human proteins. 5. Eight to 10 are essential (must be eaten); remainder (called non-essential amino acids) can be made from the essential amino acids and from carbohydrates.D. Protein Structure 1. Primary structure - what DNA codes for - the exact sequence of amino acids in a protein. 2. Secondary structure - alpha helices and pleated sheet structures which form as the polypeptide chain is produced at the ribosome. 3. Tertiary structure - final folding of the amino acid chain into a unique 3-dimensional shape which confers unique biological properties to the completed protein. The folding occurs as hydrophobic amino acid "R" groups are repelled from water and hydrophilic "R" groups are attracted to water. The shape is maintained by disulfide bridges linking parts of the chain that are juxtaposed due to the folding. 4. Quarternary structure - the protein structure resulting from two polypeptide chains interacting through non-covalent bonds. Hemoglobin has a quarternary structure consisting of 4 associated polypeptide chains - 2 alpha and 2 beta chains. 5. Proteins can change their shape subtly when they act as enzymes and attach to substrates, cofactors and coenzymes. 6. Drastic alterations of protein shape, most commonly due to application of heat or acid are said to denature the protein. The change in shape is permanent, the protein loses its "native" qualities.