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Adapted from Wikipedia and the ChemWiki
The collagen triple helix.
(a) First high-resolution crystal structure of a collagen triple helix, formed from (ProHypGly)–(ProHypAla)–(ProHypGly) [Protein Data Bank (PDB) entry 1cag].
(b) View down the axis of a (ProProGly) triple helix [PDB entry 1k6f ] with the three strands depicted in space-filling, ball-and-stick, and ribbon representation.
(c) Ball-and-stick image of a segment of collagen triple helix [PDB entry 1cag], highlighting the ladder of interstrand hydrogen bonds.
(d) Stagger of the three strands in the segment in panel c.
Collagen
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2846778/
Annu Rev Biochem. 2009; 78: 929–958.
doi: 10.1146/annurev.biochem.77.032207.120833Collagen, the rotating image on the left in the Title Box, is a protein found in animal skin, bone, muscle and connective tissue (ligaments and tendons). It accounts for about 30% of all protein in humans. Collagen is a molecule made up of ~3,000 amino acids (residues) which are evenly distributed in three intertwined, cross-linked chains that provide significant structural rigidity as seen above. Twenty-eight different types of collagen composed of at least 46 distinct polypeptide chains have been identified in vertebrates, and many other proteins contain collagenous domains. Although the claim is contested, it has been reported that intact collagen has been discovered in soft tissue of the fossilized bones of a 68 million-year-old Tyrannosaurus rex fossil, which if correct would be the oldest protein detected to date.
As you would expect, collagen affects the texture of meat in foods. Fish has little collagen and is tender. Beef is relatively high in collagen and is "tougher". Meats can be tenderized by breaking down the structural organization of the collagen, i.e. denaturing the protein. There are several ways to denature collagen. Marinating meat with acids (vinegar or wine) will do it and treating meat with other highly specialized proteins called enzymes will do it. Boiling or stewing for a long period of time will transform it from a water insoluble substance into a water soluble, gummy, glue-like material that is 98-99% protein. The word collagen is derived from a Greek word meaning "glue producing", which is one commercial application for the denatured protein. Another commercial use is as gelatin, a thickener in foods.
The worldwide production amount of gelatin is ~375,000 metric tons per year. Commercial gelatin is made primarily from meat and leather by-products. Gelatin is derived from pork skins, pork, horses, and cattle bones, or split cattle hides, which are prepared by different curing, acid, and alkali processes to extract the dried collagen hydrolysate. These processes may take several weeks.
Gelatin can also be prepared in the home. Boiling cartilaginous cuts of meat or bones in water results in gelatin being dissolved to form an aqueous solution. Depending on the concentration, the resulting stock (when cooled) will naturally form a jelly or gel. Examples of foods that contain gelatin are desserts, trifles, aspic, marshmallows, candy corn, and confections such as Peeps, gummy bears, fruit snacks, and jelly bellies. Gelatin is used as a stabilizer, thickener, or texturizer in foods such as yogurt, cream cheese, and margarine, also, in fat-reduced foods to simulate the mouthfeel of fat and to create volume.
While many processes exist to convert collagen to gelatin, they all have one common chemical feature. The intermolecular and intramolecular bonds which stabilize insoluble collagen must be broken, and the hydrogen bonds which stabilize the collagen triple helix must also be broken.
An enzyme is a globular protein that performs as a biochemical catalyst. It enables chemical change and speeds up a reaction, but it is unchanged itself. It repeats its function again and again in reaction after reaction. There are tens of thousands of different enzymes present in each of us. Every enzyme has a special role such as rhodopsin in vision, trypsin in digestion and acetylcholinesterase in transmission of nerve impulses, which govern all muscle control. Enzymes are even related to taste, smell, memory, moods, emotions and behavior.........all human senses and experiences. They are prodigous biological molecules.
Certain enzymes, proteases, can denature gelatin causing further breakdown of the protein. Among common proteases are: papain, present in papaya and sold as meat tenderizer, bromelain, present in uncooked pineapple, actinidin in kiwi fruit, and ficin, found in figs. The image to the right in the Title Box is a protease, trypsin. It breaks down collagen to smaller chemical pieces which do not have the same functional or structural properties as collagen. The reddish spirals are called helices and the yellow ribbons are called sheets. These two arrangements of atoms are common to many proteins. The protein's shape is most important in determining its chemical activity.
The four structural levels of proteins are:
• 1o (primary): The sequence of amino acids, eg. ARDV: Ala.Arg.Asp.Val.
H2N- on the left and on the right -COOH• 2o (secondary): Structures which include, folds, turns, alpha-helices, and beta-sheets held in place by hydrogen bonds.
• 3o (tertiary): 3-d arrangement of all atoms in a single polypeptide chain.
• 4o (quaternary): Arrangement of all polypeptide chains into a functional protein, eg. hemoglobin with 4 strands: 2 pairs of 2 chains, one "alpha" and one "beta"This experiment examines the enzymatic effects on the overall protein structure of protein produced from non-human collagen.An example is bovine collagen, which has a primary structure for a single strand on the left and an overall structure on the right.
Collagen is central to certain medical and cosmetic treatments.
A Google search of Collagen Beauty Treatments produced 2,720,000 hits (April 2016). The vast majority of these Web sites are commercial, .com domains. The Food & Drug Administration (FDA) has approved four physician administered, directly injected collagen products for use as skin “fillers” in human treatment. The American Academy of Dermatology (https://www.aad.org/) cautions that side effects and alternatives should be considered in choosing any treatment. Among the most popular invasive collagen promoting, “non-filler” treatments are: MICRONEEDLING, where tiny needles are used to poke holes in the skin, as the skin heals, collagen synthesis is stimulated. BEE VENOM FACIAL, which stimulates the production of collagen, but establishing that there is an absence of allergies to bee stings is absolutely needed. VAMPIRE “FACE-LIFT” where a patient’s blood is drawn and processed to produce a platelet-rich plasma, which is then injected back into the patient’s face. Pain and bruising can occur, and the full-effect takes weeks to months with multiple sessions often needed. PLACENTA FACIAL which uses an injectable serum derived from sheep placenta that stimulates collagen production.
Non-invasive, topically applied over-the-counter products with ingredients such as retinol, a form of Vitamin A, are alternatives to invasive needle treatments.
Retinol has an alcohol function and is found in many foods. It is present in beef, chicken, turkey, fish, milk, and packaged breakfast cereals. The retinol form of Vitamin A is oxidized to the aldehyde form (retinal), which is essential for vision, and also for healthy, soft skin and tissues.
Common side effects of topical retinol treatment is skin irritation, peeling, redness, itching, dryness, and sun sensitivity.
The experiment and activity consists of two parts:
Part I relates to Human Collagen (report form)
Part II relates to the Enzyme (protease) effects on collagen (gelatin) (report form)
Post Lab Questions:
- Based on your observations, explain the differences in enzymatic activity between (C.) fresh, (D.) canned, and (E.) microwaved pineapple on the denaturing of proteins.
- When making pineapple Jell-O, would you use fresh, microwaved, or canned pineapple? Why?
Refer to the Energy Diagram above.
3. If Ea1 represents protein being hydrolyzed with bromelain as a catalyst and Ea2 is protein reacting with papain as a catalyst, which reaction is faster bromelain or papain? Briefly explain your answer.
4. Compare your experimental observations for reaction (A) and reaction (C). Do your results agree with the data presented in question #3? Briefly explain.
5. Consider the Energy Diagram and the total intra- and intermolecular bonds in uncooked, untreated protein. What happens in the enzymatic treatment of proteins in food? Does the nutritional value in eating the protein increase, decrease, or stay the same after treating with protease enzymes before ingesting the food? Briefly explain in terms of the total bonds in all four structural protein levels before and after enzyme treatment.
6. Do you think that a steak treated with meat tenderizer and then grilled would be more or less tender than the same steak marinated with canned pineapple juice? (Both steaks were cooked the same way and treated for the same length of time.) Explain your answer.
7. Would papain catalytically degrade the protein in chickpeas (garbanzo beans), dahl, and other grams which are common in vegan diets throughout the world. If so, would this make nutritional sense to advocate in establishing a worldwide food policy? Briefly explain.
