PROTEIN

Objectives 2. Investigate the properties of carbohydrates, lipids, and proteins. 2.4 Describe the relationship between amino acids and proteins with reference to the peptide bond. 2.5 Discuss enzymes using a series of key words which should be included in a concept web with the heading of proteins. (The key words are substrate, enzyme)substrate complex, lock and key, catalyst, factors affecting enzyme activity [temperature; relative concentration of substrate], enzymes, and coenzymes.) 2.7 Recognize the value of proteins by using examples from the human body.

Why are proteins important? Proteins are one of the key building blocks of cells and perform a wide range of functions. Important structural molecules – collagen in muscles and connective tissues, keratin in hair and nails Involved in all metabolic activities Generate motion – myosin in muscle cells Some serve as hormones – chemical messengers released by cells in the body that influence cellular activity in other parts of the body Transport oxygen – hemoglobin in red blood cells Defense – antibodies produced by the immune system Source of energy – excess proteins in diet are decomposed as an energy sources

What is a protein? Proteins are the most complex of all nutrients They are made up of smaller molecules called amino acids. There are 20 different amino acids that organisms use to build proteins. The human body can synthesis 12 of these amino acids, but must obtain the other 8 from food sources. The 8 that must be obtained are called essential amino acids Amino acids consist of a central carbon atom attached to a single hydrogen atom; and amino acid group (H 2 N), a carboxyl group (COOH) and a side chain (represented by R) that varies among the 20 different amino acids. A protein is formed when many amino acids are joined together H H H O H H O | | | || | | || …H 2 N – C – COOH… … – N – C – C – N – C – C – O – … | | | R R R

Where do proteins come from? There are many plant and animal source of protein All animal sources of protein contain all 8 essential amino acids. Good sources of animal protein include dairy products, eggs, and meats Most plant protein sources are missing at least one essential amino acid. Therefore people who do not eat animal protein must be sure to eat a large combination of protein sources to get the essential amino acids Good sources of plant protein come from legumes (beans), whole grains and nuts

Transamination Transamination refers to the transfer of an amine group from one molecule to another The reaction is catalyzed by a family of enzymes called transaminases The transamination results in the exchange of an amine group on one acid with a ketone group on another acid (analogous to a double replacement reaction)

Structure of proteins There are four levels of protein structure Primary structure – the sequential order of amino acids Secondary structure – the characteristic spiral shape caused by the chain twisting. The two structures are the alpha helix and the beta pleated sheet Tertiary structure – the spiral structure folds into a unique three-dimensional shape caused by reactions between the amino acids Quaternary structure: when polypeptides (short chains of amino acid monomers linked by peptide bonds) bond to form an even larger protein with a globular or fibrous structure Video:

Video

Denaturation Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure (uncoil and lose their shape) by application of some external stress or compound. These include Addition of a strong acid or base A concentration of inorganic salt Heat Addition of heavy metals Addition of alcohol When a protein or amino acid has been denatured they are no longer able to function

Limiting Amino Acids Limiting amino acids are essential amino acids that are in short supply in the body In order to relieve the effects of limiting amino acids the body will take two or more incomplete protein sources to make a complete one in a process called mutual supplementation

Enzymes An enzyme is a protein which catalyzes functions in the body. A catalyst is a compound that speeds up the rate of reaction but is not used up in the reaction Substrate – the compound that is changed in the reaction with an enzyme Active site – the place where the substrate binds with the enzymes Enzyme-substrate complex – the molecule of the substrate bound with the enzyme Products – the reacted parts of the substrate

Enzyme reaction Substrate Enzyme Active site Bond H2OH2O 1. The substrate, sucrose consists of glucose and fructose bonded together 2. The substrate binds with the enzyme to form the enzyme- substrate complex 3. The binding of the substrate and enzyme places stress on the glucose- fructose bond and the bond breaks 4. Products are released, and the enzyme is free to bind with other substrates

Lock and Key Analogy In 1894, Emil Fischer postulated that each enzyme and substrate are specific to each other much like a lock and key. Only the correct key (substrate) will fit into the key hole (active site) each lock (enzyme)

Factors which affect enzyme activity pH- Enzyme function is best at a pH of 7.4. If the pH is to high it will denature the enzyme and will no longer function Temperature – To a certain extent, the higher the temperature the faster the enzyme works because the substrates are moving faster. The enzyme will be denatured and not function anymore Inhibitors – Stop enzymes from functioning. There are two types Competitive inhibitors which have a similar shape to the substrate and therefore can “compete” with the enzyme Non-competitive inhibitors which do not bind to the active site but block the enzyme substrate complex from forming. They react with portions of the action site, changing the enzymes shape so it doesn’t function anymore

Athletes and Protein Athletes require more protein then non- athletes Strength athletes require times as much protein and endurance athletes require times as much Regular exercise stimulates tissue growth and causes tissue damage, which must be repaired by additional proteins This is what causes athletes to “bulk up” and why athletes must ingest protein before and after a work out.

Too much protein Weight gain – a lot of protein contains a high amount of cholesterol and fat from animals. Reduced liver and brain function – when you eat protein your body produces ammonia, a toxin that your liver makes harmless. Eating protein causes your liver to become overworked allowing ammonia and other toxins to build up in your body, which can lead to decline in brain and nervous system function

Too little protein Kwashiorkor – “under nutrition” under weight, dry skin, dry fragile hair that may fall out easily. Can lead to bloated swollen looking stomach Muscle Degradation – without the sufficient protein your body will begin to break down muscles in order to use the components of the muscle else where Compromised Hormone and Immune Function – Amino acids are required to create different hormones. Lack of amino acids can lead to hormone imbalance Marasmus – a severe form of malnutrition. Characterized by a look of skin and bones, and a loss of energy

Video