Protein Metabolism - NUTN 301 Lecture Notes PDF

4/21/2022 Learning objectives  Explain how amino acids (AA) are modified in the NUTN 301: Nutrients...

4/21/2022 Learning objectives  Explain how amino acids (AA) are modified in the NUTN 301: Nutrients body ◦To make other AA and their metabolism I ◦To make other non-protein compounds ◦To provide energy LECTURE 16: PROTEIN METABOLISM  Discuss the role of proteins  Describe the quality of proteins in foods 2 1 2 Transamination: using AA to make other AA Transamination: mechanism/example  Associated with synthesis of non-essential AA  Involves transfer of the amino group of an amino acid to a carbon skeleton to form a new amino acid  Involves transamino-tranferase enzymes 3 4 Use of amino acids for energy/fat deposition Use of  AA to be used for energy, enter the tricarboxylic acid (TCA) amino acids cycle via: 1. Conversion to pyruvate for glucose synthesis for 2. Conversion to Acetyl CoA for fat deposition energy/fat 3. Directly enter the TCA for fuel deposition  Amino acids must be deaminated before they can be incorporated into the metabolic pathways for energy or fat deposition 5 6 1  4/21/2022 Deamination Amino acids to glucose The AA loses the amino group without  Gluconeogenesis - when carbohydrate is not available, transfer to another carbon skeleton protein can be used for glucose production Deamination produces ammonia which  The preferred fuel for the central nervous system is is converted to urea in the liver and glucose excreted  If glucose is not provided by food or body stores, body will Remaining carbon skeleton (called a breakdown body proteins to provide glucose for the brain keto acid) ◦ May be used to make fat or used to  To keep this from happening adequate amounts of foods make other AA that can provide glucose must be supplied 7 8 Incorporation of amino acids into non- Amino acids to fat nitrogen containing compounds  Surplus amino acids cannot be stored as such and  Tyrosine: therefore must be converted to other compounds ◦ Used to make the neurotransmitters norepinephrine and epinephrine which relay nervous system messages throughout the  Amino acids that are converted to Acetyl CoA are made body into fatty acids and stored as triglycerides if energy is not ◦ Converted into the pigment melanin needed  Tryptophan  Thus excess intake of protein foods can lead to weight gain ◦ Serves as precursor for niacin (vitamin) and serotonin (neurotransmitter important for sleep regulation, appetite control and sensory perception) 9 10 Regulating fluid balance  Associated with the blood proteins albumins and Some selected protein globulins  Inadequate protein intake can lead to lower functions concentrations of these proteins in the blood stream ◦Leading to build up of fluid in body tissues causing oedema (can lead to serious health conditions) 11 11 12 2  4/21/2022 Acid-base regulators Transporters  Proteins help maintain the balance between acids and bases within the body  Some proteins carry nutrients and other molecules in the body fluids fluids:  Normal body processes continually produce acids and bases ◦ Haemoglobin carries oxygen from the lungs to the cells ◦ Problem: could upset the blood's acid-base balance ◦ Lipoproteins transport lipids around the body  In an acid solution, hydrogen ions (H+) abound; the more H+, the more ◦ Special transport proteins carry vitamins and minerals concentrated the acid, proteins, which have (-) charges on their surfaces, attract H+  Some transport proteins act as "pumps," picking up compounds on one side of the membrane and releasing them on the other side  Extremes of acidosis and alkalosis can cause working proteins to denature. ◦ E.g. denatured hemoglobin loses its capacity to carry oxygen.  Transport proteins could pass nutrients to storage proteins that will ◦ Can lead to coma and death hold the nutrient until it is needed 13 14 13 14 Source of energy and glucose Other roles of proteins  Energy is need for the proper functioning of body cells  Blood clotting ◦ In a tissue injury i.e. a cut, a rapid chain of events leads to the  Proteins will be sacrificed to provide energy and glucose production of fibrin that causes liquid blood to clot ◦ Times of starvation ◦ Later, the protein collagen forms a scar to replace the clot and ◦ Insufficient carbohydrate intake permanently heal the wound  Vision  Tissue protein will be broken down to make amino acids ◦ The pigments in the cells of the eye's retina are molecules of the available for energy or glucose production protein opsin which responds to light by changing its shape, ◦ Leading to a loss of lean body tissue starting the nerve impulses that carry the sense of sight to the brain 15 16 15 16 Protein quality  Reflection of whether the protein source provides all the essential amino acids needed by the body ◦Low quality proteins fail to provide all the essential amino Proteins in foods acids needed to support the body’s work  Also takes into account the digestibility of the protein source: ◦ Measure of the amount of amino acid that is absorbed from a given protein intake 17 17 18 3  4/21/2022 Limiting amino acids Complete protein  To make proteins, a cell must have all the needed AA available  It is a protein source that contains all the essential amino simultaneously acids in relatively the same amounts as the body  The liver can produce any nonessential AA in short supply for the cell requires  If an essential AA is missing, the cell must break down its own proteins  It may or not contain all the non-essential amino acids to obtain it ◦ To prevent protein breakdown, all 9 essential AA must be supplied by the diet  Generally animal source proteins are complete ◦ If there is a shortage of any essential AA in the diet, protein synthesis is affected  Plant source proteins tend to be limiting in one or more  An essential amino acid supplied in less than the amount needed to amino acids support protein synthesis is called a limiting amino acid 19 20 4