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Lecture 5

Lecture 5 - Amino Acids.doc

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Health Studies
HLTH 230
Jeffery Lalonde

Lecture 6 – Protein: Amino Acids Proteins -commonly associated with strength and muscle -muscle cells need physical activity and many nutrients – not only protein! -have a structural and functional role in cells -emphasis on protein (mainly meat) can often be at the expense of other foods in the diet -excess meat may result in high saturated fat intakes -found in milk, eggs, legumes, and many whole grains *can get protein from a variety of different foods, not only meat! Chemistry Overview -contain same atoms as carbohydrate and fat -carbon (C) -oxygen (O) -hydrogen (H) -also contain nitrogen (N) Amino Acids amino: means “nitrogen containing” amino acids: links in a protein chain -all have the same basic structure -central carbon atom with: -hydrogen (H) -amino group (NH2) -acid group (COOH) -unique side chain *side group changes with different amino acids -unique side groups (figure 6-2) -side groups on amino acids vary from one a.a. to another Lecture 6 – Protein: Amino Acids -make proteins more ‘complicated’ than lipids/carbs -‘simplest’ a.a.: glycine (has 1 hydrogen atom as a side group) -amino acids share a common structure but differ in size, shape, electrical charge nonessential amino acids (11) -can be synthesized by the body with: -a nitrogen to form an amino group -fragments of carbohydrate and fat to form the rest of the structure -protein from food generally supplies these a.a. essential amino acids (9) -cannot be made by the body in sufficient quantities -must be supplied by the diet Non Essential Amino Acids Essential Amino Acids (11) (9) Alanine Histidine Arginine Isoleucine Asparagine Leucine Aspartic Acid Lysine Cysteine Methionine Glutamic Acid Phenylalanine Lecture 6 – Protein: Amino Acids Glutamine Threonine Glycine Tryptophan Proline Valine Serine Tyrosine Conditionally essential amino acids: non essential amino acid that becomes essential (must be supplied by the diet) under some circumstances when the need for it exceeds the body’s ability to produce it -ex. Tyrosine -body uses phenylalanine to make tyrosine -if body does not have enough phenylalanine, enough tyrosine cannot be made -so you need to take in tyrosine -> becomes essential -body cannot convert phenylalanine to tyrosine if an individual has Phenylketonuria (PKU) Proteins -a.a. bound together by peptide bonds through condensation reactions -dipeptide: 2 amino acids bonded together -tripeptide: 3 amino acids bonded together -polypeptide: chain of many a.a. bonded together -protein chain length -generally a few dozen to several hundred amino acids long Lecture 6 – Protein: Amino Acids -Amino acid sequences – Primary Structure -very diverse (20 different amino acids) -possibilities for polypeptide chains is tremendous -Polypeptide shapes – Secondary Structure -determined by weak electrical attractions within chain -positively charged hydrogens attract nearby negatively charged oxygen -sections of chain may twist into helix or fold into a pleated sheet, giving proteins strength and stability -Polypeptide tangles – Tertiary Structure -long polypeptide chains twist and fold into a variety of complex tangled shapes -side groups may attract or repel each other -side groups may be hydrophilic or hydrophobic, therefor chains fold so that: -hydrophilic side groups on surface, near water -hydrophobic side groups are hidden in the middle -disulfide bridges also determine tertiary structure -shape gives characteristics -ex. Spherical structures that can carry materials or linear structures form tendons *shape determines function! -Multiple Polypeptide Interactions – Quaternary Structures (Figure 6-5) -quaternary structure involves interactions between 2 or more polypeptides -some polypeptides work together in large complexes Lecture 6 – Protein: Amino Acids -ex. Hemoglobin – a protein that carries oxygen is made up of 4 polypeptide chain Insulin -small protein that consists of 51 a.a. in 2 short polypeptide chains -polypeptides joined by 2 disulfide bridges (bonds between sulfur groups of cysteine) -one of the polypeptide chains is joined to itself by a disulfide bridge -must be injected in individuals with diabetes, not swallowed -will be denatured in stomach so it needs to be injected protein denaturation: change in a protein’s shape, and consequence loss of function brought about by heat, agitation, acid, base, alcohol, heavy metals, or other agents -Ex. Egg whites when heated, milk exposed to acid, stiffening of egg whites when whipped -in the body, proteins are denatured by stomach acid Digestion and Absorption of Protein Overview -dietary proteins do not directly become body proteins -dietary proteins supply amino acids for the body to make proteins -polypeptide are broken by enzymes into shorter and shorter strands, and finally into a.a. Protein Digestion Mouth -little protein digestion occurs in mouth -protein foods are crushed and moistened to be swallowed Stomach Lecture 6 – Protein: Amino Acids -partial breakdown (hydrolysis) of proteins -hydrochloric acid -denatures peptide strands, allowing digestive enzymes to access peptide bonds -converts pepsinogen into pepsin (its active form) -pepsin cleaves large polypeptides into smaller polypeptides and some a.a. *Pepsinogen is a proenzyme/zymogen which is the inactive form of an enzyme Small Intestine -pancreatic and intestinal proteases act on polypeptide chains -polypeptides are hydrolyzed into short peptide chains, tripeptides, dipeptides, and a.a. -peptidase enzymes, on the membrane surface of the intestine, split most dipeptides and tripeptides into single a.a. (a few escape digestion and enter the blood intact) *Note: Proteases are enzymes that hydrolyze protein enteropeptidase: converts pancreatic trypsinogen to trypsin trypsin: inhibits trypsinogen synthesis -cleaves peptide bonds next to lysine and arginine -converts pancreatic procarboxypeptidases to carboxypeptidases -converts pancreatic chymotrypsinogen to chymotrypsin chymotrypsin: cleaves peptide bonds next to the a.a. phenylalanine, tyrosin, tryptophan, methionine, asparagines, and histidine carboxypeptidases: cleave a.a. from acid (carboxyl) ends of polypeptides elastase and collegenase: cleave polypeptides into smaller polypeptides and tripeptides intestinal tripeptidases: cleave tripeptides to dipeptides and a.a. intestinal dipepsidases: cleave dipeptides into a.a. Lecture 6 – Protein: Amino Acids intestinal aminopeptidases: cleave a.a from amino ends of small polypeptides Protein Absorption -a.a. and some dipeptides & tripeptides are transported by carriers into intestinal cells -inside the intestinal cells a.a. may be used for energy or used to synthesize needed compounds -a.a. that are not used in intestinal cells ultimately enter capillaries and are transported to liver Nutrition Misconceptions addressed a) Enzymes in food -some foods contain enzymes -advertisements may falsely encourage individuals... -to eat certain foods that contain enzymes to help digestion -not to eat certain foods as enzymes will “digest your cells” -enzymes in food are actually digested: mainly protein (ex. Bromelain - enzyme in pineapple) -no jello and pineapple because jello is a protein...pineapple has Bromelain -> jello will not set -even digestive enzymes are digested when they leave the stable pH of their environment -ex. Pepsin from stomach is digested in inc. pH of small intestine Lecture 6 – Protein: Amino Acids b) Amino acid supplements are better than protein? -myth: a.a. supplements prevent the body from overworking as they don’t require digestion -fact: body easily handles breakdown of proteins (unless certain medical conditions like short bowel syndrome are present) -fact: one amino can overwhelm a transporter, and prevent other a.a. from being picked up -can have problems because you are not getting the other a.a. Proteins in the Body -20,000 to 25,000 genes in the body code for hundreds of thousands of protein Protein Synthesis -instructions for making every protein in a person’s body are filed in the DNA of the nucleus of every cell -delivering instructions -> cell needs to be informed of sequence of a.a. for a needed protein -DNA template to make mRNA -> transcription -mRNA carries code to ribosome -> ribosomes are protein factories -mRNA specifies sequence of amino acids -> translation, tRNA (collects a.a. from cell fluid) *sequencing errors can occur -sequence of a.a. in each protein determines its shape -remember: shape is related to function -miscopied protein can alter function! Sequencing Errors *errors in sequencing = causes protein to have a change in function -miscopied a.a. can change protein Lecture 6 – Protein: Amino Acids Sickle-cell anemia -2 out of the 4 polypeptide chains in hemoglobin have valine in place of glutamic acid -change in sequence -> change in shape of hemoglobin -diminished capacity to carry oxygen -red blood cells with abnormal hemoglobin become a sickle, or crescent shape, rather than their usual disc shape Roles of Protein Structural Materials structural materials: form building blocks of muscle, blood, and skin -ex. Build bone and teeth: collagen (matrix of protein) is laid and filled with crystals of calcium, fluoride, and other minerals matrix: basic structure that gives form to a development structure collagen: protein from which connective tissues like scars, tendons, ligaments and foundations of bones and teeth are made -Ex. Collagen roles -to provide material of ligaments and tendons -strengthens arteries -holds torn tissue together in scars *vitamin C -collagen breaks down = scars open up -proteins are needed for replacement of cells -lifespan of skin = 30 days -hair, fingernails -GI tract - replaced every few days Enzymes: proteins that facilitate chemical reactions but are not changed in the process -some proteins act as enzymes (fig 6-9) Lecture 6 – Protein: Amino Acids -only digestive enzymes have been discussed -there are also enzymes to build, ex. build bone -text book uses analogy of a marriage *enzyme is like a minister helps to bond 2 things together -can do it multiple times b/c it is not changed in the process hormones: elicited from glands as a response to altered conditions to act on a target tissue to elicit a specific response -some hormones are proteins -ex. insulin -rise in blood glucose -insulin is released from pancreas -insulin stimulated glucose to enter cells Regulators of fluid balance -help maintain body’s fluid balance -body fluids contained both inside and outside of cell (intracellular and extracellular fluids) -extracellular fluid can be found within blood vessels (intravascular) or between cells (interstitial) Normal Fluid Balance Lecture 6 – Protein: Amino Acids -fluids and a variety of materials are exchanged between cells and blood -proteins are large and therefor can not pass freely across capillary walls -proteins generally remain in the cells and plasma -some plasma proteins do leak out of plasma into interstitial fluid Abnormal Fluid Balance -critical illness or protein malnutrition leads to plasma proteins leaking out of blood vessels -proteins attract water causing swelling (edema) Protein-related causes of edema include -excessive protein losses cause by inflammation and critical illness -inadequate protein synthesis caused by liver disease -inadequate protein in diet *inadequate consumption of protein -> drop in concentration of proteins below normal -excess fluid build up in surrounding tissues (not enough protein in blood to counteract force) Acid-Base Regulators - BUFFERS -normal body processes continually produce acids and bases that are transported to kidneys and lungs for excretion -acid: mainly hydrogen ions -proteins have (-) charges on surfaces -> able to attract hydrogen ions, decreasing the acidity -maintain acid-base balance by accepting/releasing H+ ions -blood’s acidity tightly controlled with extremes: acidosis/alkalosis leading to coma and death *very important in maintaining pH -> the second pH changes, proteins will be denatured and causes huge problems in the body Lecture 6 – Protein: Amino Acids Transporters (fig. 16-10) -some proteins carry nutrients and other molecules around the body -some act as pumps -ex. Hemoglobin carries oxygen Lipoproteins transport lipids around the body Antibodies: large protein molecules produced by immune system in response to invasion of foreign invaders -proteins can defend against disease -viruses enter cells and multiply -body detects invading viruses and manufactures antibodies -with insufficient protein, body can not make army of antibodies to fight against disease Source of energy and glucose -proteins can be sacrificed for energy, if inadequate calories/carbs are being taken in -body will break down its tissue proteins to make a.a. available for energy or glucose production (gluconeogenesis) Other Roles -blood clotting: fibrin-string of proteins form a clot -vision: Opsin responds to light by changing its shape -> nerve impulses to brain Protein Metabolism Protein turnover and amino acid pool protein turnover: degradation and synthesis of proteins -proteins continuously being made and broken down within each cell -proteins break down and a.a. join the a.a. from food within cells and circulating blood Lecture 6 – Protein: Amino Acids amino acid pool: supply of a.a. derived from either food proteins or body proteins that collect in cells and circulating blood and stand ready to be incorporated into proteins and other compounds/used for energy Nitrogen Balance --in healthy adults -protein synthesis roughly the same amount as breakdown -intake is roughly the same as that lost with nitrogen excretion in urine and feces -nitrogen equilibrium: when nitrogen intake = nitrogen excretion -can be used to measure protein -aka zero nitrogen balance *someone in nitrogen balance is healthy/taking in enough protein Positive nitrogen status (+) -more protein syn
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