Protein: Amino Acids Chapter 6
Amino Acids • Atoms in All Amino Acids • Carbon, hydrogen, oxygen + nitrogen • Amino Acid Structure • Central Carbon with 4 spaces • Hydrogen • Amino group • Acid group • Unique side group or side chain
Amino Acid Side group varies Amino group Acid group
Identical except for Side Group Glycine Alanine Aspartic acid Phenylalanine
The Essential Amino Acids Isoleucine (Ile) - for muscle production, maintenance and recovery after workout. Involved in hemoglobin formation, blood sugar levels, blood clot formation and energy. Leucine (Leu) - growth hormone production, tissue production and repair, prevents muscle wasting, used in treating conditions such as Parkinson’s disease. Lysine (Lys) - calcium absorption, bone development, nitrogen maintenance, tissue repair, hormone production, antibody production. Methionine (Met) - fat emulsification, digestion, antioxidant (cancer prevention), arterial plaque prevention (heart health), and heavy metal removal.
The Essential Amino Acids • Phenylalanine (Phe) - tyrosine synthesis and the neurochemicals dopamine and norepinephrine. Supports learning and memory, brain processes and mood elevation. • Threonine (Thr) monitors bodily proteins for maintaining or recycling processes. • Tryptophan (Trp) - niacin production, serotonin production, pain management, sleep and mood regulation. • Valine (Val) helps muscle production, recovery, energy, endurance; balances nitrogen levels; used in treatment of alcohol related brain damage. • Histidine (His) - the 'growth amino' essential for young children. Lack of histidine is associated with impaired speech and growth. Abundant in spirulina, seaweed, sesame, soy, rice and legumes.
The Chemist’s View of Proteins • More complex than starches- a glucose chain • Or fats- carbon chains attached to glycerol • Twenty amino acids like an alphabet • Different characteristics • Essential amino acids- must come from food • Nonessential amino acids- body can make • Conditionally essential- When body cannot make nonessential, then it has to be in diet. Ex: phenylketonuria
Protein Made from Amino Acids • Proteins (like words) • Peptide bonds link amino acids (the letters) • Condensation reactions • Amino acid sequencing • Primary structure – chemical bonds • Secondary structure – electrical attractions • Tertiary structure – hydrophilic & hydrophobic • Quaternary structure – two or more polypeptides
Amino Acid Chains • Amino acid chains are linked by peptide bonds in condensation reactions. • a. Dipeptides have two amino acids bonded together. • b. Tripeptides have three amino acids bonded together. • c. Polypeptides have more than two amino acids bonded together.
Four Levels of Structure • Primary structure: amino acid sequence • Secondary structure: weak electrical attractions within a polypeptide chain (shape) • The shape of a protein provides stability. • Tertiary structure: polypeptide tangles • Hydrophilic and hydrophobic side groups attraction and repulsion
Four Levels of Structure • Quaternary Structures • Multiple polypeptide interactions • Some polypeptides function independently. • Some polypeptides need to combine with other polypeptides to function correctly. • An example of a quaternary structure is hemoglobin, which is composed of 4 polypeptide chains.
The Chemist’s View of Proteins • Protein • Denaturation • Disruption of stability • Uncoil and lose shape • Stomach acid • Heat (cooking)
Four highly folded polypeptide chains form the globular hemoglobin protein. Iron Heme, the nonprotein portion of hemoglobin, holds iron. The amino acid sequence determines the shape of the polypeptide chain.
Insulin is Curly (Sulfur Bonds)
Protein Digestion • Mouth chews it up • Stomach • Hydrochloric acid denatures proteins • Pepsinogen converted to pepsin by HCl • Small intestine • Hydrolysis: Proteases hydrolyze protein into short peptide chains called oligopeptides, which contain four to nine amino acids. • Peptidases split proteins into amino acids.
Protein Absorption [Animation 0606] • Used by intestinal cells for energy or synthesis of necessary compounds. • Amino acids are transported to the liver via capillaries
Protein Absorption • Transport into intestinal cells • Uses of amino acids by intestinal cells • Unused amino acids transported to liver • Enzyme pepsin is digested in higher pH of SI • Predigested proteins unbeneficial for healthy people
Protein Synthesis • Protein is constantly being broken down and synthesized in the body by unique genetic information of each person • Amino acid sequences of proteins • genes in DNA in cell nuclei • Diet • Adequate protein • Essential amino acids
Protein Synthesis • DNA template to make mRNA • Transcription • mRNA carries code to ribosome • Ribosomes are protein factories • mRNA specifies sequence of amino acids • Translation • tRNA • Sequencing errors
Protein Synthesis • Gene expression and protein synthesis • Capability of body cells • Protein needs met by cell-regulated gene expression • Dietary influence on gene expression • PUFA influences gene expression for lipases, hence development of CHD
Two of Protein’s Roles • Growth and maintenance • Building blocks for most body structures • Collagen matrix for bones • Replacement of dead or damaged cells • Enzymes catalyze • Breakdown rxns (catabolism) • Building up rxns (anabolism)
B New compound A B A B A Enzyme Enzyme Enzyme The separate compounds, A and B, are attracted to the enzyme’s active site, making a reaction likely. The enzyme forms a complex with A and B. The enzyme is unchanged, but A and B have formed a new compound, AB. Stepped Art
Roles of Proteins • Hormones regulate processes • Messenger molecules • Transported in blood to target tissues • Regulators of fluid balance • Edema- classic imbalance • Acid-base regulators • Attract hydrogen ions • Transporters – specificity
Regulators of Fluid Balance • Plasma proteins can leak out of the blood into the tissues and attract water, causing swelling (edema). • In critical illness and inflammation • Inadequate protein synthesis caused by liver disease • Inadequate dietary protein intake
Acid-Base Regulators • Act as buffers by keeping solutions acidic or alkaline. • Acids release hydrogen ions in a solution. • Bases accept hydrogen ions in a solution. • Acidosis- high levels of acid in blood and body fluids. • Alkalosis- high levels of alkalinity in blood and body fluids.
Transporters • Carry lipids, vitamins, minerals and oxygen in the body. • Ex: Heme Fe captured from SI by a protein then attached to globin. Hemo- globin carries O2 from lungs to cells. • Act as pumps in cell membranes, transferring compounds from one side of the cell membrane to the other.
Transport Proteins Animation 0610
Antibodies • Fight antigens- bacteria and viruses • Provide immunity to fight an antigen more quickly the second time exposure occurs • Immunity: molecular memory
Other Roles of Protein • Source of energy and glucose in starvation or insufficient carbohydrate intake (gluconeogenesis) • Blood clotting by producing fibrin, which forms a solid clot. • Vision by creating light-sensitive pigments in the retina (opsin)
Preview of Protein Metabolism • Protein turnover & amino acid pool • Continual production and destruction • Amino acid pool pattern is fairly constant • Used for protein production • Used for energy if stripped of nitrogen, degrades/converts to glucose or stored as TG
Nitrogen Balance • Zero Nitrogen Balance: synthesis = degradation • Positive and negative nitrogen balance • Amino acids from food are called exogenous- protein ingested • Amino acids from within the body are called endogenous- protein
Nitrogen Balance Determinants • Positive • Growing years • Pregnancy • Recovery, healing • Negative • Burns, injuries • Diseases, infections • Starvation or very low-protein diet
Preview of Protein Metabolism • Making other compounds from amino acids • Neurotransmitters (epi- and norepi-), melanin pigment and thyroxine are made from tyrosine. • Niacin and serotonin made from tryptophan. • Energy from glucose and fatty acids preferred • Body has no protein “storage” like adipose or glycogen • Inadequate dietary protein- wasting of lean body tissue
Preview of Protein Metabolism • Fat production from excess protein • Energy and protein exceed needs • Carbohydrate intake is adequate • Can contribute to weight gain • Deaminating amino acids • Stripped of nitrogen-containing amino group • Ammonia • Keto acid
Amino Acids for Energy and Fat • Muscle and organ protein available for energy if needed • Amino acids whittled down to glucose, nitrogen exits in urine. • Excess calories in protein form are deaminated (nitrogen excreted) and converted into fat
Preview of Protein Metabolism • Make proteins & nonessential amino acids from dietary protein • Breakdown of body protein to obtain essential amino acid not in diet • Keto-acid + N needed for nonessentials • Liver cells and nonessential amino acids • Converting ammonia to urea • Liver – ammonia and carbon dioxide • Dietary protein
Transamination and Synthesis of Nonessential Amino Acid Side group Side group Side group Side group Keto acid A Amino acid B Amino acid A Keto acid B + + The body can transfer amino groups (NH2) from an amino acid to a keto acid, forming a new nonessential amino acid and a new keto acid. Transamination reactions require the vitamin B6 coenzyme.
Side group Side group Deamination of a Nonessential Amino Acid Amino acid Keto acid The deamination of an amino acid produces ammonia (NH3) and a keto acid. Side group Side group Synthesis of a Nonessential Amino Acid Amino acid Keto acid Given a source of NH3, the body can make nonessential amino acids from keto acids.
Ammonia (NH3) • Byproduct of deamination from protein metabolism • In the liver: 2NH3 + CO2 = H2O + urea • Liver releases urea into blood • Kidneys filter urea out of blood • Protein intake, Urea production Water consumption needed to avoid dehydration
Ammonia Ammonia Carbon dioxide UREA SYNTHESIS Water Urea
Amino acids Bloodstream Ammonia (NH3) + CO2 Liver Urea Urea Bloodstream Kidney Urea To bladder and out of body
Converting Ammonia to Urea • Ammonia and carbon dioxide are combined in the liver to make urea, body’s principle vehicle for excreting unused nitrogen • Liver Dz: High serum NH3 • The kidneys filter urea out of the blood. • Renal Dz: High serum urea