Protein: Amino Acids

Chapter 6

Amino Acids

 Atoms in All Amino Acids  Carbon, hydrogen, oxygen +

nitrogen

 Amino Acid Structure  Central Carbon with 4 spaces 1.

Hydrogen 2.

Amino group 3.

Acid group 4.

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.

Condensation Rxn to Dipeptide

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.

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Protein Absorption

 Used by intestinal cells for energy or synthesis of necessary compounds.

 Amino acids are transported to the liver via capillaries

Protein Digestion

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

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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 Sequencing Error

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)

Enzyme Action of Proteins

A B A B 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.

A B New compound Enzyme 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

Fluid Imbalance

Acid-Base Regulators

    Act as

buffers

by keeping solutions acidic or alkaline.

Acids Bases Acidosis-

fluids.

release hydrogen ions in a solution.

accept hydrogen ions in a solution.

high levels of acid in blood and body 

Alkalosis-

body fluids.

high levels of alkalinity in blood and

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 O 2 from lungs to cells.

 Act as pumps in cell membranes, transferring compounds from one side of the cell membrane to the other.

Transport Proteins

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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 (NH 2 ) from an amino acid to a keto acid, forming a new nonessential amino acid and a new keto acid. Transamination reactions require the vitamin B 6 coenzyme.

Side group Side group Deamination of a Nonessential Amino Acid Amino acid Keto acid The deamination of an amino acid produces ammonia (NH 3 ) and a keto acid.

Side group Side group Keto acid Amino acid Given a source of NH 3 , the body can make nonessential amino acids from keto acids.

Synthesis of a Nonessential Amino Acid

Ammonia (NH

3

)

 Byproduct of deamination from protein metabolism  In the liver: 2NH 3 + CO 2 = H 2 O + urea  Liver releases urea into blood  Kidneys filter urea out of blood  Protein intake, Urea production Water consumption needed to avoid dehydration

Ammonia

UREA SYNTHESIS

Carbon dioxide Ammonia Water Urea

Amino acids Bloodstream Ammonia (NH3) + CO 2 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 NH 3  The kidneys filter urea out of the blood.

 Renal Dz: High serum urea

Protein Quality

 Two factors  Digestibility  With other foods consumed  Animal (90-99%) vs. plant proteins (>90% for soy and legumes)  Amino acid composition  Essential amino acid consumption  Nitrogen-containing amino groups  Limiting amino acid thwarts synthesis

Protein Quality

 Reference protein- the protein gold standard  Preschool age children’s requirements  High-quality proteins  Animal proteins  Plant proteins  Complementary proteins  Low-quality proteins combined to provide adequate levels of essential amino acids

Legumes Grains Together Ile Lys Met Trp

Complementary Protein

Protein Regulations for Food Labels

  Quantity of protein in grams Percent Daily Value  Not mandatory unless  Protein claims  Consumption by children under 4 years old  Quality of protein also figures into DV

Protein-Energy Malnutrition (PEM)

   Insufficient intake of protein, energy, or both Prevalent form of malnutrition worldwide Impact on children  Poor growth  Most common sign of malnutrition   Adult PEM in AIDS, TB, anorexia nervosa Conditions leading to PEM- food shortage

Protein-Energy Malnutrition (PEM)

 Marasmus  Chronic PEM  Children 6 to 18 months  Poverty  Little old people – just “skin and bones”  Impaired growth, wasting of muscles, impaired brain development, lower body temperature  Digestion and absorption

Protein-Energy Malnutrition (PEM)

 Kwashiorkor  Acute PEM  Children 18 months to 2 years  Develops rapidly  Aflatoxins  Edema, fatty liver, inflammation, infections, skin and hair changes, free-radical iron  Marasmus-Kwashiorkor mix

Protein-Energy Malnutrition

Protein-Energy Malnutrition (PEM)

 Infections  Degradation of antibodies  Fever.

 Fluid imbalances and

dysentery.

 Anemia  Dysentery  Heart failure and possible death.

 Rehydration and nutrition intervention

Health Effects of Protein

 High-protein diets  Heart disease  Animal protein /animal fat intake  Homocysteine levels  Cancer  Animal foods, not protein content of diet  Acceleration of kidney deterioration

Health Effects of Protein

 High animal protein diets  Osteoporosis  Calcium excretion increases  Weight control  Satiety  Adequate protein, moderate fat, and sufficient carbohydrate better support weight loss.

Recommended Protein Intakes

 Need for dietary protein  Source of essential amino acids  Practical source of nitrogen  10 to 35 percent of daily energy intake  RDA  Adults: 0.8 grams / kg of body weight / day  Athletes: 1.2-1.7 g/kg/day  Elderly: 1.0-1.2 g/kg/day unless diabetic  Pregnant / Lactating: 1.1-1.3 g/kg/day

Recommended Intakes of Protein

 Protein in abundance  Intake in U.S., Canada and most developed countries  Self-inflicted protein deficiencies  Key diet principle – moderation

Nutritional Genomics

  New field Nutrigenomics  Nutrients influence gene activity  Nutrigenetics  Genes influence activity of nutrients  Human genome

Genomics Primer

2 Chromosome 1 Nucleus 3 DNA 4 5 Gene Cell 1 The human genome is a complete set of genetic material organized into 46 chromosomes, located within the nucleus of a cell.

2 A chromosome is made of DNA and associated proteins.

3 The double helical structure of a DNA molecule is made up of two long chains of nucleotides. Each nucleotide is composed of a phosphate group, a 5-carbon sugar, and a base.

4 The sequence of nucleotide bases (C, G, A, T) determines the amino acid sequence of proteins. These bases are connected by hydrogen bonding to form base pairs (C).

—adenine (A) with thymine (T) and guanine (G) with cytosine 5 A gene is a segment of DNA that includes the information needed to synthesize one or more proteins.

Nutritional Genomics

Genes Food and nutrients Nutritional genomics Nutritional genomics examines the interactions of genes and nutrients. These interactions include both nutrigenetics and nutrigenomics.

Genes Nutrigenetics Nutrient absorption Nutrient use and metabolism Nutrient requirements Food and nutrient tolerances Nutrigenetics (or nutritional genetics) examines how genes influence the activities of nutrients.

Gene mutation Gene expression Gene programminga a Nutrigenomics Food and nutrients Nutrigenomics, which includes epigenetics, examines how nutrients influence the activities of genes.

A Genomics Primer

 DNA  46 chromosomes  Nucleotide bases  Gene expression  Genetic information to protein synthesis  Gene presence vs. gene expression  Epigenetics  DNA methylation

Nutrients and phytochemicals 1 Substances generated during metabolism 1 Nutrients and phytochemicals can interact directly with genetic signals that turn genes on or off, thus activating or silencing gene expression, or indirectly by way of substances generated during metabolism.

Gene expression activated or silenced 2 Protein synthesis starts or stops 3 Disease prevention or progression 2 3 Activating or silencing a gene leads to an increase or decrease in the synthesis of specific proteins.

These processes ultimately affect a person’s health.

Genetic Variation and Disease

 Genome variation  About 0.1 percent  Goal of nutritional genomics  Customize recommendations that fit individual needs  Single-gene disorders  Phenylketonuria (PKU)

Genetic Variation and Disease

 Multigene disorders  Study expression and interaction of multiple genes  Sensitive to environmental influences  Example  Heart disease  Single nucleotide polymorphisms (SNPs)