Proteins & Amino Proteins & Amino AcidsAcids

Chapter 6

Where do we get it?

Animal foods– Also provide B vitamins and minerals such

as iron, zinc and calcium Plant foods

– Also provide B vitamins, iron, zinc, fiber and calcium, but in less absorbable forms

Differences in fiber and fat content

Protein’s Building Blocks: Protein’s Building Blocks: Amino AcidsAmino Acids

Variety in Amino Acid Variety in Amino Acid StructureStructure

Chemist’s View of Proteins

More complex than carbohydrates or fats

Twenty amino acids Different

characteristics 9 essential amino

acids The rest are either

nonessential or conditionally essential

Chemist’s View of Chemist’s View of ProteinsProteins

Peptide bonds link amino acids Condensation reactions Multiple amino acids linked together: polypeptide Protein: one or more polypeptide chains

Amino acid sequencing and protein structure Primary structure – chemical bonds Secondary structure – electrical attractions Tertiary structure – hydrophilic & hydrophobic Quaternary structure – two or more polypeptides

Primary Structure: Amino Primary Structure: Amino Acid SequenceAcid Sequence

Secondary Structure: Secondary Structure: Alpha Helix and Beta Alpha Helix and Beta SheetSheet

Tertiary and Quaternary Tertiary and Quaternary StructureStructure

Tertiary Structure

Primary through quaternary structure

Protein Shape Protein Shape and Functionand Function

Denaturation Disruption of stability Uncoil and lose

shape Occurs with

exposure to acid or high heat

Mutations: deviations in primary structure

Mutations: Sickle Cell Anemia

If structure is altered, shape and function may be affected

Protein Protein Digestion & Digestion & AbsorptionAbsorption

Use of Amino Acids in Use of Amino Acids in BodyBody

Protein SynthesisProtein Synthesis

Basis of uniqueness of each person DNA is the template

Holds the code for amino acid sequences Structural proteins give us our shape Enzymes give us our metabolism

Protein synthesis happens in every cell Diet can influence gene expression Sequencing errors can affect function

DNA DNA Transcription & Transcription & Translation into Translation into

ProteinProtein

Sequencing Errors: Point Sequencing Errors: Point MutationMutation

Roles of ProteinsRoles of Proteins

Growth and maintenance Building blocks for most body structures

Collagen Replacement of dead or damaged cells

Enzymes Assist in break down, build up, and transform

substances Catalysts: speed up chemical reactions

Stepped Art

Enzyme Enzyme Enzyme

AB

BA

BANew compound

Fig. 6-9, p. 181

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.

Roles of ProteinsRoles of Proteins Hormones

Messenger molecules Transported in blood to target tissues

Regulators of fluid balance Hold fluid in the blood Without these proteins:

edema Acid-base regulators

Function as buffers Transporters – specificity

Insulin: A Protein Insulin: A Protein HormoneHormone

Protein Transporter: Protein Transporter: The Sodium-Potassium The Sodium-Potassium PumpPump

Roles of ProteinsRoles of Proteins Antibodies

Defend body against disease

Energy and glucose Alternative glucose

source during starvation and insufficient carbohydrate intake

Movement: contractile proteins in muscle

Energy from Energy from ProteinProtein

Protein MetabolismProtein Metabolism Protein turnover & amino acid pool

Continual production and destruction Need dietary protein to maintain supply

If needed for energy and glucose Wasting of lean body tissue

Can lower BMRExtreme deprivation: organ proteins compromisedPrevented by adequate intake of calories,

carbohydrates, and fats

Protein MetabolismProtein Metabolism Making proteins & nonessential amino acids

If essential amino acid needed, body breaks down its own proteins Rate of protein synthesis may be compromised Limiting amino acid

Nonessentials can be synthesized Making other compounds

Neurotransmitters, hormones Melanin

Nonessential Amino Acid Synthesis When a nonessential amino acid is not

available from the diet, it can be made in the body by the process of transamination.

Protein MetabolismProtein Metabolism Making fat

Energy and protein exceed needs Carbohydrate intake is adequate Can contribute to weight gain Creates nitrogenous waste

Nitrogenous waste In liver – ammonia converted to urea Filtered out of blood and excreted in

urine by kidneys

Nitrogenous Waste: UreaNitrogenous Waste: Urea

Protein intake and urea production

Production increases in proportion to dietary protein Water consumption important in high protein diets

Two factors Digestibility

Animal proteins Plant proteins

Amino acid composition Essential amino acid consumption Nitrogen-containing amino groups Limiting amino acid

Protein Protein QualityQuality

Health Effects of ProteinHealth Effects of Protein High-protein diets

Heart disease Increase risk correlated with high animal-

protein intakeDifferences among protein selections

CancerCertain protein-rich foods, not protein

content of diet, influence risk Individuals with kidney disease

Acceleration of kidney deterioration

Health Effects of ProteinHealth Effects of Protein High-protein diets

OsteoporosisCalcium excretion increasesHigh animal protein intake more closely

correlated with bone mineral loss Ideal amount has not been determined,

and there are multiple influences on bone health

Weight controlSatiation and satiety

Recommended Recommended Intakes of ProteinIntakes of Protein

Intake in U.S. and Canada typically adequate or more than adequate

Dietary sourcesServing sizes: what we get vs. what we

needWhat is a standard serving size of meat?

Key diet principle – moderation Leave room on the plate for other good stuff!

Protein and Amino Acid Protein and Amino Acid SupplementsSupplements

Protein powders Muscle work vs. protein supplements

Athletic performance Whey protein Impact on kidneys?

Amino acid supplements Potential risks associated with intake Lysine & tryptophan