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Protein Structure. Pages 36-53 in textbook. Protein. Composed of C, H, O, N, (S, P) Component of every body tissue Vary widely in chemical composition, physical properties, size, shape, solubility and biological function Common unit = amino acid 20 commonly found

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Protein structure

Protein Structure

Pages 36-53 in textbook


  • Composed of C, H, O, N, (S, P)

  • Component of every body tissue

  • Vary widely in chemical composition, physical properties, size, shape, solubility and biological function

  • Common unit = amino acid

    • 20 commonly found

    • 10 required in animal diets


  • Approximately 50% of DM in most animal cells is protein

    • Exception? adipocytes!!

  • Made of 20+ amino acids (AA)

    • Peptide bond

  • The sequence of amino acids determines the function of the particular protein in the body

Biological functions of proteins
Biological Functions of Proteins

  • Principal organic chemical constituents of body organs and soft tissues

  • Enormous functional diversity

    • Cell membrane structure and function

    • Enzymes

    • Hormones and other chemical messengers

    • Immune factors (antibodies)

    • Fluid balance

    • Acid-base balance

    • Transport

    • Source of energy and glucose

Structural and mechanical
Structural and Mechanical

  • Collagen

    • Bone and skin

  • Keratin

    • Hair and nails

  • Motor proteins

    • Make muscles work!


  • Proteins that catalyze (speed up) chemical reactions without being used up or destroyed in the process

  • Anabolic (putting things together) and catabolic (breaking things down) functions

  • Examples

    • Digestion

      • Salivary amylase

      • Trypsin


  • Chemical messengers that are made in one part of the body but act on cells in other parts of the body

  • Note that "steroid hormones" are not proteins!

  • Examples

    • Insulin

    • CCK

    • Some reproductive hormones

Receptors carriers
Receptors, Carriers

  • Transport materials across cell membranes

Transport proteins
Transport Proteins

  • Transport substances in the blood

    • Lipoproteins (transport lipids)

    • Hemoglobin (transports oxygen and carbon dioxide)

Fluid balance
Fluid Balance

  • Proteins in the blood help maintain appropriate fluid levels in the vascular system

  • Fluid is forced into tissue spaces by blood pressure generated by pumping action of the heart

  • Fluid returns to blood because of “osmotic pressure”

Acid base balance
Acid-Base Balance

  • Body works to keep pH of blood near 7.45

  • Homeostasis IMPORTANT

  • Proteins help “buffer” blood to keep pH acceptable

Immune function antibodies
Immune Function (Antibodies)

  • Antibodies are proteins that attach to and inactivate bacteria and viruses that cause infection

Source of glucose
Source of Glucose

  • When excess protein is fed…

    • Some amino acids converted to glucose

Source of energy
Source of Energy

  • Proteins are the last to be used for energy!

    • Occurs in starvation and low carbohydrate diets

Amino acids

Building blocks of protein


Amino Acids

Amine group

Carboxyl group

Amino acid structural isomers
Amino Acid – Structural Isomers

  • L-isomer found in nature and used in the animal body

Classification of amino acids



Net charge










Classification of Amino Acids


  • Essential

    • Amino acids not synthesized in sufficient amounts in the animal’s body

    • Required in the diet

  • Nonessential

    • Adequately synthesized in the tissue

      • No specific requirement

  • Vary by species

Essential amino acids











Essential Amino Acids

Conditionally essential amino acids
Conditionally Essential Amino Acids

  • Amino acids that can become essential in certain physiologic conditions

    • Example: taurine in cats

    • Example: proline in young pigs

    • Example: tyrosine becomes essential in people with “phenylketonuria (PKU)”

      • PKU; 1 in 15,000 babies

      • Hydroxylation of phenylalanine normally forms tyrosine

        • Tyrosine important in adrenaline, noradrenaline, thyroxine and melanin synthesis

Phenylketonuria pku

Phenylalanine (essential aa)

Tyrosine (nonessential aa)

Phenylketonuria (PKU)

  • Normal situation:

Phenylalanine (essential aa)

Tyrosine (nonessential aa)

  • In PKU:

    • Phenylalanine builds up

      Can cause mental retardation

      Condition inherited from parents (genetic)

Pku symptoms
PKU Symptoms

  • VERY FEW symptoms if diagnosed early and diet strictly regulated

  • IF NOT:

    • Lighter skin, hair and eyes than siblings

      • Phenylalanine important in synthesis of melanin

    • Delayed mental and social skills

    • Head size significantly below normal

    • Hyperactivity

    • Jerking movements of the arms or legs

    • Mental retardation (severe if not diagnosed and treated early)

    • Seizures

    • Skin rashes

    • Tremors

    • Unusual positioning of hands

Pku treatment
PKU Treatment

  • EXTREMELY low phenylalanine intake

    • Diet for life

    • Special low-phenylalanine infant formula

      • Used for life

    • Low or no milk, eggs

    • No aspartame (NutraSweet)

    • Fish oil supplements

      • Hard to get enough essential fatty acids on low phenylalanine diet

    • Iron supplements

Protein structure1

Primary (10)

Sequence of amino acids

Secondary (20)

Twisting of chains into coiled structures

α helix

Β sheet

H bonding

Tertiary (30)

Grouping of secondary structures

Secondary structures coil and fold into layers

H and disulfide bonds

Quaternary (40)

Several tertiary structures linked

Large complex proteins

Protein Structure

Denaturation of protein
Denaturation of Protein

  • “Native” form of protein most biologically active

  • Disruption of the 3-D structure destroys the function

  • Denaturation = break H bonds

    • Heat

    • Chemicals

Protein definitions
Protein Definitions

Crude protein (CP)

Total N-containing compounds in a feed

To calculate the protein percentage, a feed is first chemically analyzed for N content

Protein definitions1
Protein Definitions

Unavailable protein or insoluble crude protein

Calculated from N that is bound to the acid detergent fiber (ADF) fraction of the feed

Normally, about 1% protein on a DM basis is found in this fraction

Values greater than 1% indicate heat damage

Protein definitions2
Protein Definitions

 Available protein

Determined by subtracting unavailable protein from crude protein

Protein definitions3
Protein Definitions

Rumen degradable protein (RDP)

Protein or N that is degraded in the rumen by microorganisms and incorporated into microbial protein or freed as ammonia

Protein definitions4
Protein Definitions

Soluble protein

The protein fraction composed of both non-protein nitrogen (NPN) and true proteins that are rapidly degraded in the rumen

It is normally expressed as a percent of the crude protein

Protein definitions5
Protein Definitions

Rumen undegradable protein (RUP)

Protein or N that is not degraded in the rumen by microorganisms but is available to be digested by the ruminant

Protein definitions6
Protein Definitions

 Non-protein nitrogen (NPN)

All nitrogen fed to animals is not necessarily found in proteins

NPN reflects other sources of nitrogen

An important source of NPN in the ruminant diet is urea

Rumen bacteria can utilize many NPN sources to produce microbial proteins, thus providing amino acids to the cow