PROTEINS

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Proteins
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Objectives

• Write the general formula for an amino acid.
• Define a peptide bond and write a formula that
  shows what this bond looks like.
• Define and show the relationship between a
  protein and polypeptide.
• Define essential amino acids and complete
  proteins.

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Objectives

• Write formulas and/or structures that will
  illustrate what is meant by primary, secondary
  and tertiary structure of a protein.
• Explain what denaturation is and how it can be
  produced.
• Describe at least two human diseases that result
  from improper protein nutritional practices.

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Protein Prime importance
Found in Cells (2/3 of dry cell weight )
Tissues All body fluids
except urine and bile Not
stored for future use (like
carbohydrates and lipids)
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• Proteins ?
• Major components of

Skin, nails, claws, hair, wool, feathers, hooves,
muscles, tendons and cartilage.
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• Proteins ?
• Essential Functions

? Support (keratin/collagen) ? Enzymes
(specific catalysts) ? Transport
(channel proteins/hemoglobin) ?
Defense (antibodies) ?
Hormones (regulatory - insulin)
? Motion (actin/myosin)
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Protein Composition
Polymers Amino Acid Monomers 20 amino acids in
proteins
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Amino Acids
acid group
amino group
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Amino Acids
Some are chemically neutral.
Glycine has 1 carboxyl group and 1 basic group.
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Amino Acids
Some are chemically acidic.
Glutamic acid has two carboxyl groups only 1
amino acid.
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Amino Acids
Some are chemically basic.
Lysine has two amino groups and 1 carboxyl.
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Amino Acids
Differ in nature of R group.
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Amino Acids
Some are hydrophobic.
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Amino Acids
Some are hydrophilic.
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Peptide
Two or more amino acids bonded together.
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Peptide Bond

• Covalent bond between amino acids.
• Electrons shared unevenly (O2 is more
  electro-negative than N2).
• Polarity permits hydrogen bonding between parts
  of a polypeptide.

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Polypeptides

• Chains of many amino acids joined by peptide
  bonds.
• Proteins may contain more than one polypeptide
  chain.
• Can have large numbers of amino acids.
• Since amino acids differ by R group proteins
  differ by a particular sequence of the R groups.

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Protein Functions

• Enzymatic
• Structural
• Storage
• Transport
• Hormonal
• Receptor
• Contractile
• Defensive
• Regulatory
• Sensory

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Enzymatic Action
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Protein Structure

• Shape determines function.

Animation Protein Structure Introduction
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Interactions and Protein Shape

• Hydrogen bonds
• Disulfide bridges
• Ionic bonds
• Van der Waals attractions
• Hydrophilic/hydrophobic reactions

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Interactions and Protein Shape
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Interactions and Protein Shape

• R group of cysteine ends with a sulfhydryl group
• (-SH)
• Enables one chain of amino acids to connect to
  another by a disulfide bond (-S-S-).

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Interactions and Protein Shape
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Interactions and Protein Shape
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Interactions and Protein Shape
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Levels of Protein StructurePrimary
The specific sequence of amino acids joined by
peptide bonds.
Animation Primary Protein Structure
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Primary StructureHistorical Perspective
- Fredrick Sanger determined first protein
sequence (insulin). - Broke into fragments and
determined AA sequence of fragments. - Then
determined sequence of fragments. - Required ten
years research modern automated sequencers
analyze sequences in hours.
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Levels of Protein StructureSecondary

• The specific geometric shape caused by
  intramolecular and intermolecular hydrogen
  bonding.

Animation Secondary Protein Structure
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Levels of Protein StructureSecondary

• ? Helix
• Discovered by Linus Pauling and
• Robert Corey.
• Oxygen partially -, hydrogen partially .
• Hydrogen bonding between the CO
• of one AA and the N-H of another.
• Hydrogen bonding between every fourth
• AA acid holds spiral shape of an alpha
• helix.
• In keratin ? helices covalently bonded by
• disulfide (-S-S-) linkages between two
• cysteine amino acids.

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Levels of Protein StructureSecondary

• ? Pleated Sheet
• Polypeptides turn back upon themselves
• Hydrogen bonding between extended lengths.
• keratin includes feathers, hooves, claws, beaks,
  scales and horns silk

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Levels of Protein StructureMotifs

• Folds or creases
• Beta ribbon
• Greek Key
• Omega loop
• Helix-loop-helix
• Zinc finger
• Helix-turn-helix
• Beta hairpin

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Greek Key
4 beta strands folded over into a sandwich shape.
It is named for its resemblance to the Greek key
meander pattern in art.
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Omega Loop
W

• Named after its shape, the Greek capital letter
  Omega
• Consists of a loop of any length and any amino
  acid sequence.

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Helix-Loop-Helix
Two a helices connected by a loop. Some of these
facilitate DNA binding.
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Zinc Finger
Protein (blue) containing three zinc fingers in
complex with DNA (orange). The Zinc ions are
green. (Transcription Factors)
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Helix-Turn-Helix

• Binds to major groove of DNA through hydrogen
  bonds and various Van der Waals interactions with
  exposed bases.
• Two a helices joined by a short strand of amino
  acids
• Found in many proteins that regulate gene
  expression.

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Beta Hairpin

• Two beta strands that look like a hairpin.
• Beta strands are adjacent in primary sequence and
  oriented in an antiparallel arrangement in the
  hairpin

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Levels of Protein StructureTertiary

• Result when proteins of secondary structure are
  folded, due to various interactions Between R
  groups of their constituent amino acids.

Animation Tertiary Protein Structure
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Levels of Protein StructureQuarternary

• Results when two or more polypeptides combine.
• - Hemoglobin is globular protein with a
  quaternary structure of four polypeptides.
• - Collagen is a fibrous protein consisting
  of three polypeptides coiled like a rope
• - Most enzymes have a quaternary structure.

Animation Quaternary Protein Structure
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(No Transcript)
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Sickle-Cell Disease

• Slight change in primary structure can affect a
  proteins structure and ability to function
• Sickle-cell disease, an inherited blood disorder,
  results from a single amino acid substitution in
  the protein hemoglobin.

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Chaperone Proteins

• Special proteins which help new proteins fold
  correctly.
• Chaperone deficiencies may play a role in
  facilitating certain diseases.

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Denaturation Of Proteins
Loss of normal configuration a physical
change. Once a protein loses it normal shape, it
cannot perform its usual function. Sometimes will
renature.
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How Proteins Can Be Denatured

• Temperature
• Cooking an egg
• Albumin congeals
• Addition of hydrogen or hydroxide ions (large pH
  changes)
• Adding acid to milk
• Causes curdling
• Vigorous Shaking
• Organic Solvents
• Salts of heavy metals (mercury, silver lead)
• Detergents
• Ultraviolet Radiation

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Essential Amino Acids
Dietary requirements Not synthesized
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Essential Amino Acids
methionine or cysteine leucine isoleucine
lysine phenylalanine (or tyrosine)
threonine, typtophan valine
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Complete Proteins
Proteins that contain all essential amino acids.
They are usually derived from animal sources.
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Protein Deficiency Diseases

• Marasmus Kwashiokor
• Two of the most common childrens diseases
  worldwide.
• Weaned diet deficient in protein.

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Kwashiokor

• Sufficient calories, insufficient protein.
• Symptoms
• Loss of appetite
• Diarrhea
• Enlarged liver
• Pigmented skin
• Apathy
• Irritability
• Bloated belly

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Marasmus

• Inadequate calories and protein
• Symptoms similar to Kwashikor
• Swollen belly
• Loss of muscular tone
• Rough, leathery skin
• Generally retarded physical and mental
  development