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Biochemistry VI. Proteins & Enzymes. Proteins. Large, complex organic molecules Made of smaller monomers: Amino Acids Categories of proteins: Structural Proteins Storage Proteins Transport Proteins Defensive Proteins Enzymes. Structural Proteins.

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Biochemistry vi

Biochemistry VI

Proteins & Enzymes


  • Large, complex organic molecules

  • Made of smaller monomers: Amino Acids

  • Categories of proteins:

    • Structural Proteins

    • Storage Proteins

    • Transport Proteins

    • Defensive Proteins

    • Enzymes

Structural proteins
Structural Proteins

  • Used to provide structure and support for certain parts of organisms

  • Examples:

    • Keratin in hair/horns of animals

    • Collagen in connective tissues

    • Silk in spider webs

Storage proteins
Storage Proteins

  • Used to store other molecules for later use

  • Examples:

    • Casein in milk

    • Ovalbumin in egg whites

    • Zein in corn seeds

Transport proteins
Transport Proteins

  • Used to assist in the transport of molecules into and out of a cell or other membrane

  • Examples:

    • Hemoglobin (O2 carrier) in red blood cells

    • Integral membrane proteins

Defensive proteins
Defensive Proteins

  • Used to protect cells and organisms against foreign substances or life forms

  • Examples:

    • Antibodies

    • Cell surface recognition proteins

    • Poisons made by plants, insects, snakes, etc.


  • Regulate the rate of chemical reactions

  • Examples:

    • DNA polymerase and helicase

    • Lactase

    • Peroxidase

    • Sucrase

Amino acids
Amino Acids

  • The building blocks of proteins

  • 20 total amino acids

  • Some can be synthesized by humans, others must be consumed

  • Carbon w/ 4 groups:

    • Amine

    • Carboxyl (acid)

    • Hydrogen

    • R group (varies)

Amino acid r groups
Amino Acid R Groups

  • R Groups determine the physical and chemical properties of the protein

  • They can be polar, nonpolar, acidic, or basic (importance?)

  • They can also be used for the attachment of other inorganic groups that are essential for the functioning of the protein

    • Heme group on hemoglobin bonds to Fe2+

    • Other organic co-enzymes from our diet (vitamins)

Putting amino acids together
Putting Amino Acids Together

  • To build a protein, the amino acids must be connected by peptide bonds

  • Peptide bonds connect the amine group of one amino acid to the carboxyl group of the next

  • This bond is caused by a dehydration reaction

  • A chain of connected amino acids is called a polypeptide

Where do a a s come from
Where Do A.A.s Come From?

  • Many foods contain amino acids in the form of protein

  • When we digest protein, we recycle the amino acids and re-assemble them into our proteins

Structure of a protein
Structure of a Protein

  • The code in the DNA recipe is a sequence of A’s, T’s, C’s and G’s

  • The corresponding RNA copy of the recipe contains this code, which is read in 3’s

    • AUG, GGC, CUA, AAU, GCC, etc…

  • Every 3 letter combination translates into 1 specific amino acid

  • The chain of amino acids has a specific sequence

Structure of protein
Structure of Protein

  • Primary Structure

    • A unique sequence of amino acids in a polypeptide chain

  • Secondary Structure

    • Repeated folds and coils of a polypeptide chain

  • Tertiary Structure

    • Irregular contortions from bonding of the side chains of the various amino acids

  • Quaternary Structure

    • overall protein structure that results from the aggregation of tertiary subunits

Fibrous proteins
Fibrous Proteins

  • Found only in animals

  • Rod or wire-like shapes

  • Usually structural/storage

  • Water insoluble (hydrophobic R-groups)

  • Common in connective tissues, tendons, bone matrix, and muscle fiber

  • Examples: keratins, collagens, elastins

Globular proteins
Globular Proteins

  • Soluble in aqueous solutions (water)

  • Apolar amino acids are oriented toward the center of the globe-like structure

  • Used as enzymes, messengers (hormones), transporters

  • Examples: hemoglobin,

    immunoglobulins, insulin

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  • Enzymes speed up metabolic reactions

  • Enzymes: catalytic proteins

  • Catalyst: reduces the activation energy

  • Activation energy (Ea): energy required to start a reaction


  • Substrate: reactant an enzyme works on

  • Active site: pocket where substrate is worked on

  • Induced fit: brings chemical groups into positions that enhance their ability to work between the enzyme and substrate

  • Effects of temperature and pH: enzymes have an optimal temperature and pH they work within

  • Metabolic pathways consist of chains or cycles of enzymes


  • Cofactors: helpers bound into active site

  • Coenzyme: an organic cofactor

  • Competitive inhibitors: block the active site

  • Non-competitive inhibitors: bind to another part of the enzyme, inhibiting work

  • Allosteric site: receptor site away from the active site, where other molecules regulate activity


  • Feedback (end-product) Inhibition: metabolic pathway is switched off by its end product

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