Globular Proteins Hemoglobin

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Globular Proteins Hemoglobin Myoglobin

• Myoglobin - monomer. Single peptide chain and one
  heme unit
• The heme unit contains an Fe atom
  (prosthetic group)
• Hemoglobin - tetramer. Four peptide chains and
  four heme units

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Protein Reactions

• Hydrolysis disruption of 1 structure by heating
  in a strong acid or strong base solution
• Reverse of peptide bond formation
• Usually, enzyme catalyzed
• This is how organisms obtain AA from digested
  protein
• Denaturation disruption of 2, 3 and 4
  structures

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• Denaturing Action - Mechanism of Operation
• Heat
• H bonds are broken by increased vibrational
  energy.(coagulation of egg white albumin on
  frying.)
• Ultraviolet Radiation
• Similar to heat (sunburn) H bonds are broken
• Strong Acids or Bases
• salt formation disruption of hydrogen bonds.
• (skin blisters and burns, protein precipitation.)
  
• Urea Solution
• competition for hydrogen bonds.(precipitation of
  soluble proteins.)
• Some Organic Solvents (e.g. ethanol acetone)
  change ionic groups. (disinfectant action and
  precipitation of protein.)
• Agitation
• shearing of hydrogen bonds.(beating egg white
  albumin into a meringue.)

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Physical and Chemical Denaturing Agents.
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Denaturation Human Hair
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Conjugated Proteins

• Proteins that contain prosthetic groups
• Glycoproteins
• Lipoproteins
• Metalloproteins

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Collagen is a fibrous protein, and is also a
glycoprotein. Glucose and Galactose attach to
5-Hydroxylysine. Carbs cross-link triple helices
into fibril arrangements. Heat ruptures H bonds.
Collagen from tendons, hooves, etc. denatures and
hydrolyzes when boiled in alkaline conditions
and reforms in a chaotic pattern as gelatin
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Lipoproteins lipid protein
LDL (low density lipoproteins) "particles" found
in blood that contain cholesterol. Sphere with
single layer, outer boundary made of a
phospholipid. Core of sphere holds esterified
cholesterol. Inserted into shell are proteins
called apoB proteins. HDL (high density
lipoproteins) similar except have apoA protein
inserted into phospholipid shell.
esterified cholesterol
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Heart Attcack Risk
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Structure of an immunoglobulina defense
glycoprotein
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Review can you Describe the biological role of
various peptide hormones,
neurotransmitters, antioxidants Compare and
contrast simple to conjugated, and fibrous to
globular proteins Show products created from
protein hydrolysis Compare and contrast physical
and chemical denaturing agents, how they
denature proteins Explain the role and structural
differences of glycoproteins and lipoproteins
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Enzymes
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What is an enzyme? Enzymes are usually proteins
often globular proteins. They act as catalysts
for biochemical reactions Can be described in
terms of primary, secondary, tertiary, and
(sometimes) quaternary structures. Held
together by hydrogen bonds, disulfide bonds,
salt bridges, and hydrophobic interactions.
Sound familiar?
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• Enzyme structure 2 categories
• Simple enzymes composed of just protein
• Conjugated enzyme protein non-protein
• Protein part apoenzyme
• Non-protein part cofactor (prosthetic group)

Active enzymes usually involve "cofactors"
Sometimes inorganic ions, or Small organic
molecules (a coenzyme) - many vitamins act as
coenzymes Cofactors are often needed to complete
the catalytically active structure of an enzyme.
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Biochemical reactions need enzymes to occur.
Why? What do enzymes do?
Biochemistry takes place at 37 oC in aqueous
environment. At typical laboratory reaction
conditions, to hydrolyze (saponify) fats Boil
them with concentrated NaOH for hours. Enzymes
called lipases do the same thing (hydrolyze fats)
at 37 oC without NaOH and it takes minutes.
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Catalysts increase the rate of a rxn, but are
not consumed or produced by the rxn. They do
not change Keq of a rxn. Catalysts do not
change the Equilibrium position. ltgt lt-gt
lt-gt Catalysts lower the energy barrier
between reactants and products.
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Enzyme nomenclature
An enzyme name describes its function Suffix
ase e.g. Protease, decarboxylase,
ligase Older names may have the suffix
in e.g. Pepsin, trypsin, subtilisin, thrombin
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Prefix describes enzyme action (function)
Prefix usually names the type of reaction the
enzyme is involved in Oxidoreductase Redox
reactions Hydrolase Hydrolysis of
bonds Substrate chemical enzyme acts
upon Specific substrate may also be in the
name Glucose oxidase Or (less frequently) only
the substrate is in the name Protease, lipase,
lactase, etc.