Download Chapter 3 An Introduction to Organic Compounds - Linn

4/29/2015
Proteins
Chapter 3
An Introduction to
Organic Compounds
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Most varied of the biomolecules
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Also called polypeptides
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Make up more than half the dry weight of cells
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Categorized by function
Lecture 3: Proteins
Protein Functions
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Storage
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Protein Functions
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Energy for embryo, young, other organisms
Structure
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Macroscopic examples: tendons, ligaments,
hair, nails (collagen, keratin)
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Cellular level examples: actin,
actin, tubulin
Protein Functions
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Transport
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Proteins that carry other molecules from one
place to another
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Examples: hemoglobin, kinesins
Protein Functions
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Catalysis
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Enzymes are proteins
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Protein Functions
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Defense
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Protein Functions
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Antibodies, interferons produced in response
to infection
Coordination and growth (signaling)
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Hormones (e.g. insulin, growth hormone)
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Communication (receptors)
Protein Functions
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Buffering
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Proteins are both acids and bases at the same
time
Proteins
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Protein monomer = amino acids
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20 amino acids
Amino Acids
Exam 3!
Final Exam!
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Can be arranged to form an astounding variety
of proteins
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Much the way only 26 letters make thousands
of words
Amino Acids
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General structure
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Numbers 11-3 are the same for all amino acids
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α-Carbon in center
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The R group is different for each amino acid
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4 single bonds with other atoms or groups
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Significantly change the properties of the amino
acid
1.
Hydrogen (H)
2. Amine (NH2)
3. Carboxyl (COOH)
4. Variable (R)
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Amino Acids
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Two amino acids combine by dehydration
synthesis to form a dipeptide
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Bond is a covalent bond called a peptide bond
Amino Acids
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The process is repeated to elongate the polymer
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polypeptide
First makes a dipeptide
dipeptide,, then a polypeptide
Protein Structure
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Protein function depends on 4 levels of structure
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Primary – number and order of amino acids
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Secondary – local folding patterns
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Tertiary – overall 3D folding
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Quaternary – interaction of 2 or more fully
assembled proteins
Example: Hemoglobin
Example: Sickle Cell Anemia
Normal RBC
Sickle RBC
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Example: Sickle Cell Anemia
Protein Structure
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How do these interactions form?
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Primary – covalent (peptide) bonds between
amino acids
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Secondary – hydrogen bonds between R
groups
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Tertiary and quaternary – interactions
between R groups
Protein Structure
Protein Structure
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All proteins have primary, secondary structure
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Most proteins do not have quaternary structure
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Most have tertiary structure
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Fibrous proteins have 1°
1°, 2°
2°, and 4
4°°, but not 3
3°°
Polar R groups move out
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Water insoluble
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Non--polar R groups move in
Non
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Examples: collagen, keratin
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Typically form spherical shape – referred to
as “globular”
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Soluble in water
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Sickle Cell Anemia
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Caused by defect in 1° structure
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Leads to defect in 4° structure
Protein Structure
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Biological activity of a protein highly dependent
on shape
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Changes in shape = denaturation
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Protein shape is maintained by hydrogen bonds
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Anything that alters hydrogen bonds can
denature a protein
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Heat, pressure, pH, heavy metals, alcohol,
UV light
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Denaturation
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How does food preservation exploit
denaturation?
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Blanching, pickling, cheesecheese-making, acid,
pressure-canning, pasteurizing
pressure-
Denaturation
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Sometimes denaturation is reversible
(sometimes not)
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Denatured protein
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May fold inappropriately
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May not be functional
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May disrupt other cellular functions
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•
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Sickle cell anemia
Cystic fibrosis
Prions
Enzymes
Cell Differentiation
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Biological catalyst
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Binds to substrate by active site
Having cells that differ in appearance and
function
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Product(s) made and released = reusable
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Lowers activation energy but provides no energy
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Speeds up reaction
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Highly dependent on proteins and enzymes
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May require a coco-factor to bring active site to
final form (vitamin, mineral)
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Major advantage of being multicellular
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Specialization – perform very few tasks, but
do them well
Enzyme Regulation
Enzyme Regulation
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Cell can micromanage its function by controlling
rate of enzyme function
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Cell can micromanage its function by controlling
rate of enzyme function
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Environmental conditions
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Environmental conditions
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Temperature
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pH
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Enzyme Regulation
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Cellular influences
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Enzyme Regulation
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Substrate concentration
Cellular influences
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Enzyme Regulation
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Cellular influences
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Enzyme Regulation
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Competitive inhibition
Cellular influences
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Enzyme Regulation
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Cellular influences
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Enzyme inactivation: nonnon-competitive
inhibition
Enzyme concentration
Competitive inhibition
Enzyme Regulation
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Cellular influences
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Enzyme inactivation: nonnon-competitive
inhibition
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Enzyme Regulation
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Cellular influences
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Enzyme inactivation: coco-factors
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