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Proteins

Terms in this set (21)

Primary Structure
Most basic structural protein classification. A sequence of amino acids joined linearly through peptide bonds, forming a polypeptide chain.
Secondary Structure
A primary structure with a recurring pattern that form short localized polypetide chain regions. (ex. α-helix)
Tertiary Structure
Proteins 3-D configuration resulting from folding of the secondary structure. May have several α-helix.
Quaternary Structure
Polypeptide subunits forming a specified geometric shape. Governed/connected by: charged molecules, hydrophobic effect, H-bonding & Van der Waals forces.
Biochemical requirements of 3-D structures
- Proteins fold to create a specific binding site(s), directly related to the protein's function
- Proteins have flexibility and rigidity, able to undergo conformational changes and maintain folding capabilities during synthesis
- External surface must be compatible with environment (able to withstand Δing pH/temp as needed)
- Proteins retain stability
- Proteins should be degradable
Proline
Not apart of the α-helix, "helix breaker"
β-sheets (Antiparallel)
The same polypeptide strand folded back on itself. These run in opposite directions, giving a hydrophobic and hydrophilic polarity on each side. Pleated for optimal bonding.
β-sheets (Parallel)
The carbonyl O of one peptide bond is H-bonded to N on alternate strand. The peptide strand runs in the same direction. Pleated for optimal bonding.
Non repetitive Secondary Structures
- Contain bends, loops or turns within proteins that link secondary structures together to form tertiary structures.
- Characterized by abrupt change in directions
- Often found at protein surfaces
- Can link globular proteins (Ω-structure)
Lactate Dehydrogenase (LD)
- Tertiary structure with 6 stranded β-sheet motif (6 secondary structures)
- The highest activity in the tissue with the greatest glucose metabolism (high-low: brain, RBC, kidney, liver, lung, heart, spleen)
- LD is an enzyme with different isoforms [LDH-1(HHHH) - LDH-5 (MMMM)]
Membrane Spanning Receptor Process
1. Hormone (1st messenger) binds to receptor
2. Receptor activates G protein, migrates
3. G protein activates adenylyl cyclase
4. Adenylyl cyclase converts ATP to cAMP
5. cAMP activates kinase, which triggers a response based on 1st messengers direction
Myoglobin (Mb)
Tertiary structure composed of 8 α-helices bound by coil structures. Mb binds O₂ that is released by Hb.
Hemoglobin (Hb)
Quaternary structure made up of two subunits (2α- & 2β chains or 2αβ-protomers)
Creatine Kinase (CK)
Enzyme molecule made up of two proteins
Immunoglobulin (Antibodies)
- Gamma globulin portion of blood
- Proteins secreted by plasma cells, capable of binding specifically with antigen detected by B-cells
- T- or Y- shaped monomer of four looping linked polypeptide chains
- Composed of 2 identical heavy and light chains
- Variable regions form two identical antigen-binding sites
- Constant regions determine antibody class
Classes of Ig
- Ig M
- Ig A
- Ig D
- Ig E
- Ig G
Ig M
- A pentamer; first antibody released
- Potent agglutinating agent
- Readily fixes and activates complement
Ig A
- Monomer or dimer; in mucus and other secretions
- Helps prevent entry of pathogens
Ig D
- Monomer attached to the surface of B-cells
- Functions as a BCR
Ig G
- Monomer; 75-85% of antibodies in plasma
- From secondary and late primary responses
- Crosses the placental barrier
Ig E
- Monomer active in some allergies and parasitic infections
- Causes mast cells and basophils to release histamine
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