BIOCHEMISTRY QUESTION 1991: L. PETERSON/AP BIOLOGY
Carbon is a very important element in living systems.
a. Describe the various characteristics of the carbon atom that makes possible
the building of a variety of biological molecules.
b. Explain how reactions involving carbon-containing compounds can contribute
to the greenhouse effect.
c. The following structures are examples of two different categories of biological
compounds. Describe how each category of compounds is important to the
structure and function of living systems.
Category I Category II
+NH3 H
O
CH2 +NH3 - C - C
O-
CH2 CH2
O SH
O = P - O-
O
CH2 - CH - CH2
O O
C = O C = O
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CH
CH2 CH
CH2 CH2
CH2 CH2
CH2 CH2
CH3 CH3
STANDARDS:
A. CHARACTERISTICS OF CARBON ATOMS: (Max of 4 points)
__Ready availability, abundance
__Atom small in size, outer (valence) electrons close to nucleus, so forms stable (strong) bonds
__4 electrons in a valence-capacity of 8, forms 4 bonds to 4 other atoms
__Forms covalent bonds
__Can bond to other carbon atoms, no upper limit to size of carbon compounds
__Bond angles form tetrahedron, resulting in 3-D structures, chains, rings, not just planar
__Can form multiple C-C, C=C, C=C bonds
__Can form isomers, different structures - same number and kind of atoms
__Functional groups/combine with a variety of other elements
__BONUS POINT: if get 3 above - Uniqueness, only Carbon has all of these characteristics
B. REACTIONS CONTRIBUTING TO GREENHOUSE EFFECT: (Max of 4 points)
__Overview: Increase in gas concentration (CO2, CO, CFC) causes greenhouse effect
__CO & CO2 from respiration and combustion, or volatilization of limestone
__CH4 from correct source - livestock, microbes, landfills, swamps, oil wells, etc.
__CFCs from industrial activities, refrigerants, plastic foam, etc.
PHYSICAL MECHANISMS OF HEATING:
__Ozone destruction / more energy (UV) gets in
__Trapping of Energy - "Blanket" traps heat or Reflection of Sun's Energy (technically incorrect
but common use in texts)
__Good technical description of absorption, reradiation and wavelength shift leading to
production or long wave infrared absorbed by greenhouse gases
__Concept of sinks:
CO2 removal by photosynthesis, CaCO3 formation, soluble in oceans, etc.
CO2 addition by forest destruction, industry, etc.
C. BIOLOGICAL MOLECULES: (Max of 5 points)
(Cannot get 10 points for this question without mentioning both category I and II)
CATEGORY I:
__Identification of molecule / category: Phospholipid, phosphoglyceride, fat, lipid,
phosphatidylethanolamine / polypeptide.
__Characteristics of molecule: Hydrophobic/hydrophilic, polar/nonpolar,
amphipathic, or non-water soluble, high E bonds,
sat/unsat C-C bonds.
__Structural uses of molecule: membrane, lipid bilayer, fluid mosaic.
__Functions of molecule (for example):
(2 Max) Phospholipids: Regulation of membrane permeability, fluidity
Fats: Structural, insulation, energy storage, water-proofing
Steroids/Sterols: Hormonal, membrane fluidity
Cholesterol: Animal membranes
Fat soluble Vitamins: Coenzymes
Prostaglandins: Neural modulators
Waxes: Water-proofing
CATEGORY II:
__Identification of molecule / category: Amino acid / protein / cysteine
__Recognizing cysteine's role in disulfide bond formation
__Characteristics of molecule: Side chains variable
Peptide bonds may be formed
Subunit (monomer, building block) of protein
Levels of protein structure / zwitterion / as buffers
__Structural roles: Keratin, collagen, cytoskeletal (tubulin, actin), etc.
__Functional roles: Enzymatic - speed reactions
(2 Max) (pepsin, glucose oxidase, etc.)
Transport (Hb, Myb, permeases, HDL/LDL)
Regulatory (oligopeptides, ex. hypothalamic releasing
factors, insulin, glucagon, etc.)
Contractile - actin, myosin
Protection - antibodies