BIO 330 Cell Biology
Spring 2011
Lecture Outline
Chemistry of the Cell
I. The Importance of Carbon
A. Basic nature of carbon
Valence of 4  4 covalent bonds
Single, double, and triple bonds
B. High stability of carbon-containing molecules
Breaking carbon-carbon bonds requires high energy
C. Diversity of carbon-containing molecules
Hydrocarbons
Functional groups
Negatively charged at pH 7.4 – carboxyl & phosphate
Positively charged at pH 7.4 – amino
Neutral at pH 7.4, but polar – hydroxyl, sulfhydryl, carbonyl, aldehyde
D. Carbon-containing molecules can form stereoisomers
Tetrahedral structure
Asymmetry
Biologically relevant
Examples – L-alanine vs D-alanine; D-glucose
II. The Importance of water
A. Polarity
Bond angle is critical, causes polarity (partial charges)
Electronegative at oxygen end
B. Cohesion
Hydrogen bonds between water molecules
Allows for:
High surface tension
High boiling point
High specific heat
High heat of vaporization
C. Temperature-stabilizing capacity
High specific heat
Hydrogen bonds act as buffer for increased energy
Buffer cells from heat released during chemical reactions
High heat of vaporization
Cooling effect of sweating, panting, etc.
D. Universal solvent
Most molecules in cells are polar = hydrophilic
Some are nonpolar = hydrophobic
Spheres of hydration
BIO 330 Cell Biology
Spring 2011
Lecture Outline
III. The Importance of Selectively Permeable Membranes
A. Physical composition
Phospholipids
Glycolipids
Membrane proteins
Sterols (cholesterol, ergosterol, phytosterol)
Membrane lipids are amphipathic
B. Fluid-mosaic model
Lipid bilayer
Proteins – may be embedded in or associated with the lipid bilayer
Transport proteins
Enzymes
Receptors
Electron carriers (e.g., mitochondrial membranes)
C. Membranes are selectively permeable
Very small molecules diffuse across membranes freely
E.g., water, oxygen, carbon dioxide, ethanol, urea
Large molecules cannot pass freely through membrane – need help
Ions cannot pass freely through membrane – need help
Transport proteins
Hydrophilic channel
Carrier
IV. The Importance of Synthesis by Polymerization of Small Molecules
A. Macromolecules
Polymers of repeating subunits (monomers)
B. Hierarchical structure of a cell
Organic molecules
Biological macromolecules
Supramolecular structures
Organelles / subcellular structures
Cell
C. Four types of macromolecules
Protein
Nucleic acid
Polysaccharide
Lipids
Informational macromolecules – nucleic acids
Structural / functional – protein
Storage / structural – polysaccharides
D. Stepwise polymerization of monomers
BIO 330 Cell Biology
Spring 2011
Lecture Outline
6 basic principles in polymerization
1 – Macromolecules are synthesized by stepwise polymerization of similar or identical
small molecules (monomers)
2 – This occurs by condensation reactions (removal of water)
3 – Monomers must be activated prior to condensation
4 – Activation involves coupling of monomer to carrier molecule
5 – Energy needed for condensation reaction is delivered by ATP
6 – Macromolecules have inherent directionality
E. Degradation of macromolecules
Hydrolysis reactions use water to break bonds between adjacent monomers
V. The Importance of Self-Assembly
A. Self-Assembly of higher order structures
The information required to fold macromolecules and to incorporate them into larger
structures is inherent in the polymers themselves
No further energy or input is required
B. Protein self-assembly
Polypeptide vs mature protein
Native conformation vs denaturation vs renaturation
Polypeptide folding is spontaneous
Molecular chaperones assist assembly of some complex proteins
Assisted self-assembly
Examples of chaperones: heat shock proteins (Hsp70)
C. Noncovalent bonds and interactions are involved in macromolecular folding
Hydrogen bonds
van der Waals interactions
Hydrophobic interactions
Ionic bonds
D. Limits of self-assembly
Some materials must be added to existing structures
E.g., membranes, cell walls, chromosomes
E. Hierarchical assembly advantages
Chemical simplicity
Only 30 small precursor molecules make up most of the cell
20 amino acids
5 nitrogenous bases
2 sugars
3 lipid molecules
Efficiency of assembly
Defects are detected early
Defective subunits discarded instead of a whole protein / organelle