Chapter 2
The Chemistry of the Cell
The Chemistry of the Cell

• The Importance of Carbon
• The Importance of Water
• The Importance of Selectively
Permeable Membranes
• The Importance of Synthesis by
Polymerization of small molecules
• The Importance of Self-Assembly
The Importance of Carbon
• The most important atom in biological
molecules
• Form covalent bonds with one another and
with O, H, N, and S
– Single bond
– Double bond
– Triple bond
Carbon-Containing Molecules
Are Diverse
Carbon-Containing Molecules Can
Form Stereoisomers（立體異構物）
The Chemistry of the Cell

• The Importance of Carbon
• The Importance of Water
• The Importance of Selectively Permeable
Membranes
• The Importance of Synthesis by
Polymerization of small molecules
• The Importance of Self-Assembly
The Importance of Water
• Suitable as the universal solvent of living
system
• Is the single most abundant component of
cells and organisms (75 –85%)
The Importance of Water
• Water molecules are polar
• Water molecules are cohesive
• Water has a high temperaturestabilizing capacity
• Water are excellent solvent
Water Has a High TemperatureStabilizing Capacity
• Specific heat (比熱): absorb per gram to
increase 1 oC
• Specific heat is much higher than other
liquid- hydrogen bond
Find Out the Terms
• Hydrophilic molecule
• Hydrophobic molecule
• Amphipathic molecule
The Chemistry of the Cell

• The Importance of Carbon
• The Importance of Water
• The Importance of Selectively Permeable
Membranes
• The Importance of Synthesis by
Polymerization of small molecules
• The Importance of Self-Assembly
The Importance of Selectively
Permeable Membranes
• A membrane is a lipid bilayer with proteins
embedded it
• Membranes are selectively permeable
Membrane
• Is essentially a hydrophobic permeability
barrier
• Consists of phospholipids, glycolipids and
proteins
Membranes Are Selectively Permeable
• Non-polar: O2, CO2
• Polar: urea, ethanol, H2O
• A least 108 time less permeable to small
cation Na+, K+
• Large molecules- Transport protein- a
transmembrane protein
– Serves either as hydrophilic channel or as
carrier
The Chemistry of the Cell

• The Importance of Carbon
• The Importance of Water
• The Importance of Selectively Permeable
Membranes
• The Importance of Synthesis by
Polymerization of small molecules
• The Importance of Self-Assembly
The importance of Synthesis by
Polymerization
• Macromolecules are responsible for most
of the form and function in living systems
• Cell contain three different kinds of
macromolecules
• Macromolecules are synthesized by
stepwise polymerization of monomers
Macromolecules
•
•
•
•
Nucleic acids
Proteins
Lipids
Polysaccharides
Macromolecules are Responsible for Most
of the Form and Function in Living Systems
• Macromolecules are very important in both
the function and the structure of the cells
– Cell wall: cellulose – repeating polymer of the
glucose
– The macromolecules that are responsible for
most form and other characteristic of living
system are generated by the polymerization
of small organic molecules
The Chemistry of the Cell

• The Importance of Carbon
• The Importance of Water
• The Importance of Selectively Permeable
Membranes
• The Importance of Synthesis by
Polymerization of small molecules
• The Importance of Self-Assembly
To be Functional Protein
• Protein need to fold properly:
– linear polypeptide chains must coil and
fold in very precise
– Effects: pH, Temp, highly acidic or
alkaline
• The denaturation or renaturation of
ribonuclease
Molecular Chaperones Assist the
Assembly of Some Protein
• The self-assemble model may not
adequate for all proteins– molecular chaperones could help to reduce
the incorrect structure - assist self-assembly
• Strict self-assembly and assist selfassembly
• Molecular Chaperones
– a protein that facilitates the folding of other
proteins
– Heat-shock protein
Noncovalent Interactions Are Important
in the Folding of Macromolecules
• Covalent bone
– Not only link the monomers of a
polypeptide, also stabilize the three
dimensional structure of many protein: S-S
bond
• Non-covalent bond
– Most of the structures in the cells are held
together by much weaker forces- within
and between proteins and macromolecules
• H-bond, ionic bonds, van der Waals
interactions, hydrophobic interactions (p46)
Self-Assembly Also Occurs in
Other Cellular Structures
• Ribosomes
• Membrane
• …...
Self-Assembly Has Limits
• Some assembly system depend on
information supplied by a pre-existing
structure
– by adding new material to existing sturcture
– membrane, cell wall, chromosomes
Hierarchical Assembly Provides
Advantages for the Cells
• Biological structures are almost always
constructed in a hierarchical （等級）manner
• Hierarchical process- two advantages
– Chemical simplicity
• Almost all structures found in cells are
synthesized from about 30 small precursor
molecules (Table 3-1)
– Quality control
• allow defective components to be
discarded at an early stage