Chapter 2Chapter 2

The Chemistry of the CellThe 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 temperature-stabilizing capacity

• Water are excellent solvent

Water Has a High Temperature-Stabilizing 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 self-assembly

• 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