Chemical Composition of Cell, Slides of Cellular and Molecular Biology

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Chemical Composition of

the Cell

B. Balen

Table 2-2 Molecular Biology of the Cell (© Garland Science 2008)

2. Small organic molecules

 carbon-based compounds – up to 30 C atoms

 molecular weight 100 - 1000 kDa

 usually found free in solution

 many different fates :

 monomer subunits for building macromolecules

 source of energy for intracellular metabolic pathways

 much less abundant that the organic macromolecules – only about 1/10 of the total mass of organic matter in the cell (Table 2-2).

 around 1000 different kinds of these molecules in a typical cell

Four main types of small organic molecules:

 sugars

 fatty acids (lipids)

 amino acids

 nucleotides

Energy source

Figure 2-17 Molecular Biology of the Cell (© Garland Science 2008)

monosaccharides

Panel 2- 4 Molecular Biology of the Cell (© Garland Science 2008)

monosaccharides, disaccharides

Panel 2- 4 Molecular Biology of the Cell (© Garland Science 2008)

chitin

peptidoglycans

proteoglycans

 the reaction of two monosaccharides to form a disaccharide

condensation – two monosaccharides are joined together as a loss of one H 2 O molecule

hydrolysis – reverse reaction in which H 2 O is added

Figure 2-19 Molecular Biology of the Cell (© Garland Science 2008)

Importance :

 energy sources

• glucose – key energy source for cells → in a series of reactions is broken down to smaller molecules to release the energy
• cells use simple polysaccharides composed only of glucose units → glycogen (animal cells) and starch (plant cells)

 mechanical support

• cellulose – glucose polysaccharide (the most abundant organic chemical on Earth!)
• chitin – linear polymer of N-acetylglucosamine

 molecular markers

• glycoproteins and glycolipids of the cell membrane → selective recognition by other cells
• human blood groups

Electron micrograph of a surface of lymphocite

• extracellular carbohydrate layer - glycocalyx

Glycocalyx – simplifed diagram

2.2. Fatty acids (lipids)

palmitic acid

 Lipids → fatty acid and their derivatives → water insoluble; soluble in fats and organic solvents

 two different structural parts:

• hydrophilic head – chemically active
• hydrophobic tail – differences between hydrocarbon chains – not very active chemically
• almost all fatty acids are covalently linked to other molecules by their carboxylic acid group

saturated chain

Figure 2-21 Molecular Biology of the Cell (© Garland Science 2008)

 phospholipids

Panel 2- 5 Molecular Biology of the Cell (© Garland Science 2008)

 other lipids

Panel 2- 5 Molecular Biology of the Cell (© Garland Science 2008)

2.3. Amino acids

 all have carboxylic acid group (COOH) and amino group (NH 2 ) both linked to a single C-atom (α-carbon)

 chemical variety → side chain attached to the α-C

Ala

Figure 2-23 Molecular Biology of the Cell (© Garland Science 2008)

 amino acids linked together – peptid bond

 polypeptide or protein – two chemically distinct ends:

• NH 2 (N-terminus)
• COOH (C-terminus)

Figure 2-24 Molecular Biology of the Cell (© Garland Science 2008)