Biological Molecules - General Biology | BIOL 1001, Study notes of Biology

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Chapter 3

Biological Molecules

3.1 Why Is Carbon So Important in Biological

Molecules?

 Organic/inorganic molecules and functional groups

• (^) Organic: consisting of a carbon skeleton bonded to hydrogen atoms
• (^) Inorganic: carbon dioxide and all molecules without carbon

 Organic/inorganic molecules and functional

groups (continued)

• (^) CARBON atom is versatile
• (^) Has 4 electrons in an outermost shell
• (^) CAN hold up to 8 electrons in outer shell
• (^) Therefore, a carbon atom can become stable by forming up to four bonds.
• (^) So…organic molecules can assume complex shapes, including branched chains, rings, sheets, and helices vacant spot electron

 Functional groups: determine the characteristics

and chemical reactivity of the molecules

• (^) Less stable than the carbon backbone & more likely to participate in chemical reactions.

3.2 How Are Organic Molecules Synthesized?

• (^) Small organic molecules (called monomers) are joined to form longer molecules (called polymers )
• (^) Monomers are joined together through dehydration synthesis (or CONDENSATION RXN ), resulting in the loss of a water molecule (H2O) from dehydration synthesis   Fig. 3- -Or- Condensation rxn.

 Polymers are broken apart through hydrolysis

(“water cutting”)

• (^) Water is broken into H and OH and is used to break the bond between monomers  hydrolysis Fig. 3-

Author Animation: Monomers and Polymers

Author Animation: Hydrolysis

 All biological molecules fall into one of four

categories

1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleotides/Nucleic Acids

Table 3-2 (1 of 2)

Table 3-2 (2 of 2)

3.3 What Are Carbohydrates?

?

3.3 What Are Carbohydrates?

 Carbohydrate molecules are composed of C, H,

and O in the ratio of 1:2:

• (^) If a carbohydrate consists of just one sugar molecules, it is a monosaccharide
• (^) Two linked monosaccharides form a disaccharide
• (^) A polymer of many monosaccharides is a polysaccharide
• (^) Important energy source for most organisms
• (^) Most small carbohydrates are water-soluble due to the polar OH functional group

 There are several monosaccharides with slightly

different structures

• (^) Example:
  • (^) Glucose (C 6 H 12 O 6 ): most common in living organisms
  • (^) Sugar dissolving in water hydrogen bond hydroxyl group water Fig. 3-

 Additional monosaccharides are:

• (^) Fructose (“fruit sugar” found in fruits, corn syrup, and honey)
• (^) Galactose (“milk sugar” found in lactose)

fructose galactose

Fig. 3-

 Additional monosaccharides are: ( continued )

• (^) Ribose and deoxiribose(found in RNA and DNA, respectively) ribose deoxyribose Note “missing” oxygen atom Fig. 3-

 Disaccharides consist of two monosaccharides

linked by dehydration synthesis

• (^) Disaccharides are two-part sugars
  • (^) They are used for short-term energy storage
  • (^) When energy is required, they are broken apart into their monosaccharide sub units by hydrolysis glucose fructose sucrose dehydration synthesis   Fig. 3-

 Examples of disaccharides include:

• (^) Sucrose (table sugar) = glucose & fructose
• (^) Lactose (milk sugar) = glucose & galactose
• (^) Maltose (malt sugar) = glucose & glucose

 Polysaccharides are chains of simple sugars

• (^) Starch , an energy-storage molecule in plants formed in roots and seeds
• (^) Glycogen , an energy-storage molecule in animals, found in the liver & muscles
• (^) Both are polymers of glucose molecules (b) A starch molecule (a) Potato cells (c) Detail of a starch molecule starch grains Fig. 3-

 Polysaccharides are chains of simple sugars

(continued)

• (^) Many organisms use polysaccharides as a structural material
• (^) Cellulose (polymer of glucose) is one of the most important structural polysaccharides - (^) Found in cell walls of plants - (^) indigestible for most animals - (^) Chemical formula for starch & cellulose is the same, but they are VERY different - (^) Starch(easily digested) vs. cellulose(indigestible for most animals)

Author Animation: Carbohydrate Structure and

Function

Cellulose Structure and Function

Fig. 3-9

 Polysaccharides are chains of simple sugars

(continued)

• (^) Chitin (a polymer of modified glucose units) is found in: - (^) Outer coverings of insects, crabs, and spiders - (^) Cell walls of many fungi Fig. 3-10

3.4 What Are Lipids?

 Lipids are a diverse group of molecules that

contain regions composed almost entirely of

hydrogen and carbon

• (^) Large chains of non-polar hydrocarbons
• (^) Hydrophobic and water insoluble
• (^) use for energy storage
• (^) waterproof coverings on plant and animal bodies
• (^) Primary component of cellular membranes Fig. 3- 11a

Author Animation: Lipids