WHAT IS LIFE?

What is life?

• condition that distinguishes organisms from inorganic objects

• Life has clear-cut properties that distinguish it from everything else

• Every living thing is cellular either a single-celled or a multi-cellular creature membrane – bound contains a full set of instructions necessary for its

operation, reproduction

Figure 2-29 Molecular Biology of the Cell (© Garland Science 2008)

• All living matter is composed of

H2O

inorganic ions

small molecules

macromolecules

The chemicals of life

Small molecules: functions

• precursors for synthesis of macromolecules

• store and distribute the energy for all cellular processes

– broken down to extract chemical energy

• act as signals that direct the activities of cells

Biological molecules

• Life on earth is carbon – based: biological molecules consist primarily of carbon bonded to carbon

carbon bonded to other molecules

• Carbon can form up to 4 covalent bonds.

• Carbon may be bonded to functional groups with specific properties

Biological macromolecules

• Simplest organic molecules = Hydrocarbons; consist of carbon, hydrogen

Covalent bonds store considerable energy.

Make good fuels

Functional groups

• Specific groups of atoms attached to carbon backbones

• Have definite chemical properties

• Found in the various biomolecules

Proteins

Nucleic acids

Lipids

Carbohydrates

Common functional groups of biomolecules

Common functional groups of biomolecules

Biological molecules

• Biomolecules typically large molecules (polymers) constructed from smaller subunits (monomers)

• Biomolecules built up, broken down via water interactions

Figure 2-30 Molecular Biology of the Cell (© Garland Science 2008)

Macromolecules

• Proteins

• Nucleic acids

– DNA

– RNA

• Carbohydrates

• Lipids

Proteins

• contain an amino group (-NH2), a carboxyl group (-COOH) and an H atom, all bonded to a central carbon atom

• Formed from 20 different monomers (amino acids)

• most abundant, functionally versatile biomolecule

Proteins derived from amino acids

• A protein is composed of one or more long chains of amino acids linked by peptide bonds

Nucleic Acids

• Responsible for storage, transfer of genetic information

• 2 types: 1. Deoxyribonucleic

Acid (DNA) Encodes information

used to assemble proteins

2. Ribonucleic Acid (RNA) Reads DNA-encoded

information to direct protein synthesis

Nucleic acid structure

Figure 6-2 Molecular Biology of the Cell (© Garland Science 2008)

The flow of genetic Information

Carbohydrates

• Also known as sugars

• Molecules with a 1:2:1 ratio of C, H, O

empirical formula: (CH2O)n

examples: sugars, starch, glucose

• Since C – H covalent bonds hold much energy, carbohydrates are good energy storage molecules

The structure of glucose, a simple sugar

Carbohydrates

Two or more glucose molecules linked together can make a polymer

Functions of carbohydrates

energy stores, fuels, and metabolic intermediates

structural framework of RNA and DNA

structural elements in the cell walls of bacteria and plants

linked to many proteins and lipids

• Starch consists of chains of linked glucose molecules.

• These chains are broken down into individual glucose molecules and used to generate energy

• Consumption of excess carbohydrates leads to conversion into glycogen or fats for future use.

Structural carbohydrates

• Cellulose – found in plants

• Chitin – found in arthropods

and fungi

Lipids

• biomolecules that are insoluble in H2O but soluble in organic solvents

• A high proportion of nonpolar C – H bonds causes lipid molecules to be hydrophobic

Examples of lipids:

1. Fats (triglycerides)

2. Phospholipids

3. Steroids

Fatty acids/Triglycerides

• animal fats are usually saturated fats

solid at room temperature

• plant fats (oils) are usually unsaturated

liquid at room temperature

Lipids

Triglycerides

• store twice as much energy as carbohydrates

• May be saturated or unsaturated 1. Saturated fats - all internal carbon atoms are bonded to

at least two hydrogen atoms – maximum # of H

2. Unsaturated fats - at least one double bond between successive carbon atoms

Phospholipids

• Main component of biological membranes

• Membranes usually exist as lipid bilayer

Polar head groups in contact with H2O

Nonpolar tail lies in interior

The watery interior of cells is surrounded by the plasma membrane, a two-layered shell of phospholipids

Phospholipids

Fat-soluble vitamins

Vitamin Function Deficiency

A Roles in vision, growth, reproduction

Night blindness, cornea damage, damage to respiratory and gastrointestinal tract

D Regulation of calcium and phosphate metabolism

Rickets (children): skeletal deformaties, impaired growth;

Osteomalacia (adults): soft, bending bones

E Antioxidant Inhibition of sperm production; lesions in muscles and nerves (rare)

K Blood coagulation Subdermal hemorrhaging

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Lipids

Steroids include:

Cholesterol

Steroid hormones – e.g., estrogen, testosterone

Vitamin D