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Molecules of Life. Chapter 2 Part 2. 2.6 Organic Molecules. The molecules of life – carbohydrates, proteins, lipids, and nucleic acids – are organic molecules Organic Type of molecule that consists primarily of carbon and hydrogen atoms. Some Elemental Abundances.

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Molecules of Life

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Molecules of life

Molecules of Life

Chapter 2

Part 2

2 6 organic molecules

2.6 Organic Molecules

  • The molecules of life – carbohydrates, proteins, lipids, and nucleic acids – are organic molecules

  • Organic

    • Type of molecule that consists primarily of carbon and hydrogen atoms

Some elemental abundances

Some Elemental Abundances

Modeling an organic molecule

Modeling an Organic Molecule

Building organic molecules

Building Organic Molecules

  • Carbon atoms bond covalently with up to four other atoms, often forming long chains or rings

  • Enzyme-driven reactions construct large molecules from smaller subunits, and break large molecules into smaller ones

From structure to function

From Structure to Function

  • Cells assemble large polymers from smaller monomers, and break apart polymers into component monomers

  • Metabolism

    • All the enzyme-mediated chemical reactions by which cells acquire and use energy as they build and break down organic molecules

Monomers and polymers

Monomers and Polymers

  • Monomers

    • Molecules that are subunits of polymers

    • Simple sugars, fatty acids, amino acids, nucleotides

  • Polymers

    • Molecules that consist of multiple monomers

    • Carbohydrates, lipids, proteins, nucleic acids

Condensation and hydrolysis

Condensation and Hydrolysis

  • Condensation (water forms)

    • Process by which an enzyme builds large molecules from smaller subunits

  • Hydrolysis (water is used)

    • Process by which an enzyme breaks a molecule into smaller subunits by attaching a hydroxyl to one part and a hydrogen atom to the other

Condensation and hydrolysis1

Condensation and Hydrolysis

Condensation and hydrolysis2

Condensation and hydrolysis

Functional groups

Functional groups

2 7 carbohydrates

2.7 Carbohydrates

  • Cells use carbohydrates for energy and structural materials

  • Carbohydrates

    • Molecules that consist primarily of carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio

Complex carbohydrates

Complex Carbohydrates

  • Enzymes assemble complex carbohydrates (polysaccharides) from simple carbohydrate (sugar) subunits

  • Glucose monomers can bond in different patterns to form different complex carbohydrates

    • Cellulose (a structural component of plants)

    • Starch (main energy reserve in plants)

    • Glycogen (energy reserve in animals)

Some complex carbohydrates

Some Complex Carbohydrates

Animation structure of starch and cellulose

Animation: Structure of starch and cellulose

Animation examples of monosaccharides

Animation: Examples of monosaccharides

2 8 lipids

2.8 Lipids

  • Lipids are greasy or oily nonpolar organic molecules, often with one or more fatty acid tails

  • Lipids

    • Fatty, oily, or waxy organic compounds

  • Fatty acid

    • Consists of a long chain of carbon atoms with an acidic carboxyl group at one end

Molecules of life


  • Fats, such as triglycerides, are the most abundant source of energy in vertebrates – stored in adipose tissue that insulates the body

  • Fat

    • Lipid with one, two, or three fatty acid tails

  • Triglyceride

    • Lipid with three fatty acid tails attached to a glycerol backbone

Saturated and unsaturated fats

Saturated and Unsaturated Fats

  • Saturated fats pack more tightly than unsaturated fats, and tend to be more solid

  • Saturated fat

    • Fatty acid with no double bonds in its carbon tail

  • Unsaturated fat

    • Lipid with one or more double bonds in a fatty acid tail

Fatty acids

Fatty Acids

  • Saturated, unsaturated, cis, and trans fatty acids

Molecules of life

carboxyl group

cis double bond

trans double bond

long carbon chain

A stearic acid

B linolenic acid

C oleic acid

D elaidic acid

Fig. 2-14, p. 32



  • Phospholipids are the main structural component of cell membranes

  • Phospholipid

    • A lipid with a phosphate group in its hydrophilic head, and two nonpolar fatty acid tails



Molecules of life

one layer of lipids

one layer of lipids

B a lipid bilayer

Fig. 2-15b, p. 32



  • Waxes are part of water-repellent and lubricating secretions in plants and animals

  • Wax

    • Water-repellent lipid with long fatty-acid tails bonded to long-chain alcohols or carbon rings



  • Steroids such as cholesterol occur in cell membranes or are remodeled into other molecules (such as steroid hormones, bile salts, and vitamin D)

  • Steroid

    • A type of lipid with four carbon rings and no fatty acid tails



Phospholipid structure

Phospholipid structure

2 9 proteins

2.9 Proteins

  • A protein’s function depends on its structure, which consists of chains of amino acids that twist and fold into functional domains

  • Protein

    • Organic compound that consists of one or more chains of amino acids

Amino acid

Amino Acid

  • Amino acid

    • Small organic compound with a carboxyl group, amine group, and a characteristic side group (R)

Peptide bonds

Peptide Bonds

  • Amino acids are linked into chains by peptide bonds

  • Peptide bond

    • A bond between the amine group of one amino acid and the carboxyl group of another

  • Polypeptide

    • Chain of amino acids linked by peptide bonds

Polypeptide formation

Polypeptide Formation

Protein synthesis

Protein Synthesis

1. Primary structure (polypeptide formation)

  • A linear sequence of amino acids

    2. Secondary structure

  • Hydrogen bonds twist the polypeptide into a coil or sheet

    3. Tertiary structure

  • Secondary structure folds into a functional shape

Protein synthesis1

Protein Synthesis

4. Quaternary structure

  • In some proteins, two or more polypeptide chains associate and function as one molecule

  • Example: hemoglobin

    5. Fibrous proteins may aggregate into a larger structure, such as keratin filaments

  • Example: hair

Molecules of life

1) A protein’s primary structure consists of a linear sequence of amino acids (a polypeptide chain).

2) Secondary structure arises when a polypeptide chain twists into a coil (helix) or sheet held in place by hydrogen bonds between different parts of the molecule. The same patterns of secondary structure occur in many different proteins.









3) Tertiary structure occurs when a chain’s coils and sheets fold up into a functional domain such as a barrel or pocket. In this example, the coils of a globin chain form a pocket.

4) Some proteins have quaternary structure, in which two or more polypeptide chains associate as one molecule. Hemoglobin, shown here, consists

of four globin chains (green and blue). Each globin pocket now holds a heme group (red).


5) Many proteins aggregate by the thousands into larger structures, such as the keratin filaments that make up hair.

Protein Structure

Stepped Art

Fig. 2-18, p. 35

The importance of protein structure

The Importance of Protein Structure

  • Changes in a protein’s structure may also alter its function

  • Denature

    • To unravel the shape of a protein or other large biological molecule

Misfolded proteins prion disease

Misfolded Proteins: Prion Disease

  • Prion

    • A misfolded protein that becomes infectious

    • Example: mad cow disease (BSE) in cattle

    • Example: vCJD in humans

Variant creutzfeldt jakob disease vcjd

Variant Creutzfeldt-Jakob Disease (vCJD)

2 10 nucleic acids

2.10 Nucleic Acids

  • Nucleotide

    • Monomer of nucleic acids

    • Has a five-carbon sugar, a nitrogen-containing base, and phosphate groups

  • Nucleic acids

    • Polymers of nucleotide monomers joined by sugar-phosphate bonds (include DNA, RNA, coenzymes, energy carriers, messengers)

Molecules of life


  • The nucleotide ATP can transfer a phosphate group and energy to other molecules, and is important in metabolism

  • Adenosine triphosphate (ATP)

    • Nucleotide that consists of an adenine base, five-carbon ribose sugar, and three phosphate groups

    • Functions as an energy carrier

Functions of dna and rna

Functions of DNA and RNA

  • DNA encodes heritable information about a cell’s proteins and RNAs

  • Different RNAs interact with DNA and with one another to carry out protein synthesis

Dna and rna


  • Deoxyribonucleic acid (DNA)

    • Nucleic acid that carries hereditary material

    • Two nucleotide chains twisted in a double helix

  • Ribonucleic acid (RNA)

    • Typically single-stranded nucleic acid

    • Functions in protein synthesis

A nucleotide and nucleic acid

A Nucleotide and Nucleic Acid

2 11 impacts issues revisited

2.11 Impacts/Issues Revisited

  • Our enzymes can’t easily break down trans fats in processed foods, which causes health problems – several countries will not import foods made in the US that contain trans fats

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