The Organic Molecules of Living Organisms

• Carbon, the building block of living things– Comprises 18% of the body by weight– Forms four covalent bonds– Can form single or double bonds– Can build micro- or macromolecules

Macromolecules Are Synthesized and Broken Down within the Cell

• Dehydration synthesis– Removes equivalent of a water molecule to link

molecular units– Requires energy– Builds macromolecules from smaller subunits

• Hydrolysis– Adds the equivalent of a water molecule to break

apart macromolecules– Releases energy

• Dehydration synthesis is the reverse of hydrolysis

Figure 2.13

Sugars

Hyd

roly

sis

Deh

yd

rati

on

syn

thes

is

Carbohydrate

Energy Energy

Monomers and Polymers

Carbohydrates: Used for Energy and Structural Support

• General formula: Cn(H20)n

• Monosaccharides: simple sugars– Glucose– Fructose– Galactose– Ribose– Deoxyribose

Oligosaccharides: More than One Monosaccharide Linked Together

• Monosaccharides can be linked together via dehydration synthesis

• Disaccharides: two monosaccharides linked together– Sucrose: glucose + fructose– Maltose: glucose + glucose– Lactose: glucose + galactose

Figure 2.14a

a) The five-carbon monosaccharides ribose and deoxyribose.

Ribose Deoxyribose

Figure 2.14b

Glucose (a monosaccharide)

Fructose (a monosaccharide)

Sucrose (a disaccharide)b) Two 6-carbon monosaccharides (glucose and fructose) are

joined together by dehydration synthesis, forming sucrose.

Polysaccharides Store Energy

• Polysaccharides: thousands of monosaccharides joined in chains and branches– Starch: made in plants; stores energy– Glycogen: made in animals; stores energy– Cellulose: indigestible polysaccharide made in

plants for structural support

Figure 2.15a

Glucose Glucose

Dehydrationsynthesis

a) Glycogen is formed bydehydration synthesis fromglucose subunits.

Figure 2.15b

b) A representation of the highly branched nature of glycogen.

Lipids: Insoluble in Water

• Three important classes of lipids– Triglycerides: energy storage molecules– Phospholipids: cell membrane structure– Steroids: carbon-based ring structures

Triglycerides

• Also known as fats and oils• Composed of glycerol and three fatty acids

– Fatty acids• Saturated (in fats)• Unsaturated (in oils)

• Stored in adipose tissue• Energy storage molecules

Figure 2.16a

Glycerol

Saturatedfatty acid

a) Triglycerides (neutral fats) aresynthesized from glycerol andthree fatty acids by dehydrationsynthesis.

Figure 2.16b

b) Triglycerides with saturated fatty acids have straight tails, allowing them to pack closely together.

Figure 2.16c

c) Triglycerides with unsaturated fatty acids have kinked tails, preventing them from packing closely together.

Phospholipids

• Structure– Glycerol + two fatty acids and phosphate group– One end of molecule is water soluble (hydrophilic)– Other end of molecule is water insoluble

(hydrophobic)

• Function– Primary component of cell membranes

Figure 2.17

Phosphate

Glycerol

Fatty acid

Membrane structure

Polar head

Nonpolar tail

Steroids

• Structure– Composed of four carbon rings

• Examples:• Cholesterol• Hormones

– Estrogen– Testosterone

Figure 2.18a

a) Cholesterol: A normal component of the cell membrane.

b) Estrogen (estradiol):Female sex hormonesynthesized from cholesterol.

Figure 2.18b

c) Testosterone:Male sex hormonesynthesized from cholesterol.

Figure 2.18c

Lipid Structure and Function

Proteins

• Long chains (polymers) of subunits called amino acids

• Amino acids– 20 different types– Amino end, carboxyl end, R group

• Amino acids are joined by peptide bonds, which are produced by dehydration synthesis reactions

Figure 2.19

Amino acids with nonpolar R groups

Alanine (Ala)

Isoleucine (Ile)

Leucine (Leu)

Methionine (Met)

Phenylalanine (Phe)

Proline (Pro)

Tryptophan (Trp)

Valine (Val)

Amino acids with negatively charged R groups

Aspartic acid (Asp)

Glutamic acid (Glu)

Amino acids with uncharged polar R groups

Asparagine (Asn)

Cysteine (Cys)

Glutamine (Gln)

Glycine (Gly)

Serine (Ser)

Threonine (Thr)

Tyrosine (Tyr)

Amino acids with positively charged R groups

Arginine (Arg)

Histidine (His)

Lysine (Lys)

Figure 2.19a

Amino acids with nonpolar R groups

Alanine(Ala)

Isoleucine(Ile)

Leucine(Leu)

Methionine(Met)

Phenylalanine(Phe)

Proline(Pro)

Tryptophan(Trp)

Valine(Val)

Figure 2.19b

Amino acids with negatively charged R groups

Aspartic acid (Asp)

Glutamic acid (Glu)

Figure 2.19c

Amino acids with uncharged polar R groups

Asparagine (Asn)

Cysteine (Cys)

Glutamine (Gln)

Glycine (Gly)

Serine (Ser)

Threonine (Thr)

Tyrosine (Tyr)

Figure 2.19d

Amino acids with positively charged R groups

Arginine (Arg)

Histidine (His)

Lysine (Lys)

Figure 2.20

Aminoacids

Isoleucine (Ile) Alanine (Ala) Valine (Val)

Polypeptide

Protein Function Depends on Structure

• Primary structure– Amino acid sequence– Stabilized by peptide bonds

• Secondary structure– Alpha helix– Beta pleated sheets– Stabilized by hydrogen bonds

Protein Function Depends on Structure

• Tertiary structure– Three-dimensional shape – Stabilized by disulfide and hydrogen bonds– Creates polar and nonpolar areas in molecule

• Quaternary structure– Two or more polypeptide chains are associated

Figure 2.21a

Primary structure

(sequence ofamino acids)

Figure 2.21b

Hydrogenbonds

Secondarystructure

(orientation inspace of chainsof amino acids)

Alpha helix Beta sheet Random coil

Figure 2.21c

Alpha helix

Beta sheet

Randomcoil

Tertiarystructure

(three-dimensionalshape)

Figure 2.21d

Quaternarystructure

(number of polypeptidechains and their

association)

Protein Function Depends on Structure

• Denaturation– Permanent disruption of protein structure

• Can be damaged by temperature or changes in pH

– Leads to loss of biological function

Protein Structure

Enzymes Facilitate Biochemical Reactions

• Enzymes– Are proteins– Function as biological catalysts

• Speed up specific chemical reactions• Are not altered or consumed by the reaction

– Without enzymes, many biochemical reactions would not proceed quickly enough to sustain life

– Each enzyme is specific for a specific chemical reaction

Figure 2.22

Enzyme Reactants

Reactantsapproach enzyme

Reactantsbind to enzyme

Enzymechanges shape

Productsare released

Product

Enzymes Facilitate Biochemical Reactions

• The functional shape of an enzyme is dependent on– Temperature– pH – Ion concentration– Presence of inhibitors

Nucleic Acids Store Genetic Information

• Two types– DNA: deoxyribonucleic acid– RNA: ribonucleic acid

• Functions– Store genetic information– Provide information used in making proteins

• Nucleic acids are long chains containing subunits known as nucleotides

Nucleic Acids Store Genetic Information

• Nucleotides: building blocks of nucleic acids• Each nucleotide contains

– 5 carbon sugar • DNA nucleotides: deoxyribose• RNA nucleotides: ribose

– Nitrogenous base– Phosphate group

Figure 2.23

Adenine (A)

Phosphate

Deoxyribose

Thymine (T) Cytosine (C) Guanine (G)

Nucleic Acids Store Genetic Information

• Structure of DNA (deoxyribonucleic acid)– Double–stranded– Nucleotides contain

• Deoxyribose (sugar)• Nitrogenous bases

– Adenine – Guanine– Cytosine– Thymine

– Pairing• Adenine - Thymine• Guanine - Cytosine

Figure 2.24

Base pair

Phosphate

Sugar

Nucleotide

Nucleic Acids Store Genetic Information

• Structure of RNA (ribonucleic acid)– Single–stranded– Nucleotides contain

• Ribose• Nitrogenous bases

– Adenine– Guanine– Cytosine– Uracil

Figure 2.25

Phosphate

Ribose

Uracil

Nucleic Acid Function --- Nucleic Acids Store Genetic Information

• Nucleic acid function– DNA: instructions for making RNA– RNA: instructions for making proteins– Proteins: direct most of life’s processes– DNA → RNA → Proteins

ATP Carries Energy

• Structure and function of adenosine triphosphate (ATP)– Nucleotide – adenosine triphosphate– Universal energy source– Bonds between phosphate groups contain

potential energy– Breaking the bonds releases energy

• ATP → ADP + P + energy

Figure 2.26a

Triphosphate

Adenosine

Ribose

Adenine (A)

a) The structure of ATP.

Figure 2.26b

Hydrolysis of ATPproduces useful energyfor the cell

AdenosineAdenosine

Energy for ATP synthesiscomes from food or bodystores of glycogen or fat

b) The breakdown and synthesis of ATP.The breakdown (hydrolysis) of ATP yieldsenergy for the cell. The reaction is reversible,meaning that ATP may be resynthesizedusing energy from other sources.