CHAPTER 3The Molecules of

Cells

Life’s structural and functional diversity results from a great variety of molecules

A relatively small number of structural patterns underlies life’s molecular diversity

Organic Compounds

Always contain carbon

Tend to be large & complex

A carbon atom forms four covalent bonds (this allows carbon to form many different chemical compounds)

Carbon skeletons vary in many ways

Carbon skeletons vary in length.

Skeletons may be unbranched or branched.

Skeletons may have double bonds, which can vary in location

Skeletons may be arranged in rings

Cells make a huge number of large molecules from a small set of small

molecules• Most of the large molecules in living things

are macromolecules called polymers– Polymers are long chains of smaller molecular

units called monomers (building blocks)– A huge number of different polymers can be

made from a small number of monomers– SIZE: monomer< polymer< macromolecule

Molecules of Life• Put C, H, O, N together in different

ways to build living organisms

• What are bodies made of?– carbohydrates

• sugars & starches

– proteins– lipids– nucleic acids

• DNA, RNA

Why do we eat?• We eat to take in more of these chemicals

– Food for building materials• to make more of us (cells)• for growth• for repair

– Food to make energy• calories• to make ATP

ATP

How do we make these molecules?

We build them!

Building large molecules of life• Chain together smaller molecules

– building block molecules = monomers

• Big molecules built from little molecules– polymers

• Small molecules = building blocks

• Bond them together = polymers

Building large organic molecules

Building important polymers

sugar – sugar – sugar – sugar – sugar – sugar

nucleotide – nucleotide – nucleotide – nucleotide

Carbohydrates = built from sugars

Proteins = built from amino acids

Nucleic acids (DNA) = built from nucleotides

aminoacid

aminoacid–

aminoacid–

aminoacid–

aminoacid–

aminoacid–

How to build large molecules

• Dehydration Synthesis– building bigger molecules

from smaller molecules – building cells & bodies

• repair• growth• reproduction

+

ATP

Making and Breaking of POLYMERS

• Cells link monomers to form polymers by dehydration synthesis (building up)

Short polymer Unlinked monomerRemoval ofwater molecule

Longer polymer

Example of synthesis

amino acids protein

amino acids = building block

protein = polymer

Proteins are synthesized by bonding amino acids

Making and Breaking of POLYMERS

• Polymers are broken down to monomers by the reverse process, hydrolysis (hydro ~ add water; lysis ~ to split)

Addition ofwater molecule

How to take large molecules apart• Hydrolysis ~Digestion

– taking big molecules apart– getting raw materials

• for synthesis & growth

– making energy (ATP)• for synthesis, growth & everyday functions

+

ATP

Example of digestion

starch glucose

ATP

ATP

ATP

ATP

ATP

ATPATP

• Starch is digested to glucose

1. CARBOHYDRATES

• They range from small sugars to large polysaccharides

• Poly~ many

• Sacchar ~ sugar

• Mono ~ one

• Di ~ two

Monosaccharides are the simplest carbohydrates

• Monosaccharides are single-unit sugars (building blocks)

• These molecules typically have a formula that is a multiple of CH2O

• Monosaccharides are the fuels for cellular work

Sugars = building blocks • Names for sugars usually end in

– glucose– fructose– sucrose– maltose OH

OH

H

H

HO

CH2OH

HH

H

OH

O

glucoseC6H12O6

sucrose

fructose

maltose

-ose

Cells link single sugars to form disaccharides

• Monosaccharides can join to form disaccharides, such as sucrose (table sugar) and maltose (brewing sugar)

Polysaccharides are long chains of sugar units

• polymers of hundreds or thousands of monosaccharides linked by dehydration synthesis

• Function as– Energy storage

• Starch (plants)

• Glycogen (animals)

– Structure• Cellulose (plants cell

walls) (fiber in diet)

• Chitin ( insects)

Digesting starch vs. cellulose

starcheasy todigest

starcheasy todigest

cellulosehard todigest

cellulosehard todigest

enzyme

enzyme

Cellulose • Cell walls in plants

– herbivores can digest cellulose well– most carnivores cannot digest cellulose

• that’s why they eat meat to get their energy & nutrients

• cellulose = roughage– stays undigested– keeps material

moving in your intestines

Helpful bacteria• How can cows digest cellulose so well?

– BACTERIA live in their stomachs & help digest cellulose-rich (grass) meals

Eeeew…Chewingcud?

Lipids• composed largely of

carbon and hydrogen– They are not true

polymers– They are grouped

together because they do not mix with water (Nonpolar)

2003-2004

Lipids • Examples

– fats

– oils

– waxes

– hormones • sex hormones

– testosterone (male)

– estrogen (female)

2003-2004

Lipids

• Function:– energy storage

• very concentrated• twice the energy as carbohydrates!

– cell membrane– cushions organs– insulates body

• think whale blubber!

Lipids include fats,• Fats are lipids whose main function is long term energy storage• Other functions:

– Insulation in higher vertebrates– “shock absorber” for internal organs

• A triglyceride molecule consists of one glycerol molecule linked to three fatty acids

Fatty acid

Fatty acid

Saturated & Unsaturated fats

• fatty acids of unsaturated fats (plant oils) contain double bonds– These prevent them from

solidifying at room temperature

• Saturated fats (lard) lack double bonds– They are solid at room

temperature

2003-2004

Saturated vs. unsaturatedsaturated unsaturated

Phospholipids, waxes, and steroids are lipids

• Phospholipids are a major component of cell membranes– heads are on the

outside touching water• “like” water

– tails are on inside away from water

• “scared” of water

– forms a barrier between the cell & the outside

Other lipids in biologyWaxes form waterproof coatings

Steroids are often hormones

Other lipids in biology

• Cholesterol (Steroid) (only in animal cells)

– good molecule in cell membranes– make hormones from it

• including sex hormones

– but too much cholesterol in blood may lead to heart disease

Connection: Anabolic steroids

• Anabolic steroids are usually synthetic variants of testosterone

• Use of these substances can cause serious health problems

PROTEINS : Multipurpose molecules

• essential to the structures and activities of life

• Make up 50% of dry weight of cells

• Contain carbon, hydrogen, & oxygen PLUS nitrogen and sometimes sulfur

• Proteins are involved in – cellular structure– movement– defense– transport– Communication

• Monomers are called amino acids

collagen (skin)

Proteins

insulin

Examples– muscle

– skin, hair, fingernails, claws • collagen, keratin

– pepsin• digestive enzyme

in stomach

– insulin• hormone that controls blood sugar

levels

pepsin

Proteins are made from just 20 kinds of amino acids

• Proteins are the most structurally and functionally diverse of life’s molecules– Their diversity is based on different arrangements of amino

acids– R- variable group- which distinguishes each of the 20

different amino acids

Amino acids can be linked by peptide bonds to form polymer

• Cells link amino acids together by dehydration synthesis

• The bonds between amino acid monomers are called peptide bonds

Dehydrationsynthesis

Amino acid Amino acid

PEPTIDEBOND

Dipeptide

A protein’s specific shape determines its function

• A protein consists of polypeptide chains folded into a unique shape– The shape determines the protein’s function – A protein loses its specific function when its

polypeptides unravel

A protein’s specific shape determines its function

• A protein can change in response to the physical and chemical conditions

• Alterations in pH, salt concentration, temperature, or other factors can unravel or denature a protein

• Some proteins can return to their functional shape after denaturation -renature

NUCLEIC ACIDS : Information molecules

• 1. DNA (deoxyribonucleic acid) contains the instructions used to form all of an organism’s proteins.

• 2. RNA (ribonucleic acid) forms a copy of DNA for use in making proteins.

• They ultimately control the life of a cell

DNADNA

Nucleic Acids• Function:

– genetic material• stores information

– genes– blueprint for building proteins

» DNA RNA proteins

• transfers information– blueprint for new cells– blueprint for next generation

proteinsproteins

NUCLEIC ACIDS

• The monomers of nucleic acids are nucleotides – Each nucleotide is composed of a sugar,

phosphate, and nitrogenous base

Phosphategroup

Sugar

Nitrogenousbase (A)

NUCLEIC ACIDS

• The sugar and phosphate form the backbone for the nucleic acid

Nucleotide

Sugar-phosphatebackbone

Nucleotide chains• Nucleic acids

– nucleotides chained into a polymer

• DNA– double-sided– double helix– A, C, G, T

• RNA– single-sided– A, C, G, U

phosphate

sugar N base

phosphate

sugar N base

phosphate

sugar N base

phosphate

sugar N base

strong bonds

RNA

DNA• Double strand twists into a double

helix– weak bonds between nitrogen bases join

the 2 strands• A pairs with T

– A :: T• C pairs with G

– C :: G– the two strands can

separate when our cells need to make copies of it

– The sequence of the four kinds of nitrogenous bases in DNA carries genetic information

weak bonds

DNA

• Stretches of a DNA molecule called genes program the amino acid sequences of proteins– DNA information is transcribed into RNA, a

single-stranded nucleic acid– RNA is then translated into the primary

structure of proteins

Watson and Crick … and others…1953 | 1962