Biological Molecules (II)

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

There are four classes of biological molecules1. Carbohydrates2. Proteins3. Lipids4. Nucleic acids

Unlinkedmonomer

Short polymer

Unlinkedmonomer

Short polymer

Longer polymer

Dehydrationreaction

Hydrolysis

CARBOHYDRATES

3.4 Monosaccharides are the simplest carbohydrates

Carbohydrates range from small sugar molecules (monomers) to large polysaccharidesSugar monomers are monosaccharides, such as

glucose and fructoseThese are linked together to form the polysaccharides

3.5 Cells link two single sugars to form disaccharides

Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reactionAn example is a glucose monomer bonding to a fructose

monomer to form sucrose, a common disaccharide

Di- = two

Animation: Disaccharides

Glucose Glucose

Glucose Glucose

Maltose

3.7 Polysaccharides are long chains of sugar units

Polysaccharides are polymers of monosaccharides

Poly- = many

Starch is a storage polysaccharide composed of glucose monomers and found in plants

Glycogen is a storage polysaccharide composed of glucose, which is hydrolyzed by animals when glucose is needed

Cellulose is a polymer of glucose that forms plant cell walls

Chitin is a polysaccharide used by insects and crustaceans to build an exoskeleton

Starch granules inpotato tuber cells

Glycogengranulesin muscletissue

Cellulose fibrils ina plant cell wall

Cellulosemolecules

Glucosemonomer

GLYCOGEN

CELLULOSE

Hydrogen bonds

STARCH

LIPIDS

3.8 Fats are lipids that are mostly energy-storage molecules

Lipids are water insoluble (hydrophobic, or water fearing) compounds that are important in energy storageThey contain twice as much energy as a polysaccharide

Fats are lipids made from glycerol and fatty acids

Hydro- = of waterPhob- = fear (i.e. phobia)

Fatty acids link to glycerol by a dehydration reactionA fat contains one glycerol linked to three fatty acidsFats are often called triglycerides because of their

structure

Animation: Fats

Fatty acid

Glycerol

PhospholipidsThe polar, hydrophilic heads are in contact with

the watery environment on both sides of the membrane

The hydrophobic fatty acid ‘tails’ band together in the center

Some fatty acids contain double bondsThis causes kinks or bends in the carbon chain because

the maximum number of hydrogen atoms cannot bond to the carbons at the double bond

These compounds are called unsaturated fats because they have fewer than the maximum number of hydrogens

Fats with the maximum number of hydrogens are called saturated fats

Saturated fats tend to be solid at room temperature

Unsaturated fats are liquid at room temperature

One gram of fat stores twice as much energy as a gram of most carbohydrates

FatsTriglycerides (fats and oils):– Store energy– Insulate (blubber, etc)– Provide cushioning– Prevent dehydration– Help to maintain internal temperature

3.9 Phospholipids and steroids are important lipids with a variety of functions

Phospholipids are structurally similar to fats and are an important component of all cells

They are a major part of cell membranes, in which they cluster into a bilayer of phospholipids

The hydrophilic heads are in contact with the water of the environment and the internal part of the cell

The hydrophobic tails band in the center of the bilayer

Phospholipids of a cell membrane

Hydrophobictails

Hydrophilicheads

The phospholipid bilayer provides the cell with a structure that separates the outside from the inside of the cell; many molecules cannot move across the membrane without help

Water (outside cell)

Water (inside cell)

interior of cell membrane

Hydrophilicheads

3.9 Phospholipids and steroids are important lipids with a variety of functions

Steroids are lipids composed of fused ring structuresCholesterol is an example of a steroid that plays a

significant role in the structure of the cell membrane

http://www.youtube.com/watch?v=wnK1Kv3XkZI

In addition, cholesterol is the compound from which we synthesize sex hormones

3.10 CONNECTION: Anabolic steroids pose health risks

Anabolic steroids are synthetic variants of testosterone that can cause a buildup of muscle and bone massThey can be sold as prescription drugs and used to

treat certain diseasesThey may also be abused with serious consequences,

such as liver damage that can lead to cancer

Anabolic Steroids

Testosterone causes a build-up of muscle and bone mass in males and maintains masculine traits

Anabolic steroids mimic testosterone because of their similar structure

Anabolic steroids are prescribed to treat anemia and diseases that destroy muscle mass; birth control pills usually contain synthetic variants of estrogen and progesterone

The good, the bad and the ugly..

Anabolic steroids increase protein synthesis within cells resulting in a massive buildup of cellular tissue (“anabolism”) especially in muscle cells

Anabolic steroid use has adverse side effects:Violent mood swings (“roid rage”) and deep

depression, elevated blood pressure, increases in cholesterol levels, increased risk of heart attack, liver damage, reduced sexual function, infertility, breast development (in men), and more….

PROTEINS

3.11 Proteins are essential to the structures and functions of life

A protein is a polymer built from various combinations of 20 amino acid monomersProteins have unique structures that are directly

related to their functionsEnzymes, proteins that serve as metabolic catalysts,

regulate the chemical reactions within cells

Proteins are called polypeptides

PolypetideA chain of amino acids

A proteinMany polypeptides

strung together

Structural proteins provide associations between body parts and contractile proteins are found within muscle

Defensive proteins include antibodies of the immune system, and signal proteins are best exemplified by the hormones

Receptor proteins serve as antenna for outside signals, and transport proteins carry oxygen

Proteins

• Antibodies are defensive proteins• Hair and nails are made of proteins (“keratin”)• Muscles are pure protein (actin and myosin)• Venom is protein• Hemoglobin is a protein• Insulin and glucagon are regulatory proteins• The human growth hormone is a protein that

regulates growth

3.12 Proteins are made from amino acids linked by peptide bonds

Amino acids, the building blocks of proteins, have an amino group and a carboxyl groupBoth of these are covalently bonded to a central

carbon atomAlso bonded to the central carbon is a hydrogen atom

and other chemical group symbolized by “R”The “R” determines the type of

amino acid and what it can build

3.12 Proteins are made from amino acids linked by peptide bonds

Amino acids, the building blocks of proteins

I.e. The 26 letters of the alphabet are the building block for the English language

Carboxylgroup

Aminogroup

Amino acids are classified as hydrophobic or hydrophilicSome amino acids have a nonpolar R group and are

hydrophobicOthers have a polar R group and are hydrophilic,

which means they easily dissolve in aqueous solutions

Leucine (Leu)

Hydrophobic

Serine (Ser)

Hydrophilic

Aspartic acid (Asp)

Amino acids link together to form polymeric proteins polymeric-consisting of many repeating structural

unitsLinkage is accomplished by an enzyme-mediated

dehydration reactionThis links the carboxyl group of one amino acid to the

amino group of the next amino acidThe covalent linkage resulting is called a peptide bond

Carboxylgroup

Amino acid

Aminogroup

Amino acid

Carboxylgroup

Amino acid

Aminogroup

Amino acid

Peptidebond

Dipeptide

Dehydrationreaction

3.13 A protein’s specific shape determines its function

A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bondsThe amino acid sequence causes the polypeptide to

assume a particular shapeThe shape of a protein determines its specific function

Addiction

Endorphins bind to specific protein receptors on our brains, causing us to feel a sense of euphoria

However, many drugs mimic these endorphins and bind to the same protein receptors.

Groove

Groove

3.13 A protein’s specific shape determines its function

If for some reason a protein’s shape is altered, it can no longer functionDenaturation will cause polypeptide chains to unravel

and lose their shape and, thus, their functionProteins can be denatured by changes in salt

concentration, temperature and pH

It is VERY easy to denatureate a protein , but VERY difficult to renaturate a protein

3.14 A protein’s shape depends on four levels of structure

A protein can have four levels of structure1. Primary structure2. Secondary structure3. Tertiary structure4. Quaternary structure

The primary structure of a protein is its unique amino acid sequenceThe correct amino acid sequence is determined by the

cell’s genetic information (genes)The slightest change in this sequence affects the

protein’s ability to function, or makes an entirely new protein with a different function

Single amino acid changes can result in severe diseases. Some amino acid changes result in no negative effects.

Protein secondary structure results from coiling or folding of the polypeptideCoiling results in a helical structure called an alpha

helixFolding may lead to a structure called a pleated sheet

Coiling and folding result from hydrogen bonding between certain areas of the polypeptide chain

Many hydrogen bonds are responsible for the strength of spider silk.

Collagen

Polypeptidechain

The overall three-dimensional shape of a protein is called its tertiary structure

Tertiary structure generally results from interactions between the R groups of the various amino acids

Disulfide bridges are covalent bonds that further strengthen the protein’s shape

Two or more polypeptide chains (subunits) associate providing quaternary structureCollagen is an example of a protein with quaternary

structureIts triple helix gives great strength to connective

tissue, bone, tendons, and ligaments

Animation: Secondary Protein Structure

Animation: Quaternary Protein Structure

Animation: Tertiary Protein Structure

Animation: Protein Structure Introduction

Animation: Primary Protein Structure

Four Levels of Protein Structure

Amino acids

Primary structure

Four Levels of Protein Structure

Amino acids

Primary structure

Alpha helix

Hydrogenbond

Secondary structure

Pleated sheet

Four Levels of Protein Structure

Amino acids

Primary structure

Alpha helix

Hydrogenbond

Secondary structure

Pleated sheet

Polypeptide(single subunitof transthyretin)

Tertiary structure

Four Levels of Protein Structure

Amino acids

Primary structure

Alpha helix

Hydrogenbond

Secondary structure

Pleated sheet

Polypeptide(single subunitof transthyretin)

Tertiary structure

Transthyretin, withfour identicalpolypeptide subunits

Quaternary structure

Amino acids

Primary structure

Amino acids

Alpha helix

Hydrogenbond

Secondary structure

Pleated sheet

Polypeptide(single subunitof transthyretin)

Tertiary structure

Transthyretin, withfour identicalpolypeptide subunits

Quaternary structure

Proteins gone bad

• So what happens is a protein folds incorrectly?• Many diseases, such as Alzheimer’s and

Parkinson’s involve an accumulation of misfolded proteins

• Prions are infectious agents composed of proteins

• Prion diseases are currently untreatable and always fatal

Prions

• Prions infect and propogate by refolding abnormally into a structure that is able to convert normally-folded molecules into abnormally-structured form

• This altered form accumulates in infected tissue, causing tissue damage and cell death

• Prions are resistant to denaturation due to their extremely stable, tightly packed structure

Prions

• Prions are implicated in a number of diseases in a variety of mammals:– Bovine Spongiform Encephalopathy (“Mad Cows

Disease”) – spread by feed containing ground-up infected cattle

– Creutzfeldt-Jakob Disease – degenerative neurological disorder spread by skin grafts or human growth hormone products; Kuru is a similar disease spread by cannibalism among the Fore tribe of Papua New Guinea

Prions

• Chronic Wasting Disease – found in deer, moose, elk in U.S. and Canada

• Fatal Familial Insomnia – very rare, inherited prion disease (50 families worldwide have the responsible gene mutation); insoluble protein causes plaques to develop in the thalamus, the region of brain responsible for the regulation of sleep; fatal within several months

3.15 TALKING ABOUT SCIENCE: Linus Pauling contributed to our understanding of the chemistry

of life

After winning a Nobel Prize in Chemistry, Pauling spent considerable time studying biological moleculesHe discovered an oxygen attachment to hemoglobin

as well as the cause of sickle-cell diseasePauling also discovered the alpha helix and pleated

sheet of proteins

NUCLEIC ACIDS

3.16 Nucleic acids are information-rich polymers of nucleotides

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotidesNucleotides have three parts

1. A five-carbon sugar called ribose in RNA and deoxyribose in DNA

2. A phosphate group3. A nitrogenous base

Phosphategroup

Nitrogenousbase

(adenine)

Sugar

3.16 Nucleic acids are information-rich polymers of nucleotides

There are four DNA nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G)

RNA also has A, C, and G, but instead of T, it has uracil (U)

3.16 Nucleic acids are information-rich polymers of nucleotides

A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers when the phosphate of one nucleotide bonds to the sugar of the next nucleotideThe result is a repeating sugar-phosphate backbone

with protruding nitrogenous bases

Sugar-phosphatebackbone

Nucleotide

3.16 Nucleic acids are information-rich polymers of nucleotides

Two polynucleotide strands wrap around each other to form a DNA double helixThe two strands are associated because particular

bases always hydrogen bond to one anotherA pairs with T, and C pairs with G, producing base

pairs

RNA is usually a single polynucleotide strand

Basepair

3.16 Nucleic acids are information-rich polymers of nucleotides

A particular nucleotide sequence that can instruct the formation of a polypeptide is called a geneMost DNA molecules consist of millions of base pairs

and, consequently, many genesThese genes, many of which are unique to the species,

determine the structure of proteins and, thus, life’s structures and functions

Polymers

The key to the great diversity of proteins and DNA is arrangement – the variation in the sequence in which monomers are strung together

DNA is built of only four monomers (nucleotides) and proteins are built from only 20 kinds of amino acids; both of which are incredibly diverse: the proteins in you and a fungus are made with the same 20 amino acids

3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution

Mutations are alterations in bases or the sequence of bases in DNALactose tolerance is the result of mutationsIn many people, the gene that dictates lactose

utilization is turned off in adulthoodApparently, mutations occurred over time that

prevented the gene from turning offThis is an excellent example of human evolution

http://www.youtube.com/watch?v=qy8dk5iS1f0

DNAs structure was ‘discovered’ in 1953 by James Watson, Francis Crick and Rosalind Franklin

Temperature (°C)

0 20

Rate

of

reac

tion

Enzyme A

100

Enzyme B

40 60 80

Short polymer MonomerHydrolysis

Dehydration

Longer polymer

You should now be able to

1. Discuss the importance of carbon to life’s molecular diversity

2. Describe the chemical groups that are important to life

3. Explain how a cell can make a variety of large molecules from a small set of molecules

4. Define monosaccharides, disaccharides, and polysaccharides and explain their functions

5. Define lipids, phospholipids, and steroids and explain their functions

Copyright © 2009 Pearson Education, Inc.

You should now be able to

6. Describe the chemical structure of proteins and their importance to cells

7. Describe the chemical structure of nucleic acids and how they relate to inheritance

Copyright © 2009 Pearson Education, Inc.