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.