Download Chapter

Molecules of Life
Chapter 3
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole,
Cengage Learning 2011.
Biology, Ninth Edition, by Solomon, Berg, Martin. Brooks/Cole, Cengage Learning 2011.
3.1 Molecules of Life
 Molecules of life are synthesized by living cells
•
•
•
•
Carbohydrates
Lipids
Proteins
Nucleic acids
 Organic Compounds
• In organic compounds, covalently bonded carbon
atoms form the backbone of the molecule
Structure to Function
 Molecules of life differ in three-dimensional
structure and function
1. Carbon backbone
• A carbon atom can complete its valence shell by
forming a total of four covalent bonds
• Carbon-to-carbon bonds are strong and not easily
broken  Single, Double, Triple covalent bonds
2. Attached functional groups
 Structures give clues to how they function
Organic Compounds
 Consist primarily of carbon and hydrogen atoms
• Carbon atoms bond covalently with up to four
other atoms, often in long chains or rings
 Hydrocarbon  Hydrophobic
• An organic compound or region of one that
consists only of carbon and hydrogen atoms
 Functional groups attach to a carbon backbone
• Influence organic compound’s properties
Functional Groups
In alcohols (e.g.,
sugars, amino acids);
water soluble
hydroxyl
methyl
In fatty acid chains;
insoluble in water
carbonyl
(aldehyde)
(ketone)
In sugars, amino acids,
nucleotides; water
soluble. An aldehyde
if at end of a carbon
backbone; a ketone if
attached to an interior
carbon of backbone
carboxyl
(non-ionized)
(ionized)
In amino acids, fatty
acids, carbohydrates;
water soluble. Highly
polar; acts as an acid
(releases H+)
Fig. 3.3, p. 36
amino
In amino acids and
certain nucleotide
bases; water soluble,
acts as a weak base
(accepts H+)
(non-ionized)
(ionized)
phosphate
icon
In nucleotides (e.g.,
ATP), also in DNA,
RNA, many proteins,
phospholipids; water
soluble, acidic
Fig. 3.3, p. 36
Functional Groups:
The Importance of Position
Processes of Metabolism
 Metabolism:
• All the enzyme-mediated chemical reactions by
which cells acquire and use energy as they build
and break down organic molecules.
 Cells use energy to grow and maintain themselves
 Enzyme-driven reactions build, rearrange, and split
organic molecules
• Enzymes  a compound (protein) that speeds a
reaction without being changed by it.
Building Organic Compounds
 Cells form complex organic molecules
•
•
•
•
Simple sugars → carbohydrates
Fatty acids → lipids
Amino acids → proteins
Nucleotides → nucleic acids
 Condensation combines monomers to form polymers
• Monomer  Molecules that are subunits of polymers
• Polymers  Molecules that consists of multiple
monomers
Polyethylene: A Simple Polymer
What Cells Do to Organic Compounds
Condensation (aka Dehydration
Synthesis) and Hydrolysis
Key Concepts:
STRUCTURE DICTATES FUNCTION
 We define cells partly by their capacity to build
complex carbohydrates and lipids, proteins, and
nucleic acids
 The main building blocks are simple sugars, fatty
acids, amino acids, and nucleotides
 These organic compounds have a backbone of
carbon atoms with functional groups attached
3.2 Carbohydrates –
The Most Abundant Ones
 Carbohydrates 
• Molecules that consists primarily of carbon,
hydrogen, and oxygen atoms at a 1:2:1 ratio.
 Three main types of carbohydrates
• Monosaccharides (simple sugars)
• Oligosaccharides (short chains)
• Polysaccharides (complex carbohydrates)
 Carbohydrate functions
• Instant energy sources
• Transportable or storable forms of energy
• Structural materials
Monosaccharides (Simple Sugar):
Glucose and Fructose
Glucose (C6H12O6)
(an aldehyde)
Fructose (C6H12O6)
(a ketone)
Galactose (C6H12O6)
(an aldehyde)
(c) Hexose sugars (6-carbon sugars)
Fig. 3-6c, p. 52
Glucose
 Glucose (C6H12O6), the most abundant
monosaccharide, is used as an energy source in
most organisms
 During cellular respiration, cells oxidize glucose
molecules, converting stored energy to a form
used for cell work
 Homeostatic mechanisms maintain blood
glucose levels
Disaccharides: Sucrose
Disaccharides
• A disaccharide (two sugars) contains two
monosaccharide rings joined by a glycosidic linkage,
consisting of a central oxygen covalently bonded to
two carbons, one in each ring
• Common disaccharides:
• Maltose (malt sugar): 2 covalently linked glucose
• Sucrose (table sugar): 1 glucose + 1 fructose
• Lactose (milk sugar): 1 glucose + 1 galactose
Complex Carbohydrates (Polysaccharides):
Bonding Patterns
Polysaccharides
• A polysaccharide is a macromolecule (a single
long chain or a branched chain) consisting of
repeating units of simple sugars, usually glucose
• Common polysaccharides:
• Starches: Energy storage in plants
• Glycogen: Energy storage in animals
• Cellulose: Structural polysaccharide in plants
Starches
• starch
• Form of carbohydrate used for energy storage in
plants
• Polymer consisting of glucose
• Plant cells store starch as granules in amyloplasts
Starch: A Storage Polysaccharide
Amyloplasts
(a) Starch (stained purple) is
stored in specialized organelles,
called amyloplasts, in these cells
of a buttercup root.
Fig. 3-9a, p. 55
Complex Carbohydrates:
Starch
Glycogen
• glycogen
• Form in which glucose subunits are stored as an
energy source in animal tissues
• Similar in structure to plant starch but more
extensively branched and more water soluble
• In vertebrates, glycogen is stored mainly in liver
and muscle cells
Structure of
cellulose
c Glycogen. In animals, this
polysaccharide is a storage form
for excess glucose. It is
especially abundant in the liver
and muscles of highly active
animals, including fishes and
people.
Fig. 3.8, p. 39
Cellulose
• cellulose
• Insoluble polysaccharide composed of many
joined glucose molecules
• Structural component of plants (fibers)
• The most abundant carbohydrate
• Some microorganisms digest cellulose to
glucose
• Humans lack enzymes to hydrolyze β 1—4
linkages
Cellulose: A Structural Polysaccharide
Complex Carbohydrates:
Chitin
Key Concepts:
CARBOHYDRATES
 Carbohydrates are the most abundant biological
molecules
 Simple sugars function as transportable forms of
energy or as quick energy sources
 Complex carbohydrates are structural materials
or energy reservoirs
3.3 Greasy, Oily – Must Be Lipids
 Lipids
• Fats, phospholipids, waxes, and sterols
• Don’t dissolve in water
• Dissolve in nonpolar substances (other lipids)
 Lipid functions
• Major sources of energy
• Structural materials
• Used in cell membranes
Fats
 Lipids with glycerol molecule and one, two, or three
fatty acid tails
 Fatty acids 
• Organic compound with a chain of carbon atoms and
an acidic carboxyl group at one end
• Saturated
• Unsaturated (cis and trans)
 Triglycerides (neutral fats )
• Three fatty acid tails
• Most abundant animal fat (body fat)
• Major energy reserves
Saturated and Unsaturated Fatty Acids
• saturated fatty acids
• Contain the maximum number of hydrogen atoms
• Found in animal fat and solid vegetable
shortening
• Solid at room temperature
• unsaturated fatty acids
• Include one or more pairs of carbon atoms joined
by a double bond (not fully saturated with
hydrogen)
• Tend to be liquid at room temperature
Unsaturated Fatty Acids
• Each double bond produces a bend in the
hydrocarbon chain that prevents close alignment
with an adjacent chains
• monounsaturated fatty acids
• Fatty acids with one double bond
• Example: Oleic acid
• polyunsaturated fatty acids
• Fatty acids with more than one double bond
• Example: linoleic acid
Fatty Acids
Trans and Cis Fatty Acids
Trans Fats
 Food manufacturers hydrogenate or partially
hydrogenate cooking oils (convert unsaturated fatty
acids to saturated fatty acids) to make fat more solid
at room temperature
 In naturally-occurring unsaturated fatty acids
• the hydrogens on each side of the double bond are
on the same side of the hydrocarbon chain (cis
configuration)
 Artificial hydrogenation produces a trans
configuration
• solid at room temperature and increases risk of
cardiovascular disease
Trans and Cis Isomers
Triglyceride Formation
Phospholipids
 Main component of
cell membranes
• Hydrophilic head,
hydrophobic tails
 A lipid with a
phosphate group in
its hydrophilic head
and two nonpolar
fatty acid tails
A Phospholipid
A Phospholipid Bilayer
Waxes
 Firm, pliable, water repelling, lubricating
Cholesterol
 Membrane components; precursors of other
molecules (steroid hormones)
Steroids
• steroid
• Consists of carbon atoms arranged in four
attached rings
• Side chains distinguish one steroid from another
• Synthesized from isoprene units
• Steroids of biological importance include
cholesterol, bile salts, reproductive hormones,
cortisol and other hormones secreted by the
adrenal cortex
• Plant cell membranes contain molecules similar
to cholesterol
Steroids
 Lipid with four carbon rings
• No fatty acid tails
Key Concepts:
LIPIDS
 Complex lipids function as energy reservoirs,
structural materials of cell membranes, signaling
molecules, and waterproofing or lubricating
substances
3.4 Proteins –
Diversity in Structure and Function
 Proteins have many functions
•
•
•
•
•
•
Structures
Nutrition
Enzymes
Transportation
Communication
Defense
Protein Structure
 Built from 20 kinds of amino acids
• Amino acid  carboxyl group, amino group, and
side group (R)
Fig. 3.15, p. 42
Fig. 3.15, p. 42
Protein Synthesis
Peptide Bonds
Four Levels of Protein Structure
1. Primary structure
• Amino acids joined by peptide bonds form a
linear polypeptide chain
2. Secondary structure
• Polypeptide chains form sheets and coils
3. Tertiary structure
• Sheets and coils pack into functional domains
Four Levels of Protein Structure
4. Quaternary structure
• Many proteins (e.g. fs) consist of two or more
chains
 Other protein structures
• Glycoproteins
• Lipoproteins
• Fibrous proteins
1. Primary Structure
2. Secondary Structure
Secondary Structure of a Protein
3. Tertiary Structure
Tertiary Structure of a Protein
4. Quaternary Structure
Quaternary Structure of a Protein
3.5 Why is Protein Structure
So Important?
 Protein structure dictates function
 Sometimes a mutation in DNA results in an
amino acid substitution that alters a protein’s
structure and compromises its function
• Example: Hemoglobin and sickle-cell anemia
Normal Hemoglobin Structure
Normal Hemoglobin Structure
Sickle-Cell Mutation
VALINE
HISTIDINE
LEUCINE THREONINE PROLINE
b One amino acid substitution results in the
abnormal beta chain in HbS molecules. Instead
of glutamate, valine was added at the sixth
position of the polypeptide chain.
c Glutamate has an overall negative charge; valine
has no net charge. At low oxygen levels, this
difference gives rise to a water-repellent, sticky
patch on HbS molecules. They stick together
because of that patch, forming rodshaped clumps
that distort normally rounded red blood cells into
sickle shapes. (A sickle is a farm tool that has a
crescent-shaped blade.)
VALINE
GLUTAMATE
sickle cell
normal cell
Fig. 3.19, p. 45
Clumping of cells in bloodstream
Circulatory problems, damage to brain,
lungs, heart, skeletal muscles, gut, and
kidneys
Heart failure, paralysis, pneumonia,
rheumatism, gut pain, kidney failure
Spleen concentrates sickle cells
Spleen enlargement
Immune system compromised
Rapid destruction of sickle cells
d Melba Moore, celebrity spokesperson for sickle-cell anemia
organizations. Right, range of
symptoms for a person with two
mutated genes for hemoglobin’s
beta chain.
Anemia, causing weakness,fatigue,
impaired development,heart chamber
dilation
Impaired brain function, heart failure
Fig. 3.19, p. 45
Denatured Proteins
 If a protein unfolds and loses its threedimensional shape (denatures), it also loses its
function
 Caused by shifts in pH or temperature, or
exposure to detergent or salts
• Disrupts hydrogen bonds and other molecular
interactions responsible for protein’s shape
Key Concepts:
PROTEINS
 Peptide bond joins amino acids in proteins
 Polypeptides are a chain of amino acids linked
by peptide bonds
 Proteins are organic compounds that consists of
one or more chains of amino acids
 Structurally and functionally, proteins are the
most diverse molecules of life
 They include enzymes, structural materials,
signaling molecules, and transporters
3.6 Nucleotides, DNA, and RNAs
Nucleotide structure, 3 parts:
• Sugar
• Phosphate group
• Nitrogen-containing base
Nucleotide Functions:
Reproduction, Metabolism, and Survival
 DNA and RNAs are nucleic acids, each
composed of four kinds of nucleotide subunits
 ATP energizes many kinds of molecules by
phosphate-group transfers
 Other nucleotides function as coenzymes or as
chemical messengers
Nucleotides of DNA
DNA, RNAs, and Protein Synthesis
 DNA (double-stranded)
• Encodes information about the primary structure
of all cell proteins in its nucleotide sequence
 RNA molecules (usually single stranded)
• Different kinds interact with DNA and one another
during protein synthesis
The DNA Double-Helix
Key Concepts:
NUCLEOTIDES AND NUCLEIC ACIDS
 Nucleotides have major metabolic roles and are
building blocks of nucleic acids
 Two kinds of nucleic acids, DNA and RNA,
interact as the cell’s system of storing, retrieving,
and translating information about building
proteins
Animation: Condensation and hydrolysis
Animation: Fatty acids
Animation: Functional group
Animation: Globin and hemoglobin
structure
Animation: Nucleotide subunits of DNA
Animation: Peptide bond formation
Animation: Phospholipid structure
Animation: Secondary and tertiary
structure
Animation: Sickle-cell anemia
Animation: Structure of an amino acid
Animation: Structure of ATP
Animation: Triglyceride formation