Download 3. The Molecules of Cells

Chapter 3
The Molecules of Cells
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Got Lactose?
• Lactose intolerance illustrates the importance
of biological molecules to the functioning of
living cells and to human health
• Molecular interactions, such as those between
the gene for lactase production, the enzyme
lactase, and the milk sugar lactose, drive all
biological processes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
INTRODUCTION TO ORGANIC COMPOUNDS
3.1 Life's molecular diversity is based on the properties
of carbon
•
Organic compounds contain at least one carbon atom
•
Covalent bonding enables carbon to form complex
structures
– A carbon atom has four electrons in its outer shell
– To complete the shell, it can form four covalent
bonds
– The way bonding occurs among atoms determines
the overall shape of the molecule
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-1a
Structural
formula
Ball-and-stick
model
Space-filling
model
Methane
The 4 single bonds of carbon point to the corners of a tetrahedron.
LE 3-1b
Ethane
Propane
Carbon skeletons vary in length.
LE 3-1c
Butane
Isobutane
Skeletons may be unbranched or branched.
LE 3-1d
1-Butene
2-Butene
Skeletons may have double bonds, which can vary in location.
LE 3-1e
Cyclohexane
Benzene
Skeletons may be arranged in rings.
Animation: Carbon Skeletons
Animation: Isomers
Animation: L-Dopa
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Hydrocarbons are composed of only hydrogen
and carbon
– A series of covalently bonded carbons
forms the carbon skeleton of the molecule
– Isomers are molecules with the same
molecular formula but different structures
and properties
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.2 Functional groups help determine the
properties of organic compounds
• Functional groups are groups of atoms
attached to the carbon skeleton of molecules
– Usually participate in chemical reactions
– Give organic molecules their particular
properties
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-2
Estradiol
Female lion
Testosterone
Male lion
• Five main functional groups are important in the
chemistry of life:
– Hydroxyl group
– Carbonyl group
– Carboxyl group
– Amino group
– Phosphate group
• These groups are all polar and make
compounds containing them hydrophilic (waterloving)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.3 Cells make a huge number of large
molecules from a small set of small molecules
• Four main classes of biological
macromolecules
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cells make the most of their large molecules by
joining smaller organic monomers into chains
called polymers
– Monomers are usually linked by dehydration
reactions
• A water molecule is removed
Animation: Polymers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-3a
Short polymer
Unlinked monomer
Dehydration
reaction
Longer polymer
– Polymers are broken down to monomers by
the reverse process, hydrolysis
• A water molecule is added
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-3b
Hydrolysis
CARBOHYDRATES
3.4 Monosaccharides are the simplest
carbohydrates
• Monosaccharides (single sugars) are
carbohydrate monomers
• A monosaccharide has a formula that is a
multiple of CH2O
– Contains hydroxyl groups and a carbonyl
group
– May be isomers, such as glucose and
fructose
– May take chain or ring forms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-4b
Glucose
Fructose
LE 3-4c
Structural
formula
Abbreviated
structure
Simplified
structure
3.5 Cells link two single sugars to form
disaccharides
• Two monosaccharides can join to form a
disaccharide
– Linked by a dehydration reaction
– Example: two glucose monomers form the
disaccharide maltose
Animation: Disaccharides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-5
Glucose
Glucose
Maltose
CONNECTION
3.6 How sweet is sweet?
• We perceive a sweet taste when a chemical
binds to the sweet receptor on the tongue
– The structure of a compound determines
how well it fits into a receptor
– The more strongly the chemical binds to the
receptor, the sweeter it is perceived to be
– The chemical can be sugar or another
compound, such as aspartame
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.7 Polysaccharides are long chains of sugar
units
•
Polysaccharides are polymers of
monosaccharides linked together by dehydration
reactions
•
Some polysaccharides are storage molecules
– Starch in plants
– Glycogen in animals
•
Some polysaccharides serve as structural
compounds
– Cellulose in plants
Animation: Polysaccharides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-7
Starch granules in
potato tuber cells
Glycogen
granules in
muscle
tissues
Cellulose fibrils in
a plant cell wall
Cellulose
molecules
STARCH
Glucose
monomer
GLYCOGEN
CELLULOSE
LIPIDS
3.8 Fats are lipids that are mostly energy-storage
molecules
• Lipids are diverse compounds consisting
mainly of carbon and hydrogen atoms
– Linked by nonpolar covalent bonds
– Hydrophobic (water-fearing)
Animation: Fats
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Fats, also called triglycerides, are lipids whose
main function is energy storage
– Polymers of fatty acids (usually three
molecules) and one glycerol molecule
– Formed by dehydration reactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Saturated fatty acids
– Contain the maximum number of
hydrogens
– Have no double bonds between carbons
• Unsaturated fatty acids
– Contain fewer than the maximum possible
hydrogens
– Have double bonds between carbons
• Oils are liquid fats
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.9 Phospholipids, waxes, and steroids are lipids
with a variety of functions
– Phospholipids
– Contain two fatty acid groups and the
element phosphorus
– Are a major component of cell membranes
• Waxes
– Consist of a single fatty acid linked to an
alcohol
– Form waterproof coatings
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• Steroids
– Have backbones bent into rings, as in
cholesterol
– Are often hormones or the basis of
hormones
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
3.10 Anabolic steroids pose health risks
• Anabolic steroids are natural and synthetic
variants of the male hormone testosterone
– Build up bone and muscle mass
– Can cause serious health problems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PROTEINS
3.11 Proteins are essential to the structures and
activities of life
• A protein is a polymer constructed from amino
acid monomers
• The structure of the protein determines its
function
• The seven major classes of protein are
– Structural: hair, cell cytoskeleton
– Contractile: producers of movement in
muscle and other cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Storage: sources of amino acids, such as
egg white
– Defense: antibodies, membrane proteins
– Transport: carriers of molecules such as
hemoglobin, membrane proteins
– Signaling: hormones, membrane proteins
– Enzymes: regulators of the speed
biochemical reactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Animation: Structural Proteins
Animation: Storage Proteins
Animation: Transport Proteins
Animation: Receptor Proteins
Animation: Contractile Proteins
Animation: Defensive Proteins
Animation: Enzymes
Animation: Hormonal Proteins
Animation: Sensory Proteins
Animation: Gene Regulatory Proteins
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.12 Proteins are made from amino acids linked
by peptide bonds
•
Protein diversity is based on different
arrangements of a common set of 20 amino acid
monomers
•
Each amino acid contains
– An amino group
– A carboxyl group
– One of twenty functional ("R") groups
•
The three groups and a hydrogen atom are
bonded to a central "alpha" carbon
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-12a
Amino
group
Carboxyl (acid)
group
• The structure of the R group determines the
specific properties of each amino acid
• An amino acid may be hydrophobic or
hydrophilic, depending on the characteristics of
the R group
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-12b
Leucine (Leu)
Hydrophobic
Serine (Ser)
Aspartic acid (Asp)
Hydrophilic
• Cells link amino acids together by dehydration
synthesis
• The bonds between amino acid monomers are
called peptide bonds
• Dipeptides are two amino acids long;
polypeptides are from several to more than a
thousand amino acids long
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-12c
Carboxyl
group
Peptide
bond
Amino
group
Dehydration
reaction
Amino acid
Amino acid
Dipeptide
3.13 A protein's specific shape determines its
function
• A protein consists of one or more polypeptide
chains spontaneously folded into a unique
shape
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-13
Groove
Groove
• The folding of a polypeptide creates grooves
that enable other molecules to bind to it
• In denaturation, chemical or physical
changes can cause proteins to lose their
shape and thus their specific function
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.14 A protein's shape depends on four levels of
structure
• Primary structure: the unique sequence of
amino acids forming the polypeptide
• Secondary structure: the coiling or folding of
the chain, stabilized by hydrogen bonding
– May be alpha helix or pleated sheet (which
dominates the silk protein of a spider's web)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Tertiary structure: the overall three-dimensional
shape of the polypeptide
• Quaternary structure: the association of two or
more polypeptide chains (subunits)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-14a
Levels of Protein Structure
Amino acids
LE 3-14b
Levels of Protein Structure
Amino acids
Hydrogen
bond
Alpha helix
Pleated sheet
LE 3-14c
Levels of Protein Structure
Amino acids
Hydrogen
bond
Alpha helix
Polypeptide
(single subunit
of transthyretin)
Pleated sheet
LE 3-14d
Levels of Protein Structure
Amino acids
Hydrogen
bond
Alpha helix
Polypeptide
(single subunit
of transthyretin)
Transthyretin, with
four identical
polypeptide subunits
Pleated sheet
Animation: Protein Structure Introduction
Animation: Primary Protein Structure
Animation: Secondary Protein Structure
Animation: Tertiary Protein Structure
Animation: Quarternary Protein Structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Collagen is an example of a protein with a
quaternary structure
– Three subunits wound into a helix
– Structure provides great strength to long
fibers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
TALKING ABOUT SCIENCE
3.15 Linus Pauling contributed to our understanding of
the chemistry of life
•
Felt that the study of individual parts must come first,
then putting the parts together
•
Began his career by studying chemical bonding
•
First described the alpha helix and pleated sheet
protein structures
•
Discovered how abnormal hemoglobin causes sickle
cell disease
•
Won two Nobel prizes, for chemistry and for peace (for
helping produce a nuclear test ban treaty)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
NUCLEIC ACIDS
3.16 Nucleic acids are information-rich polymers
of nucleotides
• There are two types of nucleic acid-DNA and
RNA
• Nucleic acids are polymers of nucleotide
monomers composed of
– A five-carbon sugar
– A phosphate group
– A nitrogenous base-adenine (A), thymine
(T), cytosine ( C), and guanine (G) in DNA;
A, G, C, and uracil (U) in RNA
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-16a
Nitrogenous
base (A)
Phosphate
group
Sugar
• Nucleotide monomers are formed into a
polynucleotide with a sugar-phosphate
backbone and attached nitrogenous bases
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-16b
Nucleotide
Sugar-phosphate
backbone
• Hydrogen bonding between nitrogenous
bases creates the final structure of the
nucleic acid
– RNA usually consists of a single
polynucleotide strand
– DNA is a double helix
• Two polynucleotides are twisted around
each other
• Nitrogenous bases protruding from the
backbone pair with each other, A with T
and G with C
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 3-16c
Base
pair
– Specific sequences of DNA make up genes
that program the amino acid sequences of
proteins
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings