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Chapter 3
The Molecules of Cells
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
INTRODUCTION TO ORGANIC
COMPOUNDS
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3.1 Life’s molecular diversity is based on the
properties of carbon
 Diverse molecules found in cells are composed of
carbon bonded to
– other carbons and
– atoms of other elements.
 Carbon-based molecules are called organic
compounds.
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3.1 Life’s molecular diversity is based on the
properties of carbon
 By sharing electrons, carbon can
– bond to four other atoms and
– branch in up to four directions.
 Methane (CH4) is one of the simplest organic
compounds.
– Four covalent bonds link four hydrogen atoms to the
carbon atom.
– Each of the four lines in the formula for methane
represents a pair of shared electrons.
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3.1 Life’s molecular diversity is based on the
properties of carbon
 Methane and other compounds composed of only
carbon and hydrogen are called hydrocarbons.
 Carbon, with attached hydrogens, can bond
together in chains of various lengths.
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Figure 3.1A
Structural
formula
Ball-and-stick
model
Space-filling
model
The four single bonds of carbon point to the corners of a tetrahedron.
3.1 Life’s molecular diversity is based on the
properties of carbon
 A carbon skeleton is a chain of carbon atoms that
can be
– branched or
– unbranched.
 Compounds with the same formula but different
structural arrangements are call isomers.
Animation: L-Dopa
Animation: Carbon Skeletons
Animation: Isomers
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Figure 3.1B
Length. Carbon skeletons vary in length.
Ethane
Propane
Branching. Skeletons may be unbranched
or branched.
Butane
Isobutane
Double bonds. Skeletons may have double bonds.
1-Butene
2-Butene
Rings. Skeletons may be arranged in rings.
Cyclohexane
Benzene
Figure 3.1B_1
Length. Carbon skeletons vary in length.
Ethane
Propane
Figure 3.1B_2
Branching.
Skeletons may be unbranched
or branched.
Butane
Isobutane
Figure 3.1B_3
Double bonds. Skeletons may have double bonds.
1-Butene
2-Butene
Figure 3.1B_4
Rings. Skeletons may be arranged in rings.
Cyclohexane
Benzene
3.2 A few chemical groups are key to the
functioning of biological molecules
 An organic compound has unique properties that
depend upon the
– size and shape of the molecule and
– groups of atoms (functional groups) attached to it.
 A functional group affects a biological molecule’s
function in a characteristic way.
 Compounds containing functional groups are
hydrophilic (water-loving).
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3.2 A few chemical groups are key to the
functioning of biological molecules
 The functional groups are
– hydroxyl group—consists of a hydrogen bonded to an
oxygen,
– carbonyl group—a carbon linked by a double bond to
an oxygen atom,
– carboxyl group—consists of a carbon double-bonded
to both an oxygen and a hydroxyl group,
– amino group—composed of a nitrogen bonded to two
hydrogen atoms and the carbon skeleton, and
– phosphate group—consists of a phosphorus atom
bonded to four oxygen atoms.
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Table 3.2
Table 3.2_1
Table 3.2_2
3.2 A few chemical groups are key to the
functioning of biological molecules
 An example of similar compounds that differ only in
functional groups is sex hormones.
– Male and female sex hormones differ only in functional
groups.
– The differences cause varied molecular actions.
– The result is distinguishable features of males and
females.
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Figure 3.2_1
Testosterone
Estradiol
Figure 3.2_2
Figure 3.2_3
3.3 Cells make a huge number of large molecules
from a limited set of small molecules
 There are four classes of molecules important to
organisms:
– carbohydrates,
– proteins,
– lipids, and
– nucleic acids.
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3.3 Cells make a huge number of large molecules
from a limited set of small molecules
 The four classes of biological molecules contain
very large molecules.
– They are often called macromolecules because of their
large size.
– They are also called polymers because they are made
from identical building blocks strung together.
– The building blocks of polymers are called monomers.
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3.3 Cells make a huge number of large molecules
from a limited set of small molecules
 Monomers are linked together to form polymers
through dehydration reactions, which remove
water.
 Polymers are broken apart by hydrolysis, the
addition of water.
 All biological reactions of this sort are mediated by
enzymes, which speed up chemical reactions in
cells.
Animation: Polymers
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3.3 Cells make a huge number of large molecules
from a limited set of small molecules
 A cell makes a large number of polymers from a
small group of monomers. For example,
– proteins are made from only 20 different amino acids
and
– DNA is built from just four kinds of nucleotides.
 The monomers used to make polymers are
universal.
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Figure 3.3A_s1
Short polymer
Unlinked
monomer
Figure 3.3A_s2
Unlinked
monomer
Short polymer
Dehydration reaction
forms a new bond
Longer polymer
Figure 3.3B_s1
Figure 3.3B_s2
Hydrolysis
breaks a bond
CARBOHYDRATES
Carbohydrates
range from small
sugar molecules
(monomers) to
large
polysaccharides.
Glucose
(an aldose)
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Fructose
(a ketose)
Figure 3.4C
6
5
4
1
3
2
Structural
formula
Abbreviated
structure
Simplified
structure
Examples of Carbohydrates
 Monosaccharides:
– Glucose, fructose, galactose
– Range from 3 to 7 Carbons in length
 Disaccharides:
– Maltose = Glucose---Glucose
– Lactose = Glucose---Galactose
– Sucrose = Glucose---Fructose
 Polysaccharides:
– Long chains of monosaccharides
– Glycogen, starch, cellulose are all long glucose chains
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Function of Carbohydrates
 Carbohydrates are used as:
– the main fuels for cellular work (immediate energy)
– used as raw materials to manufacture other organic
molecules.
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Figure 3.5_s1
Glucose
Glucose
Monosaccharides can be linked together by a
dehydration reaction
Figure 3.5_s2
Glucose
Glucose
Monosaccharides
can be linked
together by a
dehydration
reaction
Maltose
Polysaccharides are long chains of sugar units
 Polysaccharides may function as
– storage molecules or
– structural compounds.
 Starch is used by plants for energy storage.
 Glycogen is used by animals for energy storage
 Cellulose forms plant cell walls.
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Figure 3.7
Starch granules
in potato tuber cells
Glycogen granules
in muscle
tissue
Cellulose microfibrils
in a plant cell wall
Starch
Glucose
monomer
Glycogen
Cellulose
Hydrogen bonds
Cellulose
molecules
LIPIDS
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3.8 Fats are lipids that are mostly energy-storage
molecules
 Lipids
– are water insoluble (hydrophobic, or waterfearing) compounds,
– are important in long-term energy storage,
– contain twice as much energy as a polysaccharide,
and
– consist mainly of carbon and hydrogen
atoms linked by nonpolar covalent bonds.
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3 Categories of Lipids
 We will consider three types of lipids:
– Triglycerides (fats),
– phospholipids, and
– steroids.
 A triglyceride is a large lipid made from two kinds
of smaller molecules,
– glycerol and
– 3 fatty acids.
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Figure 3.8B
Glycerol
Triglyceride = 1
glycerol covalently
attached to 3 fatty
acids
Fatty acid
Figure 3.8C
Triglyceride = Glycerol
1 glycerol covalently
attached to 3 fatty
acids
Fatty acids can be:
•Saturated
•Unsaturated
Fatty acids
Phospholipids
 Phospholipids contain two fatty acids attached to
glycerol.
– A phosphate functional group replaces the other fatty
acid
– Used to build cell membranes
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Figure 3.9A-B
Phosphate
group
Phospholipids
Glycerol
Hydrophilic heads
Water
Hydrophobic tails
Symbol for phospholipid
Water
Steroids and Cholesterol
 Steroids are lipids in which the carbon skeleton
contains four fused rings.
 Cholesterol is a
– common component in animal cell membranes and
– starting material for making steroids, including sex
hormones.
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Figure 3.2
Testosterone
Estradiol
PROTEINS
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Proteins are made from amino acids
 Proteins are
– involved in nearly every
function in your body and
– very diverse,
– 50,000 - 100,000 proteins, each
with a specific structure and
function, in the human body.
 Proteins are composed of
differing arrangements of a
common set of just 20
amino acids.
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Amino
group
Carboxyl
group
Proteins are made from amino acids
 Amino acids are classified as either
– hydrophobic or hydrophilic.
Hydrophobic
Leucine (Leu)
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Hydrophilic
Serine (Ser)
Aspartic acid (Asp)
Figure 3.11C_s1
Amino acids are joined together by a dehydration reaction
Carboxyl
group
Amino acid
Amino
group
Amino acid
Figure 3.11C_s2
Amino acids are joined together by a dehydration reaction
Carboxyl
group
Amino acid
Amino
group
Amino acid
Peptide
bond
Dehydration
reaction
Dipeptide
A protein’s specific shape determines its function
 Proteins are distinguished by:
– The combination of sequence of amino acids
– The linear sequence of amino acids in a protein is called the PRIMARY
STRUCTURE of the protein
– 3D structure
 The amino acid sequence causes the protein to assume a
particular shape.
 The shape of a protein determines its specific function.
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Figure 3.13A
Primary structure
Amino
acid
Figure 3.13A-D_s4
Four Levels of Protein Structure
Primary structure
Amino
acids
Amino acids
Secondary structure
Hydrogen
bond
Beta pleated
sheet
Alpha helix
Tertiary structure
Transthyretin
polypeptide
Quaternary structure
Transthyretin, with four
identical polypeptides
A protein’s specific shape determines its function
 Functions of proteins:
– Enzymes catalyze chemical reactions.
– Structural proteins provide associations between body parts.
– Contractile proteins are found within muscle.
– Defensive proteins include antibodies of the immune system.
– Signal proteins are best exemplified by hormones and other
chemical messengers.
– Receptor proteins transmit signals into cells.
– Transport proteins carry oxygen.
– Storage proteins serve as a source of amino acids for developing
embryos.
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NUCLEIC ACIDS
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3.14 DNA and RNA are the two types of nucleic
acids
 DNA(deoxyribonucleic acid)
– DNA is provides genetic information
– DNA is inherited from an organism’s parents.
– DNA provides instructions for production of proteins in a cell.
 DNA works through an intermediary, ribonucleic acid
(RNA).
– DNA is transcribed into RNA.
– RNA is translated into proteins.
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Figure 3.14_s1
Gene
DNA
Figure 3.14_s2
Gene
DNA
Nucleic acids
Transcription
RNA
Figure 3.14_s3
Gene
DNA
Nucleic acids
Transcription
RNA
Translation
Amino
acid
Protein
Nucleic acids are built from nucleotides
 Nucleotides have three parts:
– a five-carbon sugar called ribose in RNA and
deoxyribose in DNA,
– a phosphate group, and
– a nitrogenous base.
Nitrogenous
base
(adenine)
Phosphate
group
Sugar
DNA vs. RNA
 DNA nitrogenous bases are
– adenine (A),
– thymine (T),
– cytosine (C), and
– guanine (G).
 DNA sugar = deoxyribose
 RNA
– also has A, C, and G,
– but instead of T, it has uracil (U).
 RNA sugar = ribose
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Figure 3.15B
A
T
C
G
T
Sugar-phosphate
backbone
Nucleotide
DNA vs. RNA
 DNA = 2 strands of nucleotides that form a double
helix.
– The two strands pair thru contacts with nucleotide bases
– A pairs with T
– C pairs with G
 RNA is usually a single polynucleotide strand.
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Figure 3.15C
C
A
G
C
C
T
G
A
T
C
G
A
Base
pair
T
T
A
G
T
A
A
T
A
C
T
Figure 3.UN01
Dehydration
Short polymer
Monomer
Hydrolysis
Longer polymer
Figure 3.UN03_1
Classes of Molecules
and Their Components
Carbohydrates
Monosaccharides
Functions
Examples
Energy for cell,
raw material
a.
b.
Starch, glycogen
Plant cell support
c.
Energy storage
d.
e.
Phospholipids
Hormones
f.
Lipids
(don’t form polymers)
Glycerol
Fatty acid
Components of a fat molecule
Figure 3.UN03_2
Classes of Molecules
and Their Components
Proteins
g.
h.
i.
Amino acid
Nucleic Acids
Functions
Examples
j.
Lactase
k.
Hair, tendons
l.
Muscles
Transport
m.
Communication
Signal proteins
n.
Antibodies
Storage
Receive signals
Egg albumin
Receptor protein
Heredity
r.
s.
DNA and RNA
p.
o.
Nucleotide
q.