3.4 Carbohydrates
•  Carbohydrates are used for energy or
sometimes as structural molecules
§  a carbohydrate is any molecule that contains the
elements C, H, and O in a 1:2:1 ratio
§  the sizes of carbohydrates varies
•  simple carbohydrates – made up of one or two monomers
•  complex carbohydrates – long polymers
Figure 3.3(c)
Polymers are built
from monomers:
carbohydrate
3.4 Carbohydrates
•  Simple carbohydrates are small
§  monosaccharides consist of only one monomer
subunit
•  an example is the sugar glucose (C6H12O6)
§  disaccharides consist of two monosaccharides
•  an example is the sugar sucrose, which is formed by joining
together two monosaccharides, glucose and fructose
Figure 3.14 The structure of glucose
3.4 Carbohydrates
•  Complex carbohydrates are long
polymer chains
§  because they contain many C-H bonds, these
carbohydrates are good for storing energy
•  these bond types are the ones most often broken
by organisms to obtain energy
§  the long chains are called polysaccharides
3.4 Carbohydrates
•  Plants and animals store energy in
polysaccharide chains formed from glucose
§  plants form starch
§  animals form glycogen
•  Some polysaccharides serve structural functions
and are resistant to digestion by enzymes
§  cellulose is found in the cell walls of plants
§  chitin is found in the exoskeletons of many
invertebrates and in the cell walls of fungi
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TABLE 3.1 Carbohydrates and Their Functions
Example
Carbohydrate
Table 3.1
Carbohydrates
and their
functions
Description
Transport Disaccharides
Lactose
Glucose is transported within some organisms as a disaccharide.
In this form, it is less readily metabolized because the normal
glucose-utilizing enzymes of the organism cannot break the
bond linking the two monosaccharide subunits. One type of
disaccharide is called lactose. Many mammals supply energy
to their young in the form of lactose, which is found in milk.
Another transport disaccharide is sucrose. Many plants transport
glucose throughout the plant in the form of sucrose, which is
harvested from sugarcane to make granulated sugar.
O
O
O
Sucrose
CH2OH
O
CH2OH
O
O
CH2OH
Storage Polysaccharides
Starch
o
o
o
o
o
o
o
Glycogen
Organisms store energy in long chains of glucose molecules
called polysaccharides. The chains tend to coil up in water,
making them insoluble and ideal for storage. The storage
polysaccharides found in plants are called starches, which can
be branched or unbranched. Starch is found in potatoes and in
grains, such as corn and wheat.
In animals, glucose is stored as glycogen. Glycogen is similar to
starch in that it consists of long chains of glucose that coil up in
water and are insoluble. But glycogen chains are much longer
and highly branched. Glycogen can be stored in muscles and
the liver.
o
o
o
o
o
o
o
Structural Polysaccharides
Cellulose
o
o
o
o
o
o
o
Chitin
o c
o c
N
N
o
o
o c
o
N
o
o
o
o
o
o
o
o
N
N
N
o c
o c
o c
Cellulose is a structural polysaccharide found in the cell walls of
plants; its glucose subunits are joined in a way that cannot be
broken down readily. Cleavage of the links between the glucose
subunits in cellulose requires an enzyme most organisms lack.
Some animals, such as cows, are able to digest cellulose by
means of bacteria and protists they harbor in their digestive
tract, which provide the necessary enzymes.
Chitin is a type of structural polysaccharide found in the
external skeletons of many invertebrates, including insects and
crustaceans, and in the cell walls of fungi. Chitin is a modifi ed
form of cellulose with a nitrogen group added to the glucose
units. When cross-linked by proteins, it forms a tough, resistant
surface material.
(cow, potatoes, leaves): © Corbis RF; (sugarcane): © PhotoLink/Getty RF; (arm): © Getty RF; (lobster): © Scott Johnson/Animals Animals
3.5 Lipids
•  Lipids – fats and other molecules that are not
soluble in water
§  lipids are nonpolar molecules
§  lipids include fats, phospholipids, and many other
molecules
Figure 3.3(d) Polymers are built from monomers: lipid
3.5 Lipids
• 
Fats are used for long-term energy storage
§ 
fats have two subunits
1.  fatty acids
2.  glycerol
§ 
§ 
fatty acids are chains of C and H atoms
Glycerol contains three carbons and forms the
backbone to which three fatty acids are attached
3.5 Lipids
•  Fatty acids have different chemical
properties due to the number of hydrogens
that are attached to chain of carbons
§  if the maximum number of hydrogens are
attached, then the fat is called saturated
§  if there are fewer than the maximum attached,
then the fat is called unsaturated
Figure 3.17 Saturated and
unsaturated fats
3.5 Lipids
•  Biological membranes involve lipids
§  phospholipids make up the two layers of the membrane
§  cholesterol (a steroid) is embedded within the membrane
•  Lipids also include oils, other steroids, rubber, waxes,
and pigments
Figure 3.16
Lipids are a key
component of
biological
membranes
Chapter 04
Lecture and
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4.1 Cells
•  All cells are small
§  most cells can only be observed under a
microscope
•  Robert Hooke first described cells in 1665
•  Cells are fundamentally important
•  Matthias Schleiden in 1838 recognized that cells
were fundamental to plant composition
•  Theodor Schwann in 1839 reported that all animal
tissues also are comprised of cells
Figure 4.1 The size of cells and their contents
4.1 Cells
• 
Cell theory states the importance of cells to life
1.  All organisms are composed of one or more cells
2.  Cell are the smallest living things
3.  Cells arise only by division of previously existing
cells
4.1 Cells
•  Cells are not all the same size, but most cells
are small because larger cells do not function as
efficiently
§  larger cells are more difficult to control because of the
distance between the command center at the core
and the peripheral regions
§  organisms that are comprised of many, small cells are
at an efficiency advantage over organisms comprised
of few, larger cells
4.1 Cells
•  Smaller cells also have a greater surface
area
§  a cell’s surface provides the interior’s only
opportunity to interact with the environment
§  as cell size increases, the volume grows more
rapidly than surface area
4.1 Cells
•  Most cells are too small to be viewed by the
naked eye, which has limited resolution
•  resolution refers to the minimum distance that two points
can be apart and still be distinguished as two separated
points
•  the limit of resolution of the human eye is about 100
micrometers
•  One way to increase resolution is to increase
magnification, such as by using a microscope
4.1 Cells
•  Different types of microscopes are used to
increase magnification for viewing
§  compound light microscopes use sets of magnifying
lenses to resolve structures that are separated by
more than 200 nanometers
§  electron microscopes have 1000 times the resolving
power of light microscopes and can resolve objects as
close as 0.2 nanometers apart
Figure 4.3 A scale of visibility
4.2 Prokaryotic Cells
•  There are two major types of cells
§  prokaryotic
•  lacks a nucleus and does not have an extensive
system of internal membranes
•  all bacteria and archaea have this cell type
§  eukaryotic
•  has a nucleus and has internal membranebounded compartments
•  all organisms other than bacteria or archaea have
this cell type
4.2 Prokaryotic Cells
•  Prokaryotes are the simplest cellular
organisms
§  have a plasma membrane surrounding a
cytoplasm without interior compartments
•  some bacteria have additional outer layers to the
plasma membrane
–  cell wall comprised of carbohydrates to confer rigid
structure
–  capsule may surround the cell wall
4.2 Prokaryotic Cells
•  The interior of the prokaryotic cell shows simple
organization
§  cytoplasm is uniform with little or no internal support
framework
§  ribosomes (sites for protein synthesis) are scattered
throughout the cytoplasm
§  nucleoid region (an area of the cell where DNA is
localized)
•  not membrane-bounded, so not a true nucleus
4.2 Prokaryotic Cells
•  Other structures sometimes found in prokaryotes
relate to locomotion, feeding, or genetic
exchange
§  a flagellum (plural, flagella) is a threadlike structure
made of protein fibers that extends from the cell
surface
•  may be one or many
•  aids in locomotion and feeding
§  pilus (plural, pili) is a short flagellum
•  aids in attaching to substrates and in exchanging genetic
information between cells
Figure 4.5 Organization of a
prokaryotic cell
4.3 Eukaryotic Cells
•  Eukaryotic cells are larger and more
complex than prokaryotic cells
§  have a plasma membrane encasing the
cytoplasm
•  internal membranes form compartments called
organelles
•  the cytoplasm is semi-fluid and contains a network
of protein fibers that form a scaffold called a
cytoskeleton
4.3 Eukaryotic Cells
•  Many organelles are immediately
conspicuous under the microscope
§  nucleus
•  a membrane-bounded compartment for DNA that
gives eukaryotes (literally, “true-nut”) their name
§  endomembrane system
•  gives rise to the internal membranes found in the
cell
•  each compartment can provide specific conditions
favoring a particular process
4.3 Eukaryotic Cells
•  Not all eukaryotic cells are alike
§  the cells of plants, fungi, and many protists
have a cell wall beyond the plasma
membrane
§  all plants and many protists contain organelles
called chloroplasts
§  plants contain a central vacuole
§  only animal cells contain centrioles
Figure 4.6 Structure of an animal cell
Figure 4.7 Structure of a plant cell
4.4 The Plasma Membrane
•  The plasma membrane is conceptualized
by the fluid mosaic model
§  a sheet of lipids with embedded proteins
•  the lipid layer forms the foundation of the
membrane
•  the fat molecules comprising the lipid layers are
called phospholipids
4.4 The Plasma Membrane
•  A phospholipid has a
polar head and two nonpolar tails
•  The polar region contains
a phosphate chemical
group and is watersoluble
•  The non-polar region is
comprised of fatty acids
and is water-insoluble
Figure. Phospholipid structure
4.4 The Plasma Membrane
•  A lipid bilayer forms spontaneously whenever a
collection of phospholipids is placed in water
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(a)
Polar
(hydrophilic) region
Nonpolar (hydrophobic) region
(b)
Figure. The phospholipid bilayer
4.4 The Plasma Membrane
•  The interior of the lipid bilayer is
completely nonpolar
§  no water-soluble molecules can freely cross
through it
§  cholesterol is also found in the interior
•  it affects the fluid nature of the membrane
•  its accumulation in the walls of blood vessels can
cause plaques
•  plaques lead to cardiovascular disease
4.4 The Plasma Membrane
•  Another major component of the membrane is a
collection of membrane proteins
§  some proteins form channels that span the membrane
•  these are called transmembrane proteins
§  other proteins are integrated into the structure of the
membrane
•  for example, cell surface proteins are attached to the outer
surface of the membrane and act as markers
Figure. Proteins are embedded within
the lipid bilayer
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Phospholipids
Polar areas
of protein
Polar
hydrophilic
heads
Nonpolar
hydrophobic
tails
Polar
hydrophilic
heads
Cholesterol
Nonpolar
areas
of protein
Phospholipid
Protein channel
Cholesterol
Receptor protein
Cell identity
marker
4.5 The Nucleus: The Cell’s Control
Center
•  The nucleus is the command and control center
of the cell
§  it also stores hereditary information
•  The nuclear surface is bounded by a doublemembrane called the nuclear envelope
§  groups of proteins form openings called nuclear
pores that permit proteins and RNA to pass in and
out of the nucleus
4.5 The Nucleus: The Cell’s Control
Center
•  The DNA of eukaryotes is packaged into
segments and associated with protein
§  this complex is called a chromosome
•  the proteins enable the DNA to be wound tightly
and condense during cell division
•  when the cell is not dividing, the chromosomes
exist as threadlike strands called chromatin
–  protein synthesis occurs when the DNA is in the
chromatin form
4.5 The Nucleus: The Cell’s Control
Center
•  The cell builds proteins on structures
called ribosomes
§  ribosomes consist of ribosomal RNA (rRNA)
and several different kinds of proteins
•  Ribosomes are assembled in a region of
the nucleus called the nucleolus
Figure 4.8 The nucleus