Download 1. Describe the steps of the scientific method. 2. Define the terms

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Describe the steps of the scientific method.
Define the terms hypothesis, theory, and law.
What are the common characteristics of all living things?
Describe the levels of organization of life beginning with the smallest living unit and
progressing up in complexity to ecosystems.
Compare and contrast DNA and RNA.
Describe the 3 types of molecular bonds. Which is strongest and which is weakest?
What properties of water make it important for life? Briefly describe each of these
properties.
What properties of Carbon make it important for life? How do those properties
make life possible?
How are biological molecules formed? How are they broken down?
What are carbohydrates and what functions do they perform?
What are proteins and what functions do they perform?
What are lipids and what functions do they perform?
What are nucleic acids and what functions do they perform?
What is a plasma membrane? What is it composed of? What functions does it
serve?
Define diffusion and osmosis.
Describe the processes of passive transport across a plasma membrane.
Describe the processes of active transport across a plasma membrane.
Compare and contrast prokaryotic and eukaryotic cells.
Describe the form and function of the organelles common to most eukaryotic cells.
Describe the endosymbiont hypothesis of organelle formation and provide an
example.
Scientific Principles
 Biology is a scientific discipline
 All scientific inquiry is based on a small set
of assumptions or principles
• Natural causality – events have natural causes
• Uniformity in space and time
• Similar perception – observations of other
humans are reliable
The Scientific Method
 Scientific inquiry is
a rigorous method
for making
observations
 The Scientific
Method for inquiry
follows stepwise…
The Scientific Method
 Scientific experimentation tests the
assertion that a single variable causes a
particular observation
 The experiment must rule out the influence
of other possible variables on the recorded
observations
 Controls are incorporated into
experiments
 Controls keep untested variables constant
 Scientific method is illustrated by
Francesco Redi’s experiment
Limitations of the Scientific Method
 Can never be sure all untested variables
are controlled
 Conclusions based on the experimental
data must remain tentative
 Results of experimentation must be
communicated thoroughly and accurately
to other scientists for repetition
 Repetition by other scientists adds
verification that findings can be used as
the basis for further studies
Scientific Theory
 A scientific theory is a general explanation
for important natural phenomena
• It is extensively and reproducibly tested
• It is more like a principle or natural law
(e.g. atomic, gravitational, and cell theories)
• If compelling evidence arises, a theory may
be modified
 Biosphere
 Ecosystem
• All organisms
• All abiotic factors
 Community
 Population
 Organism
•
•
•
•
•
organ systems
organs
tissues
cells
molecules
ECOSYSTEM LEVEL
Eucalyptus forest
COMMUNITY LEVEL
All organisms in
eucalyptus forest
POPULATION LEVEL
Group of flying foxes
ORGANISM LEVEL
Flying fox
Brain
ORGAN SYSTEM LEVEL
Nervous system
ORGAN LEVEL
Brain
Spinal cord
Nerve
TISSUE LEVEL
Nervous
tissue
CELLULAR LEVEL
Nerve cell
MOLECULAR LEVEL
Molecule of DNA
Figure 1.1
1.3 What Is Life?
 Characteristics of living things
Living things are organized and complex.
Living things grow and reproduce.
Living things respond to stimuli.
Living things acquire and use material and
energy.
• Living things use DNA to store information.
•
•
•
•
Fig. 1-8
 Each level of organization builds on the one
below it
 At each level, new properties emerge
Biological function starts at the chemical level
ATOMS AND MOLECULES
2.1 What Are Atoms?
 Elements:
 substances that cannot be broken down by
ordinary chemical means (ex/ carbon)
 all atoms belong to one of 96 types of
naturally occurring elements
 life requires about 25 of these elements
2.1 What Are Atoms?
 Atoms:
 basic structural unit of matter
 consist of charged particles
 protons (+)
 neutrons (0)
 electrons (-)
 smallest particle of an element
 each element has a unique number of protons
(atomic number)
 Atoms are electrically neutral because they
have and equal number of positive protons
and negative electrons
2
Protons
Nucleus
2
Neutrons
2
Electrons
Helium atom
 Electrons are arranged in shells
 Electrons orbit around atomic nuclei at specific
distances called electron shells
 the outermost shell determines the chemical
properties of an atom
Outermost electron shell (can hold 8 electrons)
Electron
HYDROGEN (H)
Atomic number = 1
First electron shell (can hold 2 electrons)
CARBON (C)
Atomic number = 6
NITROGEN (N)
Atomic number = 7
OXYGEN (O)
Atomic number = 8
Energy Capture and Release
 Life depends on electrons capturing and
releasing energy
• Electron shells correspond to energy levels
• Energy exciting an atom causes an electron
jump from a lower- to higher-energy shell
• Later, the electron falls back into its original
shell, releasing the energy
2.2 How Do Atoms Form Molecules?
 Molecules: two or more atoms of one or
more elements held together by interactions
among their outermost electron shells
• Atoms interact with one another according to
two basic principles:
• An inert atom will not react with other atoms
when its outermost electron shell is
completely full or empty.
• A reactive atom will react with other atoms
when its outermost electron shell is only
partially full.
Atoms Interact
 Reactive atoms gain stability by electron
interactions (chemical reactions)
• Electrons can be lost to empty the outermost
shell
• Electrons can be gained to fill the outermost
shell
• Electrons can be shared with another atom
where both atoms have full outermost shells
• When atoms combine to fill their outer shells
they gain stability
Ionic Bonds
 Formed by passing an electron from one
atom to another
 One partner becomes positive, the other
negative, and they attract one another.
• Na+ + Cl– becomes NaCl (sodium chloride)
 Positively or negatively charged atoms are
called ions.
• + cation
• - anion
Covalent Bonds
 Atoms with partially full outer electron
shells can share electrons
 Two electrons (one from each atom) are
shared in a single covalent bond
 Covalent bonds are found in H2 (single
bond), O2 (double bond), N2 (triple bond)
and H2O
 Covalent bonds are much stronger than
ionic bonds but vary in their stability
Covalent Bonds
 Covalent bonds produce either nonpolar or
polar molecules.
 Nonpolar molecule: atoms in a molecule
equally share electrons that spend equal time
around each atom, producing a nonpolar
covalent bond
Polar Covalent Bonds
 Atoms within a molecule may have
different nuclear charges
 Those atoms with greater positive nuclear
charge pull more strongly on electrons in a
covalent bond
 A molecule with polar bonds may be polar
overall
 H2O is a polar molecule
• The (slightly) positively charged pole is
around each hydrogen
• The (slightly) negatively charged pole is
around the oxygen
Hydrogen Bonds
 Polar molecules like water have partially
charged atoms at their ends
 Hydrogen bonds form when partial
opposite charges in different molecules
attract each other
 The partially positive hydrogens of one
water molecule are attracted to the partially
negative oxygen on another
 Hydrogen bonds are rather weak but can
collectively be quite strong
 Hydrogen bonds
H
(+)
O
(–)
H
(+)
H
(+)
O
(–)
H
(+)
hydrogen
bonds
Fig. 2-7
Why Is Water So Important To Life?
 Water interacts with many other molecules.
• Oxygen released by plants during
photosynthesis comes from water.
• Water is used by animals to digest food.
• Water is produced in chemical reactions that
produce proteins, fats, and sugars.
Why Is Water So Important To Life?
 Many molecules dissolve easily in water.
• Water is an excellent solvent, capable of
dissolving a wide range of substances
because of its positive and negative poles.
• example NaCl dropped into H2O
• The positive end of H2O is attracted to Cl–.
• The negative end of H2O is attracted to Na+.
• These attractions tend to pull apart the
components of the original salt.
Why Is Water So Important To Life?
 Water-insoluble molecules are hydrophobic
• Water molecules repel and drive together
uncharged and nonpolar molecules like fats
and oils
• The “clumping” of nonpolar molecules is called
hydrophobic interaction
Why Is Water So Important To Life?
 Hydrogen bonding between water
molecules causes them to stick together.
• Cohesion: water molecules stick together
• Water molecules can form a chain in
delivering moisture to the top of a tree
• Cohesion of water molecules along a
surface produces surface tension
 Water molecules stick to polar or charged
surfaces in the property called adhesion
• Adhesion helps water climb up the thin tubes
of plants to the leaves (capillary effect)
Why Is Water So Important To Life?
 Water can form ions.
• Water dissociates to become H+ and OH–.
• The relative abundance of ions determine pH
(–)
O
H
water
(H2O)
O
H
(+)
+
H
H
hydroxide ion
(OH–)
hydrogen ion
(H+)
Acid, Basic, and Neutral Solutions
 The relative concentrations of H+ and OHions determine pH.
• Acid solutions have more H+ (protons).
• Alkaline solutions have more OH– (hydroxyl
ions).
• A base is a substance that combines with H+,
reducing their numbers.
• pH measures the relative amount of H+ and
OH– in a solution.
Acid, Basic, and Neutral Solutions
 The degree of acidity of a solution is
measured using the pH scale
• pHs 0-6 are acidic (H+ > OH-)
• pH 7 is neutral (H+ = OH-)
• pH 8-14 is basic (OH- > H+)
Acid, Basic, and Neutral Solutions


A buffer is a compound that accepts or
releases H+ in response to pH change
The bicarbonate buffer found in our
bloodstream prevents pH change
Why Is Water So Important To Life?
 Water stabilizes temperature
• Temperature reflects the speed of molecular
motion
• It requires 1 calorie of energy to raise the
temperature of 1g of water 1oC (specific
heat), so it heats up very slowly
• Because it heats up very slowly water
moderates the effect of temperature change
• Very low or very high temperatures may
damage enzymes or slow down or halt
important chemical reactions
Water Stabilizes Temperature
 Water requires a lot of energy to turn from
liquid into a gas (heat of vaporization)
• Evaporating water uses up heat from its
surroundings, cooling the nearby
environment (ex/ sweating)
 Water requires a lot of energy to be
withdrawn in order to freeze (heat of
fusion)
• Therefore the nearby environment will be
warmer than it otherwise would be
Water Forms an Unusual Solid: Ice



Most substances become more dense
when they solidify from a liquid
Water molecules spread slightly during
crystallization (freezing)
Because of this ice is less dense than
liquid water
Water Forms an Unusual Solid: Ice



Because of its lower density ice floats in
liquid water
Ponds and lakes freeze from the top down
Lower water is protected by the surface
layer of ice.
• Large bodies of water rarely freeze completely
• Life can survive in cold water underneath ice.
• Spring thaw pushes nutrient-rich bottom water
to surface
Why Is Water So Important To Life?
 Like no other common substance on earth,
water naturally exists in all three physical
states: solid, liquid, and gas
Organic vs. Inorganic in Chemistry
 Organic refers to molecules containing a
carbon skeleton
 Inorganic refers to carbon dioxide and all
molecules without carbon
2.4 Why Is Carbon So Important To Life?
 Carbon can combine with other atoms in
many ways to form a huge number of
different molecules.
 Carbon has four electrons in its outermost
shell, leaving room for four more electrons
from other atoms (4 covalent bonds).
 Carbon atoms are versatile and can form
single, double, or triple bonds and rings.
Why Is Carbon So Important To Life?
 Arrangement of atoms determines
molecular shape.
 Shape determines function of molecules
Structural
formula
Ball-and-stick
model
Space-filling
model
Methane
The 4 single bonds of carbon point to the corners of a tetrahedron.
Why Is Carbon So Important To Life?
 The great variety of substances found in
nature is constructed from a limited pool of
atoms.
 Organic molecules have a carbon skeleton
and some hydrogen atoms.
 Much of the diversity of organic molecules is
due to the presence of functional groups.
Functional (R) Groups
 Functional groups in organic molecules
confer chemical reactivity and other
characteristics
• groups of atoms that participate in chemical
reactions
• determine the chemical properties of
molecules
• Examples: acidity, solubility
What affects solubility in water?
 Molecules with +/- charge are usually
hydrophilic or “water-loving”
 Molecules with no charge and non-polar are
usually hydrophobic and not soluble in water
2.5 How Are Biological Molecules Joined
Together Or Broken Apart?
 Biomolecules are polymers (chains) of
subunits called monomers
 A huge number of different polymers can be
made from a small number of monomers
 Biomolecules Are Joined Through
Dehydration and Broken by Hydrolysis
Organic Molecule Synthesis
 Monomers are joined together through
dehydration synthesis
 An H and an OH are removed, resulting in
the loss of a water molecule (H2O)
Organic Molecule Synthesis
 Polymers are broken apart through
hydrolysis (“water cutting”)
 Water is broken into H and OH and used to
break the bond between monomers
Organic Molecule Synthesis
 All biological molecules fall into one of four
broad categories:
•
•
•
•
Carbohydrates
Lipids
Proteins
Nucleic Acids
2.6 What Are Carbohydrates?



Composition:
C, H, and O in the ratio of 1:2:1
Types by size:
•
•
•
Simple or single sugars are
monosaccharides
Two linked monosaccharides are
disaccharides
Long chains of monosaccharides are
polysaccharides
Monosaccharides

Basic monosaccharide structure
•
•
•


Backbone of 3-7 carbon atoms
Many –OH and –H functional groups
Usually found in a ring form in cells
Simple sugars provide important energy
sources for organisms.
Most small carbohydrates are watersoluble due to the polar OH functional
groups
Disaccharides
 Disaccharides are two-part sugars
• Sucrose (table sugar) = glucose + fructose
• Lactose (milk sugar) = glucose + galactose
• Maltose (malt sugar)= glucose + glucose
glucose
fructose
CH2OH
O
H H
HOCH2
CH2OH
O
O
H
H
+
HO
OH
H
H
OH
OH
sucrose
HO
H
OH
HO
H
dehydration
CH2OH synthesis
H H
HO
HOCH2
H
OH
H
H
OH
O
H
OH
H
O
H
O
H
HO
H
CH2OH
Polysaccharides
 Monosaccharides are linked together to
form chains (polysaccharides)
 Polysaccharides are used for energy
storage and structural components
Polysaccharides
 Storage polysaccharides
• Starch (polymer of glucose)
• Formed in roots and seeds as a form of
glucose storage
• Glycogen (polymer of glucose)
• Found in liver and muscles
Polysaccharides
 Structural polysaccharides
• Cellulose (polymer of glucose)
• Found in the cell walls of plants
• Indigestible for most animals due to
orientation of bonds between glucoses
• Chitin (polymer of modified glucose units)
• Found in the outer coverings of insects,
crabs, and spiders
• Found in the cell walls of many fungi
2.7 What Are Lipids?
 Molecular characteristics of lipids
• Lipids are molecules with long regions
composed almost entirely of carbon and
hydrogen.
• The nonpolar regions of carbon and hydrogen
bonds make lipids hydrophobic and insoluble
in water.
What Are Lipids?
 Lipids are diverse in structure and serve in
a variety of functions
•
•
•
•
Energy storage
Waterproofing
Membranes in cells
Hormones
What Are Lipids?
 Lipid classification
• Group 1: Oils, fats, and waxes
• Group 2: Phospholipids
• Group 3: Steroids
Lipids
 Group 1: Oils, fats, and waxes
• Formed by dehydration synthesis
• 3 fatty acids + glycerol  triglyceride
• Contain only carbon, hydrogen, and oxygen
• Contain one or more fatty acid subunits in long
chains of C and H with a carboxyl group
(–COOH)
• Ring structure is rare
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Fats and oils form by dehydration synthesis
from three fatty acid subunits and one
molecule of glycerol.
etc.
CH2
CH2
CH2
H
H C OH
O
CH
HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH
H C OH
O
HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
H C OH
H
glycerol
+
O
HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
fatty acids
Fig. 2-16
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Fats and oils formed by dehydration synthesis
are called triglycerides.
• Triglycerides are used for long-term energy
storage in both plants and animals.
etc.
CH2
CH2
CH2
H
O
CH
H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH
+
O
H
O
O
H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
+
H
O
H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.
H
+
H
triglyceride
H
H
O
H
3 water
molecules
Fig. 2-16
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Characteristics of fats
• Solidity is due to the prevalence of single or
double carbon bonds
• Fats are solid at room temperature.
• Fats have all carbons joined by single
covalent bonds.
• The remaining bond positions on the
carbons are occupied by hydrogen atoms.
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Fatty acids of fats are said to be saturated and
are straight molecules that can be stacked.
(a) Beef fat (saturated)
Fig. 2-18a
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Characteristics of oils
• Oils are liquid at room temperature.
• Some of the carbons in fatty acids have
double covalent bonds.
• There are fewer attached hydrogen atoms,
and the fatty acid is said to be unsaturated.
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Unsaturated fatty acids have bends and kinks
in fatty acid chains and can’t be efficiently
stacked.
(b) Peanut oil (unsaturated)
Fig. 2-18b
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Characteristics of waxes
• Waxes are solid at room temperature.
• Waxes are highly saturated.
• Waxes are not a food source.
• Waxes are composed of long hydrocarbon
chains and are strongly hydrophobic
Lipids
 Group 1: Oils, fats, and waxes (continued)
• Waxes form waterproof coatings
• Leaves and stems of plants
• Fur in mammals
• Insect exoskeletons
• Used to build honeycomb structures
Lipids
 Group 2: Phospholipids
• Phospholipids: form dual layered plasma
membranes around all cells
• Construction
• like oils except one fatty acid is replaced by a
phosphate group attached to glycerol.
• 2 fatty acids + glycerol + a short polar
functional group
• water-soluble heads and water-insoluble tails.
Lipids
 Group 2: Phospholipids (continued)
• The phosphate end of the molecule is water
soluble; the fatty acid end of the molecule is
water insoluble.
CH3
O–
H3C - N+- CH2 - CH2 -O-P- O -CH2 O
CH3
O HC-O-C- CH2 -CH2 - CH2 - CH2 - CH2 - CH2 - CH2 -CH
O
CH
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
H2C-O-C- CH2 -CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 -CH3
polar head
(hydrophilic)
glycerol
fatty acid tails
(hydrophobic)
Fig. 2-19
Lipids
 Group 3: Steroids
• Steroids contain four fused carbon rings.
• Various functional groups protrude from the
basic steroid “skeleton”.
• Examples of steroids
• Cholesterol
• Found in membranes of animal cells
• Male and female sex hormones
2.8 What Are Proteins?
 Functions of proteins
• Proteins act as enzymes to catalyze (speed)
many biochemical reactions.
• They provide structure (ex/ elastin)
• They can act as energy stores.
• They are involved in carrying oxygen around
the body (hemoglobin).
• They are involved in muscle movement.
 Proteins are formed from chains of amino
acids.
 All amino acids have the same basic
structure:
•
•
•
•
A central carbon
An attached amino group
An attached carboxyl group
An attached variable group (R variable
group)
group
• Some are hydrophobic
• Some are hydrophilic
amino
group
hydrogen
carboxylic
acid group
 Amino acid monomers join to form chains by
dehydration synthesis.
• Proteins are formed by dehydration reactions
between individual amino acids.
• The –NH2 group of one amino acid is joined to
the –COOH group of another, with the release
of H2O and the formation of a new peptide (two
or more amino acids).
• The resultant covalent bond is a peptide bond
 Long chains of amino acids are known as
polypeptides or just proteins
 The sequence of amino acids in a protein
dictates its three dimensional structure
 This structure gives proteins their functions.
• Long chains of amino acids fold into threedimensional shapes in cells, which allows the
protein to perform its specific functions.
• When a protein is denatured, its shape has
been disrupted and it may not be able to
perform its function.
Four Levels of Structure
 Proteins exhibit up to four levels of structure
• Primary structure is the sequence of amino
acids linked together in a protein
• Secondary structures are helices and
pleated sheets
• Tertiary structure refers to complex foldings
of the protein chain held together by disulfide
bridges, hydrophobic/hydrophilic interactions,
and other bonds
• Quaternary structure is found where multiple
protein chains are linked together
Three Dimensional Structures
 The type, position, and number of amino
acids determine the structure and function of
a protein
• Precise positioning of amino acid R groups
leads to bonds that determine secondary and
tertiary structure
• Disruption of these bonds leads to denatured
proteins and loss of function
Nucleic Acids
 Nucleotides are the monomers of nucleic
acid chains
 All nucleotides are made of three parts
• Phosphate group
• Five-carbon sugar
• Nitrogen-containing base
Molecules of Heredity
 Two types of polymers of nucleic acids
• DNA (deoxyribonucleic acid) found in
chromosomes
• Carries genetic information needed for
protein construction
• RNA (ribonucleic acid)
• Copies of DNA used directly in protein
construction
Molecules of Heredity
 Two types of nucleotides
• Ribonucleotides (A, G, C, and U) found in
RNA
• Deoxyribonucleotides (A, G, C, and T) found
in DNA
Molecules of Heredity
 Each DNA molecule consists
of two chains of nucleotides
that form a double helix
Other Nucleotides
 Nucleotides act as intracellular messengers
 Nucleotides act as energy carriers
• Adenosine triphosphate (ATP) carries
energy stored in bonds between phosphate
groups
 Nucleotides as enzyme assistants
3.1 What Does The Plasma Membrane Do?
 The cell plasma membrane separates the
cell contents from the external environment.
 The membrane acts as a gatekeeper,
regulating the passage of molecules into
and out of the cell.
Plasma Membrane
 Functions of the plasma membrane
• Isolates the cell’s contents from
environment
• Regulates exchange of essential
substances
• Communicates with other cells
• Creates attachments within and between
other cells
• Regulates biochemical reactions
Structure Of The Plasma Membrane
 Phospholipids are the basis of membrane
structure
• Polar, hydrophilic head
• Two non-polar, hydrophobic tails
CH3
CH2
CH2
CH2
CH2
CH2
CH2
–
CH3
O
+
H3C N CH2 CH2 O P O CH2 O
CH3
CH2
CH
O HC O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH
O
H2C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
tails
(hydrophobic)
head
(hydrophilic)
Fig. 3-2
The Phospholipid Bilayer
 Hydrophobic and hydrophilic interactions
drive phospholipids into bilayers
•
•
•
•
Double row of phospholipids
Polar heads face outward and inward
Non-polar tails mingle within the membrane
Cholesterol in animal membranes keeps
them flexible
The Phospholipid Bilayer
 Individual phospholipid molecules are not
bonded to one another
 Some of the phospholipids have
unsaturated fatty acids, whose double
bonds introduce “kinks” into their “tails”
 The above features make the membrane
fluid
Plasma Membrane as Gatekeeper
 The phospholipid bilayer blocks the passage of
most molecules.
 The embedded proteins selectively transport,
respond to, and recognize molecules.
 There are three types of membrane proteins—
transport proteins, receptor proteins, and
recognition proteins.
Membrane Proteins Form a Mosaic

Proteins are embedded in the
phospholipid bilayer
•
•
•
Some proteins can float and drift
Other proteins are anchored by protein
filaments in the cytoplasm
Many proteins have attached
carbohydrates (glycoproteins)
Movement of Molecules in Fluids
 Definitions relevant to substance
movement
• A fluid is a substance that can move or
change shape in response to external forces
• A solute is a substance that can be
dissolved (dispersed as ions or molecules)
in a solvent
• A solvent is a fluid capable of dissolving a
solute
Movement of Molecules in Fluids
 Definitions relevant to substance
movement (continued)
• The concentration of molecules is the
number of them in a given volume unit
• A gradient is a physical difference in
temperature, pressure, charge, or
concentration in two adjacent regions
Movement of Molecules in Fluids
 Why molecules move from one place to
another
• Substances move in response to a
concentration gradient
• Molecules move from high to low
concentration (diffusion) until
dynamic equilibrium is reached
Movement of Molecules in Fluids
 The greater the concentration gradient, the
faster the rate of diffusion
 Diffusion cannot move molecules rapidly
over long distances
3.6 How Do Diffusion And Osmosis Affect
Transport Across The Plasma Membrane?
 Concentration gradients of ions and
molecules exist across the plasma
membranes of all cells
 There are two types of movement across
the plasma membrane
• Passive transport
• Energy-requiring transport
Movement Across Membranes
 Passive transport
• Substances move down their concentration
gradients across a membrane
• No energy is expended
• Membrane proteins and phospholipids may
limit which molecules can cross, but not the
direction of movement
Movement Across Membranes
 Energy-requiring transport
• Substances are driven against their
concentration gradients
• Energy is expended
Passive Transport
 Plasma membranes are selectively
permeable
• Different molecules move across at different
locations and rates
• A concentration gradient drives all three
types of passive transport: simple diffusion,
facilitated diffusion, and osmosis
Passive Transport
 Simple diffusion
• Lipid soluble molecules (e.g. vitamins A and E,
gases) and very small molecules diffuse directly
across the phospsholipid bilayer
Passive Transport
 Facilitated diffusion
• Water soluble molecules like ions, amino acids, and
sugars diffuse with the aid of channel and carrier
transport proteins
Passive Transport
 Osmosis – the special case of water
diffusion
• Water diffuses from high concentration (high
purity) to low concentration (low purity)
across a membrane
• Dissolved substances reduce the
concentration of free water molecules (and
hence the purity of water) in a solution
• The flow of water across a membrane
depends on the concentration of water in the
internal or external solutions
Passive Transport
 Comparison terms for solutions on either
side of a membrane
• Isotonic solutions have equal concentrations
of water and equal concentrations of dissolved
substances
• No net water movement occurs across the
membrane
Passive Transport
• A hypertonic solution is one with lower water
concentration or higher dissolved particle
concentration
• Water moves across a membrane towards
the hypertonic solution
• A hypotonic solution is one with higher water
concentration or lower dissolved particle
concentration
• Water moves across a membrane away
from the hypotonic solution
3.7 How Do Molecules Move Against A
Concentration Gradient?
 Energy-requiring transport processes
• During active transport, the cell uses energy to
move substances against a concentration
gradient.
• Membrane proteins regulate active transport.
Active Transport
 Active-transport membrane proteins move
molecules across using ATP
• Proteins span the entire membrane
• Often have a molecule binding site and an
ATP binding site
• Often referred to as pumps
Endocytosis
 Cells import large particles or substances
via endocytosis
 Plasma membrane pinches off to form a
vesicle in endocytosis
• Types of endocytosis
• Pinocytosis
• Receptor-mediated endocytosis
• Phagocytosis
Endocytosis
 Types of endocytosis
• Pinocytosis (“cell drinking”) brings in droplet of
extracellular fluid
Endocytosis
 Types of endocytosis
• Receptor-mediated endocytosis moves specific
molecules into the cell
Endocytosis
 Types of endocytosis
• Phagocytosis (“cell eating”) moves large particles or
whole organisms into the cell
Exocytosis
 Exocytosis
• Vesicles join the membrane, dumping out contents in
exocytosis
What Is the Cell Theory?
 Tenets of Modern Cell Theory
• Every living organism is made of one or more
cells
• The smallest organisms are made of single
cells while multicellular organisms are made
of many cells
• All cells arise from pre-existing cells
4.1 What Features Are Shared By All Cells?




Cells are the smallest unit of life.
Cells are enclosed by a plasma membrane.
Cells use DNA as a hereditary blueprint.
Cells contain cytoplasm, which is all the
material inside the plasma membrane and
outside the DNA-containing region.
 Cells obtain energy and nutrients from their
environment.
4.1 What Features Are Shared By All Cells?
 Cell function limits cell size.
• Most cells are small, ranging from 1 to 100
micrometers in diameter
• Cells need to exchange nutrients and wastes
with the environment
• No part of the cell can be far away from the
external environment
Cell Function Limits Cell Size
• Diffusion of molecules across cell membranes
limits the diameter of cells.
• As cells get bigger, their nutrient and waste
elimination needs grow faster than the
membrane area to accommodate them.
tallest trees
10 m
1m
10 cm
1 cm
adult human
visible with unaided
human eye
 Relative sizes
Diameter
100 m
chicken egg
frog embryo
100 m
10 m
1 m
Units of measurement:
1 meter (m) = 39.37 inches
1 centimeter (cm) = 1/100 m
1 millimeter (mm) = 1/1,000 m
1 micrometer (m) = 1/1,000,000 m
1 nanometer (nm) = 1/1,000,000,000 m
10 nm
1 nm
0.1 nm
visible with
special electron
microscopes
100 nm
most eukaryotic cells
visible with conventional
electron microscope
visible with
light microscope
1 mm
mitochondrion
most bacteria
virus
proteins
diameter of DNA double helix
atoms
Fig. 4-1
All Cells Share Common Features
 A plasma membrane encloses all cells and
regulates material flow
 Cytoplasm is the fluid interior where a cell’s
metabolic reactions occur
• Contains organelles
• Fluid portion (cytosol) contains water, salts,
and organic molecules
All Cells Share Common Features
 All cells use DNA (deoxyribonucleic acid) as
a hereditary blueprint
 All cells use RNA (ribonucleic acid) to copy
DNA to make proteins
All Cells Share Common Features
 All cells obtain energy and nutrients from the
environment
 All cells use common building blocks to
build the molecules of life
Some Cell Types Have Cell Walls

Stiff coatings on outer surfaces of
bacteria, plants, fungi, and some protists
are cell walls
•
•
Cells walls support and protect fragile cells
and are usually porous
Cell walls are composed of polysaccharides
like cellulose or chitin
4.2 How Do Prokaryotic And Eukaryotic
Cells Differ?
 There are two kinds of cells.
• Prokaryotic cells
• Are found only in two groups of singlecelled organisms—the bacteria and
archaea
• Eukaryotic cells
• Are structurally more complex cells
• Possess a membrane-enclosed nucleus
• Probably arose from prokaryotic cells
Prokaryotic Cells




No nuclear membrane or membranebound organelles present
Some have internal membranes used to
capture light
Cytoplasm contains ribosomes used for
protein synthesis
Cytoplasm may contain food granules
Prokaryotic Cells
 Much smaller than eukaryotic cells (< 5 µm
long)
 Have a simple internal structure
 Surrounded by a stiff cell wall, which
provides shape and protection
 Can take the shape of rods, spheres, or
helices
Prokaryotic Cells



Some propelled by flagella
Infectious bacteria may have
polysaccharide adhesive capsules and
slime layers on their surfaces
Pili and fimbriae are protein projections
in some bacteria that further enhance
adhesion
There Are Two Basic Cell Types
 Eukaryotic
• True nucleus
• Includes Protist, Fungi, Plant, and
Animal cells
4.3 What Are The Main Features Of
Eukaryotic Cells?
 Eukaryotic cells are > 10 µm long
 The cytoskeleton provides shape and
organization
 A variety of membrane-enclosed organelles
perform specific functions
Major Features
 Nucleus: contains DNA
 Mitochondria: produce energy
 Endoplasmic reticulum: synthesizes
membrane components and lipids
 Golgi apparatus: molecule sorting center
 Lysosomes: digest cellular membranes or
defective organelles
 Microtubules: make up the cytoskeleton
4.4 What Role Does The Nucleus Play?
 The nucleus is the largest organelle
in the cell.
• It is bounded by a nuclear envelope.
• It contains granular-looking chromatin.
• It contains the nucleolus.
The Nucleus
 The nuclear envelope separates
chromosomes from cytoplasm
• Envelope is a double membrane with
nuclear pores for transport
• Some smaller materials can move through
the pores, while others, such as DNA, are
excluded.
• Outer membrane is studded with ribosomes
The Nucleus
 The nucleus
nuclear
envelope
nucleolus
nuclear
pores
nucleus
nuclear
pores
chromatin
(a) Structure of the nucleus
(b) Yeast cell
Fig. 4-5
The Nucleus
 The nucleus contains DNA in various
configurations
• Compacted chromosomes (during cell
division)
• Diffuse chromatin (as DNA directs reactions
through an RNA intermediate by coding for
proteins)
The Nucleus
 Darker area within the nucleus called the
nucleolus
• Functions as the site of ribosome synthesis
• Ribosomes synthesize proteins
• Ribosomes are composed of RNA and
proteins
4.5 What Roles Do Membranes Play In
Eukaryotic Cells?
 The plasma membrane isolates the cell, and
alternately, helps it interact with its
environment.
• The phospholipid bilayer contains globular
proteins that regulate the transport of
molecules into and out of the cell.
• Plant, fungi, and some protist cells also have a
cell wall outside the plasma membrane, which
acts as a protective coating.
System of Membranes
 Vesicles are membranous sacs that
transport substances among the separate
regions of the membrane system
System of Membranes
 The endoplasmic reticulum (ER) forms a
series of enclosed, interconnected channels
within cell
• There are two forms of ER:
• Rough endoplasmic reticulum: is studded
with ribosomes
• Smooth endoplasmic reticulum: has no
ribosomes
System of Membranes
 Smooth ER has no ribosomes
• Contains enzymes that detoxify drugs (in liver
cells)
• Synthesizes phospholipids and cholesterol.
• Together with rough ER are the sites of new
membrane synthesis for the cell.
System of Membranes
 Rough ER is studded with ribosomes on
outside
• Produces proteins and phospholipids destined
for other membranes or for secretion (export)
• Together with rough ER are the sites of new
membrane synthesis for the cell.
System of Membranes
 The Golgi Apparatus is a set of stacked
flattened sacs
• Receive proteins from ER (via transport
vesicles) and sorts them by destination
• Modify some molecules (e.g. proteins to
glycoproteins)
• Package material into vesicles for transport
System of Membranes

Three fates of substances made in the
membrane system:
1. Secreted proteins made in RER, travel
through Golgi, then are exported through
plasma membrane
2. Digestive proteins made in RER, travel
through Golgi, and are packaged as
lysosomes for use in cell
3. Membrane proteins and lipids made in ER,
travel through Golgi, and replenish or
enlarge organelle and plasma membranes
Vacuoles
 Fluid-filled sacs with a single membrane
 Functions of vacuoles
• Contractile vacuoles in freshwater
organisms used to collect and pump water
out
• Many plant cells have a large central
vacuole.
Mitochondria Extract Food Energy
 Function as the “powerhouses of the cell”
• Mitochondria extract energy from food
molecules
• Extracted energy is stored in high-energy
bonds of ATP
• Energy extraction process involves anaerobic
and aerobic reactions
Major Features
 Animal and plant cells differ with regards to
cell walls, chloroplasts, plastids, central
vacuoles, and centrioles
Chloroplasts
 Chloroplasts are specialized organelles to
convert solar energy into sugars
 The thylakoid membranes in chloroplasts
contain chlorophyll and other pigments
that capture sunlight and make sugar,
CO2, and water (photosynthesis)
Plants Use Plastids for Storage


Plastids found only in plants and
photosynthetic protists
Surrounded by a double membrane

Functions
•
•
Storage for photosynthetic products like
starch
Storage of pigment molecules giving color
to ripe fruit
Cytoskeleton
 The cytoskeleton provides shape, support,
and movement.
• All organelles in the cell do not float about the
cytoplasm, but instead, are attached to a
network of protein fibers called the
cytoskeleton.
Cilia and Flagella
 Functions
• Cilia or flagella may be used to move cell
about
• Cilia may be used to create currents of moving
fluid in their environment