1. Describe the steps of the scientific method.2. Define the terms hypothesis, theory, and law.3. What are the common characteristics of all living things?4. Describe the levels of organization of life beginning with the smallest living unit and
progressing up in complexity to ecosystems.5. Compare and contrast DNA and RNA.6. Describe the 3 types of molecular bonds. Which is strongest and which is weakest?7. What properties of water make it important for life? Briefly describe each of these
properties.8. What properties of Carbon make it important for life? How do those properties
make life possible?9. How are biological molecules formed? How are they broken down?10. What are carbohydrates and what functions do they perform?11. What are proteins and what functions do they perform?12. What are lipids and what functions do they perform?13. What are nucleic acids and what functions do they perform?14. What is a plasma membrane? What is it composed of? What functions does it
serve?15. Define diffusion and osmosis.16. Describe the processes of passive transport across a plasma membrane.17. Describe the processes of active transport across a plasma membrane.18. Compare and contrast prokaryotic and eukaryotic cells.19. Describe the form and function of the organelles common to most eukaryotic cells.20. 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
ORGAN SYSTEM LEVEL Nervous system
ORGAN LEVEL Brain
Brain Spinal cord
Nerve
TISSUE LEVEL Nervous
tissue
CELLULAR LEVEL Nerve cell
MOLECULAR LEVEL Molecule of DNA Figure 1.1
Fig. 1-8
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.
Each level of organization builds on the one below it
At each level, new properties emerge
ATOMS AND MOLECULES
Biological function starts at the chemical level
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
Helium atom
2
2
2
Protons
Neutrons
Electrons
Nucleus
HYDROGEN (H)Atomic number = 1
CARBON (C)Atomic number = 6
NITROGEN (N)Atomic number = 7
OXYGEN (O)Atomic number = 8
Electron
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
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
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
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
Ionic Bonds
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 H2 O
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
H2 O 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
Fig. 2-7
hydrogen bonds
O (–)
H (+)
H (+)
O (–)
H (+)
H (+)
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.
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 H2 O• The positive end of H2 O is attracted to Cl–. • The negative end of H2 O 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?
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
hydrogen ion (H+)
hydroxide ion (OH–)
water(H2 O)
+(+)(–)
O
HH
O
H
H
The relative concentrations of H+ and OH-
ions 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
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
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
Why Is Water So Important To Life?
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
Like no other common substance on earth, water naturally exists in all three physical states: solid, liquid, and gas
Why Is Water So Important To Life?
Organic refers to molecules containing a carbon skeleton
Inorganic refers to carbon dioxide and all molecules without carbon
Organic vs. Inorganic in Chemistry
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.
Structural formula
Ball-and-stick model
Space-filling model
Methane
The 4 single bonds of carbon point to the corners of a tetrahedron.
Arrangement of atoms determines molecular shape.
Shape determines function of molecules
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.
Why Is Carbon So Important To Life?
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
Functional (R) Groups
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 (H2 O)
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 water- soluble 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 sucrose
dehydration synthesis
OHO
HOCH2
OH
HO
CH2 OH
H H
OH
H OH
H
H
O HO
OCH2 OH
H H
OH
H OH
H
H
H
H
HOCH2 OHH
HOCH2 H
H
H
HOCH2 OH
O
OH
O
OHH
OH
+
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
Lipid classification• Group 1: Oils, fats, and waxes• Group 2: Phospholipids• Group 3: Steroids
What Are 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.
Fig. 2-16
glycerol fatty acids
CH2CHO CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.O
CH2CHO CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.O
CH2CHO CH2 CH2 CH2 CH2 CH2 CH2 CHO
C OHHH
C OHH
C OHHH
CH2CH
CH2
CH2
etc.
+
Lipids
triglyceride 3 water molecules
OHH
OHH
OHH
+
+
CH2C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc.O
CH2C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2
CH2
CH2 etc.O
CH2C CH2 CH2 CH2 CH2 CH2 CH2 CHO
CHH
CH
C
O
O
OHH
CH2CH
CH2
CH2
etc.
+
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.
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
Beef fat (saturated)(a)
Group 1: Oils, fats, and waxes (continued)• Fatty acids of fats are said to be saturated and
are straight molecules that can be stacked.
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
Peanut oil (unsaturated)(b)
Group 1: Oils, fats, and waxes (continued)• Unsaturated fatty acids have bends and kinks
in fatty acid chains and can’t be efficiently stacked.
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
polar head glycerol
(hydrophilic) (hydrophobic)
fatty acid tails
CH3 O–
OO
CH3
CH CH2CH2
CH2CH2
CH2CH2
CH2CH3
H3 C N+- CH2 - CH2-O-P-O-CH2 O
HC-O-C-CH2-CH2- CH2 -CH2- CH2 - CH2-CH2 -CH
H2 C-O-C-CH2-CH2 - CH2 -CH2 - CH2 - CH2-CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH3
-
Group 2: Phospholipids (continued)• The phosphate end of the molecule is water
soluble; the fatty acid end of the molecule is water insoluble.
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
Lipids
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 group)
• Some are hydrophobic• Some are hydrophilicamino
group
hydrogen
variable group
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 H2 O 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 three-
dimensional 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
Fig. 3-2head
(hydrophilic)
tails (hydrophobic)
H2 C OOC CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
CH
CH2 CH2 CH2 CH2 CH2 CH2 CH2 CHHC O C
OH3 C N CH2 CH2 O P O CH2
CH3
CH3+
–
O
O
Phospholipids are the basis of membrane structure• Polar, hydrophilic head• Two non-polar, hydrophobic tails
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.
Fig. 4-1
frog embryo
most eukaryotic cells
mitochondrion
most bacteria
virus
proteinsdiameter of DNA double helix
chicken egg
atoms1 micrometer (m) = 1/1,000,000 m1 nanometer (nm) = 1/1,000,000,000 m
1 centimeter (cm) = 1/100 m1 millimeter (mm) = 1/1,000 m
Units of measurement:1 meter (m) = 39.37 inches
adult human
tallest treesDiameter
visi
ble
with
una
ided
hum
an e
ye
visi
ble
with
lig
ht m
icro
scop
e
visi
ble
with
con
vent
iona
lel
ectr
on m
icro
scop
e
visi
ble
with
spec
ial e
lect
ron
mic
rosc
opes
100 m
10 m
1 m
10 cm
1 cm
1 mm
100 m
10 m
1 m
100 nm
10 nm
1 nm
0.1 nm
Relative sizes
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 single- celled 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 membrane- bound 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
nucleus
nuclearpores
(b) Yeast cell
nuclearenvelope
nuclearpores
nucleolus
chromatin
(a) Structure of the nucleus
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