AP Biology Unit 1 Chapters 1-7 Introduction, Biochemistry and Cells.
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Transcript of AP Biology Unit 1 Chapters 1-7 Introduction, Biochemistry and Cells.
AP BiologyUnit 1
Chapters 1-7
Introduction, Biochemistry and Cells
Chapter One: Overview: Inquiring About Life
• An organism’s adaptations to its environment are the result of evolution
– For example, the ghost plant is adapted to conserving water; this helps it to survive in the crevices of rock walls
• Evolution is the process of change that has transformed life on Earth
© 2011 Pearson Education, Inc.
Figure 1.1
Figure 1.3
Order
Evolutionary adaptation
Response tothe environment
Reproduction
Growth anddevelopment
Energy processing
Regulation
Theme: New Properties Emerge at Each Level in the Biological Hierarchy
• Life can be studied at different levels, from molecules to the entire living planet
• The study of life can be divided into different levels of biological organization
© 2011 Pearson Education, Inc.
The biosphere
EcosystemsTissues
Organs andorgan systems
Communities
Populations
Organisms
OrganellesCells
Atoms
Molecules
Figure 1.4
Theme: Organisms Interact with Other Organisms and the Physical Environment
• Every organism interacts with its environment, including nonliving factors and other organisms
• Both organisms and their environments are affected by the interactions between them
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Animals eatleaves and fruitfrom the tree.
Leaves take incarbon dioxidefrom the airand releaseoxygen.
Sunlight
CO2
O2
Cyclingof
chemicalnutrients
Leaves fall tothe ground andare decomposedby organismsthat returnminerals to thesoil.
Water andminerals inthe soil aretaken up bythe treethroughits roots.
Leaves absorblight energy fromthe sun.
Figure 1.5
Theme: Life Requires Energy Transfer and Transformation
• A fundamental characteristic of living organisms is their use of energy to carry out life’s activities
• Work, including moving, growing, and reproducing, requires a source of energy
• Living organisms transform energy from one form to another– For example, light energy is converted to chemical
energy, then kinetic energy• Energy flows through an ecosystem, usually entering as
light and exiting as heat© 2011 Pearson Education, Inc.
Figure 1.6
Heat
Producers absorb lightenergy and transform it intochemical energy.
Chemicalenergy
Chemical energy infood is transferredfrom plants toconsumers.
(b) Using energy to do work(a) Energy flow from sunlight toproducers to consumers
Sunlight
An animal’s musclecells convertchemical energyfrom food to kineticenergy, the energyof motion.
When energy is usedto do work, someenergy is converted tothermal energy, whichis lost as heat.
A plant’s cells usechemical energy to dowork such as growingnew leaves.
Theme: Structure and Function Are Correlated at All Levels of Biological Organization
• Structure and function of living organisms are closely related
– For example, a leaf is thin and flat, maximizing the capture of light by chloroplasts
– For example, the structure of a bird’s wing is adapted to flight
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Figure 1.7
(a) Wings(b) Wing bones
Theme: The Cell Is an Organism’s Basic Unit of Structure and Function
• The cell is the lowest level of organization that can perform all activities required for life
• All cells– Are enclosed by a membrane– Use DNA as their genetic information
© 2011 Pearson Education, Inc.
Eukaryotic cellProkaryotic cell
Cytoplasm
DNA(no nucleus)
Membrane
Nucleus(membrane-enclosed)
Membrane
Membrane-enclosed organelles
DNA (throughoutnucleus) 1 m
Figure 1.8
Theme: The Continuity of Life Is Based on Heritable Information in the Form of DNA
• Chromosomes contain most of a cell’s genetic material in the form of DNA (deoxyribonucleic acid)
• DNA is the substance of genes• Genes are the units of inheritance that transmit
information from parents to offspring• The ability of cells to divide is the basis of all
reproduction, growth, and repair of multicellular organisms
© 2011 Pearson Education, Inc.
Figure 1.9
25 m
Nucleus
DNA
Cell
Nucleotide
(b) Single strand of DNA
A
C
T
T
A
A
T
C
C
G
T
A
G
T
(a) DNA double helix
A
Figure 1.11
Theme: Feedback Mechanisms Regulate Biological Systems
• Feedback mechanisms allow biological processes to self-regulate
• Negative feedback means that as more of a product accumulates, the process that creates it slows and less of the product is produced
• Positive feedback means that as more of a product accumulates, the process that creates it speeds up and more of the product is produced
© 2011 Pearson Education, Inc.
Animation: Negative Feedback
Animation: Positive Feedback
Negativefeedback
A
B
D
C
Enzyme 2
Enzyme 3
D
DDExcess Dblocks a step.
(a) Negative feedback
Enzyme 1
Figure 1.13a
W
Enzyme 4
XPositive feedback
Excess Zstimulates a step.
Y
Z
ZZ
Z
(b) Positive feedback
Enzyme 5
Enzyme 6
Figure 1.13b
Evolution, the Overarching Theme of Biology
• Evolution makes sense of everything we know about biology
• Organisms are modified descendants of common ancestors
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• Evolution explains patterns of unity and diversity in living organisms
• Similar traits among organisms are explained by descent from common ancestors
• Differences among organisms are explained by the accumulation of heritable changes
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Figure 1.15
(a) Domain Bacteria (b) Domain Archaea
(c) Domain Eukarya
2 m
2 m
100 m
Kingdom Plantae
Kingdom Fungi
Protists
Kingdom Animalia
Unity in the Diversity of Life
• A striking unity underlies the diversity of life; for example
– DNA is the universal genetic language common to all organisms
– Unity is evident in many features of cell structure
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Figure 1.16
Cilia ofParamecium
15 m
Cross section of a cilium, as viewedwith an electron microscope
0.1 m
Cilia ofwindpipecells
5 m
Concept 1.3: In studying nature, scientists make observations and then form and test hypotheses
• The word science is derived from Latin and means “to know”
• Inquiry is the search for information and explanation• The scientific process includes making observations,
forming logical hypotheses, and testing them
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Figure 1.23
The Role of Hypotheses in Inquiry
• A hypothesis is a tentative answer to a well-framed question
• A scientific hypothesis leads to predictions that can be tested by observation or experimentation
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• For example,– Observation: Your flashlight doesn’t work– Question: Why doesn’t your flashlight work?– Hypothesis 1: The batteries are dead– Hypothesis 2: The bulb is burnt out
• Both these hypotheses are testable
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• Hypothesis-based science often makes use of two or more alternative hypotheses
• Failure to falsify a hypothesis does not prove that hypothesis– For example, you replace your flashlight bulb, and
it now works; this supports the hypothesis that your bulb was burnt out, but does not prove it (perhaps the first bulb was inserted incorrectly)
© 2011 Pearson Education, Inc.
Questions That Can and Cannot Be Addressed by Science
• A hypothesis must be testable and falsifiable– For example, a hypothesis that ghosts fooled with the
flashlight cannot be tested• Supernatural and religious explanations are outside
the bounds of science
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The Flexibility of the Scientific Method
• The scientific method is an idealized process of inquiry• Hypothesis-based science is based on the “textbook”
scientific method but rarely follows all the ordered steps
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Figure 1.26
(a) Artificial kingsnake
(b) Brown artificial snake that has been attacked
Experimental Controls and Repeatability
• A controlled experiment compares an experimental group (the artificial kingsnakes) with a control group (the artificial brown snakes)
• Ideally, only the variable of interest (the effect of coloration on the behavior of predators) differs between the control and experimental groups
• A controlled experiment means that control groups are used to cancel the effects of unwanted variables
• A controlled experiment does not mean that all unwanted variables are kept constant
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• In science, observations and experimental results must be repeatable
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Chapter TWO:The Chemical Context of Life
Chapter 2
• Atoms in a molecule attract electrons to varying degrees
• Electronegativity is an atom’s attraction for the electrons in a covalent bond
• The more electronegative an atom, the more strongly it pulls shared electrons toward itself
© 2011 Pearson Education, Inc.
Figure 2.13
H H
H2O+ +
–
O
Hydrogen Bonds
• A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
• In living cells, the electronegative partners are usually oxygen or nitrogen atoms
© 2011 Pearson Education, Inc.
Figure 2.16
Water (H2O)
Ammonia (NH3)
Hydrogen bond
–
–
+
+
+
+
+
Chapter THREE:Water and Life
Chapter 3
Concept 3.1: Polar covalent bonds in water molecules result in hydrogen bonding
• The water molecule is a polar molecule: the opposite ends have opposite charges
• Polarity allows water molecules to form hydrogen bonds with each other
© 2011 Pearson Education, Inc.
Animation: Water Structure
Figure 3.2
Hydrogenbond
Polar covalentbonds
+
+
+
+
Figure 3.UN02
2 H2O Hydroxideion (OH)
Hydroniumion (H3O+)
+
Acidification: A Threat to Water Quality
• Human activities such as burning fossil fuels threaten water quality
• CO2 is the main product of fossil fuel combustion
• About 25% of human-generated CO2 is absorbed by the oceans
• CO2 dissolved in sea water forms carbonic acid; this process is called ocean acidification
© 2011 Pearson Education, Inc.
Figure 3.11
CO2
CO2 + H2O H2CO3
H+ + HCO3
H+ + CO32 HCO3
CaCO3 CO32 + Ca2+
H2CO3
Chapter FOUR: Carbon and the Molecular Diversity of Life
Chapter 4
Figure 4.4
Hydrogen(valence 1)
Oxygen(valence 2)
Nitrogen(valence 3)
Carbon(valence 4)
Figure 4.UN02
Estradiol
Testosterone
• The seven functional groups that are most important in the chemistry of life:
– Hydroxyl group– Carbonyl group– Carboxyl group– Amino group– Sulfhydryl group– Phosphate group– Methyl group
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Figure 4.9f
Phosphate
STRUCTURE
EXAMPLE
NAME OFCOMPOUND
FUNCTIONALPROPERTIES
Organic phosphates
Glycerol phosphate
• Contributes negativecharge to the moleculeof which it is a part(2– when at the end ofa molecule, as at left;1– when locatedinternally in a chain ofphosphates).
• Molecules containingphosphate groups havethe potential to reactwith water, releasingenergy.
ATP: An Important Source of Energy for Cellular Processes
• One phosphate molecule, adenosine triphosphate (ATP), is the primary energy-transferring molecule in the cell
• ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups
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Figure 4. UN04
Adenosine
Figure 4. UN05
AdenosineAdenosine
Reactswith H2O
Inorganicphosphate
ATP ADP
Energy
Chapter FIVE: The Structure and Function of Large Biological Molecules
Chapter 5
Figure 5.2a
(a) Dehydration reaction: synthesizing a polymer
Short polymer Unlinked monomer
Dehydration removesa water molecule,forming a new bond.
Longer polymer
1 2 3 4
1 2 3
Figure 5.2b
(b) Hydrolysis: breaking down a polymer
Hydrolysis addsa water molecule,breaking a bond.
1 2 3 4
1 2 3
Figure 5.7b
(b) Starch: 1–4 linkage of glucose monomers
(c) Cellulose: 1–4 linkage of glucose monomers
41
41
Figure 5.9
Chitin forms the exoskeletonof arthropods.
The structureof the chitinmonomer
Chitin is used to make a strong and flexiblesurgical thread that decomposes after thewound or incision heals.
Figure 5.10
(a) One of three dehydration reactions in the synthesis of a fat
(b) Fat molecule (triacylglycerol)
Fatty acid(in this case, palmitic acid)
Glycerol
Ester linkage
Figure 5.11
(a) Saturated fat(b) Unsaturated fat
Structuralformula of asaturated fatmolecule
Space-fillingmodel of stearicacid, a saturatedfatty acid
Structuralformula of anunsaturated fatmolecule
Space-filling modelof oleic acid, anunsaturated fattyacid
Cis double bondcauses bending.
Figure 5.12
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilichead
Hydrophobictails
(c) Phospholipid symbol(b) Space-filling model(a) Structural formula
Hyd
roph
ilic
head
Hyd
roph
obic
tails
Figure 5.13
Hydrophilichead
Hydrophobictail
WATER
WATER
Figure 5.15a
Enzymatic proteins
Enzyme
Example: Digestive enzymes catalyze the hydrolysisof bonds in food molecules.
Function: Selective acceleration of chemical reactions
Figure 5.15b
Storage proteins
Ovalbumin Amino acidsfor embryo
Function: Storage of amino acidsExamples: Casein, the protein of milk, is the majorsource of amino acids for baby mammals. Plants havestorage proteins in their seeds. Ovalbumin is theprotein of egg white, used as an amino acid sourcefor the developing embryo.
Figure 5.15c
Hormonal proteins
Function: Coordination of an organism’s activitiesExample: Insulin, a hormone secreted by thepancreas, causes other tissues to take up glucose,thus regulating blood sugar concentration
Highblood sugar
Normalblood sugar
Insulinsecreted
Figure 5.15d
Muscle tissue
Actin Myosin
100 m
Contractile and motor proteins
Function: Movement
Examples: Motor proteins are responsible for theundulations of cilia and flagella. Actin and myosinproteins are responsible for the contraction ofmuscles.
Figure 5.15e
Defensive proteins
Virus
Antibodies
Bacterium
Function: Protection against diseaseExample: Antibodies inactivate and help destroyviruses and bacteria.
Figure 5.15f
Transport proteins
Transportprotein
Cell membrane
Function: Transport of substancesExamples: Hemoglobin, the iron-containing protein ofvertebrate blood, transports oxygen from the lungs toother parts of the body. Other proteins transportmolecules across cell membranes.
Figure 5.15g
Signalingmolecules
Receptorprotein
Receptor proteins
Function: Response of cell to chemical stimuliExample: Receptors built into the membrane of anerve cell detect signaling molecules released byother nerve cells.
Figure 5.15h
60 m
Collagen
Connectivetissue
Structural proteins
Function: SupportExamples: Keratin is the protein of hair, horns,feathers, and other skin appendages. Insects andspiders use silk fibers to make their cocoons and webs,respectively. Collagen and elastin proteins provide afibrous framework in animal connective tissues.
© 2011 Pearson Education, Inc.
Animation: Structural Proteins
Animation: Storage Proteins
Animation: Transport Proteins
Animation: Receptor Proteins
Animation: Contractile Proteins
Animation: Defensive Proteins
Animation: Hormonal Proteins
Animation: Sensory Proteins
Animation: Gene Regulatory Proteins
Polypeptides
• Polypeptides are unbranched polymers built from the same set of 20 amino acids
• A protein is a biologically functional molecule that consists of one or more polypeptides
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Four Levels of Protein Structure
• The primary structure of a protein is its unique sequence of amino acids
• Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain
• Tertiary structure is determined by interactions among various side chains (R groups)
• Quaternary structure results when a protein consists of multiple polypeptide chains
© 2011 Pearson Education, Inc.
Animation: Protein Structure Introduction
Figure 5.20aPrimary structure
Aminoacids
Amino end
Carboxyl end
Primary structure of transthyretin
• Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word
• Primary structure is determined by inherited genetic information
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Animation: Primary Protein Structure
Figure 5.20b
Secondarystructure
Tertiarystructure
Quaternarystructure
Hydrogen bond
helix
pleated sheet strand
Hydrogenbond
Transthyretinpolypeptide
Transthyretinprotein
• The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone
• Typical secondary structures are a coil called an helix and a folded structure called a pleated sheet
© 2011 Pearson Education, Inc.
Animation: Secondary Protein Structure
• Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents
• These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions
• Strong covalent bonds called disulfide bridges may reinforce the protein’s structure
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Animation: Tertiary Protein Structure
• Quaternary structure results when two or more polypeptide chains form one macromolecule
• Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
• Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains
© 2011 Pearson Education, Inc.
Animation: Quaternary Protein Structure
Figure 5.25-3
Synthesis ofmRNA
mRNA
DNA
NUCLEUSCYTOPLASM
mRNA
Ribosome
AminoacidsPolypeptide
Movement ofmRNA intocytoplasm
Synthesisof protein
1
2
3
Figure 5.26ab
Sugar-phosphate backbone5 end
5C
3C
5C
3C
3 end(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nucleoside
Nitrogenousbase
5C
3C
1C
Chapter SIX: A Tour of the Cell
Chapter 6
Figure 6.2 10 m
1 m
0.1 m
1 cm
1 mm
100 m
10 m
1 m
100 nm
10 nm
1 nm
0.1 nm Atoms
Small molecules
Lipids
Proteins
Ribosomes
VirusesSmallest bacteria
MitochondrionMost bacteriaNucleus
Most plant andanimal cells
Human egg
Frog egg
Chicken egg
Length of somenerve andmuscle cells
Human height
Una
ided
eye
Ligh
t mic
rosc
opy
Elec
tron
mic
rosc
opy
Super-resolution
microscopy
Brightfield(unstained specimen)
Brightfield(stained specimen)
50 m
Confocal
Differential-interference-contrast (Nomarski)
Fluorescence
10 m
Deconvolution
Super-resolution
Scanning electronmicroscopy (SEM)
Transmission electronmicroscopy (TEM)
Cross sectionof cilium
Longitudinal sectionof cilium
Cilia
Electron Microscopy (EM)
1 m
10 m
50 m
2 m
2 m
Light Microscopy (LM)
Phase-contrast
Figure 6.3
Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions
• The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic
• Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells
• Protists, fungi, animals, and plants all consist of eukaryotic cells
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• Metabolic requirements set upper limits on the size of cells
• The surface area to volume ratio of a cell is critical• As the surface area increases by a factor of n2, the
volume increases by a factor of n3
• Small cells have a greater surface area relative to volume
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Surface area increases whiletotal volume remains constant
Total surface area[sum of the surface areas(height width) of all boxsides number of boxes]
Total volume[height width length number of boxes]
Surface-to-volume(S-to-V) ratio[surface area volume]
1
5
6 150 750
1
1251251
1.26 6
Figure 6.7
A Panoramic View of the Eukaryotic Cell
• A eukaryotic cell has internal membranes that partition the cell into organelles
• Plant and animal cells have most of the same organelles
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BioFlix: Tour of an Animal Cell
BioFlix: Tour of a Plant Cell
Figure 6.8a
ENDOPLASMIC RETICULUM (ER)
RoughER
SmoothER
NuclearenvelopeNucleolusChromatin
Plasmamembrane
Ribosomes
Golgi apparatus
LysosomeMitochondrion
Peroxisome
Microvilli
MicrotubulesIntermediate filaments
Microfilaments
Centrosome
CYTOSKELETON:
Flagellum NUCLEUS
NUCLEUS
Nuclearenvelope
Nucleolus
Chromatin
Golgiapparatus
Mitochondrion
Peroxisome
Plasma membrane
Cell wall
Wall of adjacent cell
Plasmodesmata
Chloroplast
Microtubules
Intermediatefilaments
Microfilaments
CYTOSKELETON
Central vacuole
Ribosomes
Smoothendoplasmicreticulum
Roughendoplasmic
reticulum
Figure 6.8c
Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell
• Components of the endomembrane system– Nuclear envelope– Endoplasmic reticulum– Golgi apparatus– Lysosomes– Vacuoles– Plasma membrane
• These components are either continuous or connected via transfer by vesicles
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Figure 6.11 Smooth ER
Rough ER
ER lumen
CisternaeRibosomes
Smooth ERTransport vesicle
Transitional ER
Rough ER 200 nm
Nuclearenvelope
Figure 6.12
cis face(“receiving” side ofGolgi apparatus)
trans face(“shipping” side ofGolgi apparatus)
0.1 m
TEM of Golgi apparatus
Cisternae
Figure 6.15-3
Smooth ER
Nucleus
Rough ER
Plasmamembrane
cis Golgi
trans Golgi
NucleusEndoplasmicreticulum
Nuclear envelope
Ancestor ofeukaryotic cells(host cell)
Engulfing of oxygen-using nonphotosyntheticprokaryote, whichbecomes a mitochondrion
Mitochondrion
Nonphotosyntheticeukaryote
Mitochondrion
At leastone cell
Photosynthetic eukaryote
Engulfing ofphotosyntheticprokaryote
Chloroplast
Figure 6.16
Figure 6.17a
Intermembrane space
Outer
DNA
Innermembrane
Cristae
Matrix
Freeribosomesin themitochondrialmatrix
(a) Diagram and TEM of mitochondrion0.1 m
membrane
Figure 6.18a
RibosomesStroma
Inner and outermembranes
Granum
1 mIntermembrane spaceThylakoid(a) Diagram and TEM of chloroplast
DNA
Peroxisomes: Oxidation
• Peroxisomes are specialized metabolic compartments bounded by a single membrane
• Peroxisomes produce hydrogen peroxide and convert it to water
• Peroxisomes perform reactions with many different functions
• How peroxisomes are related to other organelles is still unknown
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Figure 6.19
ChloroplastPeroxisome
Mitochondrion
1 m
Centrosomes and Centrioles• In many cells, microtubules grow out from a
centrosome near the nucleus• The centrosome is a “microtubule-organizing center”• In animal cells, the centrosome has a pair of
centrioles, each with nine triplets of microtubules arranged in a ring
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Centrosome
Longitudinalsection ofone centriole
Centrioles
Microtubule
0.25 m
Microtubules Cross sectionof the other centriole
Figure 6.22
Figure 6.30a
EXTRACELLULAR FLUIDCollagen
Fibronectin
Plasmamembrane
Micro-filaments
CYTOPLASM
Integrins
Proteoglycancomplex
• Functions of the ECM– Support– Adhesion– Movement– Regulation
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Chapter SEVEN: Membrane Structure and Function
Chapter 7
Figure 7.2
Hydrophilichead
Hydrophobictail
WATER
WATER
Figure 7.3
Phospholipidbilayer
Hydrophobic regionsof protein
Hydrophilicregions of protein
Figure 7.4
Knife
Plasma membrane Cytoplasmic layer
Proteins
Extracellularlayer
Inside of extracellular layer Inside of cytoplasmic layer
TECHNIQUE
RESULTS
Figure 7.5
Glyco-protein
Carbohydrate
Glycolipid
Microfilamentsof cytoskeleton
EXTRACELLULARSIDE OFMEMBRANE
CYTOPLASMIC SIDEOF MEMBRANE
Integralprotein
Peripheralproteins
Cholesterol
Fibers of extra-cellular matrix (ECM)
Figure 7.7
Membrane proteins
Mouse cellHuman cell Hybrid cell
Mixed proteinsafter 1 hour
RESULTS
Figure 7.8
Fluid
Unsaturated hydrocarbontails
Viscous
Saturated hydrocarbon tails
(a) Unsaturated versus saturated hydrocarbon tails
(b) Cholesterol within the animal cell membrane
Cholesterol
Figure 7.10
Enzymes
Signaling molecule
Receptor
Signal transduction
Glyco-protein
ATP
(a) Transport (b) Enzymatic activity (c) Signal transduction
(d) Cell-cell recognition (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM)
Figure 7.11
Receptor(CD4)
Co-receptor(CCR5)
HIV
Receptor (CD4)but no CCR5 Plasma
membrane
HIV can infect a cell thathas CCR5 on its surface,as in most people.
HIV cannot infect a cell lackingCCR5 on its surface, as in resistant individuals.
Figure 7.12
Transmembraneglycoproteins
ER
ER lumen
Glycolipid
Plasma membrane:Cytoplasmic face
Extracellular face
Secretoryprotein
Golgiapparatus
Vesicle
Transmembraneglycoprotein Secreted
protein
Membraneglycolipid
Figure 7.15
Hypotonicsolution
Osmosis
Isotonicsolution
Hypertonicsolution
(a) Animal cell
(b) Plant cell
H2O H2O H2O H2O
H2O H2O H2O H2OCell wall
Lysed Normal Shriveled
Turgid (normal) Flaccid Plasmolyzed
Figure 7.17
EXTRACELLULARFLUID
CYTOPLASM
Channel protein Solute
SoluteCarrier protein
(a) A channel protein
(b) A carrier protein
Figure 7.18-6
EXTRACELLULARFLUID
[Na] high[K] low
[Na] low[K] high
CYTOPLASM
Na
Na
Na
1 2 3
456
Na
Na
Na
Na
Na
Na
K
K
K
K
K
K
P P
PP i
ATP
ADP
Figure 7.19Passive transport Active transport
Diffusion Facilitated diffusion ATP
How Ion Pumps Maintain Membrane Potential
• Membrane potential is the voltage difference across a membrane
• Voltage is created by differences in the distribution of positive and negative ions across a membrane
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• Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane
– A chemical force (the ion’s concentration gradient)– An electrical force (the effect of the membrane
potential on the ion’s movement)
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• An electrogenic pump is a transport protein that generates voltage across a membrane
• The sodium-potassium pump is the major electrogenic pump of animal cells
• The main electrogenic pump of plants, fungi, and bacteria is a proton pump
• Electrogenic pumps help store energy that can be used for cellular work
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Figure 7.20
CYTOPLASM
ATP EXTRACELLULARFLUID
Proton pumpH
H
H
H
H
H
Cotransport: Coupled Transport by a Membrane Protein
• Cotransport occurs when active transport of a solute indirectly drives transport of other solutes
• Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
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Figure 7.21
ATP
H
H
HH
H
H
H
H
Proton pump
Sucrose-H
cotransporter
SucroseSucrose
Diffusion of H
Figure 7.22
Solutes
Pseudopodium
“Food” orother particle
Foodvacuole
CYTOPLASM
Plasmamembrane
Vesicle
Receptor
Ligand
Coat proteins
Coatedpit
Coatedvesicle
EXTRACELLULARFLUID
Phagocytosis Pinocytosis Receptor-Mediated Endocytosis