Cell Structure and Function
Chapter 4
4.1 What is a Cell?
Each cell has a plasma membrane, cytoplasm, and a nucleus (in eukaryotic cells) or a nucleoid (in prokaryotic cells)
Fig. 4.3, p. 52
DNA
cytoplasm
plasma membrane
a Bacterial cell (prokaryotic)
Fig. 4.3, p. 52
DNA in nucleus
cytoplasm
plasma membrane
b Plant cell (eukaryotic)
Fig. 4.3, p. 52
DNA in nucleus
cytoplasm
plasma membrane
c Animal cell (eukaryotic)
Components of Cell Membranes
Lipid bilayer
“head”
two “tails”
Fig. 4.4, p. 53
Fig. 4.4, p. 53
fluid
fluid
lipid bilayer
Fig. 4.4, p. 53
one layerof lipidsone layerof lipids
membraneprotein
extracellularenvironment
cytoplasm
Cell Size and Shape
Surface-to-volume ratio limits cell size
Key Concepts: WHAT ALL CELLS HAVE IN COMMON
Each cell has a plasma membrane, a boundary between its interior and the outside environment
The interior consists of cytoplasm and an innermost region of DNA
4.2 How Do We See Cells?
Three key points of the cell theory:• All organisms consist of one or more cells• The cell is the smallest unit that retains the
capacity for life• A cell arises from the growth and division of
another cell
Relative Sizes
Fig. 4.6, p. 54
Microscopes
Different microscopes use light or electrons to reveal details of cell shapes or structures
Fig. 4.7, p. 55light source (in base)
Ocular lens enlargesprimary image formedby objective lenses.
Objective lenses (those closestto specimen) form the primaryimage. Most compound lightmicroscopes have several.
stage supportsmicroscope slide
Condenser lenses focuslight rays through specimen.
illuminator
path of light rays (bottom to top) to eye
prism thatdirects rays toocular lens
incoming electron beam
condenser lens (focuses a beam of electrons onto specimen)
objective lens
intermediate lens
projector lens
viewing screen (orphotographic film)
specimen
Fig. 4.7, p. 55
Five Different Views
Key Concepts: MICROSCOPES
Microscopic analysis supports three generalizations of the cell theory:• Each organism consists of one or more cells and
their products• A cell has a capacity for independent life• Each new cell is descended from a living cell
4.3 Membrane Structure and Function
Each cell membrane is a boundary (lipid bilayer) that controls the flow of substances across it
Fluid mosaic model• Membrane is composed of phospholipids, sterols,
proteins, and other components• Phospholipids drift within the bilayer
Membrane Proteins
Many proteins are embedded in or attached to cell membrane surfaces• Receptors, transporters, communication proteins,
and adhesion proteins
Plasma (outer) membrane also incorporates recognition proteins
Common Membrane Proteins
Fig. 4.9, p. 57
A calcium pumpmoves calcium ionsacross the membrane;requires ATP energy.
EXTRACELLULAR FLUID
phospholipid
LIPIDBILAYER
CYTOPLASMprotein filaments of the cytoskeleton
B cell receptor.It binds to bacteria,other foreign agents.
Recognition protein thatidentifies a cell as belongingto one’s own body.
A glucose transporterallows glucose to crossthe membrane througha channel in its interior.
An ATP synthase,which makes ATP whenH+ crosses a membranethrough its interior.
Membrane Structure Studies
Fig. 4.10, p. 57
proteins fromboth cellsin fused
membrane
human cell mouse cell
fusion intohybrid cell
Key Concepts: COMPONENTS OF CELL MEMBRANES
All cell membranes are mostly a lipid bilayer (two layers of lipids) and a variety of proteins
The proteins have diverse tasks, including control over which water-soluble substances cross the membrane at any given time
4.4 Introducing Prokaryotic Cells
Bacteria and archaeans• The simplest cells• The groups with greatest metabolic diversity
Biofilms • Shared living arrangements of prokaryotes
Prokaryote Structure
Cell wall• Surrounds plasma membrane
Flagella• Used for motion
Pili• Protein filaments used for attachment• “Sex” pilus transfers genetic material
Prokaryote Structure
Prokaryote Structure
Fig. 4.11, p. 58
bacterial flagellum
pilusplasma membrane
DNA in nucleoid
cytoplasm, with ribosomes
Most prokaryotic cells have a cellwall outside the plasma membrane,and many have a thick, jellylikecapsule around the wall. cell
wallcapsule
4.5 Microbial Mobs
Biofilm formation
Key Concepts:PROKARYOTIC CELLS
Archaeans and bacteria are prokaryotic cells which have few, if any, internal membrane-enclosed compartments
In general, they are the smallest and structurally the simplest cells
4.6 Introducing Eukaryotic Cells
Start with a nucleus and other organelles• Carry out specialized functions inside a cell
Fig. 4.14, p. 60
mitochondria
plasmamembrane
nucleus
Fig. 4.14, p. 60
nucleus
cell wall
plasmamembrane
centralvacuole
chloroplast
Components of Eukaryotic Cells
4.7 Components of The Nucleus
Nucleus separates DNA from cytoplasm• Chromatin (all chromosomal DNA with proteins)• Chromosomes (condensed)
Nucleolus assembles ribosome subunits
Nuclear envelope encloses nucleoplasm• Pores, receptors, transport proteins
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
Nucleus and Nuclear Envelope
Fig. 4.15, p. 61
cytoplasm
nuclear envelope
chromatin
nucleolus
Fig. 4.15, p. 61
nuclear envelope’souter lipid bilayermerging with anER membrane
nucleus
chromatin
pore across thenuclear envelope
nucleoplasm
nucleolus
Fig. 4.15, p. 61
cytoplasm
nuclear pore
nuclear envelope(two lipid bilayers)
4.8 The Endomembrane System
Endoplasmic reticulum (ER) • An extension of the nuclear envelope• RER modifies new polypeptide chains• SER makes lipids; other metabolic functions
Golgi bodies • Further modify polypeptides• Assemble lipids
The Endomembrane System
Vesicles • Endocytic and exocytic: Transport or store
polypeptides and lipids• Peroxisomes: Digest fatty acids and amino acids;
break down toxins and metabolic by-products • Lysosomes: Intracellular digestion (animals)• Central vacuole: Storage; fluid pressure (plants)
Endomembrane System
Endomembrane System
Endomembrane System
Fig. 4.16, p. 62
vesicles
nucleus
rough ER
smooth ER
Golgi body
Fig. 4.16, p. 62
the cell nucleus
chromatin
nucleolus nuclear envelope(two lipid bilayers)
pore
cytoplasm
ribosome vesicle
rough ER
Fig. 4.16, p. 62
smooth ER channel, cross-section
plasma membraneGolgi bodysmooth ER
budding vesicle
4.9 Mitochondria and Chloroplasts
Mitochondria • Break down organic compounds by aerobic
respiration (oxygen-requiring)• Produce ATP
Chloroplasts• Produce sugars by photosynthesis
Mitochondria and Chloroplasts
Fig. 4.18, p. 63
thylakoids(inner membranesystem folded intoflattened disks)
two outermembranes
stroma
4.10 Visual Summary: Plant Cells
Visual Summary: Animal Cells
CENTRAL VACUOLE
LYSOSOME-LIKE VESICLE
GOLGI BODY
SMOOTH ER
ROUGH ER
RIBOSOMES
NUCLEUS
CHLOROPLAST
CYTOSKELETON
MITOCHONDRION
PLASMODESMA
PLASMA MEMBRANE
CELL WALL
Fig. 4.19, p.65
nuclear envelopenucleolusDNA innucleoplasm
microtubulesmicrofilamentsintermediatefilaments(not shown)
a Typical plant cell components.
CYTOSKELETON
MITOCHONDRION
CENTRIOLES
LYSOSOME
GOLGI BODY
SMOOTH ER
ROUGH ER
RIBOSOMES
NUCLEUS
PLASMA MEMBRANE
microtubulesmicrofilamentsintermediatefilaments
nuclear envelopenucleolusDNA innucleoplasm
b Typical animal cell components. Fig. 4.19, p. 64
PLASMA MEMBRANE
MITOCHONDRION
CENTRIOLES
RIBOSOMES
ROUGH ER
SMOOTH ER
GOLGI BODY
LYSOSOME
CYTOSKELETONmicrotubulesmicrofilamentsintermediatefilaments
NUCLEUSnuclear envelopenucleolusDNA innucleoplasm
b Typical animal cell components. Fig. 4-19, p. 64
Stepped Art
4.11 Cell Surface Specializations
Most prokaryotes, protists, fungi, all plant cells have a cell wall around their plasma membrane• Protects, supports, maintains cell shape• Primary and secondary cell walls
Plasmodesmata across cell walls connect plant cells
Plant Cell Walls
Plant Cell Walls
Fig. 4.20, p. 66
pipelinemade ofabuttingcell walls
plasma membrane
middlelamella
cytoplasm
primarycell wall
secondarycell wall(added inlayers)
primarycell wall
Fig. 4.20, p. 66
middle lamella
Plasmodesmata
plasmodesma
middle lamella
Plant Cuticle
Protective surface secretion, limits water loss
Fig. 4.21, p. 67
photosyntheticcell inside leaf
thick, waxycuticle atleaf surface
cell of leafepidermis
Extracellular Matrixes
Surrounds cells of specific tissues
Animal Cell Junctions
Connect cells of animals• Adhering junctions, tight junctions, gap junctions
Fig. 4.23, p. 67
adhering junction
free surface ofepithelial tissue
different kinds oftight junctions
gap junction
basement membrane(extracellular matrix)
Key Concepts: EUKARYOTIC CELLS
Cells of protists, plants, fungi, and animals are eukaryotic; they have a nucleus and other membrane-enclosed compartments
They differ in internal parts and surface specializations
4.12 The Dynamic Cytoskeleton
Components of the cytoskeleton• Microtubules• Microfilaments• Intermediate filaments (in most)
Fig. 4.12, p. 59
Fig. 4.12, p. 59
Fig. 4.12, p. 59
Components of the Cytoskeleton
Fig. 4.24, p. 68
tubulinsubunit
25 nm
Fig. 4.24, p. 68
actinsubunit
5–7 nm
Fig. 4.24, p. 68
8–12 nm
onepolypeptide
chain
Cytoskeleton Function
Organizes and moves cell parts
Reinforces cell shape
Interactions between motor proteins and microtubules in cilia, flagella, and pseudopods can move the whole cell
Motor Protein: Kinesin
Moves vesicles along microtubules
Flagellum and Pseudopods
Eukaryotic Flagella and Cilia: Dynein
Eukaryotic Flagella and Cilia: Dynein
Fig. 4.27, p. 69
dynein arms
proteinspokes
plasmamembrane
pair of microtubules in a central sheath
pair ofmicrotubules
dynein arms
basal body
Key Concepts: A LOOK AT THE CYTOSKELETON
Diverse protein filaments reinforce a cell’s shape and keep its parts organized
As some filaments lengthen and shorten, they move chromosomes or other structures to new locations
Animation: Animal cell junctions
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Animation: Cell membranes
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Animation: Common eukaryotic organelles
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Animation: Cytoskeletal components
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Animation: Flagella structure
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Animation: How a light microscope works
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Animation: How an electron microscope works
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Animation: Lipid bilayer organization
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Animation: Motor proteins
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Animation: Nuclear envelope
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Animation: Overview of cells
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Animation: Plant cell walls
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Animation: Structure of a chloroplast
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Animation: Structure of a mitochondrion
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Animation: Surface-to-volume ratio
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Animation: The endomembrane system
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Animation: Typical prokaryotic cell
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