Cell Structure and Function Chapter 4. 4.1 What is a Cell? Each cell has a plasma membrane,...

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

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

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

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

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

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

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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Cell Structure and Function Chapter 4. 4.1 What is a Cell? Each cell has a plasma membrane,...

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