Cell StructureChapter 33.1 Impacts/IssuesFood For ThoughtBacteria in our intestines make vitamins and keep us healthy but other bacteria make toxins that can contaminate foods and even kill us

Video: Food for thought3.2 What, Exactly, Is a Cell?

Cells are the fundamental units of all life

All cells start life with a plasma membrane, cytoplasm, and a region of DNA which, in eukaryotic cells only, is enclosed by a nucleusExamples of CellsSome single-celled organisms (protists)

Cell Structure

A plasma membrane surrounds the cell and controls which substances move in and out

Plasma membraneA cells outermost membrane

Lipid bilayerStructural foundation of cell membranes; mainly phospholipids arranged tail-to-tail in a bilayerA Lipid Bilayer

Cytoplasm

An important part of homeostasis is maintaining the composition of cytoplasm, which differs from fluid outside the cell

CytoplasmSemifluid substance enclosed by a cells plasma membrane

Organelles

Cell metabolism occurs in cytoplasm and internal compartments, including organelles

OrganelleStructure that carries out a specialized metabolic function inside a cellProkaryotes and EukaryotesCells are classed as eukaryotes or prokaryotes based on how DNA is housed in the cell Nucleus Organelle with two membranes that holds a eukaryotic cells DNA

NucleoidRegion of cytoplasm where DNA is concentrated in a prokaryotic cell

Surface-to-Volume Ratio

Cells must be small to efficiently exchange materials with their environment

Surface-to-volume ratio limits cell size and influences cell shape

Surface-to-volume ratioA relationship in which the volume of an object increases with the cube of the diameter, but the surface areas increases with the squareSurface-to-Volume RatioAnimation: Surface-to-volume ratioThe Cell Theory

Cell theory is the fundamental theory of biology

Cell theoryAll organisms consist of one or more cellsThe cell is the smallest unit of lifeEach new cell arises from another cellA cell passes hereditary information to its offspring The Cell TheoryAnimation: Overview of cells3.3 Measuring Cells

Most cells are visible only with the help of microscopes

Different types of microscopes use light or electrons to reveal different details of cells

Bacteria on the Tip of a PinBacteria are the smallest and simplest cells

Animalcules and BeastiesNo one knew cells existed until microscopes were invented

1600s: van Leeuwenhoeks microscope

Hooke, Schleiden, and Schwann1600s: Robert Hooke improved the microscope and coined the term cell

1839: Matthias Schleiden and Theodore Schwann realized cells were alive and proposed the cell theoryModern Microscopes

Different types of microscopes reveal different aspects of cell structureLight microscope (phase contrast)Light microscope (reflected light)Fluorescence microscopeTransmission electron microscopeScanning electron microscope

Same Organism, Different Microscopes

Relative Sizes

Animation: How an electron microscope worksAnimation: Wavelengths of light3.4 The Structure of Cell MembranesThe plasma membrane is basically a lipid bilayer balloon filled with fluid

The nonpolar tails of both layers are sandwiched between the polar heads

The Fluid Mosaic Model

A cell membrane is a mosaic of proteins and lipids (mainly phospholipids) that functions as a selectively permeable barrier that separates an internal environment from an external one

Fluid mosaic modelA cell membrane can be considered a two-dimensional fluid of mixed composition

Membrane Proteins

Proteins associated with a membrane carry out most membrane functionsTransport proteins passively or actively assist specific ions or molecules across a membraneEnzymes speed chemical processes Adhesion proteins help cells stick together Recognition proteins tag cells as selfReceptor proteins bind to a particular substance outside the cell

Cell Membrane Structure

Animation: Lipid bilayer organizationAnimation: Cell membranesAnimation: Fluid mosaic model3.5 Introducing Prokaryotic Cells

Domains Bacteria and Archaea make up the prokaryotes

Prokaryotes are single-celled organisms with no nucleus, but many have a cell wall and one or more flagella or pili

Prokaryote Body Plan

Cell wallSemirigid but permeable structure that surrounds the plasma membrane of some cells Consists of peptides and polysaccharides (in bacteria) or proteins (in archaeans)In some bacteria, a sticky capsule of polysaccharides surrounds the cell wall

Prokaryote Body Plan

The cytoplasm contains ribosomes, a circular DNA molecule in a nucleoid region, and may contain additional genes as plasmids

RibosomeOrganelle of protein synthesis

Prokaryote Body Plan

Surface extensions allow certain actions

FlagellumLong, slender cellular structure used for mobility

PilusA protein filament used to help cells cling to or move across surfaces, or for plasmid transferProkaryote Body Plan

Animation: Typical prokaryotic cellProkaryote Diversity

As a group, prokaryotes are the smallest and most metabolically diverse forms of life

Prokaryotes inhabit nearly all regions of the biosphere many archaeans are adapted to extreme environmentsProkaryote Diversity: Bacteria

Prokaryote Diversity: Archaeans

Biofilms

Biofilms are shared living arrangements among bacteria and other microbial organisms that provide various advantages to the community

BiofilmCommunity of different types of microorganisms living within a shared mass of slime3.6 A Peek Inside a Eukaryotic Cell

All eukaryotic cells start life with a nucleus, ribosomes, organelles of the endomembrane system (including endoplasmic reticulum, vesicles, Golgi bodies), mitochondria, and other organelles

The Nucleus

Pores, receptors, and transport proteins in the nuclear envelope control the movement of molecules into and out of the nucleus

Nuclear envelopeA double membrane that constitutes the outer boundary of the nucleusThe Endomembrane System

The endomembrane system includes rough and smooth endoplasmic reticulum, vesicles, and Golgi bodies

Endomembrane systemSeries of interacting organelles between the nucleus and plasma membraneMakes and modifies lipids and proteinsRecycles molecules and particles such as worn-out cell parts, and inactivates toxinsThe Endomembrane System

Endoplasmic reticulum (ER)A continuous system of sacs and tubes that is an extension of the nuclear envelopeRough ER is studded with ribosomes (for protein production)Smooth ER has no ribosomesThe Endomembrane SystemVesicleSmall, membrane-enclosed, saclike organelleStores, transports, or degrades its contents

PeroxisomeEnzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances

LysosomeVesicle with enzymes for intracellular digestionThe Endomembrane System

Golgi bodyOrganelle that modifies polypeptides and lipidsSorts and packages the finished products into transport vesicles

VacuoleA fluid-filled organelle that isolates or disposes of wastes, debris, or toxic materials

Mitochondria and Chloroplasts

Mitochondria and chloroplasts have their own DNA they resemble bacteria and may have evolved by endosymbiosis

MitochondrionDouble-membraned organelle that produces ATP

ChloroplastOrganelle of photosynthesisMitochondria and Chloroplasts: Bacteria-Like Organelles

Animation: Structure of a mitochondrionAnimation: Structure of a chloroplastThe Cytoskeleton

CytoskeletonDynamic network of protein filaments that support, organize, and move eukaryotic cells and their internal structures

The cytoskeleton interacts with accessory proteins, such as motor proteinsCytoskeletal ElementsMicrotubulesCytoskeletal elements involved in movementHollow filaments of tubulin subunits

MicrofilamentsReinforcing cytoskeletal elementsFibers of actin subunits

Intermediate filamentsElements that lock cells and tissues togetherCytoskeletal Elements

Motor Proteins

Motor proteins are the basis of movement they interact with microfilaments in pseudopods or (in cilia and eukaryotic flagella) microtubules

Motor proteinsEnergy-using proteins that interact with cytoskeletal elements to move cells parts or the whole cell

Motor ProteinsA motor protein moves a vesicle along a microtubule

Animation: Motor proteinsCilia and False Feet

CiliaShort, hairlike structures that project from the plasma membrane of some eukaryotic cellsCoordinated beating stirs fluid, propels motile cellsMoved by organized arrays of microtubulesExample: clears particles from airways

Flagella

Eukaryotic flagella are whiplike structures that propel cells such as sperm through fluidDifferent internal structure and motion than prokaryotic flagella

False Feet

Pseudopod (false foot)Extendable lobe of membrane-enclosed cytoplasm for movement or to engulf preyMoved by motor proteins attached to microfilaments that drag the plasma membraneExample: amoebas

Components of an Animal Cell

Animation: Common eukaryotic organellesAn Animal Cell

Animation: Structure of a mitochondrionAnimation: The endomembrane systemAnimation: Flagella structureAnimation: Nuclear envelopeAnimation: Structure of a chloroplastAnimation: Cytoskeletal components3.7 Cell Surface Specializations

Cell junctionsConnect a cell structurally and functionally to another cell or to extracellular matrix (ECM)

Extracellular matrix (ECM)Complex mixture of substances secreted by cellsSupports cells and tissuesFunctions in cell signalingTypes of Animal Cell Junctions

Tight junctionAn array of fibrous proteins that joins epithelial cells and prevents fluids from leaking between them

Adhering junctionAnchors cells to each other or to extracellular matrix

Gap junctionForms a channel across plasma membranes of adjoining animal cellsTypes of Animal Cell Junctions

Animation: Animal cell junctionsTight Junctions Around Kidney CellsCell Connections in Plants

In plants, plasmodesmata connect the cytoplasms of adjoining cells

PlasmodesmataOpen channels that extend across the primary walls of adjoining cellsAllow materials such as water, nutrients, and signaling molecules to flow through

Animation: Plant cell walls3.8 Impacts/Issues Revisited

Fresh foods marked with this symbol have been irradiated to kill bacteria potential health risks from eating irradiated foods are unknown

Digging Into Data:Organelles and Cystic Fibrosis