Chapter 5 - Cells

CellsCells

Cells are small Cells are small (mostly)(mostly)

Exceptions: Bird eggs, Exceptions: Bird eggs, neurons, some algae, neurons, some algae, and bacteria cellsand bacteria cells

Why are Cells Small?Why are Cells Small?

Cells are small because a high Cells are small because a high surface area-to-surface area-to-volume ratiovolume ratio is essential. is essential.

VolumeVolume determines the amount of chemical determines the amount of chemical activity in the cell per unit time.activity in the cell per unit time.

Surface area Surface area determines the amount of determines the amount of substances that can pass the cell boundary per substances that can pass the cell boundary per unit time.unit time.

As the Cell Gets Larger the As the Cell Gets Larger the SA:V Ratio DecreasesSA:V Ratio Decreases

Plasma Membrane (Chapter 6)Plasma Membrane (Chapter 6)

The plasma membrane The plasma membrane is the outer surface of is the outer surface of every cell, and has more every cell, and has more or less the same or less the same structure in all cells. structure in all cells.

It is made of a It is made of a phospholipid bilayer phospholipid bilayer with proteins and other with proteins and other molecules embedded.molecules embedded.

Two Types of CellsTwo Types of Cells

Prokaryotic and EukaryoticProkaryotic and Eukaryotic

BacteriaBacteria and and ArchaeaArchaea are prokaryotes. are prokaryotes.

EukaryaEukarya are eukayotes. are eukayotes.

ProkaryotesProkaryotesVery smallVery small

Individuals are single cells, Individuals are single cells, but often found in chains or but often found in chains or clusters.clusters.

Prokaryotes are very Prokaryotes are very successful—they can live on successful—they can live on a diversity of energy sources a diversity of energy sources and some can tolerate and some can tolerate extreme conditions.extreme conditions.

Image Credit--JEFF JOHNSON Hybrid Medical Animation

All Prokaryotes:All Prokaryotes:Are enclosed by a Are enclosed by a plasma plasma membranemembrane

The DNA is contained in the The DNA is contained in the nucleoidnucleoid

CytoplasmCytoplasm consists of consists of cytosol cytosol (water and dissolved material) (water and dissolved material) and suspended particlesand suspended particles

RibosomesRibosomes——sites of protein sites of protein synthesis (Free)synthesis (Free)

Specialized Prokaryotic Specialized Prokaryotic StructuresStructures

Rigid Rigid cell wall cell wall outside the outside the plasma membrane.plasma membrane.

Some bacteria have an Some bacteria have an additional additional outer outer membranemembrane..

Some bacteria have a Some bacteria have a slimy slimy capsulecapsule of of polysaccharides.polysaccharides.

Specialized Prokaryotic Specialized Prokaryotic StructuresStructures

Inner MembraneInner Membrane

PhotosynthesisPhotosynthesis

Other Other Energy-Energy- Related Related FunctionsFunctions

Usually Highly FoldedUsually Highly Folded

WHY?WHY?

Specialized Prokaryotic Specialized Prokaryotic StructuresStructures

FlagellaFlagella

Used for MovementUsed for Movement

Flagella move like a Flagella move like a “cork-screw”“cork-screw”

PiliPili

Hairlike structuresHairlike structures

Food/ Protection/ Mating Food/ Protection/ Mating (sex pili)/ Adhere to Cells(sex pili)/ Adhere to Cells

CytoskeletonCytoskeleton

Some rod-shaped bacteria Some rod-shaped bacteria have a cytoskeleton made have a cytoskeleton made of the protein actin.of the protein actin.

EukaryotesEukaryotesEukaryotic cells are up to ten times Eukaryotic cells are up to ten times largerlarger than prokaryotes. than prokaryotes.

Eukaryotic cells have membrane-enclosed compartments Eukaryotic cells have membrane-enclosed compartments called called organellesorganelles..

Each organelle has a specific role in cell functioning.Each organelle has a specific role in cell functioning.

Compartmentalization allowed eukaryotic cells to Compartmentalization allowed eukaryotic cells to specializespecialize and form the tissues and organs of multicellular organisms.and form the tissues and organs of multicellular organisms.

EukaryotesEukaryotes

EukaryotesEukaryotes

All Eukaryotes:All Eukaryotes:Plasma MembranePlasma Membrane

Cytoplasm/CytosolCytoplasm/Cytosol

RibisomesRibisomesRibosomes consist of ribosomal RNA (rRNA) Ribosomes consist of ribosomal RNA (rRNA) and more than 50 different protein molecules.and more than 50 different protein molecules.

““Free” or “Bound” RibosomesFree” or “Bound” Ribosomes

All Eukaryotes:All Eukaryotes:NucleusNucleus

Usually the largest organelle.Usually the largest organelle.

Contains the DNA Contains the DNA

Site of DNA replicationSite of DNA replication

Site where gene transcription is turned on or offSite where gene transcription is turned on or off

Assembly of ribosomes begins in a region called Assembly of ribosomes begins in a region called the the nucleolusnucleolus

NucleusNucleus

Nuclear EnvelopeNuclear Envelope- Double membrane- Double membrane

Nuclear PoresNuclear Pores

NucleoplasmNucleoplasm

Chromatin Chromatin (Chromosomes)(Chromosomes)- DNA and proteins- DNA and proteins

All Eukaryotes:All Eukaryotes:Endomembrane SystemEndomembrane System

Plasma MembranePlasma Membrane

Nuclear EnvelopeNuclear Envelope

Endoplasmic Endoplasmic ReticulumReticulum

Golgi ApparatusGolgi Apparatus

LysosomeLysosome

Endoplasmic Reticulum (ER)Endoplasmic Reticulum (ER)

Network of interconnected (single) Network of interconnected (single) membranes in the cytoplasm; has large membranes in the cytoplasm; has large surface area.surface area.

Rough ER (RER)Rough ER (RER)

Ribosomes are attached. Ribosomes are attached.

Single MembraneSingle Membrane

Newly made proteins enter the RER Newly made proteins enter the RER lumen where they are lumen where they are modifiedmodified and and foldedfolded..

Smooth ER (SER)Smooth ER (SER)

More tubular, no ribosomesMore tubular, no ribosomes

Chemically modifies small molecules Chemically modifies small molecules such as drugs and pesticidessuch as drugs and pesticides

Hydrolysis of glycogen in animal cellsHydrolysis of glycogen in animal cells

Synthesis of lipids and steroidsSynthesis of lipids and steroids

Golgi ApparatusGolgi Apparatus

Composed of flattened sacs (Composed of flattened sacs (cisternaecisternae) ) and small membrane-enclosed and small membrane-enclosed vesicles.vesicles.

Receives proteins from the RER—can Receives proteins from the RER—can further modify themfurther modify them

Concentrates, packages, sorts proteinsConcentrates, packages, sorts proteins

In plant cells, polysaccharides for cell In plant cells, polysaccharides for cell walls are synthesized herewalls are synthesized here

How do Proteins get from one How do Proteins get from one Organelle to Another?Organelle to Another?

VesiclesVesicles

Localization SequencesLocalization Sequences

Short (~20 a.a.) polypeptides linked to Short (~20 a.a.) polypeptides linked to the C or N terminous of a proteinthe C or N terminous of a protein

Allow a protein to cross a specific type of Allow a protein to cross a specific type of membranemembrane

LysosomesLysosomes

Primary lysosomes Primary lysosomes originate from the originate from the Golgi apparatus.Golgi apparatus.

They contain digestive enzymes—They contain digestive enzymes—macromolecules are hydrolyzed into macromolecules are hydrolyzed into monomers.monomers.

Phagocytosis / Secondary LysosomesPhagocytosis / Secondary Lysosomes

Food molecules enter the Food molecules enter the cell by cell by phagocytosisphagocytosis—a —a phagosomephagosome is formed. is formed.

Phagosomes fuse with Phagosomes fuse with primary lysosomes to form primary lysosomes to form secondary lysosomessecondary lysosomes. .

Enzymes in the secondary Enzymes in the secondary lysosome hydrolyze the lysosome hydrolyze the food molecules.food molecules.

All Eukaryotes:All Eukaryotes: Mitochondria Mitochondria

Cellular RespirationCellular RespirationConvert potential energy of fuel molecules to Convert potential energy of fuel molecules to into a form the cell can use into a form the cell can use

Fuel Molecules + ADP + O2 Fuel Molecules + ADP + O2 Energy (ATP) + CO2 Energy (ATP) + CO2

Most O2 in eukaryotic organisms is used up by Most O2 in eukaryotic organisms is used up by mitochondriamitochondria

Mitochondria StructureMitochondria Structure

Mitochondria have Mitochondria have twotwo membranes.membranes.

The inner membrane folds The inner membrane folds inward to form inward to form cristaecristae. . This creates a large This creates a large surface area for proteins surface area for proteins involved in cellular involved in cellular respiration reactions.respiration reactions.

The The mitochondrial matrix mitochondrial matrix contains enzymes, DNA, contains enzymes, DNA, and ribosomes.and ribosomes.

Specialized Eukaryotic Structures: PlastidsSpecialized Eukaryotic Structures: Plastids

Plants/ Some ProtistsPlants/ Some Protists

ChloroplastChloroplast

Site of photosynthesis—light Site of photosynthesis—light energy is converted to the energy is converted to the energy of chemical bondsenergy of chemical bonds

Chloroplasts have a double Chloroplasts have a double membranemembrane

LeucoplastLeucoplast

Store starches and fatsStore starches and fats

ChromoplastChromoplast

Contain red, orange, and Contain red, orange, and yellowyellow

pigments (gives color to pigments (gives color to flowers)flowers)

ChloroplastChloroplastGranaGrana

are stacks of thylakoids—made are stacks of thylakoids—made of circular compartments of the of circular compartments of the inner membrane.inner membrane.

ThylakoidsThylakoids

contain chlorophyll and other contain chlorophyll and other pigments that harvest light pigments that harvest light energy for photosynthesis.energy for photosynthesis.

StromaStroma

fluid in which grana are fluid in which grana are suspended. The stroma contains suspended. The stroma contains DNA and ribosomes.DNA and ribosomes.

Specialized Eukaryotic Structures only Specialized Eukaryotic Structures only found in Plants / Protistsfound in Plants / Protists

PeroxisomesPeroxisomes

Collect and break down toxic byproducts Collect and break down toxic byproducts of metabolism such as Hof metabolism such as H22OO22, using , using

specialized enzymesspecialized enzymes

GlyoxysomesGlyoxysomes

Only in plants—lipids are converted to Only in plants—lipids are converted to carbohydrates for growthcarbohydrates for growth

Specialized Eukaryotic Structures only Specialized Eukaryotic Structures only found in Plants / Protistsfound in Plants / Protists

VacuolesVacuolesStore waste products and toxic compoundsStore waste products and toxic compounds; some ; some may deter herbivoresmay deter herbivores

Provide structure for plant cellsProvide structure for plant cells; ; water enters the water enters the vacuole by osmosis, creating turgor pressurevacuole by osmosis, creating turgor pressure

Store anthocyanins (pink and blue pigments) in Store anthocyanins (pink and blue pigments) in flowers and fruitsflowers and fruits; the colors attract pollinators; the colors attract pollinators

Vacuoles in seeds have digestive enzymes to Vacuoles in seeds have digestive enzymes to hydrolyze stored food for early growthhydrolyze stored food for early growth

Freshwater protists may have Freshwater protists may have contractile vacuolescontractile vacuoles to to expel excess water.expel excess water.

Specialized Eukaryotic Specialized Eukaryotic Structures: Cytoskeleton Structures: Cytoskeleton

Supports and maintains cell shapeSupports and maintains cell shape

Holds organelles in positionHolds organelles in position

Moves organellesMoves organelles

Involved in cytoplasmic streamingInvolved in cytoplasmic streaming

Interacts with extracellular structures to Interacts with extracellular structures to hold cell in placehold cell in place

Components of the Components of the CytoskeletonCytoskeleton

Microfilaments Microfilaments Intermediate filaments Intermediate filaments MicrotubulesMicrotubules

Specialized Eukaryotic Specialized Eukaryotic Structures: Flagella and CiliaStructures: Flagella and Cilia

CiliaCilia

short, usually many short, usually many present, move with stiff present, move with stiff power stroke and flexible power stroke and flexible recovery strokerecovery stroke

FlagellaFlagella

Longer, usually one or two Longer, usually one or two present, movement is present, movement is snakelikesnakelike

Extracellular StructuresExtracellular Structures

Outside the Plasma MembraneOutside the Plasma Membrane

Cell Walls (Plants/Protists)Cell Walls (Plants/Protists)

Extracellular Matrix (Animals)Extracellular Matrix (Animals)

Plant Cell WallsPlant Cell Walls

Cellulose fibers Cellulose fibers are embedded in other are embedded in other complex polysaccharides and proteins.complex polysaccharides and proteins.

Adjacent plant cells are connected by Adjacent plant cells are connected by plasma membrane-lined channels called plasma membrane-lined channels called plasmodesmataplasmodesmata..

Extracellular MatrixExtracellular MatrixComposed of fibrous proteins such as Composed of fibrous proteins such as collagen, collagen, gel- likegel- like glycoproteins, and other glycoproteins, and other proteins.proteins.

Extracellular MatrixExtracellular Matrix

• Holds cells together in tissuesHolds cells together in tissues

• Contributes to properties of bone, Contributes to properties of bone, cartilage, skin, etc.cartilage, skin, etc.

• Filters materials passing between Filters materials passing between different tissuesdifferent tissues

• Orients cell movements in development Orients cell movements in development and tissue repairand tissue repair

• Plays a role in chemical signalingPlays a role in chemical signaling