Cell Structure and Function

Chapter 2

Consists of Plasma membrane

Barrier that surrounds the cytoplasm of the cell Organelles

Internal structures that carry out specialized functions

Bounded by a membrane (exception ribosome, centriole)

CytosolLiquid portion of the cell

Cell Structure (Eukaryotes)

Plant and Animal Cell

Almost all eukaryotes have a nucleus Contains

Nucleoplasm Viscous fluid similar to cytosol

Nucleolus Assembly of ribosomal subunits from proteins and RNA

Nuclear envelope Contains almost all of the DNA in a eukaryotic cell (exceptions,

mitochondria and chloroplast) Protects DNA from metabolic reactions

Nucleus

Surrounds the nucleus Double membrane – two lipid

bilayers folded togetherNuclear pores

Link inner and outer membraneProteins embedded

Function as transporters and receptors

Controls passage of molecules between nucleus and cytosol

Water and gases enter and exit the membrane freely

Nuclear Envelope

Group of interacting organelles between the nucleus and plasma membrane

FunctionsBuild lipids, enzymes, and other proteins Transportation Destroy toxins Recycle waste

The Endomembrane System

Extension of the nuclear envelopeContinuous compartment that folds

repeatedly into flattened sacs and tubesTwo Types

Rough ERContains ribosomes

Synthesis of polypeptide chains Once synthesized, proteins fold and take

shape inside ERSmooth ER

Contains no ribosomes Enzymes formed from Rough ER found

here Produce most of cells membrane lipids Break down carbohydrates, fatty acids, and

drugs and poisons

Endoplasmic Reticulum

Membrane-enclosed, saclike organelles Form from budding from other organelles or

plasma membraneFucntions

Transport proteins Digest fatty acids and amino acids (use of

enzymes)Peroxisome – inactivates hydrogen peroxide from

fatty acid breakdownVacuoles

Dispose of waste, debris and toxic materialsLysosomes – fuse with vacuole to dispose of worn out cell

components (use of enzymes)Keep turgor pressure inside plant cell

Vesicles

Folded membrane (looks like stack of pancakes)

Function Finishing and packaging of polypeptide chains

and lipids for use inside or outside of cellIncludes

Attach phosphate groups, sugarsCleave polypeptide chains

Golgi Bodies

Double bound membrane organelle

Two compartmentsMitochondrial

matrixIntermembrane

spaceContain their own

DNADivide independently

of cellFunction

Synthesize ATP

Mitochondria

TypesChloroplasts

Double membrane bound organelle

Stroma – semifluid interior, contains enzymes and DNA

Specialize in photosynthesis Contain chlorophyll

ChromoplastsStore orange and red

carotenoidsResponsible for beautiful

colours in autumnAmyloplasts

Store starch grains

Plastids (Plant Cells)

Interconnected system of many protein filaments

FunctionsReinforceOrganizeMove cell structures

Include MicrotubulesMicrofilaments

Cytoskeleton

MicrotubulesLong, hollow cylinderConsist of subunits of tubulin (protein)Form dynamic scaffolding for many cellular processes Eg. Cellular division

MicrofilamentsFibreConsists of subunits of actin (protein)Strengthen and change shape of eukaryotic cells Eg. Muscle contraction

Intermediate filamentsMost stable Consist of fibrous proteins Strengthen and maintain cell and tissue structure

(toughest)

Microtubules and Microfilaments

Organized array of microtubulesFlagella

Whiplike structure Propels cells (sperm)

CiliaHair like structure Sweeping action moves particles (lining of airway)

Pseudopod (false feet)Lobe formations Amoeba

Cilia, Flagella, Pseudopods

Located around plasma membranePorous structure Protects supports and gives shape to the cell Waxy cuticle

Covers plant cells and protects exposed surfaces of soft parts of the plant

Limits water loss on hot/dry days

Cell Wall (Plant Cells)

Non-living mixture of fibrous proteins and polysaccharides that surround cells

Functions Supports and anchors cells Separates tissues Cell signalling

Plants Cellulose

Fungi Chitin

Animals Carbohydrates and proteins Bone (Collagen)

Cells interact via cell junctions

Extracellular Matrix (ECM)

Can be described using the Fluid Mosaic Model Phospholipid bilayer Proteins

Embedded in the membrane and float freely Involved in transport and attachment Anchor cytoskeleton filaments

Glycolipids and Glycoproteins Carbohydrate groups attached to protein and lipid components Cell recognition and cell to cell interaction

Semipermeable Regulates substances moving in and out of cell

Fluid

Plasma Membrane

Membrane asymmetry

Each half of membrane serves different function

Hydrophilic HeadPhosphate

groupPolar group

Hydrophobic TailFatty acids

Align themselves in aqueous solution

Phospholipids

Depends on how densely individual lipid molecules can pack together.

Influenced by:Composition of lipid molecules

Saturated vs Unsaturated hydrocarbons Temperature

Low temperatures decrease fluidity – viscous semisolid gelTemperature related to degree of unsaturated lipids in

membrane Increase in unsaturated membrane lower gelling temperature

SterolsCholesterol – membrane stabilizer

Fluidity

TransportHydrophilic protein channelShape shifting

Enzymatic Activity Respiration and Photosynthesis

Triggering Signals Bind to specific chemicals (hormones) Binding changes the inner surface of

membrane

Attachment and Recognition Exposed to both internal and external

surfaces of membrane Serve as attachment points for

cytoskeleton elements Immune response

Membrane Proteins (Function)

Integral Membrane Proteins (transmembrane)Exposed to aqueous environment on both sides of

the membrane

Peripheral Membrane Proteins Located on surface of a membrane No interaction with hydrophobic core Held to surface by hydrogen / ionic bondsEg. Cytoskeleton

Membrane Protein (Integral/Peripheral)

No chemical energy requiredDiffusion

Net movement of a substance from a region of high concentration to a region of low concentration

Dynamic equilibrium between cells is metMolecule still randomly move through membrane but

concentration remains same

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/how_diffusion_works.html

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/diffusion_through_cell_membranes.html

Passive Membrane Transport

Substances move across a membrane unassisted

Size and charge affect the rate of diffusion across the membrane

Simple Diffusion (Passive Transport)

Diffusion of larger molecules with the help of a transport protein (integral membrane protein)

Stops when equilibrium is reachedTwo types of Transport Proteins

Channel proteinsCarrier proteins

Facilitated Diffusion

Channel ProteinsForm hydrophilic pathways in the membrane Water and certain ions can passVoltage-gated channels

Open or closed by changes in voltage across the membrane or by binding molecules

Eg. Muscle contractions

Facilitated Diffusion

Carrier Proteins Form pathways

through the membrane

Bind to a specific solute (glucose, amino acid)

Carrier protein changes shape allowing solute to move from one side of the membrane to the other

Facilitated Diffusion

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Simple Diffusion Rate of diffusion

increases as difference in concentration gradient increases

Facilitated Diffusion Maximum rate is

reached but limited by number of transport protein in membrane

Simple vs Facilitated

Passive diffusion of water across a membrane via aquaporins

Water always diffuses from an area of low solute concentration (high water concentration) to an area of greater solute concentration (low water concentration)

Three Solutions (Cell) Hypotonic

Solute concentration is high in cell (swells)Hypertonic

Solute concentration is low in cell (shrinks) Isotonic

Solute and water concentration is equal both in and outside cell

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/animation_-_osmosis.html

Osmosis

Osmosis

Substance carried across a membrane from an area of low concentration to an area of high concentration

Use of pumpATP used as energy source Two Types

Primary Active TransportSecondary Active Transport

Active Membrane Transport

Hydrolysis of ATP

Pumps that moves positively charged ions across membranes (H⁺. Ca²⁺, Na⁺, K⁺)ATP is hydrolyzedPhosphate group attaches to pump allowing ion to

bind to protein transporterProtein transporter undergoes a folding change

exposing ion to opposite side of membrane Ion is released to side of higher concentrationPhosphate group is released

This creates an electrochemical gradientEffect of voltage and difference in ion concentrationStored potential energy

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/primary_active_transport.html

Primary Active Transport

Primary Active Transport

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter5/cotransport__symport_and_antiport_.html

Uses concentration gradient of an ion as its energy sourceThis gradient was already established by primary pump. Transport solute across membraneTwo ways

SymportSolute moves through channel in the same direction as ion

AntiportSolute moves in opposite direction as ion

Secondary Active Tranport

Vesicles are used to transportATP is requiredExocytosis

Transport of proteins and waste material from cytosol to exterior of cell

EndocytosisTransport proteins and large molecules into

cytosol of the cell.

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Exocytosis and Endocytosis