CELLS

Cells• basic structural

& functional units of all living organisms

Cell Theory• cell is basic structural & functional unit

of all living organisms

• activity of organisms depends on individual & collective activities of cells

• biochemical activities dictated by sub-cellular structures of cells

• continuity of life has cellular basis– cells are produced by divisions of preexisting

cells

Major Classes• Prokaryotic

– no nucleus– DNA in nucleoid

region– bacteria

• Eukaryotic– true nucleus– contains DNA– all other cells– plant & animal

Prokaryotes• surrounded by plasma

membrane• outside membrane-cell wall • rigid• protects cells• helps maintain shape• capsule surrounds cell wall for

further protection• may contain surface

projections-pili– help adhere to surfaces

• some have very long projections-flagella– help move

Eukaryotic Cells• plant or animal • separated from external

environment by phospholipid or plasma membrane

• cytoplasm– stuff between nucleus

& plasma membrane• consists of 2 parts• cytosol

– liquid part• organelles

– intracellular structures

Plant & Animal Cells• same organelles• plant cells have several

organellesnot found in animal cells

• cell walls– extra protection

• chloroplasts– covert light energy

into chemical energy• central vacuoles

– store water & chemicals

Plasma Membrane• creates specific

compartments- functional units-organelles

• regulates exchanges with environment

• controls what goes in & out• selectively permeability

– some substances can cross easily; others have difficult time crossing or cannot cross

• crucial to metabolic functioning

• allows things to happen in one area without influencing another area

Cell Membrane• plasma membrane

• lipid bilayer

• thin

• phospholipids

• proteins

• carbohydrates

Plasma Membrane• Phospholipids-composed of

2 fatty acids & PO4 group • produces molecule with

globular, polar head– water loving-hydrophillic

• and hydrocarbon tail• straight, non-polar

– hydrophobic- water hating• head is attracted to water• tail is repealed• causes phospholipids to form

a two-layer sheet- phospholipid bilayer with hydrophobic tails facing each other & hydrophilic polar heads pointing outward

• interior of bilayer is hydrophobic

Membrane Structure & Function

• structure accounts for membrane’s selective permeability

• nonpolar, hydrophobic molecules are soluble in lipids & pass through membrane

• polar molecules & ones not soluble in lipids have more difficult time passing

Proteins in Plasma Membrane• plasma membrane described as fluid

mosaic– not static– phospholipids move in membrane– punctuated along its length with

proteins• proteins determine which hydrophilic

molecules may pass through• Integral proteins

– form part of membrane structure– bound to it

• Transmembrane proteins– traverse bilayer– some form hydrophilic channels

through which ions & molecules can enter or leave

• Peripheral proteins– loosely associated with membrane– bind to inner or outer membrane

surface– cell recognition

• recognize other cells as abnormal or normal

• called receptors

Nucleus & Nucleolus• Nucleus

– most obvious organelle in eukaryotic cells

• all eukaryote cells have nucleus

– typically spherical– found in center

• surrounded by nuclear envelope– double membrane with large

number of pores• allows for passage of

materials between nucleus & cytoplasm

• contains genetic information-DNA

• contains nucleolus– makes subunits that

comprise ribosomes

Ribosomes• made by nucleolus• travel from nucleus to

cytoplasm via nuclear pores

• synthesize proteins• most attached to

surface of endoplasmic reticulum (ER)-rough ER

• some can be found floating free in cytoplasm

Endoplasmic Reticulum• interconnected flattened tubular tunnels

continuous with outer membrane of nucleus

• all eukaryotic cells contain ER• responsible for communication in cell• part of endomembrane system• all membranous organelles belong to

system• Rough

– attached ribosomes– makes appear spotty– takes in proteins made on

ribosomes so cannot escape into cytoplasm

• Smooth– no attached ribosomes smooth– not involved in protein synthesis– steroid production

• contains enzymes required to detoxify wide variety of organic molecules

• storage site for calcium

Golgi Bodies• stacks of flattened,

membranous sacs• associated with ER• store & modify products

made by ER• one side receives

materials• once material is received it

is modified• once modified it is

transported to sending side – finished secretory products

are packaged into transport vesicles

• move to plasma membrane for export

Lysosomes• bags of digestive

enzymes surrounded by membranes– keeps enzymes out of

cytoplasm so cell does not digest itself

• breaks down macromolecules & other structures– digestive function

• fuse with food vacuoles & digest food

• destroy bacteria• recycle damaged

organelles

Vacuoles• membranous sacs• larger than vesicles• part of endomembrane

system• variety of functions• fresh water organisms

possess contractile vacuoles

• plant cells have central vacuoles– contribute to plant growth

by absorbing water & causing cells to expand

• other plant vacuoles– store organic nutrients– contain pigments that

attract insects– have poisons to protect

them from plant eaters

Mitochondria• power stations• large, usually sausage

shaped • sites of cellular respiration• burn food molecules, in

presence of O2, to release energy– aerobic respiration

• harvest energy from sugar & convert it to ATP– chemical currency all cells

• found in almost all cells of body

• number depends on cell’s energy requirements

Chloroplasts• plant cells• site of

photosynthesis light energy from sun converted into chemical energy of sugar & organic molecules

• contains green pigment, chlorophyll

Cilia & Flagella• Cilia

– shorter & more numerous than flagella

– move fluids across surfaces by producing sweeping movements

• Flagella– longer– usually one per cell– propel cells via

undulating whip like movement

• common in structure & movement

• core of microtubules wrapped in plasma membrane

• Cilia and flagella

Cytoskeleton• internal framework made of protein

filaments• like bones & muscles of cells• 3 types of fibers• Microfilaments

– slender protein strands of actin– helps cells change shape or

contract– amoeboid movement

• Intermediate fibers– fibrous proteins give them

ropelike structure– maintain cell shape & anchor

organelles• Microtubules

– straight, hollow tubes made of globular proteins-tubulins

– reinforce cell shape– also responsible for movement

of cilia & flagella

Fill in the Parts of the Typical Cell

Cell Surfaces• cells must

communicate with each other

• cell junctions

• connect cells

• allow communication

Plant Cell Connections• cell walls are multilayered• between walls is a sticky

polysaccharide– glues cells together

• cell walls are thick but not completely isolated from cells next to them

• channels or plasmodesmata connect adjacent cells– form communication system

between cells• connects cytoplasm of one cell

with its neighbor• water & small molecules are

able to pass through these channels

Animal Cell Connections• adjacent cells are

connected with junctions• Tight junctions

– binds cells closely together

• Adherens• Desmosome

– attach cells with fibers forming sheets of cells

• Gap junctions– form channels– allow water & small

molecules to pass

Cell Transport• lipid bilayers are not permeable to ions

such as K+, Na+, Ca2+,Cl- & HCO3

-

• channels are needed for passage • two basic ways materials move in & out• Passive transport mechanisms

–require no energy• Active transport mechanisms

–need energy–usually in form of ATP

Transport Types• Diffusion

– from higher to lower concentrations– gradient is formed– no energy required

• Facilitated Diffusion– diffusion using transport protein– no energy required

• Active Transport– requires energy (ATP)

• Osmosis– only water– diffusion of water across semi-permeable

membrane

Diffusion• passive • Molecules-in constant movement due to

thermal energy of heat• move from areas of higher to areas of

lower concentration• Random movement• can be made to move directionally• membrane between solution with dye on

one side and no dye on other• dye molecules move to side where less

concentrated• each molecule moves randomlynet

migration is to side with no dye• dye will continue to diffuse until both

sides have same concentration– point of dynamic equilibrium

• molecules will still move back & forth but at same rate

• there will be no change in concentration of dye on either side of membrane

Rate of Diffusion• Distance

– shorter distancesfaster diffusion

– takes less time to eliminate concentration gradient

• Size of concentration gradient– larger concentration gradients

proceed faster than smaller ones• Molecule size

– smaller molecules diffuse faster than larger ones

• Temperatures– higher temps diffuse substances

faster• Electrical forces

– opposite charges attract; similar ones are opposed

• interior of cell membrane is negative;• negative charges inside cell pulls

positively charged materials into cell

Diffusion

Facilitated Diffusion • diffusion across cell

membranes is selectively permeable

• impermeable to some substances

• others need transport proteins

• facilitated diffusion

Osmosis• diffusion of water through selectively

permeable membrane• only refers to water movement• Semi permeable membrane• total concentration of dissolved ions

& molecules on either side of membrane remains same since membrane is not permeable to them

• membrane is freely permeable to water

• whenever a solute concentration gradient exists concentration gradient exists for water as well

• water passes by diffusion from regions of lower to regions of higher solute concentration

• water diffuses toward solution with higher solute concentration or down concentration gradient for water

Isotonic Solutions• solutions of equal

solute concentrations

• do not produce osmotic flow

• movement of water in = movement of water out

• volume on both sides of membrane is unchanged

Hypotonic Solution• solutions with lower

concentrations of solute on one side of the membrane

• water moves across membrane by osmosis

• cell swells• if continues cell may

rupture

Hypertonic Solution• concentration

of solutes is greater outside cell than inside

• cell shrinks

Water Balance-Osmoregulation

• to survive cells must balance excessive water uptake or loss

• plant & bacterial cells avoid bursting in hypotonic surroundings by strong cell walls

• allows turgor to build• turgor pressure = osmotic

pressureosmosis stops• fresh water fish-hypotonic

environments use kidneys & gills to prevent water buildup

• paramecium have contractile vacuoles to bail out excess water that continually enters from hypotonic pond water

Active Transport• used to move molecules & ions

against concentration gradients

• requires energy-ATP

• high energy bonds in ATP are broken to provide energy

• concentration gradient-not required– cell can import or export regardless

of intra- & extra- cellular concentrations

• allows cells to maintain internal concentration that is different from environmental concentrations

Bulk Movement• movement of

larger molecules & large volumes of fluid

• endocytosis

• exocytosis

Endocytosis• cell ingestion• requires energy• part of plasma membrane folds inward

forming a pouch• pouch is pinched off from membrane so

incoming materials are enclosed in a vesicle-endosome

• Pinocytosis– cell drinking– ingestion of fluids or small particles– occurs in almost all cells continually– not selective

• Phagocytosis – cell eating– particles are engulfed & packaged into

food vacuoles– occurs in specialized cells such as

neutrophils & macrophages• Receptor-mediated endocytosis

– cell selects what to ingest– cholesterol is taken up by this method

Exocytosis• secretion or removal of

things from cell• membrane-bound

vesicles move to cell surface

• fuse with plasma membrane

• release contents into extracellular fluid