Prokaryotic Cells Eukaryotic Cells

•domains Bacteria & Archaea•1-10 μm•DNA located in nucleoid region•cell wall•capsule•pili•flagella

•domain Eukarya (protists, fungi, plants, & animals)•10-100 μm•DNA located in nucleus•organelles

•plasma membrane•cytosol/cytoplasm•ribosomes•chromosomes

Limits on Cell Size

• as a cell increases in size, its volume grows proportionally more than its surface area

• cells need a surface area large enough to accommodate its volume

• if the surface area : volume ratio is too great, the rate of chemical exchange with the environment may be too slow to meet the cell’s needs

Generalized Animal Cell

Generalized Plant Cell

Nucleus• contains most of the cell’s

genes• directs protein synthesis

by synthesizing mRNA• surrounded by a porous

double membrane called the nuclear envelope

• DNA is organized into chromosomes (made up of chromatin)

• nucleolus – sythesizes rRNA (ribosomal subunits)

Ribosomes• made of rRNA and protein• carry out protein synthesis• free ribosomes make proteins that function within cytosol• bound ribosomes make proteins destined for insertion

into membranes, for packaging within organelles, or for secretion

Endomembrane System• consists of membranes related through direct

physical continuity or by vesicles

• includes:• nuclear envelope• endoplasmic reticulum• Golgi apparatus• lysosomes• vacuoles & vesicles• plasma membrane

Endoplasmic Reticulum• continuous with nuclear envelope• rough ER • has ribosomes attached to surface• makes secretory proteins• makes membrane

• smooth ER• lacks ribosomes• synthesizes lipids• metabolizes carbohydrates• detoxifies drugs/poisons• stores calcium ions

Golgi apparatus• consists of flattened membranous sacs• two poles:• cis = receiving end• trans = shipping end

• modifies products of ER, stores them, “tags” them, & sends them to other destinations

• manufactures macromolecules (ex: polysaccharides)

Lysosome• contains hydrolytic

enzymes• fuse with vesicles or

vacuoles to…• digest macromolecules• recycle organic material

(ex: old organelles)• break down food• destroy invaders

Vacuoles• similar to lysosomes

because they carry out hydrolysis in plant & fungal cells

• food vacuoles store & break down food

• contractile vacuoles pump excess water out of cell

• central vacuole of plant cells stores organic compounds & ions, acts as a disposal site for waste, contains pigments, and may contain poisons for defense against predators

Mitochondrion• site of cellular respiration• enclosed by 2

membranes: outer is smooth & inner is convoluted (cristae)

• between membranes is intermembrane space

• interior is called the matrix

• contains its own DNA & ribosomes

• number in cell is related to cell’s level of metabolic activity

Chloroplast• site of photosynthesis• contains chlorophyll• found in leaf cells & cells

of other green organs• enclosed by 2 membranes

with a narrow intermembrane space

• interior fluid is called the stroma

• stroma contains stacks of membranous sacs called thylakoids (a stack of thylakoids is called a granum)

• contains its own DNA & ribosomes

Peroxisome• bound by a single layer

of phospholipids• contains enzymes that

catalyze oxidation reactions producing hydrogen peroxide (H2O2) as a by-product

• additional enzymes break down the H2O2 which is toxic to the cell

Cytoskeleton• network of fibers

extending throughout cytoplasm

• provides mechanical support to the cell

• maintains the shape of the cell

• anchors organelles• involved in cell movement

(cilia & flagella)• may also be involved in

the regulation of biochemical activities

Components of the Cytoskeleton

• microtubules– shape & support the cell– serve as tracks for the movement of organelles– separate chromosomes during cell division– “9+2” arrangement and dynein arms cause cilia &

flagella to beat– grow out from centrosome (which includes a pair

of centrioles in animal cells)

continued

• microfilaments (actin filaments)– built from molecules of actin– helps cell bear tension (pulling forces)– play a role in cell motility– works with myosin to cause muscle cell contraction in

animals & cytoplasmic streaming in plant cells

• intermediate filaments– helps cell bear tension– reinforces shape of cell– helps anchor organelles– make up nuclear lamina (lining on nuclear side of

nuclear envelope)

Cell Wall• protects & maintains

shape of plant cell• prevents excessive

uptake of water• composed primarily of

cellulose in plants & chitin in fungi

• perforated by channels called plasmodesmata that connect adjacent cells

Extracellular Matrix• consists primarily of glycoproteins (carbohydrate

attachments to membrane proteins)• most abundant glycoprotein is collagen

Intercellular Junctions

• Plant Cells– plasmodesmata = cytoplasmic channels between

adjacent plant cells

• Animal Cells– tight junctions = bind cells tightly together to prevent

fluid from leaking into surrounding tissues– desmosomes = anchoring junctions (fasten cells

together)– gap junctions = cytoplasmic channels between

adjacent animal cells