Prokaryotic and Eukaryotic Cells

Structure and Function

In general microbes or microorganisms may be either

prokaryotic (bacteria) or eukaryotic (protists, fungi,

and some animals).

However, there are some microbial organisms that

appear to be intermediates between prokaryotes and

eukaryotes (they possess a nucleus but do not have

mitochondria or chloroplasts, an example is Giardia

intestinalis.

Prokaryotes differ from eukaryotes in several ways

including but not limited to:

Characteristics Prokaryotic Eukaryotic

Types bacteria (monerans) protists, fungi, plants, and animals

Organization unicellular usually multicellular (exception some

protists)

Cell size small (0.1-10um) larger (10-100um)

Membrane-bound organelles absent present

Reproduction asexual asexual and sexual

DNA circular linear

Proteins assoc. with DNA Basic Histone

Plasma membrane No sterols Sterols

Ribosomes 70S 80S

Cytoskeleton Absent present

PROKARYOTIC

CELLS

Key Functions of Cells

A boundary that keeps the cellular contents separate from the external environment but allows for the transfer of some substances into and out of the cell.

Replication of DNA

Synthesis of cellular components

The ability to obtain energy through metabolic processes

Appendages are basically involved in

movement or adhesion

Flagella (singular flagellum) are cellular appendages that consist of three parts:

• a filament that rotates for movement

• a hook where the filament attaches

• a basal body that anchors the hook to the cell

• the arrangement of the hook/basal body articulation allows the hook with its filament to rotate 360o

Arrangements of Flagella

polar - flagella are attached at one or both ends of the cell

monotrichous - a single flagellum at one end

lophotrichous - multiple flagella arising from one or both ends

amphitrichous – a single flagellum arises from each end

peritrichous - flagella are randomly dispersed over the cell surface

Axial filaments

are modified flagella that

occur in spirochetes

Non-locomotor appendages

Pili are longer and sparser

than fimbriae.

fimbriae are involved in

adhesion and pili (found

only in Gram - bacteria)

are involved in

conjugation ( a “mating”

process).

Cell envelopes differ between taxa

but they basically consist of three

layers:

The capsule or slime layer (outermost layer) differs greatly in thickness, organization and chemical composition depending on the bacterial species. T

Beneath the outer layer lies the cell wall.

The cell membrane is a thin flexible sheet that surrounds the contents of the bacterial cell. Its functions include: transport, energy extraction, nutrient processing, and synthesis

The Gram Stain

An important tool in the identification of bacteria is the Gram stain. Some bacteria are Gram + while others are Gram - (some however, do not show a Gram reaction). Gram + bacteria stain purple (the color of the primary dye) and Gram - bacteria stain pink (the color of the counterstain or second dye). The Gram stain is a differential staining technique because different species of bacteria stain differently. The difference is a result of the composition of the cell wall.

The protoplasm or cytoplasm

is the dense gelatinous

solution within the cell

membrane that is the

primary site for the cell’s

biochemical and synthetic

processes. The following

are found within the

protoplasm of the

prokaryotic cell:

chromatin body or the

bacterial chromosome

nucleoid or nuclear region

of the cell that is

associated with the

chromatin body

plasmids are tiny circular

extrachromosomal strands

of DNA

ribosomes are small

structures consisting of

RNA and proteins that are

involved in protein

synthesis

inclusions or granules are

areas where nutrients are

concentrated

Endospores are dormant

structures produced by

some species of Bacillus

and Clostridium.

Shapes and arrangements of bacteria

There are six common shapes of bacteria: coccus, bacillus, coccobacillus, vibrio, spirochete, and spirullum and there are several arrangements of these cells: single, chains (strepto-), clusters (staphylo-), pairs (diplo-) etc.

Eukaryotic Cell

Cell Membrane Cell membrane

Structure

Components

Arrangement

Functions include

Barrier

Transport (know diffusion, osmosis, facilitated diffusion and active transport)

Recognition (e.g., self vs. non-self)

Reception (for protein hormones)

Adhesion

Nucleus

Structure and Function

– membrane similar to cell

membrane (similar

function)

– Nucleolus (formation of

ribosomes)

– Chromosomes (gene

expression)

– Nucleoplasm (matrix)

Ribosomes

• Structure

– rRNA

– Proteins

• Function

– Site of protein formation

(translation)

• Found in both

prokaryotes and

eukaryotes (different

structurally)

Endoplasmic Reticulum

• Structure membranous system of tunnels and sacs

– Rough – with ribosomes on surface

– Smooth- no ribosomes on surface

• Function

– Rough – protein synthesis

– Smooth- lipid synthesis

Golgi Apparatus

• Structure also

membranous, kind of

like a stack of pancakes

• Function processing of

lipids and proteins

Lysosomes

• Structure membrane

bound sac containing

hydrolytic enzymes

• Function digestion

Mitochondria

• Structure – cigar-

shaped, double

membrane-bound

organelle

• Function – Energy

transfer by ATP

synthesis

Chloroplast

• Structure

– Also cigar or spindle

shaped, double

membrane-bound, green

• Function

– Site of photosynthesis

OTHER STUCTURES

• Cell walls, not in animal cells

• Vacoules

• Cytoskeleton

• Cytoplasm