An Introduction to Cell Structure and Function

Theodore Schwann

Matthias Schleiden

they both developed the Cell Theory which states that all living things are composed of cells

occurs in prokaryotes and eukaryotes

does not occur in Viruses

Growth characteristics

occurs in prokaryotes and eukaryotes

viruses- occurs only inside a host cell

Reproduction characteristic

Occurs in all prokaryotes and eukaryotes

Viruses: Occurs in some viruses as a reaction to host cells

Responsiveness characteristics

occurs in all in prokaryotes and eukaryotes

Viruses: use host cells metabolism

Metabolism characteristics

present in all prokaryotes and eukaryotes

Viruses: lack cytoplasmic membrane or cellular structure

Cellular structure characteristics

Prokaryotes

(“before nucleus”)

Prokaryotes (“before nucleus”)

- it’s distinctive structural feature is not what they have, but what they lack:

a. lacks internal membrane-bound structures

b. simpler than eukaryotes

Eukaryotes

(“true nucleus”)

Eukaryotes (“true nucleus”)

have membrane surrounding their DNA, forming a nucleus

Eukaryotes (“true nucleus”)

have “true nucleus”; with membrane-bound compartments (organelles)

Eukaryotes (“true nucleus”)

larger and more complex than prokaryotes

plants

animals

protozoa

algae

fungi

examples of eukaryotes

Chloroplast

Central vacuole and tonoplast

cell wall

plasmodesmata

Not in animal cells

Lysosomes

Centrioles

Flagella (in some plant sperm)

Not in plant cells:

0.2 micrometer diameter

Virus Varicellovirus size

1 micrometer diameter of

Bacterium Staphylococcus

5 micrometer length

Parasitic protozoan Giardia size

13 cm diameter 130,000 u m

Ostrich e g g

Glycocalyces (glycocalyx: singular)

a gelatinous, sticky substance surrounding outside the cell

Glycocalyces

composed of polysaccharides or polypeptides or both

Glycocalyces

“sugar cup”

capsule

a glycocalyx which is composed of repeating units of organic chemicals firmly attached to the cell surface

Streptococcus pneumoniae

Klebsiella pneumoniae

Glycocalyces ( capsule) example

slime layer

a loose, water soluble glycocalyx; often viscous(sticky) providing attachments to surfaces

oral bacteria

example of glycocalyces (slime layer)

Flagella (flagellum: singular)

long whip-like structures that extend beyond the surface of the cell and the glycocalyx; propels the cell

Monotrichous

Amphitrichous

Lophotrichous

Peritrichous

Flagellar Arrangement of Bacteria

Fimbriae

non-motile extensions

Fimbriae

sticky proteinaceous, bristle-like projections used to adhere to one another and to substances

Fimbriae

shorter than flagella, there may be 100 per cell

Fimbriae

serves as an important function in biofilms-are slimy masses of bacteria adhering to a substrate

Pili ( Pilus: singular )

are tubules composed of a protein called pilin

Pili ( Pilus: singular )

- longer than fimbriae but shorter than flagella

- 1-10/ cell

(attachment pili)

used by bacteria to move across a substrate or towards another bacterium

(conjugation pili)

mediates the transfer of DNA from one cell to the other

Prokaryotic Cell Walls

provides structure and shape to the cell and protects it from osmotic forces

Prokaryotic Cell Walls

assists some cells in attaching to other cells or in eluding antimicrobial drugs

animal cells

note that _ do not have cell walls

Bacterial cell wall

composed of peptidoglycan, a complex polysaccharide which is composed of two regularly alternating sugars called N-acetylglucosamine (NAG) and N-acetyl muramic acid (NAM) which are structurally similar to glucose

N-acetylglucosamine (NAG) and N-acetyl muramic acid (NAM)

two regularly alternating sugars that composed the peptidoglycab which are structurally similar to glucose

NAG and NAM

chains of _are attached to other chains by cross-bridges of four amino acids (tetrapeptides)-these cross bridges are the “peptido” portion of peptidoglycan

Gram Positive Cell Walls (Purple)

Gram Negative Cell Walls (Pink)

Two Basic Types of Bacterial Cell Walls

Gram Positive Cell Walls (Purple)

with thick layer of peptidoglycan (20% of the dry weight of the cell) and unique polysaccharides called teichoic acids which are covalently linked to lipids forming lipoteichoic acids that anchor the peptidoglycan to the cell membrane

teichoic acid

unique polysaccharides

lipoteichoic acid

technically acids which are covalenrlt linked to lipids

Mycobacterium have cell walls up to 60% mycolic acid-a waxy lipid (AFB)

example of Gram Positive Cell Walls (Purple)

Gram Negative Cell Walls (Pink)

with thin layer of peptidoglycan (1-2% of the dry weight of the cell); outside this layer is a bilayer membrane composed of phospholipids, channel proteins (called porins), and lipopolysaccharides (LPS)

porins

channel proteins

lipopolysaccharides (LPS)

union lipid of sugar

lipid A (endotoxin)

The lipid portion of LPS is known as

LPS lipopolysaccharides

is released from dead cells when the cell walls disintegrates, and it may trigger fever, inflammation, shock, and blood clotting in humans

Periplasmic space

found between the cell membrane and outer membrane; this contains the peptidoglycan and periplasm

Periplasm

the gel between membrane of gram negative cells; contains water, nutrients and substances secreted by the cell (digestive enzymes, and proteins)

e.g. Mycoplasma pneumoniae

Bacteria Without Cell Walls

Archaeal Cell Walls

contains a variety of specialized polysaccharides and proteins, but NO peptidoglycan (separate group)

Gram(+) archaeal walls

like gram (+) bacteria, they have thick wall and stains purple

Gram(-) archaeal walls

have a layer of protein covering the wall, rather than a lipid membrane in gram (-) bacteria, but they stain pink.

Prokaryotic Cytoplasmic Membranes

beneath the glycocalyx and cell wall

Prokaryotic Cytoplasmic Membranes

also referred to as cell membrane or plasma membrane

Prokaryotic Cytoplasmic Membranes

composed of lipids and associated proteins

Bacterial membranes

contain phospholipids; some have sterol-like molecules called hopanoids

hopanoids

sterol-like molecules

Archaeal membranes

composed of lipids that lack phosphate groups and have branched hydrocarbons linked to glycerol by ETHER linkages instead of ester linkages

Cytoplasm of Prokaryotes

the general term used to describe the semi-liquid, gelatinous material inside a cell; it’s a semi- transparent fluid, elastic and aqueous

Cytosol

Inclusions

Nonmembranous organelles

Cytoplasm of Prokaryotes composed of

Cytosol

composed of mostly water, but also contained dissolved suspended substances, including ions, carbohydrates, lipids and wastes.

Cytosol

also contains the cell’s DNA (single, circular chromosome) which is not surrounded by a membrane in a region called nucleoid

Inclusions

are deposits found within the cytosol; may include reserve deposits of lipids, starch or compounds containing nitrogen, phosphate and sulfur

Inclusions

serve as a diagnostic tool for pathogenic bacteria

e.g. aquatic cyanobacteria

- gas vesicles (store gases in protein sacs)

magnetobacteria (store magnetites)

examples of inclusions

gas vesicles

store gases in protein sacs

magnetobacteria

store magnetites

Ribosomes

1000 ribosomes

site of protein synthesis; prokaryotic cells have about ___ ribosomes which gives the cytoplasm a grainy appearance

Svedbergs (S)

Sedimentation rate

the approximate size of ribosomes is expresses in __which is determined by either their

70s

prokaryotic ribosomes are

80S

while eukaryotic ribosomes are

ribosomal RNA (rRNA)

all ribosomes are composed of two subunits, each of which is composed of protein and a type of RNA called

antibiotics

many __ act on prokaryotic 70S ribosomes

cytoskeleton

were long thought to lack __, but recent research has revealed that rod-shaped prokaryotes have a simple one while spherical prokaryotes appear to lack

cytoskeleton

rod shaped prokaryotes have a simple one

cytoskeleton

spherical prokaryotes appear to lack

Cytoskeleton

are internal network of fibers which play a role in forming a cell’s basic shape

Glycocalyces

present in animal and protozoan cells but absent in eukaryotic cells that have cell walls

Glycocalyces

Functions:

a. anchor cells to each other

b. strengthening the cell surface

c. protection against dehydration

d. cell-to-cell recognition and communication

Flagella

differs structurally from prokaryotic cells

Flagella

the shaft is made up of tubulin arrange in chain to form microtubules

tubulin

microtubules form and made up of

Flagella

has “9+2” arrangement

Flagella

the filaments are anchored to the cell by a basal body, but NO hook connects the two parts as in prokaryotic cells arrangement of microtubules

basal body

the filaments are anchored to the cell by a

Flagella

the basal body has triplets of microtubules instead of pairs and there are no microtubules in the center, so it has a “9+0” arrangement of microtubules

“9+0” arrangement

the basal body has triplets of microtubules instead of pairs and there are no microtubules in the center, so it has a__of microtubules

cytosol

surrounded by an extension of the cell membrane and are filled with __

inside the cell

thus the flagella of eukaryotes are __, not extensions outside the cell

Flagella

may be single or multiple and are generally found at the end of the pole of the cell.

Flagella

Functions:

undulate rhythmically rather than rotating; do not move in runs and tumble

Cilia

hair-like structures; shorter and more numerous than flagella

Cilia

composed primarily of tubulin microtubules which are arranged in “9+2” arrangement of triplets in their basal bodies

cilia

NO prokaryotic cells have