Prokaryotes (Bacteria & Archaea)

Prokaryotic cells (“before” nucleus)

• lack a nucleus & other organelles

• small, single-celled

• organisms of the following types:

Bacteria

(diameter ~1-10 mm)

Archaea

Bacterial Cell Structures

Ribosome

Cytoplasm

Nucleoid

Glycocalyx

Cellwall Cell

membrane

Flagellum

Inclusions

Peptidoglycan layer of cell wall

Lipopolysaccharide

(LPS)

Outermembraneof cell wall

Cell membrane

n

O side chain(varies inlength andcomposition)

Gram-negative cell wall

Lipid A(embeddedin outermembrane)

Fatty acid

Porin

(sectioned)

Periplasmic space

Phospholipid layers

Integral

proteins

Corepolysaccharide

Porin

• thin layer of peptidoglycan

Gram-negative Cell Wall

• outer membrane containing

lipopolysaccharide (LPS)

• Lipid A (endotoxin) + polysaccharide

Peptidoglycan layer(cell wall)

Cell membrane

Teichoic acid

Integralprotein

Lipoteichoic acid

Gram-positive cell wall

Gram-positive Cell Wall

• thick-layered peptidoglycan cell wall

• NO outer membrane

Bacterial Growth Curve

Viruses

Viruses are extremely small intracellular parasites with no

metabolic ability of their own.

• have none of the characteristics of living cells

• do NOT reproduce or metabolize on their own

• do NOT respond to their environment or

• depend on host cells for their reproduction(which are typically destroyed in the process)

**It’s hard to “kill” something that’s not really alive, so

antibiotics that kill bacteria, fungi, etc, do NOT harm viruses**

E. coli (bacterium)(1000 nm x 3000 nm)

Red blood cell (10,000 nm in diameter)

Smallpox virus(200 nm x 300 nm)

Tobacco mosaic virus(15 nm x 300 nm)

Bacterialribosomes

(25 nm)

Poliovirus(30 nm)

Bacteriophage T4(50 nm x 225 nm)

Bacteriophage MS2(24 nm)

Size of Viruses

• almost all

viruses are

smaller than

the smallest

bacteria

What’s a Virus made of?

All viruses consist of at least 2 components:

Genetic Material

• usually a single DNA or RNA molecule

• can be single or double stranded, linear or circular

A Capsid• a hollow protein capsule which houses the

genetic material

Some viruses also contain:

An Envelope

• membrane from host cell with viral proteins (spikes)

that surrounds the capsid

• contains the viral genes

The Viral Capsid

Capsids are hollow, protein “shells” that:

• are an array of

protein subunits

called capsomeres

• house the genetic

material (DNA/RNA)

• are frequently

involved in host

recognition & entry

• vary in shape, size

among viruses

The Viral EnvelopeThe capsid of some viruses

is enclosed in a phospholipid

membrane called an

envelope containing viral

proteins called “spikes”:

• membrane comes

from host cell

• “spike” proteins involved

in attachment and entry

into host cell

Viral MorphologyViruses come in 4 basic morphological types:

1. Polyhedral Viruses

• capsomeres in capsid have a

“polyhedral” arrangement

2. Helical Viruses

• capsomeres in capsid have a

“helical” arrangement

4. Complex Viruses

• consist of multiple

types of structures

3. Enveloped Viruses

The Viral Reproductive CycleVIRUS

2

1

3

4

Attachment& Entry

Replication ofViral Gemone

Expression ofViral Genes

Self-assembly ofnew virus particles

DNA

Capsid

HOSTCELL

Viral DNA

ViralDNA

mRNA

Capsidproteins

5 Release from the host cell

• attachment requires highly

specific interactions between

viral capsid or envelope

proteins and host cell surface

molecules

• attachment determines the

host cells a virus can infect