Lecture 4

Prokaryote Cell Structure & Function

Cell Diagram: Mariana Ruiz, pub domain

Size of Living Things

Diagrams: http://www.cellsalive.com/howbig.htm

1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm

1mm = 1000 µm = 1000000nm

1 µm = 1000nm

The Cellular Level of Organization

Living things are constructed of cells.

Living things may be unicellular or multicellular.

Cell structure is diverse but all cells share common characteristics.

Cells are small so they can exchange materials with their surroundings.

Surface area relative to the volume decreases as size of cell increases.- limits the size of cells

___________________ states:

1. All organisms are composed of one or more cells.

2. Cells are the basic unit of structure and function in organisms.

3. All cells come only from other cells.

Two basic types of cells

Diagrams:

Prokaryotic & Eukaryotic Cell, Mariana Ruiz

__________________________________________

Prokaryotes

Tell me about Prokaryotes…

Binary Fission

Diagrams:

Prokaryotic Mariana Ruiz

Binary Fission, JW Schmidt

Prokaryote Genetics

___________

Region of cytoplasm where chromosomal DNA is located.

Usually a singular, circular chromosome

____________

Small extra piece of chromosome/genetic material.

5 - 100 genes

Not critical to everyday functions.

Can provide genetic information to promote:

- Antibiotic resistance

- Virulence factors (molecules produced by pathogen that specifically influence host's function to allow the pathogen to thrive)

- Promote conjugation (transfer of genetic material between bacteria through cell-to-cell contact)

STRUCTURE OF MICOBIAL CELLS

Prokaryotes

______________

Also known as proto-plasm.

Gel-like matrix of water, enzymes, nutrients, wastes, and gases and contains cell structures.

Location of growth, metabolism, and replication.

______________

Bacteria’s way of storing nutrients

Staining of some granules aids in identification

STRUCTURE OF MICOBIAL CELLS

Prokaryotes

_______________

Found within cytoplasm or attached to plasma membrane.

What are they made of?

What do they do?

Composed of a small (30S) subunit and a large (50S) subunit.

Cell may contain thousands of ribosomes.

_________________

Cellular "scaffolding" or "skeleton" within the cytoplasm.

Major advance in prokaryotic cell biology in the last decade has been discovery of the prokaryotic cytoskeleton.

Previously thought to be a feature only of eukaryotic cells.

Eukaryotic Cells

Diagrams/Photos:

Fluorescent Cell: NIH, Pub Domain

Prokaryotes - Plasma Membrane

Separates the cell from its environment.

Phospholipid molecules oriented so that hydrophilic (__________) heads directed outward and hydrophobic (__________) tails directed inward.

Proteins embedded in two layers of lipids (lipid bilayer).

___________________ to allow substances to pass into and out of the cell.

Diagrams:

Prokaryotic Cell, Mariana Ruiz

Membrane: NIST

Prokaryotes – Plasma Membrane as a Barrier

Primary function of plasma membrane → regulate movement of molecules entering or leaving cell.

Movement of molecules across plasma membrane requires energy.

PASSIVE TRANSPORTMovement of molecules is passive if no energy sources

of the cell are expended.

_____________ = when molecules move from a higher to a lower concentration.

What type of things might affect the rate of diffusion?

Diffusion Animation: biologycorner.com

Prokaryotes – Plasma Membrane as a BarrierPASSIVE TRANSPORT (Continued)

_____________ DiffusionProteins assist in diffusion of molecules across plasma membrane.

Movement only occurs in the presence of a concentration gradient.

Some molecules move across the membrane more quickly if diffusion is facilitated by a carrier molecule.

Diagram:

Facilitated diffusion, Mariana Ruiz

Prokaryotes – Plasma Membrane as a Barrier

Osmosis

Diffusion of ________ across the plasma membrane.

Environment surrounding cells may contain amounts of dissolved substances (solutes) that are…equal toless thangreater than …those found within the cell.

Tonicity

__________: no net movement of water between cell and environment

__________: a higher concentration of solute.

__________: a lower concentration of solute.

Water will always move toward a hypertonic environment!!

Diagrams:

Osmosis - www.scienceaid.co.uk/biology/plants/osmosis.html

Blood Cells: Mariana Ruiz

Prokaryotes – Plasma Membrane as a Barrier

_______________ TRANSPORTHow most molecules move across the plasma membrane.

Analogous to a pump moving water uphill.

Types of active transport are classified by type of energy used to drive molecules across membranes.

ATP Driven Active TransportEnergy from adenosine triphosphate (ATP) drives substances across the plasma

membrane with the aid of carrier molecules.

Diagram:

Source unknown

Peptidoglycan - Rigid mechanical support - Freely permeable to solutes

Peptidoglycan is a huge polymer of interlocking chains of identical peptidoglycan monomers.

Backbone of peptidoglycan molecule composed of two derivatives of glucose:

N-acetylglucosamine (NAG)N-acetlymuramic acid (NAM)

NAG / NAM strands are connected by interpeptide bridges.

Prokaryotes – Cell Wall

Image:

Peptindoglycan Structure: NicolasGrandjean

From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are:

Gram-positive Gram-negative

Prokaryotes - Cell Wall

Images: PHIL Public Health Image Library

Prokaryotes - Cell Wall: Gram-Negative & Gram-Positive

Image:

Prokaryotic Cell, Mariana Ruiz

Gram +-, Julian Onions

Why are these differences in cell wall structure so important?

Images: Sources unknown

Prokaryotes - Glycocalyx

Some bacteria have an additional layer outside of the cell wall called the glycocalyx.

This additional layer can come in one of two forms:

1. Slime Layer2. Capsule

STRUCTURE OF MICOBIAL CELLS

Prokaryotes - Glycocalyx Some bacteria have an additional layer outside of the cell

wall called the glycocalyx.

This additional layer can come in one of two forms:

1. ______________________glycoproteins loosely associated with the cell wall.

Slime layers cause bacteria to adhere to solid surfaces and help prevent the cell from drying out.

StreptococcusThe slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities).

Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque.

StaphylococcusThe slime layer of Gram+ Staphylococcus allows it to thrive in the salty, hypertonic environment of the skin.

Glycocalyces are not specific to Gram+ or Gram- bacteria, sometimes only some members of a certain species (strains) have a glycocalyx, whereas others don’t.

STRUCTURE OF MICOBIAL CELLS

Prokaryotes - Glycocalyx

2. ___________________

polysaccharides firmly attached to the cell wall.

Capsules adhere to solid surfaces and to nutrients in the environment.

Adhesive power of capsules is a major factor in the initiation of some bacterial diseases. Capsule also protect bacteria from being phagocitized by cells of the hosts immune system.

STRUCTURE OF PROKAROTIC CELLS

Prokaryotes - Glycocalyx Bacterial Capsule and Meningococcal Infection

Meningococcal infection is caused by meningococcal bacteria (Neisseria meningitidis).

Causes:1. meningococcal meningitis (infection of the

meninges/spinal cord)2. meningococcal septicaemia (blood

poisoning).

Of the two forms, meningococcal septicaemia is the most dangerous.

Meningococcal bacteria are the most common cause of bacterial meningitis.

Approximately 5% of people who suffer from meningococcal meningitis will die.

STRUCTURE OF PROKAROTIC CELLS

Meningococcal bacteria grow in pairs called diplococci often surrounded by a capsule coat. Over a million of these would fit on the head of a pin.

http://www.meningitisuk.org/about-meningitis/bacterial-meningitis.htm

Prokaryotes - Endospores

Dormant, tough, non-reproductive structure produced by small number of bacteria.

Primary function of endospores:__________________________________________________

Resistant to radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants.

Endospores commonly found in soil and water, where they may survive for long periods of time.

A stained preparation of Bacillus subtilis showing endospores as green and the vegetative cell as red

Image:

Stain: Jerry Keplinger, James H. Quillen College of Medicine

Procedure: Source link no longer works

STRUCTURE OF PROKAROTIC CELLS

_____________________

The most significant cause of pseudomembranous colitis

Severe infection of the colon, often happening after normal gut flora is eradicated by use of antibiotics. The C. difficile bacteria naturally resides in the body, but becomes overgrown.

C. difficile overgrowth is harmful because the bacterium releases toxins that cause:

* Bloating and constipation* Diarrhea with abdominal pain* Severe diarrhea with mucus and blood present in feces* Body aches and severe abdominal pain caused from ulcerated intestines

• Treatment includes specific anticlostridial antibiotics, e.g. metronidazole or vancomycin.

• News story link: http://www.thesun.co.uk/sol/homepage/news/article860499.ece

STRUCTURE OF PROKAROTIC CELLS

Prokaryotes – Surface Appendages

Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces.

Consist of delicate stands of proteins.

___________Long, thin extensions that allow some bacteria to move

about freely in aqueous environments.

____________ (endoflagella)Wind around bacteria, causing movement in waves.

____________ Most Gram- bacteria have these short, fine appendages

surrounding the cell. Gram+ bacteria don’t have.

No role in motility. Help bacteria adhere to solid surfaces. Major factor in virulence.

____________ Tubes that are longer than fimbriae, usually shorter than

flagella. Use for movement, like grappling hooks, and also use conjugation pili (singular = pilus) to transfer plasmids.

Images:

Flagella: Mike Jones Wiki

Axial Filament: Indiana USchool of Med

EColi: Pub Library of Science

Neisseria gonorrhoeae

Gonorrhoeae one of the most communicable disease in the US. 125 cases per 100,000. Teens 15-19 yo 634 cases per 100,000. Young adults

20-25 460 per 100,000.