The Role of Cell Organelles in Chlamydia’s Life Cycle

Goals• Study Chlamydia as a vehicle to understand the

interrelationships and functioning of various cell organelles.

• Identify potential future strategies for treating Chlamydia infections

Chlamydia Resources

Optional Reading

• “Can Chlamydia Be Stopped?” In the May 2005 edition of Scientific American

• Good overview of Chlamydia :http://www.cdc.gov/std/Chlamydia/STDFact-Chlamydia.htm

http://www.niaid.nih.gov/factsheets/stdclam.htm

http://pathmicro.med.sc.edu/mayer/chlamyd.htm

Chlamydia—a bacterial infection

Chlamydia trachomatis1. Common sexually transmitted disease (STD) – ~3.5 million Americans are infected with Chlamydia yearly

2. World's leading cause of preventable blindness – Flies transmit the bacterium to the eye

– Causes painful eye condition known as conjunctivitis

– Conjunctivitis may lead to Trachoma and then blindness

3. ~600 million infected world-wide with one or more Chlamydia strains

Chlamydia (Chlamydia trachomatis)

Signs & Symptoms• 85-90% do not show symptoms–Leads to irreversible damage before

detected• Testicular or abdominal pain • Painful urination in men• Burning and/or or itching of genitals• Discharge from genitals• Fever (late in disease)

Possible Complications1. Pelvic inflammatory disease

• Infertility (10K women/yr in USA!)• Ectopic or tubal pregnancy • Death of fetus

2. Eye infections3. Blindness4. Liver problems5. Heart problems6. Infant pneumonia

Chlamydia (Chlamydia trachomatis)

8. What “normally” happens when bacteria enter a cell?

Pelvic Inflammatory Disease

• Chlamydia over stimulates the body’s immune system

• Leads to inflammation of the fallopian tubes

• Blocks passage of eggs to uterus

• Possible Ectopic and tubal pregnancy

• Back to previous slide

Chlamydia (Chlamydia trachomatis)

Source: http://adam.about.com/reports/000046.htm

Macrophages: “Big Eaters”– Eat dead, injured,

and foreign cells– Engulfed cells

transported to lysosome for digestion

ID each of the following

1 = 2 =3 =4 =5 =

Phagocytosis—a macrophage snacking on bacteria

The formation and functions of lysosomes (Layer 1)

The formation and functions of lysosomes (Layer 2)

The formation and functions of lysosomes (Layer 3)

What happens when Chlamydia enters a cell?

Life Cycle of Chlamydia trachomatis

Source: http://pathmicro.med.sc.edu/mayer/chlamyd.htm

• Most Chlamydia infect columnar epithelial cells • Why not all cells

?

• Some may infect macrophages—the very cell that is supposed to kill bacteria!

Chlamydia Attachment

Source: http://www.chlamydiae.com/images/gifs6dec00/ctattach2.gif

Click here for detailed diagram of membrane structure

The detailed structure of an animal cell’s plasma membrane

How does Chlamydia hide itself within its host cell?

Source: “Can Chlamydia Be Stopped?” Scientific American. May 2005

Chlamydia…1. May use a tube (type III secretion

apparatus) to secrete proteins that block protein receptors on vesicle surface

• Adaptive value?

2. Divert glycolipids from golgi apparatus

• Glycolipids used to “remodel” the surface of the vesicle—adaptive value?

Future strategies for treating Chlamydia

Source: “Can Chlamydia Be Stopped?” Scientific American. May 2005

• New strategies are required since vaccines are ineffective—why don’t they work?

• Knowledge of Chlamydia’s life cycle allows for the development of future drugs

• How might a new drug work that would…1. Interfere with Chlamydia entering its host cell

2. Allow a lysosome to attach to a phagocytotic vesicle that contains Chlamydia?

3. Inhibit Chlamydia’s reproduction and growth within infected cells?

4. Halt Chlamydia’s ability to spread from cell to cell

Life Cycle of Chlamydia pneumoniaeChlamydia

pneumoniae • Colds• Bronchitis• !0% of all pneumonias

acquired outside of hospitals (300K in US/yr)

• Possibly linked to Arteriosclerosis leads to strokes & heart attacks

Source: http://www.chlamydiae.com/docs/biology/biol_devcycle.asp

Chlamydia’s Life Cycle (cont.)

Source: http://pathmicro.med.sc.edu/mayer/chlamyd.htm

1. Most Chlamydia infect columnar epithelial cells

2. Some may infect macrophages. 3. Elementary Bodies (EB)

• Rigid outer membrane that is extensively cross-linked by disulfide bonds. • Makes resistant to harsh environmental conditions both inside and outside of

the cell

4. Reticular Bodies (RB) • Non-infectious intracellular form of the Chlamydia. • Metabolically active replicating form of the Chlamydia. • Possess a fragile membrane lacking the extensive disulfide bonds

characteristic of the EB.

Summary of Chlamydia’sLife Cycle

Source: http://pathmicro.med.sc.edu/mayer/chlamyd.htm

1. The EBs bind to receptors on susceptible cells

2. Enter cell by phagocytosis

3. EBs reorganize and become RBs while inside vesicle

4. The chlamydia inhibit the fusion of the vesicle with the lysosomes and thus resist intracellular killing.

5. RBs replicate by binary fission and reorganize into EBs.

6. Each vesicle may contain 100 - 500 progeny

7. Eventually the RB and EB within the vesicle leave the cell by exocytosis

1. Nucleus:» Site of DNA, the

genetic material» Controls cellular

activities

2. Smooth Endoplasmic Reticulum:» Makes lipids and

lipids used in plasma membranes

3. Ribosomes: » Site of protein

synthesis

Eukaryotic Cell Structure

4. Rough Endoplasmic Reticulum: » Membrane bound

channel studded with Ribosomes

» Makes proteins found in other organelles and proteins exported from the cell

5. Golgi Apparatus: » Modifies newly made

proteins, lipids, and carbohydrates

6. Vesicles: » Membrane-bound

“balloons” that transport or store substances in cells

Eukaryotic Cell Structure

7. Lysosomes:» Sacs containing

enzymes that digests worn out cell parts

» Digests food ingested by phagocytosis

8. Cytoskeleton: » Protein fibers that help

a cell maintain its shape

» Some fibers involved with transport of vesicles

9. Mitochondria: » Harvests energy from

organic molecules (e.g. sugars and fats) to produce ATP—the energy “currency” of all cells!

Eukaryotic Cell Structure

Trace the pathway of a digestive enzyme from the protein’s gene to the

lysosome

Ribosome on Rough ER Producing a Protein such as GCase

– A ribosome reads mRNA to produce a protein molecule

ID of structures...1. ___________________2. ___________________3. ___________________4. ___________________

Rough E.R. to Golgi Apparatus

Transport from Golgi Apparatus Proteins modified

by Golgi Apparatus are either...Used inside cell e.g.____________________

_

Or

Exported from celle.g.

_____________________

Membrane Bound Glycolipids

– Glycolipids are normally found on membrane surfaces.

– Involved with cell – cell recognition

Synthesis of Glycolipids in Cells

1. Which organelle synthesizes lipids?2. Where are sugars added to newly made

biochemicals? i.e. where do chemical modifications occur?

(note: sugars are synthesized in the cytoplasm)

3. Trace the biosynthetic pathway of a glycolipid through the cell from where the lipid is produced to the glycolipids home in the plasma membrane

Glycolipid Synthesis and Transport

Nucleic Acids: DNA and RNA

1. Nucleic acids» are long chains of nucleotides» the “genetic molecules”

2. Nucleotides» the building blocks (monomers) of DNA and

RNA» As monomers they power almost all

processes in all cells– e.g. ATP

DNA Nucleotides1. Four Kinds of nucleotides in DNA

A = Adenine T = Thymine

G = Guanine C = Cytosine

2. Central dogma of Biology

a. The order of nucleotides in a gene determines the order of ________________________________ in a protein

– The order of _____________________ in a protein determines _______________________ of a protein which in turn determines the _____________________ of the protein.

Nucleotide Structure

Nucleotides are....

the building blocks (monomers) of DNA and RNA

As monomers they transfer energy to power almost all processes in all cells

–e.g. ATP

~26,000 genes code for proteins that perform all life functions