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Genes & BacteriaPacket #48

Chapter #18

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The Anatomy of Bacteria

Introduction

Recall that cells, and organisms, fall under two major categories Prokaryotes Eukaryotes

Based on the classification system, bacteria are prokaryotes and are found in Kingdom Archaebacteria and Eubacteria. More to come later on Kingdoms later.

A Look Inside Prokaryotes

In prokaryotes, ribosomes are present in two sizes: - 30 S (Subunits) 60 S

Contains polyamines and magnesium

Contain plasmids that have 7 – 8 genes A plasmid is a small ring of DNA that carries accessory

genes separate from those of a bacterial chromosome Plasmids may also be found in yeast; a eukaryote.

Shapes of Bacteria

Common shapes of bacterial cells Coccus

Spherical Bacillus

Rod shaped Spiral

Spirillum Rigid helix

Spirochete Flexible helix

Vibrous Comma shaped

Categories of Eubacteria—The Cell Wall

Most eubacteria have cell walls composed of peptidoglycan and can fall into two categories Gram positive bacteria Gram negative bacteria

Gram Positive vs. Gram Negative Bacteria

Gram positive bacteria Very thick wall Consisting

mostly of peptidoglycan

Gram negative bacteria Thin peptidoglycan layer

and an outer membrane resembling the plasma membrane

Some species of bacteria produce a capsule that surrounds the cell wall

Pilli & Flagella

Pilli Protein structures that extend

from the cell Help bacteria adhere to one

another or to certain other surfaces

Bacterial Flagella Produce rotary motion and

consist of Basal body Hook Filament Sex pilus 1 m

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Plasmids

Plasmids

Some of the genetic material of prokaryotes are found within plasmids. Generally, plasmids carry

genes that code for functions not essential for cell growth

Plasmids fall into two categories F plasmid

Fertility plasmid R plasmid

Resistance plasmid

F Plasmid

F plasmid Fertility factor

Allows bacteria to go through conjugation

F+ when plasmid is present

F- when plasmid is absent

R Plasmid

R Plasmid Resistance Plasmid

Carry genes that provide resistance to various antibiotics Chloramphenicol,

tetracycline and penicillin

Carry genes that provide resistance to heavy metals Arsenic and mercury

Importance of Plasmids

Plasmids are genetic material that are exchanged between individual bacteria.

Plasmids are responsible for the evolution of antibiotic resistant bacteria.

The exchange and/or the incorporation of genetic material via plasmids, is one of the foundations for genetic engineering and biotechnology. More to come in future packet

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Asexual Reproduction vs. Exchange of Genetic Material in

Prokaryotes

Introduction

There are three types of asexual reproduction mentioned in the packet. Asexual Reproduction

Binary Fission Budding Fragmentation

However, in addition to reproducing, bacteria also exchange genetic material in three processes separate from the processes for reproduction Exchange of Genetic Material

Transformation Conjugation Transduction

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Asexual Reproduction

Asexual Reproduction in Prokaryotes

Binary Fission Cell divides forming two

cells

Budding Bud forms and separates

from the mother cell

Fragmentation Walls form inside the cell Separates into several cells

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Genetic Exchange in Bacteria

Transformation

Genetic alteration of a cell resulting from the introduction, uptake and expression of foreign material (DNA) Bacterial cell takes in DNA

fragments released by another cell

Discovered by Fredrick Griffith while searching for a vaccine against bacterial pneumonia

Transduction

Process by which bacterial DNA is moved from one bacterium to another by a virus (bacteriophage) Covered previously

Lytic & lysogenic cycles

Conjugation

Two cells of two different mating types exchange genetic material through cell to cell contact. Mating types are determined by

the plasmids. (F+/F-)

Incorrectly regarded as the bacterial equivalent of sexual reproduction or mating

Does not involve the fusing of gametes and the creation of a zygote

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Review

Review I

Review II