BIOL 112 Lecture 15

« previous | Monday, October 1, 2012 | next »

Bacteria (cont'd)

Extracellular structures

Capsule: sticky outer coating around cell wall
Fimbrae ("fringe"): sticky "spines"
Conjugation (Sex pilus): transfer DNA between bacteria
Flagella: mobility; consists of basal apparatus that attaches flagella to cell; CCW = directional; CW = tumbling, splayed out (sample environment)'; combination of directional movement and tumbling (usually toward a chemical—chemotaxis) is called "random walk"

Inside Bacterial Cells

No membrane-bound organelles, but still may have internal membranes or compartmentalized proteins (e.g. for respiration or photosynthesis)
1 large circular chromosome bound w. proteins to form nucleoid body
Small circular plasmid DNA structures for contingency function (e.g. resistance to antibiotics); self-replicating; very useful tool for molecular biology

Reproduction

Asexually by binary fission (cell just divides in half) under favorable conditions

Dormant endospore (tough coating around DNA & cytoplasm) phase in unfavorable conditions. The only way to kill these things is with high temperature and high pressure (autoclaving), gamma radiation.

Sources of Genetic Diversity

Mutation is major source of diversity:

bacteria divide quickly, so more individuals accumulate more total mutations

Genetic recombination is a minor source

Conjugation: Sexual reproduction (see below)
Transformation: Taking up DNA from the environment
Transduction: DNA injected from another foreign source (e.g. phage/virus )

Conjugation

Replication of plasmid for transfer to other bacterium
New plasmid might be integrated into genome
Replication of all or part of genome for chromosomal transfer to other bacterium