Cells

The units of living things

Robert Hooke

• Looked at samples of cork wood under a simple microscope. It seemed to be composed of small compartments or “cells”.

• It would be later found that all living things are made up of one or more cells.

Two types of Cells

• Cells are divided into two types, prokaryotic (bacteria like) and eukaryotic

• Prokaryotic cells are smaller, have fewer internal structures or “organelles”, and are found in older fossil samples, so it is believed that they are a simpler more primitive type of cell

Prokaryotes

• In prokaryotes the DNA is not in a nucleus but floats exposed within the cell. The DNA is single stranded looped into a closed circle called a plasmid.

• Disadvantages to plasmids is that if damaged no guarantee of proper repair. (bacteria mutate often)

• Advantages, (some mutations are helpful) less likely to get damaged, no information is lost in each replication, so prokaryotic cells do not die of “old age”

Few internal structures

• Prokaryotes have no or very few internal structures. Mainly just folds of membranes where absorbed nutrients get caught, held close together and subjected to enzymes to help in the needed chemical reactions.

Two types of Prokaryotes

• Two major types of prokaryotes are; Archaea, and bacteria. Bacteria are further sub-divided as gram positive bacteria and gram negative.

• Archaea are believed the oldest type of living cell, and have some genes common to both prokaryotes and eukaryotes

• Archaea are often called “extremeophiles” as they can survive in extreme conditions and utilize unusual food and carbon sources

Extremeophile

• Archaea have been found living in hot springs where water temperatures rise above 100oC, in extremely salty water and even in ponds of sulfuric acid used in mining processes. There are even a few members that can survive low doses of ionizing radiation (microwave) and that can use antibiotics, like penicillin as a carbon source.

Bacteria

• Have Few organelles (ribosomes), but mostly just membranes inside the cell

• They do not have non-coding portions of DNA (interons)

• Have a cell wall made up of a sugar/protein coat called peptidoglycan.

• Two main types of bacteria are gram positive and gram negative

Positive and Negative

• Gram positive bacteria have a thick cell wall with multiple layers of peptidoglycan, while gram negative have only one or few layers of peptidoglycan. Gram negative bacteria are resistant to most antibiotics.

Bacterial reproduction

• It was originally believed that bacteria reproduced only asexually (no mixing of genes between members) by cell division.

• Studies in the 1980’s showed however that often prior to dividing bacterial cells will exchange DNA, often through a “sex pilli”

• One bacteria grow a tube like structure to a neighbor and releases some of it’s plasmid containing cytoplasm.

Pilli

Good and Bad

• We often think of bacteria as bad, many cause disease and spoil food.

• Bacteria also serve many useful purposes. They break down material releasing carbon and nitrogen based nutrients back into the environment, some fix nitrogen from the air into nitrates useable by plants. And bacteria have been engineered to produce medication (insulin), help clean up oil and salt spills, and chemicals from chemical warfare (agent orange)

• E-coli in your intestines produce vitamin K for you and are a major contributor to your “first line of defense against other microorganisms.

Assignment

• Peruse pages 367, 370 of text, answer questions 1-3 page 368, 2,3 page 370