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Lab Activity - Prokaryotes

Time: This activity will take 30 - 45 min. to complete.

Kit # 4, Oil Immersion Microscope objective that you will check out from the Science Lab Prep room.


Introduction

The introduction is adapted from Germology's Introduction to Bacteria webpage (Germology was a great website that is, unfortunately, now offline.)

All organisms are divided into one of two very broad categories: prokaryotes and eukaryotes. The most significant difference between the two groups is the general structure of the cell and most notably the region of the cell where the DNA is located. The term prokaryote refers to the lack of a nucleus - "pro"="before", "karyon"="kernal", referring to the nucleus. In contrast, "eu" = "true", so a eukaryote has a true nucleus.

For prokayotes, the DNA consists of a single DNA molecule (one chromosome) that is circular but not contained within a membrane-bound nucleus. Instead, prokaryotes have an unbound region of DNA called the nucleoid.  Here is a look at a "typical" bacterial cell:


More on Prokaryotic vs Eukaryotic Organisms

Prokaryotes, which include the Domains Bacteria and Archaea, represent the smallest and most basic form of life. Still the prokaryotes display an amazing degree of diversity and complexity.  The largest group of organisms within the prokaryotic lineage is the Bacteria.  Eukaryotic organisms constitute virtually all other cells, from the most basic yeast to cells comprising human tissues. The table below lists some of the most basic characteristics of prokaryotic (primarily Bacteria) and eukaryotic cells.

Characteristic

Prokaryotes 

Eukaryotes

Cell size

Typically <5 micrometers (um)

Typically >5 micrometers (um)

Membrane-bound nucleus

Absent

Present

Chromosome (DNA)

Single, circular chromosome

Several linear chromosomes the precise number varies for each organism

Cellular organelles 

Absent

Present

The University of California, Berkeley's Museum of Paleontology has an excellent website. Please read two pages from this site and answer the questions on your worksheet. (When you click on the link, they will open in a new window.)

Bacteria: Life History and Ecology

Part A: Archaea

Recall that archaea are in their own domain. Like true bacteria, archaea are prokaryotes. However, archaea differ from true bacteria in several ways. In some ways, archaea are more similar to eukaryotes than to true bacteria. Your text describes several key ways archaea differ from true bacteria:

Bacteria Archaea
Cell walls contain the polysaccharide peptidoglycan Cell walls don't contain the polysaccharide peptidoglycan
Distinct ribosomal proteins and RNA polymerase Ribosomal proteins and RNA polymerase similar to those of eukaryotes
Genes don't have introns (Introns are regions of DNA not coded into proteins) Genes do have introns, similar to eukaryotes

You'll look at a prepared slide of archaea. First, let's review a few rules about using microscopes

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