Bacterial Interior – Bacteria

by Vincent Racaniello, PhD

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    00:01 Let's take a look at the interior in a little more detail. We have within the cytosol the nucleoid which contains the nucleic acid of the bacteria, again there are no mitochondria in bacteria, there is no nucleus, there is no Golgi, endoplasmic reticulum, mitotic apparatus, plastids, these are all structures that are found in eukaryotic cells but we don't have them in bacteria. The nucleoid contains the nucleic acid of the bacterium where the genetic information and for bacteria it's a single molecule of circular DNA, and this molecule is tightly folded in the nucleoid, because it's very long, in the longest DNAs it would be a 1000 times longer than the length of the bacterium unless it were compacted, so there have to be specific mechanisms to wrap it up and that's what we call the nucleoid, it's a combination of proteins that bind the DNA and positively charged ions. The DNA varies in length depending on the bacteria; the shortest DNAs that we know of are only 130,000 bases long and the longest 14 million base pairs. Now in addition to this nucleoid with the chromosomal DNA, many bacteria have what we called plasmids, these are separate pieces of DNA, they are typically circular and they are not necessary for the bacteria to grow.

    01:31 But these plasmids move easily from bacteria to bacteria and they can carry things like antibiotic resistance genes, so they are very important for bacterial diseases. The interior of the bacterium is very crowded, there are lots of molecules, there are ribosomes where proteins are being made. There are all kinds of inclusions and vesicles. There are gas vesicles for example, for bacteria that live in the water that photosynthesize, they have to be near the surface of the water, so they have vesicles containing gas that allow them to float, it's quite interesting. There are organelles for photosynthesis and chemosynthesis. There are carboxysomes, these are organelles that have an enzyme to grab CO2 and use it for further processes. And there are also storage granules for the things that bacteria need, like sulfur and phosphate, calcium and glycogen. So here's an overview of our bacterial cell, let's go through the individual components and talk about what each one is made of.

    02:33 We've talked about each one of these so far today, we have the pili on the exterior which are needed for movement, these are made of proteins, the outer membrane, remember, has proteins, phospholipids and that very unusual membrane component lipopolysaccharide. The capsule is typically made up of polysaccharides or amino acids. The cell wall is peptidoglycan.

    02:57 The periplasm are those spaces between the walls and the membranes, those typically have proteins in them. The cell membrane has phospholipids and protein and the flagella are made of proteins as well. The cytoplasmic contents include of course the nucleoid which is made up of DNA and its associated proteins. We have the cytoplasm which is chock-full of things, proteins, transfer RNAs for protein synthesis, glycogen and various other inclusions and polysomes, the sites of protein synthesis on mRNA, ribosomes, transfer RNAs, riboproteins and finally the vesicles which we can't see here, that have various inclusions in them. So the bacterial cell is quite a complicated place and really these diagrams that we draw are oversimplified because we can't hope to represent that complexity.

    About the Lecture

    The lecture Bacterial Interior – Bacteria by Vincent Racaniello, PhD is from the course Microbiology: Introduction.

    Included Quiz Questions

    1. Nucleoids
    2. Mitochondria
    3. Smooth endoplasmic reticulum
    4. Rough endoplasmic reticulum
    5. Plastids
    1. Circular
    2. Spiral
    3. Helix
    4. Irregular
    5. Tangled
    1. 130,000 bases
    2. 10,000 bases
    3. 20,000 bases
    4. 30,000 bases
    5. 300,000 bases

    Author of lecture Bacterial Interior – Bacteria

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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