Ch. 15, 16 & 21

Source:  Ch. 15, 16 & 21    Tag:  prokaryotic cell reproduction
Molecular Biology II


II. Connections


1. Lysogenic & Binary Fission: When viruses attack host cells, the cells can divide and multiply in two different pathways.  A lysogenic pathway when a latent period extends the duration of the cycle because the virus does not kill the host right away.  Instead, a viral enzyme cleaves the host's chromosomal DNA, and integrates the viral genes into its base sequence.  This happens before prokaryotic fission, which is the cell reproduction mechanism for prokaryotic cells only.  Prokayotic fission can sometimes be confused with binary fission, but binary fission refers to the asexual reproductive mode among some animals where the body splits spontaneously, then both parts grow what is missing.


2. Conjugation & Bacterial Transformation: Conjugation is a mode of gene transfer that is possible when one of the cells has an F, or fertility, plasmid.  A plasmid is a small, self-replicating circle of DNA with a few genes.  Plasmids are only found in prokaryotic cells.  Bacteria are examples of prokaryotic cells.  Conjuction involves the transferring of replicated DNA from one prokaryotic cell to another.  The recipient cell receiving the replicated DNA can sometimes receive transferred DNA that has been transformed into infectious DNA.  This transformation is bacterial transformation.


3. Plasmid & Retrovirus: Plasmid is  a small, self-replicating circle of DNA with a few genes.  Plasmids are used during cell reproduction in prokaryotic cells.  A virus cannnot reproduce on its own, which means it can only reproduce when its genetic material enters the host cell and becomes replicated.  Common animal viruses, such as retroviruses, have double or single stranded DNA or RNA that has been replicated with the virus gene in it.  HIV is a retrovirus, that leads to AIDS.  A virus that weakens the immune system by destroying white blood cells  can cause the inability to fight infections such as HIV that may not otherwise be life threatening.


4. Operator & Hydrolysis: An operator is a binding site for a type of regulatory protein know as repressor, which stops transcription.  Operators can be found at the end of E. coli DNA, after three genes that code for lactose-metabolizing enzymes.  E. coli likes to consume glucose, but can settle for lactose when glucose is not present.  Lactose is a carbohydrate, and can be broken down with hydrolysis.  Hydrolysis is a cleavage reaction that uses enzymes to split molecules at specific groups.


5. Okazaki Fragments & Restriction Enzymes: Restriction enzymes cut double-stranded DNA at a specific base sequence between for and eight base pairs in length.  It makes staggered cuts that produce a sticky end on the DNA fragments.  The tail can base pair with a tail from another fragment cut by the same enzyme.  Restriction enzymes can cut base pairs form Okazaki fragments, which are the fragments of new DNA copied along with the parent strands.  Just like for the Okazaki fragments, DNA ligases seal the nicks of the base pairing between the cut fragments.


III. Few Essentials 


1. Promoters are short stretches of base sequences in DNA where regulatory proteins gather and control transcription of specific genes, often in response to hormonal signal.  Enhancers are binding sites where such proteins increase transcription rates.  Before transcription, acetylation can make histones loosen their grip so that the polymerases can access genes.  Some gene sequences can be rearranged or multiplied.  During transcript processing, exons for genes can be put together in different combinations in different types of cells.  Proteins attached to a nuclear envelope can move the transcript to the region where its supposed to be translated or stored.  Unfertilized eggs that stockpile maternal messages keep them silent with the help of controls called Y-box.  During translation, how long an mRNA lasts depends on the proteins that are attached to it and the length of its poly-A tail.  If translation is blocked, mRNA cannot attach to a ribosome when proteins bind to it, and initiation factors can be inactivated.  After translation, a new protein may be inactivated or activated.  Control of enzymes and other proteins influences many cell activities. 


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3. DNA fragments can be separated by gel electrophoresis, a technique that sorts fragments as they move through a semisolid slab of polyacrylamide in response to an electric field.  DNA fingerprinting reveals differences in the tandem repeats among individuals.  Fragments are cut; the sizes of the fragments are unique to an individual.  The fragments can be subjected to gel electrophoresis to form distinct bands according to their length.  The banding patter of the fragments is the DNA fingerprint of the individual.


4. A prokaryotic cell nearly doubles in size, then divides in two.  Each daughter cell inherits a single bacterial chromosome, a circularized, double-stranded DNA molecule that has a few proteins associated with it.  This is different from  a eukaryotic cells genome because it is smaller, only having one chromosome where eukaryotic cells have 23 chromosomes.  DNA replication is simpler in prokaryotic cells.  After the DNA replicates, the parent molecule and the cope are both anchored to the plasma membrane at adjacent sites while the cell is growing.  The growing cell moves the molecules of DNA apart.  The cytoplasm splits in two, and the result is two genetically identical daughter cells.


5. In the lytic cycle, a virus particle injects genetic material into a suitable host cell after binding to its wall.  The viral DNA directs host cell to make viral proteins and replicate viral DNA.  The viral proteins are assembled into coats around viral DNA.  The coats get tail fibers.  Lysis of the host cell is induced and infectious particles escape.  The lysogenic cycle is different because the virus does not kill the host right away.  Instead, a viral enzyme cleaves the host's chromosomal DNA, then integrates the viral genes into its base sequence.  The viral DNA is excised from the chromosome.