What is replication?
Replication is the process during which a copy of the DNA molecule is produced in order to ”pass it on” to the new daughter cell. This happens during mitosis.
Errors during replication can be lethal or extremely damaging to the organism. Why?
Because of two major reasons; first of all, the function of the gene (and thus the protein it codes for) can be altered and secondly : the change due to the error is inheritable!
How are bacterial genes named?
They are named using three italicized, lowercase letters that reflect the functions of the gene. For instance : dna reflects a gene involved in DNA replication. If several genes are involved int the same process (which, of course, is often the case) the genes are named dnaA, dnaB etc.
What is nucleotides and nucleic acids?
Nucleotides are the actual DNA /RNA bases. Nucleic acids are the DNA /RNA molecules. Hence nucleotides are the building blocks of the nucleic acids.
DNA replication is semiconservative – what does that mean?
It means that one of the DNA strains is a template for the synthesis of the new complementary strand. Thus : one original DNA molecule will divide during mitosis into two separated strands, each functioning as templates for two new strands, resulting i two new DNA molecules. The new DNA molecules consist of one old and one new strain!
Watson and Crick suggested the theory of semiconservative replication shortly after publishing their ground breaking paper in 1953 – but how was this particular theory actually proven?
By the Meselson-Stahl experiment. http://en.wikipedia.org/wiki/Meselson%E2%80%93Stahl_experiment
Where does replication begin?
At the ORI = the origin of replication. It is a sequence usually consisting of typical sequences. These sequences varies between spieces. However, AT-rich sequences are common. The ORI sequences attract the so called Pre-replication complex which unwinds the DNA and prepares it for replication. Procaryotes usually have one ORI, whereas eucaryots have several of them. Otherwise the replication process would take to long in the latter case, since the eucaryotic genome is so complex.
What is ”denaturation mapping”?
It is a method developed by Ross Inman in order to deduce that DNA replication started at specific points in the genome, the AT-rich sequences described above.
Is the replication of bacterial genome bidirectional or not?
It is bidirectional.
In what direction does synthesis of a new DNA strand proceed?
It always proceeds in 5´to 3´direction! Think ”high to low”.This is because the free OH- at the 3´carbon on the DNA molecule is the point where the phosphate group of the incoming nucleotide can be attached. See picture below!
Because the DNA strands are anti parallel this means that one strand will be synthesized continuously, whereas the other one must be synthesized in fragments. See picture below. The strand that is synthesized directly and in one direction only is called leading strand, the other one, synthesized by small so called Okazaki fragments is called lagging strand. In this way the two DNA strands can be synthesized simultaneously.
Please visit this very simplified animation of the replication process which also contains self tests and descriptions of the task for each enzyme involved!
http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html
What is Okazki- fragment?
It is a fragment of a new DNA strand that together with other Okazaki fragments build the lagging strand. The lagging strand needs to be synthesized in small fragments in order to keep up with the continuously synthesized leading strand.
How long is an Okazaki fragment?
From a few hundred to a few thousand bp – depending on cell type.
How is DNA/RNA degraded?
The enzymes responsible for DNA degradation are called : nucleases (when they degrade RNA molecules) and DNnases when they degrade DNA.There are several different nucleases but they are all divided into two large groups : endonucleases and exonucleases. The endonucleases operate at specific positions within the DNA chain, whreas the exonucleases operate at the end (think : exit) at the DNA molecules.
Why are nucleases very important to remember?
They are of great use in biotechnology! (They cut Dna molecules where we want them to be cut, so to speak).
