In living organisms, cells are frequently being replicated. In order for this to occur, the DNA

C. A chromatid is a chromosome that has been replicated but has not yet separated from its sister chromatid.

living matter. The ability of a protein to act as part of a structure, or as an

Insertion- this is the addition of an extra base onto an existing DNA strand. The resulting m-RNA base and the subsequent amino acid alignment are altered and no polypeptide chain is formed since none of the intended amino acid have been linked, the impact will have on protein called Frameshift.

On December 10, 2015, three profound individuals received the Nobel Prize in chemistry for their work on DNA repair systems. Paul Modrich, Thomas Lindahl, and Aziz Sancar studied how the cell repairs and protects the information held in its DNA; specifically, Paul Modrich focused on DNA mismatch repair. Since DNA constantly replicates, damage and incorrect pairings are expected, but enzymes watch over DNA as it replicates and repair any errors that occur. In the mismatch repair system, enzymes find the mismatch in the copy of DNA, cut the incorrect section out, and replace it with the correct sequence. Paul Modrich’s study of the mismatch repair system has provided the medical field with important information regarding cancer growth and the possibility of a cure.

We know from the induced-fit model that the binding of the substrate (DNA) causes a conformational change in the active site of the enzyme. This model refers to a methylation reaction in which the cysteine needs to interact with cytosine of the DNA. Cytosine-5-methyltransferase transfers a methyl group from S-adenosyl-L-methionine to the C5 of cytosine. Cysteine residue attacks the cytosine causing the

Central region-C possess DNA-binding domain (DBD) which is said to be the most conserved region and possess similarity in their structure. DBD contains an important short motif known as P-box which is responsible for direct DNA interaction and detection of specificity for DNA-binding. DBD also possess additional sequences that are required for the homo or heterodimerization of nuclear receptors. A pair of zinc fingers present in domain C is critically responsible for DNA specific contacts and interaction. Domain D is the less conserved domain among nuclear receptors which acts as a flexible hinge in between two domains such as C (DBD) and E (LBD) domains. In addition, domain D possesses the nuclear localization signal (NLS) that regulates the sub cellular distribution of nuclear receptors. The E region contains ligand-binding domain (LBD) is

Multiple enzymes work together to help your DNA duplicate. Helicase, one of these enzymes used to help replicate DNA, uses energy from the ATP to break apart the hydrogen bonds holding the bases together. This allows for the two parental strands of DNA to unwind and form two replication forks. Primase, also an enzyme used in DNA replication, copies a DNA parental strand by making an RNA strand complementary to it. Primase is only active when another protein is present. There are two DNA polymerases: DNA polymerase III and DNA polymerase I. DNA polymerase III catalyzes the chemical reactions for polymerization of nucleotides. DNA polymerase I is involved in removing RNA after replication. If DNA polymerase makes a mistake during synthesis,

The Hb molecule defect is specifically exhibited when a genetic point mutation occurs at the site of the Hb molecule– where a single nucleotide base has been substituted [ ]. Therefore, the mutated

Mutations are caused by errors in DNA replication or repairs, or chemical or radiation damage

The discovery of the structure of DNA has always been associated with Watson and Crick. Their double helix structure, which they developed in 1983, has been used as a model to understand how DNA self-replicates (Karp, 2009). The structure of DNA is made up of covalent bonds between 4 unique nucleotide bases. These bases bind together via complementary base pairing, therefore allowing Adenine to only bind with Thymine, and Cytosine with Guanine (Penn State, Ebery College of Science, 2016). The use of covalent bonds makes the structure strongly

This msDNA is usually small single-stranded cDNA molecule bound covalently to an RNA molecule which can fold into a stable secondary structure. Eventhough still there are no proof to conform retrons as mobile elements, copies of inserted msDNA can be found in bacterial genome (Lampson and rice 1997). In E. coli overexpression of some msDNAs has increased the number of base substitution mutations and frameshift mutations (Maas et al,. 1994). When most cellular mismatch repair proteins bind with mismatches on msDNA molecules it increase the mutagenic level. During matings of E. coli and Salmonella cells when some msDNAs are overexpressed it increase the recombination between donor and recipient DNA sequences, because of the action of mismatch repair usually the interspecific recombination frequency is normally reduced (Maas et al,. 1996). Even though the function of msDNA is still unknown it helps the bacteria to increase their mutations when the mutations are required for their survival. These retrons

The process in which DNA is copied into RNA is the process of Transcription. During this process the double stranded DNA is split and then extra nucleotides are used to construct a single stranded RNA sequence that is later used for building proteins. The enzyme known as RNA polymerase moves down the DNA strand and reads the strand to produce the RNA strand. As this process is taking place, the 3’ end of the RNA polymerase is checking the work of the 5’ side of the enzyme. When the RNA polymerase spots an error, the enzyme is placed into reverse and then corrects the mistake. The accuracy of this

It is proposed that the functions expressed by a dif site depend on chromosome location and structure, and analysis of these functions provides a way to examine the structure of the terminus region. In E. coli two recombinases are required for recombination at the dif site. Xer C and Xer D behave as site specific type I topoisomerases and relaxes the supercoiled plasmids. Without the homologous recombination stalled or broke replication forks wont reform and wont re-initiate replication. (5) If the dif is not located in the terminus region for proper function and may be replaced by loxP if the Cre recombinase is supplied. To clarify, if the dif/Xer system fail the Cre/lox system can be used in its place otherwise recombination will not occur. Cre recombinase recognizes specific DNA sequences and catalyzes recombination even if the chromosomes are not homologs. When Cre is expressed it binds to loxP sites and forms a dimer. When the dimer binds to another loxP site, it forms a tetramer. The strands are cut by the Cre protein and rejoined by DNA ligase. The orientation of the LoxP sequence matters, because it would determine whether Cre will produce a deletion, inversion, or translocation. Two LoxP sequences that go in the same direction would be recognized and cleaved by Cre, producing a deletion. If the LoxP sites are oriented in opposite directions, Cre would produce an inversion. If the LoxP sites are in different chromosomal loci, Cre

Modrich joined Duke University's faculty in 1976 and has been a Howard Hughes Investigator since 1994. He works primarily on strand-directed mismatch repair. His lab demonstrated how DNA mismatch repair serves as a copyeditor to prevent errors from DNA polymerase. Modrich performed biochemical experiments to study mismatch repair in E. coli. They later searched for proteins associated with mismatch repair in humans.

The second stage of the process is complementary base pairing. In this stage, new complementary nucleotides are positioned following the rules of complementary base pairing: adenine (A) to thymine (T) and guanine (G) to cytosine (C). Then, the binding of free nucleotide with complementary bases is catalyzed by DNA polymerase.