Question

1. Describe the structure of the DNA molecule and how this structure allows for the storage of information, the replication of DNA, and protein synthesis. • What is the double helix? What are nucleotides, polynucleotide and base pairs? Use these terms to explain the structure of DNA.

2. List the similarities and differences between the various nucleic acid molecules. • What is semi-conservative replication of DNA? How does DNA get replicated?

Answer 1

Hi,

Every living organism has a genetic code, will all the information about its structure and function. The genetic material is made up of a chemical group called Nucleic acids. They store the genetic information in the form of genes which are decoded and translated into proteins. Proteins are the integral part of structure and function of a cell, of a living being.

The Nucleic acid which is most commonly used as genetic material is called DNA, deoxy Nucleic acid. It contains three important component, one phosphate unit, one ribose sugar and one nitrogenous base. The ribose sugar consists of 5 sugar molecules which binds to nitrogen base to one end, and phosphate group to other end. The nitrogen base is found in 2 major types of nucleotides either purines and pyrimidines. Purines can be adenine or guanine. Pyrimidines can be thymine or cytosine. The phosphate group has 4 oxygen molecules bound to a phosphate atom. It gives negative charge to the DNA. The DNA monomeric units, bind or polymerase with multiple monomers to form long chain polymer of DNA. The DNA often occurs as double stranded molecules. The two chains of DNA bind to each other by hydrogen bonds between nitrogen bases. Formation of double strand, bends the DNA long strand in specific manner, like a spiral ladder. This is called the double helix. This gives rise to double stranded molecules. It is central to the molecular biology of cell.

The double helix formation depends on the specific binding of nucleotides. The purines always bind with pyrimidines in the opposite strand. A always binds with T, and G always binds to C. This is the fundamental understanding of double helix. Also the chains run in anti parallel direction, it means that the one end of a strand, has phosphate at the one end (5’) and another stand has deoxy group at the end (3’). The helix has approximately 10 bases in each turn.

The information is stored on DNA in the form of genes. A gene is a specific combination of nucleotides, ATGC. The genes are read by specific enzymes and converted to corresponding messenger RNA. The mRNA is then converted into proteins by ribosomes.

There are two major types of Nucleic acids. DNA and RNA. Both share common similarity such as nitrogen base, ribose sugar and phosphate group.Both the Nucleic acids can act as genetic material, RNA in viruses and DNA in most other organisms. The major difference is that DNA contains thymine and RNA contains uracil instead. The RNA usually occurs in single strand form, whereas DNA occurs in double strand form. RNA is less stable compared to DNA.

DNA replicated by semi conservative mode of replication.

1. The double helix opens up locally to accommodate polymerase enzyme binding.
2. The polymerase enzyme binds to the one of the strand of DNA and starts to add new nucleotides. The new nucleotides are complementary to the parental strand. Like A to T, and G to C.
3. The newly formed strand binds to one of the parental strand to form a double helix. Thus both the parental stands will get one new strand each.
4. It would look like an old strand + new strand, so it is called semi conservative.
5. Thus one DNA. chain becomes two by rep,cation, it occurs in S phase of cell cycle.