Question

Relate the 2 main jobs of DNA in the cell to the stages of the cell cycle and the processes of replication, transcription and translation. How many times in a cell’s life does the DNA undergo replication, transcription and translation?

Answer 1

The DNA is constantly read out into a particular set of mRna s which specify a particular set of proteins. these proteins function and they are degraded and replaced by new ones and the system is balanced that the cell neither grows, shrinks nor change its function.

A new cell arises when one cell divides or when two cells like, sperm and egg fuse. These events required cell replication program which is encoded in the DNA and executed by proteins. this program usually involves a period of cell growth during which proteins are made and DNA is replicated followed by cell division. It is highly regulated decision of the body to decide whether is cell will grow or divide.

Most of the Eukaryotic cells live according to an internal clock that is the proceed through a sequence of phrases called the cell cycle during which the DNA is replicated during the synthesis phase (S) and the copies are distributed to opposite ends of the cell during mitotic phase(M).

Mitosis is the mechanism in eukaryotes for dividing the genome equally during cell division. During the first Sub stage prophage, the replicated chromosomes consisting two identical chromatids are condensed into compact packets and then released into cytoplasm when the nuclear membrane breaks down. During metaphase and anaphase the chromosomes are sorted and each chromatid of a pair moves to opposite side of the cell. The end of Mitosis is marked by Re formation of a membrane around each set of chromosomes during telophase. In next stage division of cytoplasm called cytokinensis yields two daughter cells having 2n chromosomes.

The central dogma of Molecular Biology states that DNA makes RNA makes proteins.

DNA replication : Each time a cell divides the double strands of DNA split into 2 single strand, each of these single strand act as a template for a new strand of complementary DNA. as a result each new cell has its own complete genome, this process is known as DNA replication.

Transcription is the process by which DNA is copied to M RNA which carries the information required for protein synthesis. transcription takes place in 2 steps: in the first step pre- messenger RNA is formed, with the involvement of RNA polymerase enzymes. The resultant is single strand of RNA which is the reverse complement of the original DNA sequence. The Pre-mRna is thene edited to produce the desired mRna molecule in a process called splicing.

Translation the M RNA formed in transcription is the transported out of the nucleus into the cytoplasm to the ribosome. Herer it direct Protein synthesis. messenger RNA is not directly involved in protein synthesis but transfer RNA is required for this process. the process by which mRna direct Protein synthesis with the help of t RNA is called translation.

The Hay flick phenomenon is the number of times in human normal cell populations divide until cell division stops. Hay flick demonstrated that a population of normal human fetal cells in a Cell culture will divide between 40 and 60 times. Each mitosis slightly shortens each of the telomeres on the DNA of the cells. Telomere shortening inhumans eventually makes cell division impossible.

Hayflick describes three phases in the life of a cell. He name the primary culture as Phase 1. Phase 2 defined as the period when the cells are proliferating , the time of luxuriant growth. After months of doubling, the cells eventually reached phase 3, a phenomenon of senescence where a cell growth diminishes and cell division stops.