Life As We Knew It

Chapter 3: Life As We Knew It

DNA → script, not template, not mold

Same script is used differently depending on its cellular context

DNA it self isn’t the real business end of things, in the sense that it doesn’t carry out all the thousands of activities required just to keep us alive. → that job is mainly performed by the proteins.

DNA  → ACGT   A-T, C-G  C  → the most important in epigenetics

Keeping it pure

Replication

Fig 3,2 

DNA repair machinery

50,000,000,000,000 cells in a human body are all the result of perfect replication of DNA, whenever cells divide after the formation of the single-cell zygote from chapter 1.

Each cell contains six billion bases of DNA.  This sequence of six billion base-pairs is what call the genome.    It would take 190years to count all the bases in the genome of a cell.

Reading the script

The way this works is that the cell machinery reads DNA in blocks of three base-pairs at a time. Each block of three is known as a codon and may be AAA, or GCG or any other combination of A, C, G and T. 64 codons → more than enough for the 20 amino acids. → lysine is coded for by AAA and AAG. Stop codons means the end of protein coding sequence.

Messenger RNA is very like DNA. Its backbone is ribonucleic acid rather than deoxyribonucleic acid. Single stranded. It replaces the T base with a very similar but slightly different one called U

The indirect way in which DNA codes for proteins minimizes the period of time. It allows a lot of control over the amount of a specific protein that’s produced, and this creates flexibility.

The more often we drink alcohol, the more ADH protein our livers produce . ---- the cells of liver don’t  do this by increasing the number of copies of ADH gene. They do this by reading ADH gene more efficiently, producing more mRNA copies and /or  by using these mRNA copies more efficiently as protein templates.

Editing script

Region at the beginning called promoter.

Introns(inexpressed sequence) and exons( expressed sequence)--- this doesn’t code for a run of amino acids

Splicing (editing process) removes all the intron sequences and them joins up the exons to created an mRNA .

Splicing→ remove all the intron sequences and then joins up the exons to create an mRNA that codes for a continuous run of amino acids. This editing process is called splicing.

These chromosome regions become floppy and loop out like tentacles sticking out of the body of an octopus.

6,000,000,000 base-pairs, 120,000,000 code for protein ---- only 2 % of the total amount. Although we think of proteins as being the most important things our cells produce, about 98% of our genome doesn’t code for protein. ---- it’s connected with regulating gene expression through epigenetic mechanisms.  It’s now time to move on to the molecular biology of epigenetics