Function and Packaging of DNA Packaging of DNA

Function and Packaging of DNA

Packaging of DNA • When a chromosome is not dividing, it can not be seen with a light microscope. • It is unwound into chromatin. • Prokaryote DNA is usually circular and very small. • Eukaryote chromosomes have an enormous amount DNA in a relatively short length.

Packaging of DNA • Each chromosome consists of a long unbroken length of DNA. This DNA needs to be packaged to fit into the nucleus along with all the other chromosomes.

Packaging of DNA • In chromatin, the DNA is wound around proteins called Histones. • The DNA-plus-histones forms a nucleosome. • Between the nucleosome beads the DNA continues as an open string.

Packaging of DNA • When the cell divides, the chromatin gets coiled up and packaged into the chromosome shape we see under the light microscope. • The beaded strings form tight chromatin coils called chromatin fibres

Packaging of DNA • These coils form loops called Looped domains, which are attached to a non-histone protein scaffold. • These looped domains coil and fold even more to form the characteristic chromosome you see during cell division.

Function of DNA • Carries the genetic code for the proper functioning of the organism. • Has the ability to replicate itself, so life can continue. • A DNA molecule is very long, and consists of thousands of genes positioned at set places along the DNA molecule (loci/locus).

Function of DNA • A gene is a length of DNA that codes for a polypeptide chain. • Proteins are made up of one or more polypeptide chains. The gene codes for protein. • Remember proteins are both the structure of the cell and the enzymes that run the cell so DNA controls the cell by controlling protein production.

DNA Replication • Before a cell divides, the DNA starts the process of replication. • The weak H-bonds between the bases break with the help of an enzyme called helicase. • The DNA molecule unwinds and unzips. • Each side of the original ladder acts as a template for a new strand.

DNA Replication • New nucleotides come in and join up using the strict base pairing rule. – A: T – C: G • The sides of the new ladder then join by forming bonds between the sugars and phosphates of the new nucleotides.

DNA Replication • The 2 new molecules of DNA wind up around each other reforming the double-helix shape. • The process results in the formation of 2 molecules of DNA, each with one old strand one new strand. • This is called Semi-conservative replication.