Genetic Material
Hella W. Newman
I The Structure of DNA
DNA is structured by so-called deoxyribonucleicacid molecules. The are informational
molecules that encode the genetic instructions used in the development and functioning of all
known living organisms. Along with RNA and proteins, DNA is one of the three major
macromolecules that are essential for all known forms of life. Genetic information is encoded
as a sequence of nucleotides (guanine, adenine, thymine, and cytosine) recorded using the
letters G, A, T, and C. Most DNA molecules are double-stranded helices. They consist of two
long polymers of simple units called nucleotides.
II Working Form of DNA: Chromatin
Chromatin is formed from proteins and Dann and makes up the contents of the cell’s nucleus.
The chromatins main function is the packaging of Dann into a smaller volume so it can
ultimately fit into the cell, strengthening of the DANN so as to allow mitosis, and preventing
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DANN damage and controlling gene expression and DANN replication. Histones are the
primary protein components of the chromatin, they compact the DANN. Chromatin is only
found in eukaryotic cells, prokaryotic cells have a different organization of their DANN,
namely the genophore (a chromosome without a chromatin)
III Significance of Chromatin Loops
Genomic DANN gets packaged into chromatin fibers, and orgnied in higher-order structures
within the interphase nucleus. The formation of chromatin loops may provice a favorable
environment to processes like Dann replication, transcription and repair. However, since not
that much is known about the mechanistic basis of this structuration, this format can get a
little fickle. Cohesin does indeed factor into the spatial organization of Dann replication
factories in human cells. What it does, is interact with prereplication complex proteins
because it is enriched at replication origins. If Cohesin is down-regulated, the S-phase
progression is slowed down for its number of active origins is limited and ist length of
chromatin loops, corresponding with replicon units is increased. By demonstrating ist
participation in Dann replication we can see new perspectives on the role of cohesin in the
architectural organization of interphase chromatin.
IV Transport of DANN- Chromosomes
A chromosome is a piece of coiled up Dann, containing many genes and regulatory elements.
Chromosomes also contain proteins which help package the Dann and control ist functions.
Encoded in a chromosome is most or all of aan organisms genetic information. In eukaryotic
cells (cells with a membrane), nuclear chromosomes are packaged by proteins to form
condensed structures known as chromatin.
In this fashion, DANN molecules can fit in the cell’s nucleus. Chromosomes represent the
essential unit for cellular division and have to be replicated, divided and passed to their
daughtercells, so the genetic diversity and survival of their spawn is ensured.
Chromosomes are either duplicated or unduplicated. The latter being single linear strands, the
former containing two identical copies (called chromatids) joined by the centromere.
V Condensation degree
DNA condensation refers to the process of compacting DNA molecules in vitro or in vivo.
DNA diameter is about 2 nm, while the length of a stretched single molecule may be up to
several dozens of centimetres depending on the organism. While DNA is one of the stiffest
natural polymers, it is also one of the longest molecules. Therefore, means that at large
distances DNA can be considered as a flexible rope, and on a short scale as a stiff rod. Like a
garden hose, unpacked in order to cope with the constraints caused by volume, DNA has a
striking property to pack itself in the appropriate solution conditions with the help of ions and
other molecules. Usually, DNA condensation is defined as "the collapse of extended DNA
chains into compact, orderly particles containing only one or a few molecules". This
definition applies to many situations in vitro and is also close to the definition of DNA
condensation in bacteria as "adoption of relatively concentrated, compact state occupying a
fraction of the volume available". In eukaryotes, the DNA size and the number of other
participating players are much larger, and a DNA molecule forms millions of ordered
nucleoprotein particles, the nucleosomes, which is just the first of many levels of DNA
packing.