The Presentation of Group 3…

Title:

Members of the group:

Muhammad Jefri bin Mohd Yusof (A 127205)

Noor Khairatul Azni binti Mat (A 127222)

Chai Lee Chin (A 129966)

Yosmetha Mayalvanan (A 126816)

Syamimi binti Haslan (A127285)

Nucleoid Structure of Prokaryote….

• the chromosome also called nucleoid

• lacks of a membrane enclosure• supercoiling

• associated simple basic amino acids influence the folding of DNA

molecule

Location of Nucleosome.

DNA

HISTONES

What is Nucleosome?

• The fundamental repeating units of eukaryotic chromatin.

• It is used to pack the large eukaryotic genomes into the nucleus.

• It is contain of – DNA (strongly alkaline protein)– Histone (nucleic acid that contains the

genetic instructions)

WHAT IS EUCHROMATIN?• Euchromatin is a lightly packed

form of chromatin (DNA, RNA and protein) that is rich in gene concentration, and is often under active transcription.

• Unlike heterochromatin, it is found in both cells with nuclei (eukaryotes) and cells without nuclei (prokaryotes).

• Euchromatin comprises the most active portion of the genome within the cell nucleus

STRUCTURES OF EUCHROMATIN• The structure of euchromatin is reminiscent of an

unfolded set of beads along a string, where in those beads represent nucleosomes.

• Nucleosomes consist of eight proteins known as histone with approximately 147 base pairs of DNA wound around them; in euchromatin, this wrapping is loose so that the raw DNA may be accessed.

• Each core histone possesses a `tail' structure, which can vary in several ways; it is thought that these variations act as "master control switches," which determine the overall arrangement of the chromatin.

• In particular, it is believed that the presence of methylated lysine 4 on the histone tails acts as a general marker for euchromatin.

Another structure of the

Eukaryotic Chromosome…

• When the chromosomes of an organism such as wheat or pine is dissected at the molecular level, stretches of nucleotide sequence that occur once or only a few times - including the genes - represent as little as 5% of the DNA.

• Most plant and animal genomes consist largely of repetitive DNA - perhaps 30 sequence motifs, typically one to 10 000 nucleotides long, present many hundreds or thousands of times in the genome, which may be located at a few defined chromosomal sites or widely dispersed.

• A major distinction between eukaryotic and prokaryotic chromosomes is that eukaryotic chromosomes contain vast amounts of DNA between the genes.

• Repetitive DNA, with different selective pressures from those acting on genes and evolutionarily successful multigene modules, may show extensive differences in sequence motifs and abundance even between closely related species.

• The repetitive DNA in the genome is also important for evolutionary, genetic, taxonomic and applied studies.

• .

REPETITIVE DNA

FUNCTIONS• A few repetitive sequences are known to have well

defined functions.• The telomeric sequences, added at the ends of most

plant and animal chromosomes, allow a linear replication unit to be maintained, protect chromosome ends and overcome the 'end replication problem'.

• Mobile DNA sequences - such as transposons and retrotransposons - make up a high proportion of most plant and animal genomes.

• A major class, the retroelements, encode the proteins necessary for their own reverse transcription and integration, and sometimes represent 50% of the genome.

• The two most abundant and best-characterized middle-repetitive sequence families in mammalian DNA are the short, interspersed Alu1 repeats and the long, interspersed repeated elements referred to as LINE or L1 elements.

• Alu-repeats. The majority of the middle-repetitive DNA in mammalian genomes consists of numerous families of repeated sequences that are only a few hundred base pairs in length.

L1 Elements & Pseudogenes in Mammalian DNA

• One family of short, interspersed repeated elements dominates this reiterated DNA function.

• L1 elements : believed to be the only major family of long, interspersed repeated elements in primate DNA.

• The L1 family of dispersed repeated sequences consists of largely of incomplete, probably non-functional, processed pseudogene-like copies together with a small number transcriptionally-active elements.

• References:

‘Structure and function of repetitive DNA in Eukaryotes’, article by Norman Hardman, Department of Biochemistry, University of Aberdeen.

Biochem J. (1986) 234, 1-11

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