Question

A.) Describe the steps of chromatin compaction in your own words.

B.) How are centromeres and telomeres similar?

C.) What are some pieces of evidence to support endosymbiotic theory?

Answer 1

A.) Describe the steps of chromatin compaction in your own words.

• Chromatin compaction process can be defined in various level. In the first level, the histone proteins which are eight in number, arranged at regular intervals are wrapped by short stretches of the DNA double helix and the complex of DNA-histone complex is called as chromatin.The bead like histone-DNA complex is called as nucleosome which are connected to each other by linker DNA. It is in the size of about 10 nm in diameter.
• The next step of compaction is characterized by coiling of the nucleosomes and the linker DNA between them, together form chromatin fiber which is of 30 nm in diameter. The chromosome is further shortened about 50 times than the extended form by the coiling process.
• The third step in packing involves various fibrous proteins to ensure non-overlapping of chromosome in a non-dividing cell.   
• DNA replication occurs in the S phase of cell cycle, during when the chromosomes are composed of two linked sister chromatids. The fully compacted pairs of chromosomes are bound together by cohesin proteins and it is closest in centromere. The conjoined sister chromatids are of 1 µm in diameter which is visible under light microscope.

B.) How are centromeres and telomeres similar?

The centromere is a specialized multifunctional chromosomal domain which directs kinetochore assembly and play key role in chromosome segregation during cell division by providing the site for microtubule attachment. Telomeres are found at the chromosal end, nucleoprotein complexes consists of tandemly repeated simple DNA sequences which protects the chromosome ends from degradation. It also protects the integrity of linear chromosomes from unsolicited recruitment of DNA repair machineries. Depite ditinct functions, they both share many similarities such as : they direct the assembly of specific nucleoprotein complexes; and the underlying repetitive DNA sequences, are packaged into heterochromatin. They also share similarity in sequences.

C.) What are some pieces of evidence to support endosymbiotic theory?

The endo symbiotic hypothesis states that the mitochondria and chloroplast arose from prokaryotes and enters the eukaryotic cell to form a symbiotic relationship which is further supported by similarities between bacteria and these semiautonomous organelles.

• Chloroplast shares its similarity with chlorophyll that harness light energy to convert into chemical energy.
• Mitochondia resembles purple-aerobic bacteria
• They both have their own circular DNA and undergo binary fission as they were prokaryotic cells. The whole machinery comprises transcription and translation occurs within semi autonomous organelles and both use oxygen in the production of ATP, and they both do this by using the Kreb’s Cycle and oxidative phosphorylation.

All these supports the hypothesis of endosymbiotic theory.