Question

What are the stages of the cell cycle? What is happening in each one?

Decribe DNA organization in a eukaryotic chromosome.

Once translation is complete, are proteins fully formed and functional?

Answer 1

Stages of cell cycle:

1. Interphase - Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases.

In G1 Phase, cell grows and performs its normal functions.

In Synthesis (S) Phase, a cell's DNA is copied during this phase.

In G2 Phase, cell grows and prepares for mitosis.

2. M-phase (mitosis and meiosis) - It involves prophase, metaphase anaphase and telophase. In this phase cell nucleus actually divides and daughter cells are formed after cytokinesis.

3. Cytokinesis - The cell's cytoplasm divides, distributing the organelles into each of the two new cells.

DNA organisation in eukaryotic chromosome:

In eukaryotes the deoxyribonucleic acid helix is very organized into the well-defined DNA-protein complex termed as nucleosomes. Among the proteins the foremost distinguished are the histones. The histones are basic proteins that are rich in lysine and arginine. Five types of histones (H1, H2A, H2B, H3 and H4) form an octamer spheroidal structure of approximately eleven nm long and 6.5-7 nm in diameter. DNA coils around the surface of spheroidal structure of histones 166 base pairs (about 7/4 turns) before continuing onto the next and form nucleosome (an octamer of 4 histone proteins complexed with DNA). The DNA isolated from chromatin appears like string or beads. The 146 base pairs of DNA lie in the helical path and the histone-DNA assembly is known as the nucleosome core particle. H1 histone acts as linker and helps the folding of DNA into complex structure referred to as chromatin fibres that whorl to create chromatin. As a result of maximum folding of DNA, chromatin becomes visible as chromosomes.

After translation proteins undergo post-translational modification such as acetylation, glycosylation, phosphorylation, protein cleavage, disulfide bridge formation, proper folding and multimeric protein assembly. This modifications are mostly covalent modifications arising due to chemical or enzymatic modifications.