Cell Cycle and Retroviruses

Questions and Answers

What is the main function of the G2 phase in the cell cycle?

Preparation for cell division

What is the location of genes for the ribosomal subunits?

Nucleolus

What is the genetic material used by retroviruses?

RNA

What is the result of a retrovirus infecting a host cell?

A DNA copy of the retrovirus's genome is inserted into the host cell's DNA Signup and view all the answers

Which of the following is NOT involved in the processing and modification of rRNA?

Helicase Signup and view all the answers

What is the likely effect of a virus targeting the nucleolus and its components?

Favoring of viral transcription and translation Signup and view all the answers

What is the site of full assembly of mature ribosomes?

Cytoplasm Signup and view all the answers

What is the effect of viral infection on the nucleolus?

It causes redistribution of fibrillar and granular materials Signup and view all the answers

What is the nucleolus composed of?

Three distinct zones Signup and view all the answers

What is a possible outcome of a retrovirus altering the cell cycle?

Promotion of viral replication Signup and view all the answers

What do retroviruses use as part of their own replication process?

Components of the nucleolus Signup and view all the answers

What diseases are caused by retroviruses?

Cancer and AIDS Signup and view all the answers

What is the role of RNA polymerase I in the synthesis of ribosomal subunits?

Transcription of rRNA Signup and view all the answers

What is exported from the nucleus through nuclear pores?

Partially assembled ribosomal subunits Signup and view all the answers

What is the primary function of the G1 phase in the cell cycle?

Accumulation of nutrients and synthesis of proteins necessary for DNA synthesis Signup and view all the answers

During which phase of the cell cycle is chromosome replication initiated?

S phase Signup and view all the answers

What is the duration of the mitotic phase in rapidly dividing cells?

1 hour Signup and view all the answers

What occurs during the M phase of the cell cycle?

Karyokinesis and cytokinesis Signup and view all the answers

What is the purpose of the reorganization of cytoplasmic organelles before entering the mitotic cycle?

To ensure proper distribution of organelles during cell division Signup and view all the answers

What is the result of chromosome replication during the S phase?

All of the above Signup and view all the answers

What is the significance of the S phase in the cell cycle?

It is the phase during which DNA replication occurs Signup and view all the answers

What is the reason for the intense basophilia of nucleoli?

The presence of densely concentrated ribosomal RNA (rRNA) Signup and view all the answers

What is the site of ribosomal RNA synthesis and ribosomal subunit assembly?

Nucleolus Signup and view all the answers

What is the characteristic of the fibrillar and granular subregions of the nucleolus?

They have different staining characteristics Signup and view all the answers

What is the fate of processed rRNA in the nucleolus?

It is quickly associated with ribosomal proteins and exported to the cytoplasm Signup and view all the answers

What is the composition of the nucleolus?

Fibrillar and granular subregions with different staining characteristics Signup and view all the answers

What is the characteristic of euchromatin in an active nucleus?

It is diffuse and light-staining Signup and view all the answers

What is the role of nuclear pores in the nucleolus?

They are involved in the export of rRNA to the cytoplasm Signup and view all the answers

What is the characteristic of heterochromatin in an active nucleus?

It is highly electron-dense and forms smaller subdomains Signup and view all the answers

What is the organization of chromosomal regions with the genes for rRNA?

They are organized into ≥1 nucleoli Signup and view all the answers

Study Notes

Viruses and the Nucleolus

Viruses may target the nucleolus to facilitate viral transcription and translation, and alter the cell cycle to promote viral replication.
Retroviruses, a type of virus that uses RNA as its genetic material, make a DNA copy of its genome that is inserted into the host cell's DNA.
Retroviruses can cause human diseases such as some forms of cancer and AIDS.

Cell Cycle

The cell cycle consists of G1, S, G2, and M phases.
G1 phase is the longest and most variable phase, during which the cell accumulates nutrients, synthesizes RNA and proteins necessary for DNA synthesis, and prepares for cell division.
S phase involves replication of DNA, including duplication of DNA and formation of new chromatids.
G2 phase involves preparation for cell division, examination of replicated DNA, reorganization of cytoplasmic organelles, and can last around 1 hour.
M phase involves mitosis, which takes place in several stages, including karyokinesis (division of the nucleus) and cytokinesis (division of the cell).

The Nucleolus

The nucleolus is a spherical, basophilic subdomain of nuclei in cells, actively making proteins.
It is composed of fibrillar and granular subregions with different staining characteristics that reflect stages of rRNA maturation.
Genes for ribosomal subunits are localized in the interstices of the nucleolus and are transcribed by RNA polymerase I.
rRNA is processed in the nucleolus, quickly associated with ribosomal proteins, and exported to the cytoplasm through nuclear pores.

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Description

This quiz covers the cell cycle and its phases, as well as how retroviruses interact with the host cell's DNA and nucleolus to facilitate viral replication.