Cell Nucleus and Its Components

Flashcards covering key concepts related to the cell nucleus and its components.

Nucleus

Known as the 'brain of the cell', it controls and directs all activities in the cell.

Nucleolus

A sub-organelle of the nucleus that synthesizes ribosomes and performs most of the nucleus's jobs.

Chromatin

Stored form of genetic material (DNA) in the nucleus, which condenses into chromosomes during mitosis.

Nuclear Membrane

A protective barrier around the nucleus that allows for the in/out transfer of substances and protects the DNA.

Transcription

The process occurring in the nucleus where DNA is turned into RNA.

mRNA (Messenger RNA)

Acts as the messenger between DNA and ribosomes.

rRNA (Ribosomal RNA)

A building block of ribosomes.

tRNA (Transfer RNA)

Works with mRNA to help make proteins.

Protein Synthesis

The process that begins in the nucleus with transcription and involves the production of proteins.

How does the nucleus control cell activities beyond just containing DNA?

The nucleus controls cell activities primarily by regulating gene expression, deciding which genes are 'on' or 'off' based on the cell's needs and environmental signals.

What is the nuclear envelope composed of?

The nuclear envelope is a double membrane structure consisting of an inner and outer membrane, separated by a perinuclear space, and studded with nuclear pores.

What is the primary function of nuclear pores?

Nuclear pores regulate the transport of molecules, such as proteins and RNA, between the nucleus and the cytoplasm, allowing small molecules to diffuse freely and large molecules to be actively transported.

What types of molecules can freely diffuse through nuclear pores vs. those requiring active transport?

Small molecules and ions can freely diffuse through nuclear pores. Larger molecules like proteins and RNA require active transport mechanisms involving specific transport proteins.

What is the nuclear lamina and what is its function?

The nuclear lamina is a fibrous protein network located inside the inner nuclear membrane. It provides structural support to the nuclear envelope and plays a role in chromatin organization and gene regulation.

What are histones and how do they contribute to DNA packaging?

Histones are proteins around which DNA is wound, forming structures called nucleosomes. This packaging mechanism compacts the long DNA molecule into the smaller volume of the nucleus and regulates gene accessibility.

Differentiate between euchromatin and heterochromatin in terms of gene expression.

Euchromatin is a loosely packed form of chromatin that is transcriptionally active, meaning genes within it are readily expressed. Heterochromatin is a tightly packed form of chromatin that is generally transcriptionally inactive or silent.

What is the significance of chromatin condensing into chromosomes during mitosis?

Chromatin condenses into compact chromosomes during mitosis (cell division) to ensure the accurate and efficient segregation of genetic material to the daughter cells, preventing tangling and breakage.

Where does DNA replication occur within the cell and why is this location crucial?

DNA replication occurs exclusively within the nucleus. This location is crucial for maintaining the integrity and protection of the cell's genetic material before cell division.

Briefly explain the flow of genetic information according to the central dogma.

The central dogma of molecular biology describes the flow of genetic information: DNA is transcribed into RNA, and RNA is then translated into protein.

Why is pre-mRNA processed into mature mRNA in the nucleus before export?

Pre-mRNA is processed in the nucleus through splicing (removal of introns), capping, and polyadenylation. This processing ensures the stability, proper translation, and efficient export of mRNA to the cytoplasm.

How does mRNA exit the nucleus to reach the ribosomes in the cytoplasm?

Messenger RNA (mRNA) exits the nucleus through nuclear pores, a process often facilitated by specific RNA-binding proteins that escort it to the cytoplasm where ribosomes await.

Describe the specific steps or components synthesized by the nucleolus for ribosome formation.

The nucleolus is the site of ribosomal RNA (rRNA) synthesis and processing. It also assembles rRNA with imported ribosomal proteins to form ribosomal subunits, which are then exported to the cytoplasm.

Once assembled, how do ribosomal subunits get to the cytoplasm to synthesize proteins?

After being synthesized and partially assembled in the nucleolus, the large and small ribosomal subunits are individually exported through nuclear pores to the cytoplasm, where they combine to form a functional ribosome.

What general principle governs the movement of proteins into the nucleus?

The movement of proteins into the nucleus is generally governed by the presence of a Nuclear Localization Signal (NLS), a specific amino acid sequence within the protein that is recognized by import machinery (importins).

Where are proteins destined for the nucleus initially synthesized?

Proteins destined for the nucleus are initially synthesized on ribosomes freely floating in the cytoplasm, and then they are imported into the nucleus if they possess an NLS.

How does the nucleus regulate which genes are 'turned on' or 'turned off' at specific times?

The nucleus regulates gene expression through various mechanisms, including the binding of transcription factors to DNA, chromatin remodeling (changing DNA accessibility), and epigenetic modifications, responding to cellular needs and external signals.

How does the nucleus play a role in cell differentiation?

The nucleus plays a central role in cell differentiation by selectively expressing specific sets of genes, leading to the production of unique proteins that define the structure and function of specialized cell types.

Briefly explain the nucleus's involvement in programmed cell death (apoptosis).

In apoptosis, the nucleus undergoes significant changes, including DNA fragmentation and breakdown of the nuclear envelope, as part of the orderly dismantling of the cell, orchestrated by cellular signaling pathways.

How do the nucleus and cytoplasm depend on each other for cell function?

The nucleus depends on the cytoplasm for raw materials, energy, and enzymes supplied by organelles, while the cytoplasm depends on the nucleus for genetic instructions (via mRNA) to synthesize proteins and direct cellular activities.