Cell Nucleus: Structure and Function

• Cells have organelles that perform specific functions.
• The nucleus is known as the "brain" of the cell.
• It encloses and protects the cell's genetic material, DNA.
• By controlling DNA replication and expression, it determines cell functions and reproduction.
• Prokaryotic cells do not have a nucleus, while eukaryotic cells do.
• Plants, animals, and humans have eukaryotic cells.
• In chemistry, the nucleus is the center of an atom composed of protons and neutrons.

Location of Nucleus

• The nucleus is located in the center of the cell, surrounded by other organelles.
• Ribosomes are on the surface of the nucleus.
• The rough endoplasmic reticulum connects to the nucleus, with the smooth endoplasmic reticulum next to it.
• Other organelles are in the cytoplasm, surrounding the nucleus.

Nucleus Structure

• The nucleus is surrounded by the nuclear envelope, a membrane with inner and outer sections.
• The nuclear envelope has nuclear pores that allow substances to move in and out.
• Inside the nuclear envelope is the nucleoplasm, a liquid that contains chromatin.
• Chromatin is the structure created by DNA and proteins.
• During cell division, chromatin organizes into chromosomes.
• Humans have 46 chromosomes in total.
• The nucleolus, within the nucleoplasm, produces ribosomes.
• Ribosomes are formed by proteins and RNA.
• Ribosomal RNA (rRNA) exits the nucleus via nuclear pores to make proteins in the cytoplasm.

Nucleus Function

• A functioning nucleus is essential for a healthy cell.
• The nucleus controls cell division, protein production, and the behavior of other organelles.
• It determines how the cell will differentiate to handle a specific job in the body.
• The nucleus determines which parts of DNA are expressed, using genes that code for specific traits or functions.
• Differing patterns of gene expression, as determined by the nucleus, cause the varying functions and structures of each cell type.

Cellular Activities Managed by the Nucleus

• The nucleus regulates cell differentiation, DNA replication, and protein production.
• During cell division, the nucleus condenses chromatin into chromosomes and replicates them.
• Mitosis, the first phase of cell division, begins after DNA replication.
• The nuclear envelope breaks down, chromosomes are pulled to opposite sides, and the nuclear envelope reforms.
• A nucleolus appears in each nucleus then the cell duplicates remaining organelles and splits into two identical cells.
• The nucleus directs protein production by ribosomes through transcription and translation.
• Nitrogenous bases (A, G, C, T in DNA; A, G, C, U in RNA) make up the codes of DNA and RNA.
• In DNA, adenine pairs with thymine, and guanine pairs with cytosine.
• In RNA, uracil replaces thymine and bonds with adenine.
• RNA is single-stranded, copying messages from DNA and transporting them to ribosomes.

Transcription

• RNA "copies" DNA using base pairing.
• Messenger RNA (mRNA) is created and exits the nucleus through nuclear pores to the ribosomes.

Translation

• mRNA passes through the ribosome.
• Transfer RNA (tRNA) molecules bond with mRNA using base pairs and carry amino acids.
• Amino acids bond together to create the protein coded for by the DNA strand.
• Gene expression is the process by which genes in DNA direct life processes within and outside cells.
• RNA molecules, including rRNA, mRNA, and tRNA, are made in the nucleus.
• The nucleus controls when and how RNA molecules perform their duties, thus controlling all protein production.