The nucleus | Cells | MCAT | Khan Academy

Recent questions

• What is a eukaryotic cell?

  A eukaryotic cell is a type of cell that has a defined nucleus and membrane-bound organelles. Unlike prokaryotic cells, which lack a nucleus and are generally simpler in structure, eukaryotic cells are more complex and can be found in organisms such as plants, animals, fungi, and protists. The presence of a nucleus allows for the compartmentalization of genetic material, which is crucial for processes like DNA replication and transcription. Additionally, eukaryotic cells have various organelles, such as mitochondria and the endoplasmic reticulum, that perform specialized functions, contributing to the overall efficiency and regulation of cellular activities.

• How do cells transport materials?

  Cells transport materials through various mechanisms that ensure the movement of substances across their membranes and compartments. One of the primary methods is through passive transport, which includes diffusion and osmosis, allowing molecules to move from areas of higher concentration to lower concentration without energy expenditure. Active transport, on the other hand, requires energy to move substances against their concentration gradient. Additionally, cells utilize vesicular transport, where materials are enclosed in membrane-bound vesicles that can fuse with other membranes to deliver their contents. This is particularly important for transporting larger molecules or groups of molecules, such as proteins and lipids, across cellular barriers.

• What is the function of ribosomes?

  Ribosomes are essential cellular structures responsible for protein synthesis, a fundamental process in all living organisms. They translate messenger RNA (mRNA) sequences into polypeptide chains, which then fold into functional proteins. Ribosomes can be found either floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming what is known as rough ER. The location of ribosomes influences the type of proteins they produce; those on the rough ER typically synthesize proteins destined for secretion or for use in the cell membrane, while free ribosomes generally produce proteins that function within the cytosol. Overall, ribosomes play a critical role in translating genetic information into functional molecules that are vital for cellular structure and function.

• What is the role of the nucleus?

  The nucleus serves as the control center of eukaryotic cells, housing the cell's genetic material in the form of DNA. It is encased by a double membrane known as the nuclear envelope, which separates the contents of the nucleus from the cytoplasm. This compartmentalization is crucial for regulating gene expression and ensuring that the processes of DNA replication and transcription occur in a controlled environment. Within the nucleus, the nucleolus is responsible for synthesizing ribosomal RNA (rRNA) and assembling ribosomes, which are then transported to the cytoplasm for protein synthesis. The nucleus also plays a key role in cell division, as it ensures that genetic material is accurately replicated and distributed to daughter cells.

• What is the endoplasmic reticulum?

  The endoplasmic reticulum (ER) is a vital organelle in eukaryotic cells that plays a key role in the synthesis, folding, modification, and transport of proteins and lipids. It consists of a network of membranous tubules and sacs, and is divided into two types: rough ER, which is studded with ribosomes and is primarily involved in protein synthesis, and smooth ER, which lacks ribosomes and is associated with lipid synthesis and detoxification processes. The rough ER is particularly important for producing proteins that are secreted from the cell or incorporated into the cell membrane, while the smooth ER is involved in the metabolism of carbohydrates and the storage of calcium ions. The ER is interconnected with the nuclear envelope, highlighting the close relationship between these organelles in cellular function.