Cell Biology and Structure

Vacuoles are membrane-bound sacs within cytoplasm that store nutrients, waste products, and especially water in plant cells to maintain turgor pressure. The nucleus contains DNA, and mitochondria generate energy.

Cytoplasm is the gelatinous liquid that fills the inside of a cell and holds the organelles in place. The nucleus is a distinct organelle, and vacuoles and mitochondria are suspended within the cytoplasm.

According to cell theory, the cell is the fundamental structural and functional unit of all living organisms. Therefore, all living things, from single-celled bacteria to multicellular humans, are made of cells.

The cell membrane is a selectively permeable barrier that regulates the movement of substances in and out of the cell. This helps maintain a stable internal environment, unlike the nucleus which controls genetic activity.

One of the fundamental tenets of cell theory is that all cells arise from pre-existing cells through the process of cell division. They do not spontaneously generate or hatch from eggs.

The nucleus is considered the control center of the cell because it stores the cell's DNA and coordinates activities like growth, metabolism, and protein synthesis. Mitochondria focus on energy production, and Golgi bodies package proteins.

Organelles are specialized, membrane-bound structures within a cell that perform specific functions necessary for the cell's survival. They are analogous to organs in a body, but on a microscopic cellular scale.

In eukaryotic cells, genomic DNA is housed inside the nucleus, which is where transcription (the copying of DNA into mRNA) must take place. Translation then occurs in the cytoplasm on ribosomes.

In eukaryotic cells, translation occurs in the cytoplasm (either free-floating or on the rough endoplasmic reticulum) where ribosomes are located. Transcription, on the other hand, occurs in the nucleus.

Exocrine gland cells of the pancreas synthesize and secrete large quantities of digestive enzymes (proteins). Therefore, they require a highly developed rough endoplasmic reticulum and Golgi apparatus to process, package, and target these proteins for secretion.

Eukaryotic cells contain larger 80S ribosomes in their cytoplasm and on the rough endoplasmic reticulum, whereas prokaryotic cells contain smaller 70S ribosomes. Although eukaryotic organelles like mitochondria and chloroplasts contain 70S ribosomes, 80S ribosomes are the defining cytoplasmic ribosomes of eukaryotes.

Animal cells may contain small, temporary vacuoles, but they do not have the large, permanent central vacuole characteristic of plant cells. Ribosomes, lysosomes, and DNA are all present in animal cells.

The nucleus contains the cell's genetic material (DNA), making it the site for DNA replication and transcription. Photosynthesis occurs in chloroplasts, cellular respiration occurs primarily in mitochondria, and protein synthesis (translation) occurs on ribosomes in the cytoplasm.