cell

• The cell is known as the structural and functional unit of life because all living beings are formed of cells.
• There are trillion cells in the human body.
• Major parts of a cell include the nucleus, which contains DNA, and cytoplasm, which is the cellular contents between the plasma membrane and nucleus.
• The plasma membrane controls what moves in and out of the cell and is selectively permeable.
• The plasma membrane is a phospholipid bilayer, water-soluble “heads” form surfaces (hydrophilic) and water-insoluble “tails” form the interior (hydrophobic).
• The plasma membrane is permeable to lipid-soluble substances and cholesterol stabilizes the membrane.
• Cell death may be the result of the natural process of old cells dying and being replaced by new ones, or may result from such factors as disease, localized injury, or the death of the organism of which the cells are part.
• Cell death is the event of a biological cell ceasing to carry out its functions.
• Apoptosis is the death of cells which occurs as a normal and controlled part of an organism's growth or development.
• Abnormal cell division during the development of the sperm cell or the egg cell is the cause of cancer.
• Cytoplasm is a thick solution that fills each cell and is enclosed by the cell membrane.
• Cytoplasm is mainly composed of water, salts, and proteins.
• All of the organelles in eukaryotic cells, such as the nucleus, endoplasmic reticulum, and mitochondria, are located in the cytoplasm.
• A nucleus is a membrane-bound organelle that contains the cell's chromosomes and pores in the nuclear membrane allow for the passage of molecules in and out of the nucleus.
• The nuclear envelope is a porous double membrane that separates nucleoplasm from cytoplasm.
• The nucleolus is a dense collection of RNA and proteins and is the site of ribosome production.
• In the S phase, DNA replication can proceed through the mechanisms that result in the formation of identical pairs of DNA molecules — sister chromatids — that are firmly attached to the centromeric region.
• Cilia are short hair-like projections that propel substances on the cell surface.
• Passive transport mechanisms do not require energy and include simple diffusion, facilitated diffusion, osmosis, filtration, and very active period 3 Phases are involved in the cell cycle: G1 phase, the cell grows; S phase, the cell replicates DNA; G2 phase, the cell is in preparation for cell division.
• Peroxisomes are enzyme-containing sacs that break down organic molecules and detoxify alcohol.
• A flagellum is a long tail-like projection that provides motility to sperm.
• Centrosomes contain two rod-like centrioles used to produce cilia and flagella and distribute chromosomes during cell division.
• Chromatin consists of fibers of DNA and proteins and stores information for the synthesis of proteins.
• During the G1 phase, the cell is quite active at the biochemical level, accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus.
• Lysosomes are enzyme-containing sacs that digest worn out cell parts or unwanted substances.
• Mitochondrial DNA are inherited only from the mother.
• The centrosome is duplicated during the S phase.
• Microfilaments and microtubules are thin rods and tubules that support the cytoplasm and allow for movement of organelles.
• The cell cycle consists of mitosis, which divides the cell, and interphase, which prepares the cell for mitosis.
• The basic component of a cell includes the nucleus, which contains DNA, and cytoplasm, which is the cellular contents between the plasma membrane and nucleus.
• Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase.
• Growth factors and hormones stimulate cell division.
• In the G2 phase, the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation.
• Chromosome tips (telomeres) that shorten with each mitosis provide a mitotic clock.
• Cultured fibroblasts are favored for laboratory studies of this process, as they readily enter a quiescent state mimicking G0 phase when deprived of serum and rapidly reenter the cell cycle when serum is restored.
• Cell division capacities vary greatly among cell types.
• Mitosis is important to multicellular organisms because it provides new cells for growth and for replacement of worn-out cells, such as skin cells.
• The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis.
• Cells enter G0 primarily due to environmental factors, like nutrient deprivation, that limited the resources necessary for proliferation.
• Telomerase, also called telomere terminal transferase, is an enzyme made of protein and RNA subunits that elongates chromosomes by adding TTAGGG sequences to the end of existing chromosomes.