A cell is the smallest unit of a living thing and is the basic building block of all organisms.
Microscopes allow for magnification and visualization of cells and cellular components that cannot be seen with the naked eye.
Cell theory states that living things are composed of one or more cells, that the cell is the basic unit of life, and that cells arise from existing cells.
A prokaryote is a simple, unicellular organism that lacks an organized nucleus or other membrane-bound organelle.
A eukaryotic cell has a true membrane-bound nucleus and has other membranous organelles that allow for compartmentalization of functions.
The plasma membrane is made up of a phospholipid bilayer that regulates the concentration of substances that can permeate a cell.
Found within eukaryotic cells, the nucleus contains the genetic material that determines the entire structure and function of that cell.
Mitochondria are organelles that are responsible for making adenosine triphosphate (ATP), the cell's main energy-carrying molecule.
Peroxisomes neutralize harmful toxins and carry out lipid metabolism and oxidation reactions that break down fatty acids and amino acids.
Although they are both eukaryotic cells, there are unique structural differences between animal and plant cells.
The endoplasmic reticulum is an organelle that is responsible for the synthesis of lipids and the modification of proteins.
The Golgi apparatus sorts and packages materials before they leave the cell to ensure they arrive at the proper destination.
Lysosomes are organelles that digest macromolecules, repair cell membranes, and respond to foreign substances entering the cell.
Microfilaments, which are the thinnest part of the cytoskeleton, are used to give shape to the cell and support all of its internal parts.
Microtubules are part of the cell's cytoskeleton, helping the cell resist compression, move vesicles, and separate chromosomes at mitosis.
The extracellular matrix of animal cells holds cells together to form a tissue and allow tissues to communicate with each other.
Intercellular junctions provide plant and animal cells with the ability to communicate through direct contact.
Cellular communication ensures regulation of biological processes within various environments from single-celled to multicellular organisms.
The major types of signaling mechanisms that occur in multicellular organisms are paracrine, endocrine, autocrine, and direct signaling.
Receptors, either intracellular or cell-surface, bind to specific ligands, which activate numerous cellular processes.
Signaling molecules are necessary for the coordination of cellular responses by serving as ligands and binding to cell receptors.
Ligand binding to cell-surface receptors activates the receptor's intracellular components setting off a signaling pathway or cascade.
Signaling pathway induction activates a sequence of enzymatic modifications that are recognized in turn by the next component downstream.
Gene expression, vital for cells to function properly, is the process of turning on a gene to produce RNA and protein.
The rush of adrenaline that leads to greater glucose availability is an example of an increase in metabolism.
Cell growth is promoted by ligands known as growth factors.
When a cell is damaged, unnecessary, or dangerous to an organism, a cell can initiate the mechanism for cell death known as apoptosis.
Signal cascades convey signals to the cell through the phosphorylation of molecules by kinases.
Yeasts utilize cell-surface receptors, mating factors, and signaling cascades in order to communicate.
Bacterial signaling allows bacteria to monitor cellular conditions and communicate with each other.
The plasma membrane protects the cell from its external environment, mediates cellular transport, and transmits cellular signals.
The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates.
The mosaic nature of the membrane, its phospholipid chemistry, and the presence of cholesterol contribute to membrane fluidity.
Passive transport, such as diffusion and osmosis, moves materials of small molecular weight across membranes.
The hydrophobic and hydrophilic regions of plasma membranes aid the diffusion of some molecules and hinder the diffusion of others.
Diffusion is a process of passive transport in which molecules move from an area of higher concentration to one of lower concentration.
Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
Osmosis is the movement of water across a membrane from an area of low solute concentration to an area of high solute concentration.
Tonicity, which is directly related to the osmolarity of a solution, affects osmosis by determining the direction of water flow.
Osmoregulation is the process by which living things regulate the effects of osmosis in order to protect cellular integrity.
To move substances against the membrane's electrochemical gradient, the cell utilizes active transport, which requires energy from ATP.
The sodium-potassium pump maintains the electrochemical gradient of living cells by moving sodium in and potassium out of the cell.
In secondary active transport, a molecule is moved down its electrochemical gradient as another is moved up its concentration gradient.
Endocytosis takes up particles into the cell by invaginating the cell membrane, resulting in the release of the material inside of the cell.
Exocytosis is the process by which cells release particles from within the cell into the extracellular space.
The cell cycle allows multiicellular organisms to grow and divide and single-celled organisms to reproduce.
The genome of an organism consists of its entire complement of DNA, which encodes the genes that control the organism's characteristics.
Chromosomes must coil to pack DNA into the cell during cell division, a process involving 3 levels of compaction.
Cells must grow and duplicate their internal structures during interphase before they can divide during mitosis.
During the multistep mitotic phase, the cell nucleus divides, and the cell components split into two identical daughter cells.
External factors can influence the cell cycle by inhibiting or initiating cell division.
The cell cycle is controlled by three internal checkpoints that evaluate the condition of the genetic information.
The cell cycle is controlled by regulator molecules that either promote the process or stop it from progressing.
Proto-oncogenes normally regulate cell division, but can be changed into oncogenes through mutation, which may cause cancers to form.
Tumor-suppressor genes keep regulatory mechanisms of cell division under control and prevent abnormal cell growth.
Binary fission is the method by which prokaryotes produce new individuals that are genetically identical to the parent organism.
Proteins, encoded by individual genes, orchestrate nearly every function of the cell.
The central dogma describes the flow of genetic information from DNA to RNA to protein.
The genetic code is a degenerate, non-overlapping set of 64 codons that encodes for 21 amino acids and 3 stop codons.
RNA polymerase initiates transcription at specific DNA sequences called promoters.
Transcription elongation begins with the release of the polymerase σ subunit and terminates via the rho protein or via a stable hairpin.
Initiation is the first step of eukaryotic transcription and requires RNAP and several transcription factors to proceed.
Elongation synthesizes pre-mRNA in a 5' to 3' direction, and termination occurs in response to termination sequences and signals.
Eukaryotic pre-mRNA receives a 5' cap and a 3' poly (A) tail before introns are removed and the mRNA is considered ready for translation.
rRNA and tRNA are structural molecules that aid in protein synthesis but are not themselves translated into protein.
Protein synthesis, or translation of mRNA into protein, occurs with the help of ribosomes, tRNAs, and aminoacyl tRNA synthetases.
Protein synthesis involves building a peptide chain using tRNAs to add amino acids and mRNA as a blueprint for the specific sequence.
In order to function, proteins must fold into the correct three-dimensional shape, and be targeted to the correct part of the cell.