A neoplasm or tumor is a mass of cells that results from uncontrolled cell division, which is a distinguishing feature of cancer cells.
Catalase is an enzyme in peroxisomes that decomposes hydrogen peroxide (H2O2), protecting other parts of the cell from its toxic effects.
Nuclear pores are openings in the nuclear envelope that control the movement of substances between the nucleus and the cytoplasm. They consist of a circular arrangement of proteins surrounding a large central opening.
Genomic medicine aims to design new drugs and provide screening tests to enable physicians to offer more effective counseling and treatment for disorders with significant genetic components.
Gene expression is the process where a gene’s DNA is used as a template for the synthesis of a specific protein.
Reproductive cell division is the mechanism that produces gametes, involving a special two-step division process called meiosis.
Ribosomal RNA (rRNA) joins with ribosomal proteins to make ribosomes.
During prophase, chromatin fibers condense and shorten into visible chromosomes, and the mitotic spindle begins to form.
The large and small ribosomal subunits join to form a functional ribosome that facilitates the translation of mRNA into a protein. They separate once protein synthesis is complete.
The nucleus is a spherical or oval-shaped structure that usually is the most prominent feature of a cell. It is separated from the cytoplasm by a double membrane called the nuclear envelope and contains the cell's hereditary units, called genes.
The Human Genome Project was an effort that began in 1990 to sequence all of the nearly 3.2 billion nucleotides of the human genome, completed in April 2003.
Proteome refers to all of an organism’s proteins.
Somatic cell division is the process by which a somatic cell undergoes nuclear division (mitosis) and cytoplasmic division (cytokinesis) to produce two genetically identical cells.
Transcription is the process that occurs in the nucleus where the genetic information represented by the sequence of base triplets in DNA serves as a template for copying the information into a complementary sequence of codons in RNA.
The mitotic spindle is a football-shaped assembly of microtubules that forms during prophase and is responsible for separating chromosomes during cell division.
The cytoplasm consists of cellular contents between the plasma membrane and nucleus, including cytosol and organelles.
Cytokinesis is the division of a cell's cytoplasm and organelles into two identical cells. It begins in late anaphase with the formation of a cleavage furrow and is completed after telophase.
Introns are regions within a gene that do not code for parts of proteins and are removed from pre-mRNA during processing.
Mitochondria are organelles that generate most of the ATP through aerobic (oxygen-requiring) respiration and are referred to as the 'powerhouses' of the cell.
When the ribosome shifts by one codon, the tRNA previously at the P site moves to the E site and is released, while the tRNA at the A site moves to the P site.
Autophagy is the process by which lysosomes digest worn-out organelles within a cell.
Nucleoli are spherical bodies within the nucleus that function in producing ribosomes. They are clusters of protein, DNA, and RNA and are the sites of synthesis of rRNA and assembly of rRNA and proteins into ribosomal subunits.
During transcription, the information encoded in a specific region of DNA is transcribed (copied) to produce a specific molecule of RNA.
Recombinant DNA is a combination of DNA from different sources, created by inserting genes from other organisms into a host cell, causing the host to produce proteins it normally does not synthesize.
An anticodon is a triplet of nucleotides in tRNA that pairs with a complementary codon in mRNA during protein synthesis.
Two identical DNA molecules and their histones form a pair of chromatids, which are held together by a centromere.
Cilia move fluids over the cell’s surface, while flagella move the entire cell.
The initiator tRNA attaches to the start codon and fits into the P site of the ribosome, initiating the process of protein synthesis.
Proteasomes are complexes found in the cytosol and nucleus that contain proteases, enzymes that cut proteins into small peptides for degradation and recycling.
Chromatin is a complex of DNA, proteins, and some RNA found in the nucleus. In cells that are not dividing, it appears as a diffuse, granular mass.
Meiosis is a type of cell division in which the number of chromosomes in the nucleus is reduced by half.
A base triplet is a sequence of three nucleotides in DNA.
Proteasomes degrade unneeded, damaged, or faulty proteins by cutting them into small peptides.
A chromatid is one of the two identical strands of a chromosome that are joined together by a centromere during prophase of cell division.
During the S phase of interphase, DNA replication occurs, doubling the amount of DNA in preparation for cell division.
During anaphase, the centromeres split, separating the two members of each chromatid pair, which then move toward opposite poles of the cell. Once separated, the chromatids are termed chromosomes.
The G2 phase involves cell growth, continued enzyme and protein synthesis, and the completion of centrosome replication.
Proteasomes may fail to degrade abnormal proteins, leading to the accumulation of misfolded proteins in brain cells, which is observed in diseases like Parkinson's and Alzheimer's.
A nucleosome is a structural unit of chromatin, consisting of double-stranded DNA wrapped twice around a core of eight proteins called histones.
Homologous chromosomes are pairs of chromosomes that contain similar genes arranged in the same (or almost the same) order, with one member of each pair inherited from each parent.
A codon is a complementary sequence of three nucleotides transcribed from a DNA base triplet.
The nucleus controls the movement of substances between the nucleus and cytoplasm, produces ribosomes, and contains chromosomes that control cellular structure and direct cellular functions.
A kinetochore is a protein complex located at the outside of each centromere, where microtubules of the mitotic spindle attach during cell division.
Cytokinesis is the division of the cytoplasm that usually occurs during late anaphase of the mitotic phase, resulting in the formation of two separate cells.
Mitochondrial cristae are folds in the internal mitochondrial membrane that increase the surface area for chemical reactions of aerobic cellular respiration, thereby enhancing ATP production.
Chromatids are each of the two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.
During the S phase, DNA replication occurs, ensuring that the two identical cells formed during cell division will have the same genetic material.
Peroxisomes oxidize amino acids and fatty acids and detoxify harmful substances such as hydrogen peroxide and associated free radicals.
During transcription, the bases pair in a complementary manner: cytosine (C) pairs with guanine (G), guanine (G) pairs with cytosine (C), and thymine (T) pairs with adenine (A) in the RNA strand.
The plasma membrane protects cellular contents, makes contact with other cells, contains channels, transporters, receptors, enzymes, cell-identity markers, and linker proteins, and mediates the entry and exit of substances.
The centrosome is composed of a pair of centrioles plus the pericentriolar matrix.
At the A site, the anticodon of the incoming tRNA pairs with the next mRNA codon, allowing the amino acid it carries to be added to the growing peptide chain.
Genomics is the study of the relationships between the genome and the biological functions of an organism.
The cell cycle is an orderly sequence of events in which a somatic cell duplicates its contents and divides in two.
The G2 phase is the interval between the S phase and the mitotic phase, during which cell growth continues, enzymes and other proteins are synthesized, and replication of centrosomes is completed.
Mitochondria are the site of aerobic cellular respiration reactions that produce most of a cell’s ATP and play an important early role in apoptosis.
A centromere is a constricted region of a chromosome that holds the two chromatids together.
A chromosome is a highly coiled and folded DNA molecule that is combined with protein molecules.
Cyclins are cellular proteins that regulate the cell cycle by switching cyclin-dependent protein kinases (Cdk's) on and off. Their levels rise and fall during the cell cycle, and the joining of a specific cyclin and Cdk molecule triggers various events that control cell division.
Telophase is the final stage of mitosis, where chromosomal movement stops, chromosomes uncoil and revert to chromatin form, a nuclear envelope forms around each chromatin mass, nucleoli reappear, and the mitotic spindle breaks up.
Alternative splicing is a process in which pre-mRNA is spliced in different ways to produce several different mRNAs, allowing one gene to code for multiple proteins.
Side effects of chemotherapy include nausea, diarrhea, hair loss, fatigue, and decreased resistance to disease, as the drugs also kill all types of rapidly dividing cells in the body.
Tay-Sachs disease is an inherited condition characterized by the absence of a lysosomal enzyme called Hex A, leading to the accumulation of ganglioside GM2 in nerve cells, causing seizures, muscle rigidity, blindness, dementia, and early death.
Chromatin is a complex of DNA and protein found in the nucleus of cells, which condenses to form chromosomes during cell division.
Interphase is the period in the cell cycle when a cell is not dividing but is replicating its DNA, producing additional organelles, and growing.
The Golgi complex accepts proteins from the rough ER, forms glycoproteins, glycolipids, and lipoproteins, and sorts and packages molecules for transport to their destinations.
Transfer RNA (tRNA) binds to an amino acid and holds it in place on a ribosome until it is incorporated into a protein during translation. One end of the tRNA carries a specific amino acid, and the opposite end consists of a triplet of nucleotides called an anticodon.
The cytosol is composed of water, solutes, suspended particles, lipid droplets, and glycogen granules.
The rough ER synthesizes glycoproteins and phospholipids that are transferred to cellular organelles, inserted into the plasma membrane, or secreted during exocytosis.
The P (peptidyl) site binds the tRNA carrying the growing polypeptide chain during translation.
Pre-mRNA is the initial transcript that includes both introns and exons, which is processed to form functional mRNA by removing introns.
Lysosomes digest substances that enter a cell via endocytosis, transport final products of digestion into the cytosol, carry out autophagy, implement autolysis, and accomplish extracellular digestion.
Genes are the cell’s hereditary units that control cellular structure and direct cellular activities. They are arranged along chromosomes.
During translation, the RNA attaches to a ribosome, where the information contained in RNA is translated into a corresponding sequence of amino acids to form a new protein molecule.
Genetic engineering is the technology that arises from the manipulation of genetic material, allowing for the production of therapeutic substances like human growth hormone, insulin, interferon, and erythropoietin.
A promoter is a special nucleotide sequence located near the beginning of a gene where RNA polymerase attaches to the DNA to start the transcription process.
Cyclin-dependent protein kinases (Cdk's) are enzymes that can transfer a phosphate group from ATP to a protein to activate the protein; other enzymes can remove the phosphate group from the protein to deactivate it. The activation and deactivation of Cdk's are crucial in the initiation and regulation of DNA replication, mitosis, and cytokinesis.
The cytoskeleton maintains the shape and general organization of cellular contents and is responsible for cell movements.
The smooth ER synthesizes fatty acids and steroids, inactivates or detoxifies drugs, removes phosphate groups from glucose-6-phosphate, and stores and releases calcium ions in muscle cells.
A terminator is a special nucleotide sequence in DNA that specifies the end of a gene, causing RNA polymerase to detach from the transcribed RNA molecule and the DNA strand.
Chemotherapy is the use of anticancer drugs to treat cancer by stopping cell division, often by inhibiting the formation of the mitotic spindle.
Mitochondria play an important early role in apoptosis, which is the process of programmed cell death.
Proteasomes are tiny barrel-shaped structures consisting of four stacked rings of proteins around a central core that continuously destroy unneeded, damaged, or faulty proteins in the cytosol.
The nuclear envelope is a double membrane that separates the nucleus from the cytoplasm. Both layers are lipid bilayers similar to the plasma membrane, and the outer membrane is continuous with the rough ER.
The genome is the total genetic information carried in a cell or an organism.
Diploid (2n) cells are somatic cells that contain two sets of chromosomes.
The genetic code is the set of rules that relate the base triplet sequence of DNA to the corresponding codons of RNA and the amino acids they specify.
Messenger RNA (mRNA) directs the synthesis of a protein.
The mitotic (M) phase of the cell cycle consists of nuclear division (mitosis) and cytoplasmic division (cytokinesis), resulting in the formation of two identical cells.
Apoptosis is an orderly, genetically programmed cell death. It involves a triggering agent causing 'cell-suicide' genes to produce enzymes that damage the cell, leading to cell shrinkage, DNA fragmentation, and eventual ingestion by phagocytes.
Ribosomes are composed of two subunits containing ribosomal RNA and proteins; they may be free in the cytosol or attached to the rough ER.
The E (exit) site binds tRNA just before it is released from the ribosome during translation.
A stop codon signals the termination of protein synthesis, causing the ribosome to release the newly formed protein and disassemble.
Linker DNA is the string of DNA that holds adjacent nucleosomes together in the chromatin structure.
During the G1 phase, the cell is metabolically active, replicates most of its organelles and cytosolic components, and begins replication of centrosomes.
Lysosomes fuse with and digest contents of endosomes, phagosomes, and vesicles, and transport final products of digestion into the cytosol. They also digest worn-out organelles, entire cells, and extracellular materials.
The enzyme RNA polymerase catalyzes the transcription of DNA.
Mitosis is the process of nuclear division in which two sets of chromosomes are distributed into two separate nuclei, resulting in the exact partitioning of genetic information.
The G2 phase is a period in the cell cycle where cell growth continues, enzymes and other proteins are synthesized, and centrosome replication is completed.
During the S phase, replication of DNA and centrosomes takes place.
The A (aminoacyl) site binds the tRNA carrying the next amino acid to be added to the growing polypeptide chain during translation.
The G1 phase is a period in the cell cycle where the cell is metabolically active, duplicates organelles and cytosolic components, and begins centrosome replication.
During the G1 phase, a metabolically active cell duplicates most of its organelles and cytosolic components, and replication of chromosomes begins. Cells that remain in the G1 phase for a very long time and possibly never divide again are said to be in the G0 phase.
A polyribosome is a complex of several ribosomes attached to the same mRNA molecule, allowing the simultaneous translation of one mRNA into several identical proteins.
Exons are regions within a gene that code for segments of a protein and are spliced together to form functional mRNA after introns are removed.
During metaphase, the microtubules of the mitotic spindle align the centromeres of the chromatid pairs at the exact center of the mitotic spindle, forming the metaphase plate.
An initiator tRNA binds to the start codon (AUG) on mRNA, initiating translation and carrying the amino acid methionine.
Small nuclear ribonucleoproteins (snRNPs) are enzymes that cut out introns and splice together exons in pre-mRNA to form functional mRNA.
