3.8: Key Terms

Adenosine triphosphate (ATP): A high-energy compound produced by mitochondria that powers cellular processes.

Allele: A non-identical DNA sequence found in the same gene location on a homologous chromosome, or gene copy, that codes for the same trait but produces a different phenotype.

Amino acids: Organic molecules that are the building blocks of protein. Each of the 20 different amino acids have their own unique chemical property. Amino acids are also chained together to form proteins.

Ancient (aDNA): DNA that is isolated from organic remains often dating from hundreds to thousands of years ago. Also, aDNA is typically degraded (i.e., damaged) due to exposure to the elements such as heat, acidity, and humidity.

Aneuploid: A cell with an unexpected amount of chromosomes. The loss or gain of chromosomes can occur during mitotic or meiotic division.

Antibodies: Immune-related proteins that can detect and bind to foreign substances in the blood such as pathogens.

Apoptosis: A series of molecular steps that is activated leading to cell death. Apoptosis can be activated when a cell fails checkpoints during the cell cycle; however, cancer cells have the ability to avoid apoptosis.

Autosomal: Refers to a pattern of inheritance where an allele is located on an autosome.

Base pairs: Chemical bonding between nucleotides, like adenine (A) and thymine (T) or cytosine (C) and guanine (G) in DNA; or (A) and uracil (U) in RNA

Carbohydrate: Molecules composed of carbon and hydrogen atoms that can be broken down to supply energy.

Carrier: An individual who has a heterozygous genotype that is typically associated with a disease.

Cell cycle: A cycle the cell undergoes with checkpoints between phases to ensure that DNA replication and cell division occur properly.

Cell surface antigen: A protein that is found on a red blood cell’s surface.

Centromere: A structural feature that is defined as the “center” of a chromosome and which creates two different arm lengths. Term also refers to the region of attachment for microtubules during mitosis and meiosis.

Chromatin: DNA wrapped around histone complexes. During cell division, chromatin becomes a condensed chromosome.

Chromosome: DNA molecule that is wrapped around protein complexes, including histones.

Codominance: The effects of both alleles in a genotype can be seen in the phenotype.

Codons: A sequence that comprises three DNA nucleotides that together code for a protein.

Complex diseases: A category of diseases that are polygenic and are also influenced by environment and lifestyle factors.

Cytoplasm: The “jelly-like” matrix inside of the cell that contains many organelles and other cellular molecules.

Deleterious: A mutation that increases an organism’s susceptibility to disease.

Deoxyribonucleic acid (DNA): A molecule that carries the hereditary information passed down from parents to offspring. DNA can be described as a “double helix”’ shape. It includes two chains of nucleotides held together by hydrogen bonds with a sugar-phosphate backbone.

Diploid: Refers to an organism or cell with two sets of chromosomes.

DNA methylation: Methyl groups bind DNA, which modifies the transcriptional activity of a gene by turning it “on” or “off.”

DNA polymerase: Enzyme that adds nucleotides to existing nucleic acid strands during DNA replication. These enzymes can be distinguished by their processivity (e.g., DNA replication).

DNA replication: Cellular process in which DNA is copied and doubled.

DNA sequence: The order of nucleotide bases. A DNA sequence can be short, long, or representative of entire chromosomes or organismal genomes.

Dominant: Refers to an allele for which one copy is sufficient to be visible in the phenotype.

Elongation: The assembly of new DNA from template strands with the help of DNA polymerases.

Enzymes: Proteins responsible for catalyzing (accelerating) various biochemical reactions in cells.

Epigenetic profile: The methylation pattern throughout a genome—that is, which genes (and other genomic sites) are methylated and unmethylated.

Epigenetics: Changes in gene expression that do not result in a change of the underlying DNA sequence. These changes typically involve DNA methylation and histone modifications. These changes are reversible and can also be inherited by the next generation.

Euchromatin: Loosely coiled chromosomes found within the nucleus that is accessible for regulatory processing of DNA.

Eukaryote: Single-celled or multicelled organism characterized by a distinct nucleus, with each organelle surrounded by its own membrane.

Exon: Protein-coding segment of a gene.

Gametes: Haploid cells referred to as an egg and sperm that will fuse together during sexual reproduction to form a diploid organism.

Gene: Segment of DNA that contains protein-coding information and various regulatory (e.g., promoter) and noncoding (e.g., introns) regions.

Genetic recombination: A cellular process that occurs during meiosis I in which homologous chromosomes pair up and sister chromatids on different chromosomes physically swap genetic information.

Genome: All the genetic information of an organism.

Genotype: The combination of two alleles that code for or are associated with the same gene.

Genotyping: A molecular procedure that is performed to test for the presence of certain alleles or to discover new ones.

Haploid: Cell or organism with one set of chromosomes (n = 23).

Helicase: A protein that breaks the hydrogen bonds that hold double-stranded DNA together.

Heterozygous: Genotype that consists of two different alleles.

Histones: Protein that DNA wraps around to assist with DNA organization within the nucleus.

Homologous chromosomes: A matching pair of chromosomes wherein one chromosome is maternally inherited and the other is paternally inherited.

Homozygous: Genotype that consists of two identical alleles.

Incomplete dominance: Heterozygous genotype that produces a phenotype that is a blend of both alleles.

Initiation: The recruitment of proteins to separate DNA strands and begin DNA replication.

Interphase: Preparatory period of the cell cycle when increased metabolic demand allows for DNA replication and doubling of the cell prior to cell division.

Introns: Segment of DNA that does not code for proteins.

Karyotyping: The microscopic procedure where the number of chromosomes in a cell is determined.

Lagging strand: DNA template strand that is opposite to the leading strand. Therefore, DNA replication proceeds discontinuously, generating Okazaki fragments.

Leading strand: DNA template strand in which replication proceeds continuously.

Lipids: Fatty acid molecules that serves various purposes in the cell, including energy storage, cell signaling, and structure.

Meiosis: The process that gametes undergo to divide. The end of meiosis results in four haploid daughter cells.

Mendelian genetics: A classification given to phenotypic traits that are controlled by a single gene.

Messenger RNA (mRNA): RNA molecule that is transcribed from DNA. Its tri-nucleotide codons are “read” by a ribosome to build a protein.

Microarray technology: A genotyping procedure that utilizes a microarray chip, which is a collection of thousands of short nucleotide sequences attached to a solid surface that can probe genomic DNA.

Microbiome: The collective genomes of the community of microorganisms that humans have living inside of their body.

Mitochondrial DNA (mtDNA): Circular DNA segment found in mitochondria that is inherited maternally.

Mitochondrion: Specialized cellular organelle that is the site for energy production. It also has its own genome (mtDNA).

Mitosis: The process that somatic cells undergo to divide. The end of mitosis results in two diploid daughter cells.

Mutation: A nucleotide sequence variation from the template DNA strand that can occur during replication. Mutations can also happen during recombination.

Next-generation sequencing: A genotyping technology that involves producing millions of nucleotide sequences (from a single DNA sample) that are then read with a sequencing machine. It can be used for analyzing entire genomes or specific regions and requires extensive program-based applications.

Nuclear envelope: A double-layered membrane that encircles the nucleus.

Nucleic acid: A complex structure (like DNA or RNA) that carries genetic information about a living organism.

Nucleotide: The basic structural component of nucleic acids, which includes DNA (A, T, C, and G) and RNA (A, U, C, and G).

Nucleus: Double-membrane cellular organelle that helps protect DNA and regulation of nuclear activities.

Okazaki fragment: Short DNA strands derived from DNA replication on the lagging strand. They were discovered by Reiji and Tsuneko Okazaki in the 1960s.

Organelle: A structure within a cell that performs specialized tasks that are essential for the cell. There are different types of organelles with their own function.

Pathogenic: A genetic mutation (i.e., allele) that has a harmful phenotypic disease-causing effect.

Penetrance: The proportion of how often the possession of an allele results in an expected phenotype. Some alleles are more penetrant than others.

Phenotype: The physical appearance of a given trait.

Phospholipid bilayer: Two layers of lipids that form a barrier due to the properties of a hydrophilic (water-loving) head and a hydrophobic (water-repelling) tail.

Polygenic trait: A phenotype that is controlled by two or more genes.

Polymerase chain reaction (PCR): A molecular biology procedure that can make copies of genomic DNA segments. A small amount of DNA is used as a starting template and is then used to make millions of copies.

Primer: A primer is a small sequence of nucleotides that bind DNA to start the process of DNA replication or PCR.

Prokaryote: A single-celled organism characterized by lack of a nucleus and membrane-enclosed organelles.

Promoter: The region of a gene that initiates transcription. Transcription factors can bind and DNA methylation may occur at a promoter site, which can modify the transcriptional activities of a gene.

Protein: Chain of amino acids that fold into a three dimensional structure that allow a cell to function in a variety of ways.

Protein synthesis: A multi-step process by which amino acids are strung together by RNA machinery read from a DNA template.

Recessive: Refers to an allele whose effect is not normally seen unless two copies are present in an individual’s genotype.

Ribonucleic acid (RNA): Single-stranded nucleic acid molecule.There are different RNAs found within cells and they perform a variety of functions, such as cell signaling and involvement in protein synthesis.

Ribosomal RNA (rRNA): A ribosome-bound molecule that is used to correctly assemble amino acids into proteins.

Ribosome: An organelle in the cell found in the cytoplasm or endoplasmic reticulum. It is responsible for reading mRNA and protein assemblage.

RNA polymerase: An enzyme that catalyzes the process of making RNA from a DNA template.

Sanger-sequencing: A process that involves the usage of fluorescently labeled nucleotides to visualize DNA (PCR fragments) at the nucleotide level.

Semi-conservative replication: DNA replication in which new DNA is replicated from an existing DNA template strand.

Sequencing: A molecular laboratory procedure that produces the order of nucleotide bases (i.e., sequences).

Sister chromatids: During DNA replication, sister chromatids are produced on the chromosome. In cell division, sister chromatids are pulled apart so that two cells can be formed. In meiosis, sister chromatids are also the sites of genetic recombination.

Somatic cells: Diploid cells that comprise body tissues and undergo mitosis for maintenance and repair of tissues.

Splicing: The process by which mature mRNAs are produced. Introns are removed (spliced) and exons are joined together.

Sugar phosphate backbone: A biochemical structural component of DNA. The “backbone” consists of deoxyribose sugars and phosphate molecules.

Telomere: A compound structure located at the ends of chromosomes to help protect the chromosomes from degradation after every round of cell division.

Termination: The halt of DNA replication activity that occurs when a DNA sequence “stop” codon is encountered.

Tissue: A cluster of cells that are morphologically similar and perform the same task.

Transcription: The process by which DNA nucleotides (within a gene) are copied, which results in a messenger RNA molecule.

Transcription factors: Proteins that bind to regulatory regions of genes (e.g., promoter) and increase or decrease the amount of transcriptional activity of a gene, including turning them “on” or “off.”

Transfer RNA (tRNA): RNA molecule involved in translation. Transfer RNA transports amino acids from the cell’s cytoplasm to a ribosome.

Translation: The process by which messenger RNA codons are read and amino acids are “chained together” to form proteins.

X-linked: Refers to a pattern of inheritance where the allele is located on the X or Y chromosome.