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October, 2006
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Genes: A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms.

Organization of Genes

JoVE 10786

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. Genes themselves consist of protein-coding exons and non-coding introns. Introns are excised once the sequence is transcribed to mRNA, leaving only exons to code for proteins.

In eukaryotic genomes, genes are separated by large stretches of DNA that do not code for proteins. However, these intergenic regions carry important elements that regulate gene activity, for instance, the promoter where transcription starts, and enhancers and silencers that fine-tune gene expression. Sometimes these binding sites can be located far away from the associated gene. As researchers investigated the process of gene transcription in eukaryotes, they realized that the final mRNA that codes for a protein is shorter than the DNA it is derived from. This difference in length is due to a process called splicing. Once pre-mRNA has been transcribed from DNA in the nucleus, splicing immediately removes introns and joins exons together. The result is protein-coding mRNA that moves to the cytoplasm and is translated into protein. One of the largest human genes, DMD, is over two million base pairs long. This gene encodes the muscle protein dystrophin. Mutations in DMD cause muscular dystrophy, a disorder characteri

 Core: Biology


JoVE 11094

Plant morphogenesis—the development of a plant’s form and structure—involves several overlapping developmental processes, including growth and cell differentiation. Precursor cells differentiate into specific cell types, which are organized into the tissues and organ systems that make up the functional plant.

Plant growth and cell differentiation are under complex hormonal control. Plant hormones regulate gene expression, often in response to environmental stimuli. For example, many plants form flowers. Unlike stems and roots, flowers do not grow throughout a plant’s life. Flowering involves a change in the identity of meristems—regions of the plant containing actively-dividing cells that form new tissues. In addition to internal signals, environmental cues—such as temperature and day length—trigger the expression of meristem identity genes. Meristem identity genes enable the conversion of the shoot apical meristem into the inflorescence meristem, allowing the meristem to produce floral rather than vegetative structures. The inflorescence meristem produces the floral meristem. Cells in the floral meristem differentiate into one of the flower organs—sepals, petals, stamens, or carpels—according to their radial position, which dictates the expression of organ identity genes. The ABC hypo

 Core: Biology

Evolutionary Relationships- Concept

JoVE 10561

Humans have been attempting to properly classify living things since Aristotle made the first attempt during the 4th century BC. Aristotle’s system was improved upon during the Renaissance and then, subsequently, by Carolus Linnaeus in the mid 1700’s. These more formal classification and organization systems grouped species by their physical similarity to one another. For example,…

 Lab Bio

Antibiotic Selection

JoVE 10807

Researchers use antibiotic resistance genes to identify bacteria that possess a plasmid containing their gene of interest. Antibiotic resistance naturally occurs when a spontaneous DNA mutation creates changes in bacterial genes that eliminate antibiotic activity. Bacteria can share these new resistance genes with their offspring and other bacteria. The overuse and misuse of antibiotics have created a public health crisis, as resistant and multi-resistant bacteria continue to develop. Antibiotics, such as penicillin, are drugs that kill or stop bacterial growth. Bacteria that naturally or artificially acquired antibiotic resistance genes do not respond to antibiotics. Scientists exploit this by designing plasmids—small, self-replicating pieces of DNA—that carry both an antibiotic resistance gene and a gene of interest. Antibiotic resistance is an integral part of DNA cloning that allows a researcher to identify cells that absorbed a DNA of interest. The researcher’s DNA of interest is introduced into bacterial cells using a process called transformation. Bacterial transformation involves temporarily creating small holes in the bacterial cell wall to permit the uptake of external DNA such as a plasmid. Only some bacterial cells absorb new DNA. Since the plasmid includes both the DNA of interest and a gene that confers resistance to a spe

 Core: Biology

Agrobacterium-Mediated Immature Embryo Transformation of Recalcitrant Maize Inbred Lines Using Morphogenic Genes

1Department of Agronomy, Iowa State University, 2Department of Applied Science and Technology, Corteva Agriscience, 3Crop Bioengineering Center, Iowa State University, 4Interdepartmental Plant Biology Major, Iowa State University, 5Interdepartmental Genetics and Genomics Major, Iowa State University

JoVE 60782



JoVE 10984

Prokaryotes can control gene expression through operons—DNA sequences consisting of regulatory elements and clustered, functionally related protein-coding genes. Operons use a single promoter sequence to initiate transcription of a gene cluster (i.e., a group of structural genes) into a single mRNA molecule. The terminator sequence ends transcription. An operator sequence, located between the promoter and structural genes, prohibits the operon’s transcriptional activity if bound by a repressor protein. Altogether, the promoter, operator, structural genes, and terminator form the core of an operon. Operons are usually either inducible or repressible. Inducible operons, such as the bacterial lac operon, are normally “off” but will turn “on” in the presence of a small molecule called an inducer (e.g., allolactose). When glucose is absent, but lactose is present, allolactose binds and inactivates the lac operon repressor—allowing the operon to generate enzymes responsible for lactose metabolism. Repressible operons, such as the bacterial trp operon, are usually “on” but will turn “off” in the presence of a small molecule called a corepressor (e.g., tryptophan). When tryptophan—an essential amino acid—is abundant, tryptophan binds and activates the

 Core: Biology
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