Chapters 16-20 Biology Vocabulary Review

Comprehensive vocabulary flashcards covering molecular genetics, gene expression, regulation, viruses, and biotechnology from Chapters 16 through 20.

DNA replication

The process by which a DNA molecule is copied; also called DNA synthesis.

Transformation

(1) The conversion of a normal animal cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.

Bacteriophage

A virus that infects bacteria.

Virus

An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope.

Double helix

The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.

Antiparallel

Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite $5' \rightarrow 3'$ directions).

Semiconservative model

Type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand.

Origin of replication

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.

Replication fork

A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized.

Primer

A short stretch of RNA with a free $3'$ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication.

DNA polymerase

An enzyme that catalyzes the elongation of new DNA (for example, at a replication fork) by the addition of nucleotides to the $3'$ end of an existing chain.

Okazaki fragments

A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together to make up the lagging strand of newly synthesized DNA.

DNA ligase

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the $3'$ end of one DNA fragment (such as an Okazaki fragment) to the $5'$ end of another DNA fragment (such as a growing DNA chain).

Mismatch repair

The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

Nuclease

An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.

Telomere

The tandemly repetitive DNA at the end of a eukaryotic chromosome's DNA molecule.

Nucleoid

A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated.

Chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

Heterochromatin

Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.

Euchromatin

The less condensed form of eukaryotic chromatin that is available for transcription.

Gene expression

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

Transcription

The synthesis of RNA using a DNA template.

Messenger RNA

A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.

Translation

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule.

Ribosomes

A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit.

Primary transcript

An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.

Codons

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

RNA Polymerase

An enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand.

Promoter

A specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

Terminator

In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.

Transcription unit

A region of DNA that is transcribed into an RNA molecule.

Transcription factors

A regulatory protein that binds to DNA and affects transcription of specific genes.

Transcription initiation complex

The completed assembly of transcription factors and RNA polymerase bound to a promoter.

RNA processing

Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the $5'$ and $3'$ ends.

RNA splicing

After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons).

Introns

A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed.

Exons

A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed.

Transfer RNA

An RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA.

Ribosomal RNAs

RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.

Polyribosomes

A group of several ribosomes attached to, and translating, the same messenger RNA molecule.

Signal recognition particle (SRP)

A protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER.

Mutation

A change in the nucleotide sequence of an organism's DNA or in the DNA or RNA of a virus.

Point mutation

A change in a single nucleotide pair of a gene.

Nonsense mutations

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

Insertion

A mutation involving the addition of one or more nucleotide pairs to a gene.

Frameshift mutation

A mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.

Mutagen

A chemical or physical agent that interacts with DNA and can cause a mutation.

Operon

A unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a coordinately regulated cluster of genes whose products function in a common pathway.

Repressor

A protein that inhibits gene transcription. In prokaryotes, repressors bind to the DNA in or near the promoter. In eukaryotes, repressors may bind to control elements within enhancers, to activators, or to other proteins in a way that blocks activators from binding to DNA.

Regulatory gene

A gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

Inducer

A specific small molecule that binds to a bacterial repressor protein and changes the repressor's shape so that it cannot bind to an operator, thus switching an operon on.

Activator

A protein that binds to DNA and stimulates gene transcription. In prokaryotes, activators bind in or near the promoter; in eukaryotes, activators generally bind to control elements in enhancers.

Differential gene expression

The expression of different sets of genes by cells with the same genome.

Histone acetylation

The attachment of acetyl groups to certain amino acids of histone proteins.

DNA methylation

The presence of methyl groups on the DNA bases (usually cytosine) of plants, animals, and fungi. (The term also refers to the process of adding methyl groups to DNA bases.)

Epigenetic inheritance

Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence of a genome.

Control elements

A segment of noncoding DNA that helps regulate transcription of a gene by serving as a binding site for a transcription factor.

Enhancers

A segment of eukaryotic DNA containing multiple control elements, usually located far from the gene whose transcription it regulates.

Alternative RNA splicing

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

Proteasomes

A giant protein complex that recognizes and destroys proteins tagged for elimination by the small protein ubiquitin.

MicroRNAs (miRNAs)

A small, single-stranded RNA molecule, generated from a hairpin structure on a precursor RNA transcribed from a particular gene.

Small interfereing RNAs (siRNAs)

One of multiple small, single-stranded RNA molecules generated by cellular machinery from a long, linear, double-stranded RNA molecule.

Differentiation

The process by which a cell or group of cells become specialized in structure and function.

Morphogenesis

The cellular and tissue-based processes by which an animal body takes shape.

Induction

The process in which one group of embryonic cells influences the development of another, usually by causing changes in gene expression.

Pattern formation

The development of a multicellular organism's spatial organization, the arrangement of organs and tissues in their characteristic places in three-dimensional space.

Positional information

Molecular cues that control pattern formation in an animal or plant embryonic structure by indicating a cell's location relative to the organism's body axes. These cues elicit a response by genes that regulate development.

Morphogen

A substance, such as Bicoid protein in Drosophila, that provides positional information in the form of a concentration gradient along an embryonic axis.

Oncogene

A gene found in viral or cellular genomes that is involved in triggering molecular events that can lead to cancer.

p53 gene

A tumor-suppressor gene that codes for a specific transcription factor that promotes the synthesis of proteins that inhibit the cell cycle.

Capsid

The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape.

Viral envelope

A membrane, derived from membranes of the host cell, that cloaks the capsid, which in turn encloses a viral genome.

Host range

The limited number of species whose cells can be infected by a particular virus.

Lytic cycle

A type of phage replicative cycle resulting in the release of new phages by lysis (and death) of the host cell.

Restriction enzyme

An endonuclease (type of enzyme) that recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes). The enzyme cuts at specific nucleotide sequences (restriction sites).

Retrovirus

An RNA virus that replicates by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome; an important class of cancer-causing viruses.

Reverse transcriptase

An enzyme encoded by certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.

HIV

The infectious agent that causes AIDS. HIV is a retrovirus.

AIDS

The symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections.

Vaccine

A harmless variant or derivative of a pathogen that stimulates a host's immune system to mount defenses against the pathogen.

Epidemic

A general outbreak of a disease.

Pandemic

A global epidemic.

Viroid

A plant pathogen consisting of a molecule of naked, circular RNA a few hundred nucleotides long.

Prion

An infectious agent that is a misfolded version of a normal cellular protein. Prions appear to increase in number by converting correctly folded versions of the protein to more prions.

Recombinant DNA

A DNA molecule made in vitro with segments from different sources.

Biotechnology

The manipulation of organisms or their components to produce useful products.

Genetic engineering

The direct manipulation of genes for practical purposes.

Plasmid

A small, circular, double-stranded DNA molecule that carries accessory genes separate from those of a bacterial chromosome; in DNA cloning, used as vectors carrying up to about $10{,}000\text{ base pairs}$ ($10\text{ kb}$) of DNA.

Restriction site

A specific sequence on a DNA strand that is recognized and cut by a restriction enzyme.

Restriction fragments

A DNA segment that results from the cutting of DNA by a restriction enzyme.

Sticky end

A single-stranded end of a double-stranded restriction fragment.

Complementary DNA (cDNA)

A double-stranded DNA molecule made in vitro using mRNA as a template and the enzymes reverse transcriptase and DNA polymerase.

Nucleic acid hybridization

The process of base pairing between a gene and a complementary sequence on another nucleic acid molecule.

Nucleic acid probe

In DNA technology, a labeled single-stranded nucleic acid molecule used to locate a specific nucleotide sequence in a nucleic acid sample.

Polymerase chain reaction (PCR)

A technique for amplifying DNA in vitro by incubating it with specific primers, a heat-resistant DNA polymerase, and nucleotides.

Gel electrophoresis

A technique for separating nucleic acids or proteins on the basis of their size and electrical charge, both of which affect their rate of movement through an electric field in a gel made of agarose or another polymer.

Restriction fragment length polymorphism

A single nucleotide polymorphism (SNP) that exists in the restriction site for a particular enzyme, thus making the site unrecognizable by that enzyme and changing the lengths of the restriction fragments formed by digestion with that enzyme.

Southern blotting

A technique that enables specific nucleotide sequences to be detected in samples of DNA. It involves gel electrophoresis of DNA molecules and their transfer to a membrane (blotting), followed by nucleic acid hybridization with a labeled probe.

Northern blotting

A technique that enables specific nucleotide sequences to be detected in samples of mRNA. It involves gel electrophoresis of RNA molecules and their transfer to a membrane (blotting), followed by nucleic acid hybridization with a labeled probe.

RNA interference (RNAi)

A technique used to silence the expression of selected genes.