Cell Bio Test 3 key terms

alternative splicing

the production of different mRNAs and proteins from the same gene by splicing its RNA transcripts in different ways

aminoacyl-tRNA synthetase

during protein synthesis, an enzyme that attaches the correct amino acid to a tRNA molecule to form a “charged” aminoacyl-tRNA

anticodon

set of three consecutive nucleotides in a transfer RNA molecule that recognizes, through base-pairing, the three nucleotide codon on a messenger RNA molecule; this interaction helps to deliver the correct amino acid to a growing polypeptide chain

codon

group of three consecutive nucleotides that specifies a particular amino acid or that starts or stops protein synthesis; applies to the nucleotides in an mRNA or in a coding sequence of DNA

exon

segment of a eukaryotic gene that is transcribed into RNA and dictates that amino acid sequence of part of a protein

gene

unit of heredity containing the instructions that dictate the characteristics or phenotype of an organism; in molecular terms, a segment of DNA that directs the production of a particular protein or functional RNA molecule

gene expression

the process by which a gene makes a product that is useful to the cell or organism by directing the synthesis of a protein or an RNA molecule with characteristic activity

general transcription factor

proteins that assemble on the promoters of eukaryotic genes near the start site of transcription and load the RNA polymerase in the correct position

genetic code

set of rules by which the information contained in the nucleotide sequence of a gene and its corresponding RNA molecule is translated into the amino acid sequence of a protein

initiator tRNA

special tRNA that initiates the translation of an mRNA on a ribosome. it always carries the amino acid methionine

intron

noncoding sequences within a eukaryotic gene that is transcribed into an RNA molecule but is then excised by RNA splicing to produce an mRNA

messenger RNA

RNA molecule that specifies the amino acid sequence of a protein

noncoding RNA

an RNA molecule that is the final product of a gene and does not code for protein. these RNAs serve as enzymatic, structural, and regulatory components for a wide variety of processes in the cell

polyadenylation

the addition of multiple adenine nucleotides to the 3’ end of a newly synthesized mRNA molecule

promoter

DNA sequence that initiates gene transcription; includes sequences recognized by RNA polymerase and its accessory proteins

protease

enzyme that degrades proteins by hydrolyzing their peptide bonds

proteasome

large protein machine that degrades proteins that are damaged, misfolded, or no longer needed by the cell; its target proteins are marked for destruction primarily by the attachment of a short chain of ubiquitin

reading frame

one of the three possible ways in which a set of successive nucleotide triplets can be translated into protein, depending on which nucleotide serves as the starting point

ribonucleic acid

molecule produced by the transcription of DNA; usually single-stranded, it is a polynucleotide composed of covalently linked ribonucleotide subunits. serves a variety of informational, structural, catalytic, and regulatory functions in cells

ribosomal RNA

RNA molecule that forms the structural and catalytic core of the ribosome

ribosome

large macromolecular complex, composed of RNAs and proteins, that translates a messenger RNA into a polypeptide chain

ribozyme

an RNA molecule with catalytic activity

RNA capping

the modification of the 5’ end of a maturing RNA transcript by the addition of an atypical nucleotide

RNA polymerase

enzyme that catalyzes the synthesis of an RNA molecule from a DNA template using ribonucleoside triphosphate precursors

RNA splicing

process in which intron sequences are excised from RNA molecules in the nucleus during the formation of a mature messenger RNA

RNA transcript

RNA molecule produced by transcription that is complementary to one strand of DNA

small nuclear RNA

RNA molecules containing on the order of 200 nucleotides that participate in RNA splicing

spliceosome

large assembly of RNA and protein molecules that splices introns out of pre-mRNA in the nucleus of eukaryotic cells

transcription

process in which RNA polymerase uses one strand of DNA as a template to synthesize a complementary RNA sequence

transfer RNA

small RNA molecules that serve as an adaptor that “reads” a codon in mRNA and serves as the source of the amino acid added to the growing polypeptide chain

translation

process by which the sequence of nucleotides in a messenger RNA molecule directs the incorporation of amino acids into protein

translation initiation factor

protein that promotes the proper association of ribosomes with mRNA and is required for the initiation of protein synthesis

ubiquitin

small protein that can be covalently attached to other proteins; a major role is to mark target proteins for degradation by the proteasome

RNA processing

broad term for the modifications that a precursor mRNA undergoes as it matures into an mRNA. it typically includes 5’ capping, RNA splicing, and 3’ polyadenylation

cell memory

the ability of differentiated cells and their descendants to maintain their identity

combinatorial control

describes the way in which groups of transcription regulators work together to regulate the expression of a single gene

differentiation

process by which a pluripotent cell undergoes a progressive, coordinated change to a more specialized cell type, brought about by large-scale changes in gene expression

DNA methylation

the enzymatic addition of methyl groups to cytosine bases in DNA; this covalent modification generally turns off genes by attracting proteins that block gene expression

epigenetic inheritance

the transmission of a heritable pattern of gene expression from one cell to its progeny that does not involve altering the nucleotide sequence of the DNA

gene expression

the process by which a gene makes a product that is useful to the cell or organism by directing the synthesis of a protein or an RNA molecule with a characteristic activity

induced pluripotent stem cells

somatic cell that has been reprogrammed to resemble and behave like a pluripotent embryonic stem cell through the artificial introduction of a set of genes encoding particular transcription regulators

long noncoding RNA

class of RNA molecules ore than 200 nucleotides in length that does not encode proteins. often used to regulate gene expression

microRNA

small noncoding RNA that controls gene expression by base pairing with a specific mRNA to regulate its stability and its translation

positive feedback loop

an important form of regulation in which the end product of a reaction or pathway stimulates continued production or activity; can control a variety of biological processes, including enzyme activity, cell signaling, and gene expression

post-transcriptional control

regulation of gene expression that occurs after transcription of the gene has begun; examples include RNA splicing and translational control

promoter

DNA sequence that initiates gene transcription; includes sequences recognized by RNA polymerase and its accessory proteins

regulatory DNA sequence

DNA sequence to which a transcription regulator binds to determine when, where, and in what quantities a gene is to be transcribed into RNA

regulatory RNA

RNA molecule that plays a role in controlling gene expression

reporter gene

gene encoding a protein whose activity is easy to monitor experimentally; used to study the expression pattern of a target gene or the localization of its protein product

RNA interference

cellular mechanism activated by double-stranded RNA molecules that results in the destruction of RNAs containing a similar nucleotide sequence. it is widely exploited as an experimental tool for preventing the expression of selected genes

small interfering RNA

short length of RNA produced from double-stranded RNA during the process of RNA interference. it base-pairs with complementary sequences in other RNAs, leading to the inactivation or destruction of the target RNA

transcriptional activator

a protein that binds to a specific regulatory region of DNA to stimulate transcription of an adjacent gene

transcriptional repressor

a protein that binds to a specific regulatory region of DNA to prevent transcription of an adjacent gene

transcription regulator

protein that binds specifically to a regulatory DNA sequence to switch a gene either on or off

Alu sequence

family of mobile genetic elements that comprises about 10% of the human genome; this short, repetitive sequence is no longer mobile on its own, but requires enzymes encoded by other elements to transpose

conserved synteny

the preservation of gene order in the genomes of different species

exon shuffling

mechanism for the evolution of new genes; in the process, coding sequences from different genes are brought together to generate a protein with a new combination of domains

gamete

cell type in a diploid organism that carries only one set of chromosomes and is specialized for sexual reproduction. a sperm or egg; also called a germ cell

gene duplication and divergence

a process by which new genes can form; involves the accidental generation of an additional copy of a stretch of DNA containing one or more genes, followed by an accumulation of mutations that over time can alter the function or expression of either the original or its copy

gene family

a set of related genes that has arisen through a process of gene duplication and divergence

germ line

the lineage of reproductive cells that contributes to the formation of a new generation of organisms, as distinct from somatic cells, which form the body and leave no descendants in the next generation

homologous gene

describes genes, chromosomes, or any structures that are similar because of their common evolutionary origin; can also refer to similarities between protein sequences or nucleic acid sequences

horizontal gene transfer

process by which DNA is passed from the genome of one organism to that of another, even to an individual from another species; this contrasts with “vertical” gene transfer, which refers to the transfer of genetic information from parent to progeny

L₁ element

type of retrotransposon that contributes 15% of the human genome; also called the LINE-1

mobile genetic element

short segment of DNA that can move from one location in a genome to another; an important source of genetic variation in most genomes; also called a transposon

open reading frame (ORF)

long sequence of nucleotides that contains no stop codon; used to identify potential protein-containing sequences in DNA

phylogenetic tree

diagram showing the evolutionary relationships among groups of organisms/proteins

point mutation

change in a single nucleotide pair in a DNA sequence

purifying selection

preservation of a specific nucleotide sequence in a population of organisms by the elimination of individuals carrying mutations that interfere with biological function

retrotransposon

type of mobile genetic element that moves by being first transcribed into an RNA copy that is reconverted to DNA by reverse transcriptase and inserted elsewhere in the chromosomes

retrovirus

RNA-containing virus that replicates in a cell by first making a double-stranded DNA intermediate that becomes integrated into the cell’s chromosome

reverse transcriptase

enzyme that makes a double-stranded DNA copy from a single-stranded RNA template molecule; present in retroviruses and as part of the transposition machinery of retrotransposons

single-nucleotide polymorphism (SNP)

form of genetic variation in which one portion of the population differs from another in terms of which nucleotide is found at a particular position in the genome

somatic cell

any cell that forms part of the body of a plant or animal that is not a germ cell or germ-line precursor

transposon

general name for short segments of DNA sequence that can move from one location to another in the genome; also known as mobile genetic elements

virus

particle consisting of nucleic acid enclosed in a protein coat and capable of replicating within a host cell and spreading from cell to cell