Unit 6 Flashcards
AIDS (acquired immunodeficiency syndrome)
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
Anticodon
A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA
Bacteriophage
A virus that infects bacteria; also called a phage
Base-pair substitution
The replacement of one nucleotide and its partner in the complementary DNA strand with another pair of nucleotides
Codon
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code
Capsid
The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape
Conjugation
In prokaryotes, the direct transfer of DNA between two cells that are temporarily joined. In ciliates, a sexual process in which two cells exchange haploid micronuclei.
Corepressor
A small molecule that cooperates with a repressor protein to switch an operon off.
Double helix
The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape
DNA polymerases
An enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain
DNA ligase
A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3’ end of a new DNA fragment to the 5’ end of a growing chain
Exons
A coding region of a eukaryotic gene. Exons, which are expressed, are separated from each other by introns
F factor
A fertility factor in bacteria; a DNA segment that confers the ability to form pili for conjugation and associated functions required for the transfer of DNA from donor to recipient. It may exist as a plasmid or be integrated into the bacterial chromosome
F plasmid
The plasmid form of the F factor
Frameshift mutation
A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the following nucleotides into codons
Helicase
An enzyme that untwists the double helix of DNA at the replication forks
HIV (human immunodeficiency virus)
The infectious agent that causes AIDS. HIV is a retrovirus
Introns
A non-coding, intervening sequence within a eukaryotic gene
Inducer
A specific small molecule that inactivates the repressor in an operon
Leading strand
The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5’ -> 3’ direction
Lagging strand
A discontinuously synthesized DNA strand that elongates in a direction away from the replication fork
Lytic cycle
A type of viral (phage) replication cycle resulting in the release of new phages by lysis (and death) of the host cell
Lysogenic cycle
A phage replication cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage and does not kill the host
Mismatch repair
The cellular process that uses special enzymes to fix incorrectly paired nucleotides
Messenger RNA
A type of RNA, synthesized from DNA, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein
Mutations
A change in the DNA of a gene, ultimately creating genetic diversity
Mutagens
A chemical or physical agent that interacts with DNA and causes a mutation
Missense mutation
The most common type of mutation, a base pair substitution in which the new codon makes sense in that it still codes for an amino acid
Nuclease
An enzyme that hydrolyzes DNA and RNA into their component nucleotides
Nucleotide excision repair
The process of removing and then correctly replacing a damaged segment of DNA using the undamaged strand as a guide
Nonsense mutation
A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein
Nucleoid
A dense region of DNA in a prokaryotic cell
Origins of replication
Site where the replication of a DNA molecule begins
Operator
In prokaryotic DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon
Operon
A unit of genetic function common bacteria and phages, consisting of coordinately regulated clusters of genes with related functions
Primer
A polynucleotide with a free 3’ end, bound by complementary base pairing to the template strand, that is elongated during DNA replication
Primase
An enzyme that joins RNA nucleotides to make the primer
Promoter
A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA
Point mutations
A change in a gene at a single nucleotide pair
Prions
And infectious form of protein that may increase in number by converting related proteins to more prions
Plasmid
A small ring of DNA that carries accessory genes separate from those of a bacterial chromosome; also found in some eukaryotes, such as yeast
Replication fork
A Y-shaped region on a replicating DNA molecule where new strands are growing
RNA processing
Modification of RNA before it leaves the nucleus, a process unique to eukaryotes
Reading frame
The way a cell’s mRNA translating machinery groups the mRNA nucleotides into codons
RNA polymerase
An enzyme that links together the growing chain of ribonucleotides during transcription
Okazaki fragments
A short segment of DNA synthesized on a template strand during DNA replication. Many Okazaki fragments make up the lagging strand of a newly synthesized DNA
R plasmids
A bacterial plasmid carrying genes that confer resistance to certain antibiotics
Repressor
A protein that suppresses the transcription of a gene
Regulatory gene
A gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes
Semiconservative model
type of DNA replication in which the replicated double helix consists of one old strand, derived from the old molecule, and one newly made strand
Reverse transcriptase
An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis
Poly-A-Tail
The modified end of the 3’ end of an mRNA molecule consisting of the addition of some 50 to 250 adenine molecules
Restriction enzymes
A degradative enzyme that recognizes and cuts up DNA (including that of certain phages) that is foreign to a bacterium
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
Topoisomerase
A protein that functions of DNA replication, helping to relieve strain in the double helix ahead of the replication fork
Telomeres
The protective structure at each end of a eukaryotic chromosome. Specifically, the tandemly repetitive DNA at the end of the chromosome’s DNA molecule
Telomerase
An enzyme that catalyzes the lengthening of telomeres. The enzyme includes a molecule of RNA that serves as a template for new telomere segments
Transcription
The synthesis of RNA on a DNA template
Translation
The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of “language” from nucleotides to amino acids
Template strand
The DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript
Terminator
In prokaryotes, a special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene
Transcription unit
A region of a DNA molecule that is transcribed into an RNA molecule
Transcription factors
A regulatory protein that binds to DNA and stimulates transcription of specific genes
Transcription initiation complex
The completed assembly of transcription factors in RNA polymerase bound to the promoter
TATA box
A promoter DNA sequence crucial in forming the transcription initiation complex
Transfer RNA
An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA
Transduction
1) A DNA transfer process in which phages carry bacterial genes from one host cell to another. 2) In cellular communication, the conversion of a signal from outside the cell to a form that can bring about a specific cellular response
Viral envelopes
A membrane that cloaks the capsid that in turn encloses a viral genome
Virulent phages
A phage that reproduces only by a lytic cycle
Temperate phages
A phage that is capable of reproducing by either the lytic or lysogenic cycle
Vaccines
A harmless variant or derivative of a pathogen that stimulates a host’s immune system to mount defenses against the pathogen
Viroids
A plant pathogen composed of molecules of naked circular RNA only several hundred nucleotides long
RNA splicing
The removal of non-coding portions (introns) of the RNA molecule after initial synthesis
