CH 1 book terms Flashcards
alleles
One of several alternative forms of a gene occupying a given
locus on a chromosome.
annealing/hybridization
The renaturation of a duplex structure from single strands that were obtained by denaturing duplex DNA.
antiparallel
two polynucleotide chains running in opposite directions
antisense/template strand
the sequence of mRNA is complementary to the sequence of one strand of DNA
back mutations
A mutation that reverses the effect of a mutation that had inactivated a gene; thus, it restores the original sequence or function of the gene product.
base pairing
hydrogen bonding between bases
bivalent
The structure containing all four chromatids (two representing each homologue) at the start of meiosis.
causes of point mutations
- Chemical modification of DNA directly changes one base into a different base.
- An error during the replication of DNA causes the wrong base to be inserted into a polynucleotide.
central dogma
DNA to RNA to polypeptide
chiasma
The point of synapsis between homologs
chromatid
Either of the two threadlike strands formed when a
chromosome duplicates during the early stages of cell division. The two strands are held together at the centromere and separate into daughter chromosomes during anaphase.
chromosome
A discrete unit of the genome carrying many genes. Each
consists of a very long molecule of duplex DNA and an
approximately equal mass of proteins (in eukaryotes).
cis-acting
A site that affects the activity only of sequences on its own molecule of DNA (or RNA); this property usually implies that the site does not code for protein.
coding/sense strand
the sequence of mRNA is identical (apart from the replacement of T with U) to the other strand of DNA
codon
Each trinucleotide sequence
colinear
The relationship that describes the 1:1 correspondence of a sequence of triplet nucleotides to a sequence of amino acids.
denaturation
A molecule’s conversion from the physiological conformation to some other (inactive) conformation. In DNA, this involves the separation of the two strands due to breaking of hydrogen bonds between bases.
DNA polymerases
An enzyme that synthesizes a daughter strand(s) of DNA (under direction from a DNA template). Any particular enzyme may be involved in repair or replication (or both).
DNases
degrade DNA
endonucleases
break individual phosphodiester linkages within RNA or DNA molecules, generating discrete fragments
exons
The sequences that are transcribed, retained, and joined in the mature mRNA
exonucleases
remove nucleotide residues one at a time from the end of the molecule, generating mononucleotides
forward mutations
A mutation that inactivates a functional gene
frameshift mutation
A genetic mutation formed through the addition or deletion of nucleotide bases such that the reading frame is thrown off. The resulting polypeptide formed is usually abnormally short or abnormally long and most likely nonfunctional.
gain-of-function mutations
A mutation that causes an increase in the normal gene activity. It sometimes represents acquisition of certain abnormal properties. It is often, but not always, dominant.
gene expression
The process by which information from a gene is used to synthesize an RNA or polypeptide product
genetic code
The relationship between a sequence of DNA and the sequence of the corresponding polypeptide
genetic recombination
the generation of new combinations of alleles at each generation in diploid organisms
genome
a long sequence of deoxyribonucleic acid (DNA) that provides the complete set of hereditary information carried by the organism as well as its individual cells
heteroduplex DNA
DNA that is generated by base pairing between complementary single strands derived from the different parental duplex
molecules; it occurs during genetic recombination
heteromultimer
A protein composed of two or more different polypeptide chains.
homomultimer
A molecular complex (such as a protein) in which the subunits are identical.
hotspots
A site in the genome at which the frequency of mutation (or
recombination) is very much increased, usually by at least an order of magnitude relative to neighboring sites.
induced mutations
Mutations that result from the action of a mutagen. The mutagen may act directly on the bases in DNA or it may act indirectly to trigger a pathway that leads to a change in DNA sequence.
introns
these internal DNA sequences are initially transcribed but are excised and are not present in the mature mRNA
leaky mutations
A less severe type of mutation where the amino acid substitution does not completely deactivate a certain function of
the protein, but rather decreases its function or makes it less effective.
linkage
The tendency of genes to be inherited together as a result of their location on the same chromosome; measured by percent recombination between loci.
linking number
In a closed molecule of DNA, the number of times one strand crosses over another in space.
locus
The position on a chromosome at which the gene for a particular trait resides; it may be occupied by any one of the alleles for the gene
loss-of-function mutation
A mutation that eliminates or reduces the activity of a gene. It is often, but not always, recessive.
major groove
A fissure running the length of the DNA double helix that is 22 Å across.
melting temperature
The midpoint of the temperature range over which the strands of DNA separate
messenger RNA
a nucleic acid intermediate actually used to synthesize a polypeptide
minor groove
A fissure running the length of the DNA double helix that is 12 Å across.
multiple alleles
A non-Mendelian pattern of inheritance where more than two alleles code for a trait. In most cases, the result is that more than two phenotypes are possible based on the dominance pattern of the individual alleles.
mutagens
Substances that increase the rate of mutation by inducing changes in DNA sequence, directly or indirectly.
nucleoside
pentose sugar linked to a nitrogenous base
nucleotide
A nucleoside linked to a phosphate at the 5′
carbon
null mutation
A mutation that completely eliminates the function of a gene.
overwound
DNA has more base pairs per turn
point mutation
changes only a single base pair
polymorphism
The simultaneous occurrence in the population of alleles
showing variations at a given position.
polynucleotide
a long chain of nucleotides
positive vs negative supercoiling
Twisting in the same direction produces positive supercoiling, which overwinds the DNA so that there are fewer base pairs per turn.
Twisting in the opposite direction produces negative supercoiling, or underwinding, so there are more base pairs per turn.
prion
proteinaceous infectious agent
purine
A double-ringed nitrogenous base, such as adenine or guanine.
pyrimidine
A single-ringed nitrogenous base, such as cytosine, thymine, or uracil.
renaturation
The reassociation of denatured complementary single strands of a DNA double helix.
replication fork
The point at which strands of parental duplex DNA are separated so that replication can proceed.
reverse transcription
RNA is converted into a single-stranded DNA
revertants
Reversions of a mutant cell or organism to the wild-type phenotype.
ribosome
A large assembly of RNA and proteins that synthesizes proteins under direction from an mRNA template.
RNA polymerase
An enzyme that synthesizes RNA using a DNA template.
RNases
degrade RNA
roles of proteins
they can form part of the structure of the organism; have the capacity to build the structure; perform the metabolic reactions necessary for life; and participate in regulation as transcription factors, receptors, key players in signal transduction pathways, and other molecules
second-site reversion
A second mutation suppressing the effect of a first mutation.
semiconservative replication
DNA replication accomplished by separation of the strands of a parental duplex, each strand then acting as a template for synthesis of a complementary strand.
silent mutations
A mutation that does not change the sequence of a polypeptide because it produces synonymous codons.
splicing
The process of excising introns from RNA and connecting the exons into a continuous mRNA.
spontaneous mutations
Mutations occurring in the absence of any added reagent to increase the mutation rate, as the result of errors in replication (or other events involved in the reproduction of DNA) or by random changes to the chemical structure of bases.
structural genes
A gene that codes for any RNA or polypeptide product other than a regulator.
supercoiling
the double helix can also wind around itself to change the overall conformation, or topology, of the DNA molecule in space
suppression mutation
A second event eliminates the effects of a mutation without reversing the original change in DNA.
tetrad
A four-part structure that forms during the prophase of meiosis. Consists of two homologous chromosomes, each composed of two sister chromatids.
topological isomers
Molecules with the same chemical formula but different bond connectivities, thus resulting in different topologic structures.
trans-acting
A product that can function on any copy of its target DNA. This implies that it is a diffusible protein or RNA.
transcription
when a RNA copy of the coding strand of the DNA is produced
transition
the substitution of one pyrimidine by the other, or of one purine by the other
translation
Synthesis of Protein on an mRNA template
mRNA to protein
transversion
a purine is replaced by a pyrimidine, or vice versa
true reversion
A mutation that restores the original sequence of the DNA.
twisting number
In the DNA double helix, the rotation of one strand about the other.
types of point mutations
transition and transversion
underwound
fewer base pairs per turn
