Kapitel 4 Flashcards
Describes the relative orientation of the two strands in a DNA double helix or two paired regions of a polypeptide chain; the polarity of one strand is opposite to that of the other.
antiparallel
Two nucleotides in an RNA or DNA molecule that are held together by hydrogen bonds—for example - G paired with C - and A paired with T or U.
base pair
Constricted region of a mitotic chromosome that holds sister chromatids together. This is also the site on the DNA where the kinetochore forms so as to capture microtubules from the mitotic spindle. (Figure 4–43)
centromere
Complex of DNA - histones - and non-histone proteins found in the nucleus of a eukaryotic cell. The material of which chromosomes are made.
chromatin
Structure composed of a very long DNA molecule and associated proteins that carries part (or all) of the hereditary information of an organism. Especially evident in plant and animal cells undergoing mitosis or meiosis - during which each chromosome becomes condensed into a compact rodlike structure visible in the light microscope.
chromosome
(1) Of nucleic acid sequences: capable of forming a perfect base-paired duplex with each other. (Figure 4–4) (2) Of other interacting molecules - such as an enzyme and its substrate: having biochemical or structural features that marry up - so that noncovalent bonding is facilitated. (Figure 2–3)
complementary
Variation between individuals in a population in the number of copies of large blocks of DNA. The variation arises from duplications and deletions of these sequences.
copy number variations (CNVs)
Polynucleotide formed from covalently linked deoxyribonucleotide units. The store of hereditary information within a cell and the carrier of this information from generation to generation. (Figure 4–3 and Panel 2–6 - pp. 100–101)
deoxyribonucleic acid (DNA)
The three-dimensional structure of DNA - in which two antiparallel DNA chains - held together by hydrogen-bonding between the bases - are wound into a helix. (Figure 4–5)
double helix
Inheritance of phenotypic changes in a cell or organism that do not result from changes in the nucleotide sequence of DNA. Can be due to positive feedback loops of transcription regulators or to heritable modifications in chromatin such as DNA methylation or histone modifications. (Figure 7–53)
epigenetic inheritance
Region of an interphase chromosome that stains diffusely; “normal” chromatin - as opposed to the more condensed heterochromatin.
euchromatin
Segment of a eukaryotic gene that consists of a sequence of nucleotides that will be represented in mRNA or in a mature transfer - ribosomal - or other functional noncoding RNA molecule. In protein-coding genes - exons code for the amino acids in the protein - plus the 3 and 5 untranslated regions of the mRNA. A typical vertebrate gene consists of many exons separated from one another by noncoding DNA segments called introns. (Figure 4–15)
exon
The totality of genetic information belonging to a cell or an organism; in particular - the DNA that carries this information.
genome
Chromatin that is highly condensed even in interphase; generally transcriptionally inactive. (Compare with euchromatin.)
heterochromatin
One of a group of small abundant proteins - rich in arginine and lysine - that combine to form the nucleosome cores around which DNA is wrapped in eukaryotic chromosomes. (Figure 4–24)
histone
“Linker” (as opposed to “core”) histone protein that binds to DNA where it exits from a nucleosome and helps package nucleosomes into the 30-nm chromatin fiber. (Figure 4–30)
histone H1
Genes - proteins - or body structures that are similar as a result of a shared evolutionary origin.
homologous
The maternal and paternal copies of a particular chromosome in a diploid cell.
homologous chromosomes (homologs)
Noncoding region of a eukaryotic gene that is transcribed into an RNA molecule but is then excised by RNA splicing during production of the mRNA or other functional RNA. (Figure 4–15)
intron
Display of the full set of chromosomes of a cell - arranged with respect to size - shape - and number.
karyotype
Huge chromosome paired in preparation for meiosis - found in immature amphibian eggs; consisting of large loops of chromatin extending out from a linear central axis. (Figure 4–47)
lampbrush chromosome
Highly condensed duplicated chromosome as seen at mitosis - consisting of two sister chromatids held together at the centromere.
mitotic chromosome
A prominent structure in the nucleus where rRNA is transcribed and ribosomal subunits are assembled. (Figure 4–9)
nucleolus
Beadlike structure in eukaryotic chromatin - composed of a short length of DNA wrapped around an octameric core of histone proteins. The fundamental structural unit of chromatin. (Figures 4–22 and 4–23)
nucleosome
Giant chromosome in which the DNA has undergone repeated replication and the many copies have stayed together in precise alignment. (Figures 4–50 and 4–51)
polytene chromosome
Alteration in gene expression resulting from change in the position of the gene in relation to other chromosomal domains - especially heterochromatic domains. When an active gene is placed next to heterochromatin - the inactivating influence of the heterochromatin can spread to affect the gene to a variable degree - giving rise to position effect variegation. (Figure 4–31)
position effect variegation
Nucleotide sequence of DNA that has accumulated multiple mutations that have rendered an ancestral gene inactive and nonfunctional.
pseudogene
Natural selection operating in a population to slow genome changes and reduce divergence by eliminating individuals carrying deleterious mutations.
purifying selection
Location on a DNA molecule at which duplication of the DNA begins. (Figures 4–19 and 5–23)
replication origin
A variation between individuals in a population due to a relatively common difference in a specific nucleotide at a defined point in the DNA sequence.
single-nucleotide polymorphism (SNP)
End of a chromosome - associated with a characteristic DNA sequence that is replicated in a special way. Counteracts the tendency of the chromosome otherwise to shorten with each round of replication. From Greek telos - end - and meros - portion.
telomere
Single strand of DNA or RNA whose nucleotide sequence acts as a guide for the synthesis of a complementary strand. (Figure 1–3)
template
