Chp. 24- Genes and Chromosomes

Chromosomes

a single large DNA molecule and its associated proteins and often associated regulatory or structural RNA; containing many genes; stores and transmits genetic information

Phenotype

the observable characteristics of an organism

Regulatory Sequences

a DNA sequence involved in regulating the expression of a gene; for example, a promoter or operator 

Replicative Forms 

any of the full-length structured forms of a viral chromosome that serve as distinct replication intermediates 

Introns

a sequence of nucleotides in a gene that is transcribed but removed from the RNA transcript before translation; also called intervening sequence

Exons

the segment of a eukaryotic gene that encodes a portion of the final product of the gene; a segment of RNA that remains after posttranscriptional processing and is transcribed into a protein incorporated into the structure of RNA

Simple Sequence DNA (SSR)

highly repeated, non-translated segments of DNA in eukaryotic chromosomes; most often associated with the centromeric region. It’s function is unknown. Also called satellite DNA.

Centromere

a specialized site in a chromosome serving as the attachment point for the mitotic or meiotic spindle

Telomeres 

a specialized nucleic acid structure at the ends of linear eukaryotic chromosomes 

Supercoiling

the twisting of a helical (coiled) molecule on itself; a coiled coil

DNA Relaxed State

any DNA that exists in its most stable, untrained structure; typically the B form under most cellular conditions

Topology

the study of properties of an object that do not change under continuous deformations such as twisting or bending 

Linking Number

the number of times one closed circular DNA strand is wound about another; the number of topological links holding the circles together

Super helical Density

in a helical model such as DNA, the number of supercoils (super helical turns) relative to the number of coils (turns) in the relaxed molecule

Topoisomers

different forms of a covalently closed, circular DNA molecule that differ only in linking number

Topoisomerases

enzymes that introduce positive or negative supercoils in closed circular duplex DNA

Catenanes 

two or more polymeric molecules interlinked by one or more noncovalent topological links, resembling the links of a chain 

Platonemic

describes a structure in a molecular polymer that has a net twisting of strands about each other in a simple regular way

Chromatin

a filamentous complex of DNA, histones, and other proteins, constituting the eukaryotic chromosome

Histones 

the family of basic proteins that associate tightly with DNA in the chromosome of all eukaryotic cells 

Nucleosomes

in eukaryotes, a structural unit for packaging chromatin; consists of a DNA strand wound around a histone core

Heterochromatin

the regions of chromosomes that are condensed in which gene expression is generally suppressed

Topologically Associating Domains (TADs)

large DNA loops within chromosomes constrained at the base and encompassing 800,000 or more base pairs of DNA; found in both transcriptionally active and inactive chromosomal regions

Long Noncoding RNAs (lncRNAs)

a functional class of RNA, more than 200 nucleotides long, that does not encode protein, but can have roles in chromosome structure and function

Chromosome Territory

a region of the nucleus preferentially occupied by a particular chromosome

Nucleoid

in bacteria, the nuclear zone that contains the chromosome but has no surrounding membrane