DNA composition

nucleotide

deoxyribose sugar, nitrogenous base, phosphate group

nucleoside

deoxyribose sugar and nitrogenous base only

pentose sugar

5-carbon sugar that has either an -H (DNA) or an -OH group (RNA) at the 2’ carbon

purines

nitrogenous bases composed of two ring structures (adenine and guanine)

pyrimidines

nitrogenous bases composed of one ring structure (cytosine and thymine)

phosphodiester bonds

linkage between the 3’ OH of one pentose sugar with the 5’ phosphate group of another; connection between nucleotides, forms backbone of DNA molecule

hydrogen bonds

link complementary bases together; A/T double bond, C/G triple bond

plasmids

dispensable chromosomes in prokaryotic genome; not compulsory for life, usually contain antibiotic-resistance genesC-

C-value

total amount of DNA in the haploid genome, measures number of nucleotides; generally correlates to species complexity

chromatin

complex of DNA and protein

purpose of chromosome structure

reduce volume of genetic material, prevent breakage/damage, manage gene expression

histones

most abundant protein type in histones; positively charged to bind to negatively charged DNAn

nucleosome

DNA looped around a histone

euchromatin

chromatin whose degree of packing varies throughout the cell cycle; actively transcribed, few repeat sequences; most condensed during metaphase, least condensed during synthesis phase

heterochromatin

usually remains packed, high in repetitive sequences, transcriptionally inactive

constitutive heterochromatin

always condensed, found at telomeres and centromeres

facultative heterochromatin

can be inactive (heterochromatin) in some cells and active (euchromatin) in others; Barr bodies

centromeres

where spindle fibers attach, high in heterochromatin, unique DNA structure

telomeres

repeated non-functional sequences to protect the ends of chromosomes; ends restored by telomerase in embryos and cancer cells only, age-dependent shortening