Nucleic Acids, Chromosome, and Genome Structure Flashcards
purines
ATP/GTP
pyrimidines
UTP/CTP
Describe the hydrogen bonding between bases.
AT, GC base-pairing
Chargaff’s rule
in any sample of dsDNA, the amount of adenine euqls the amount of thymine, the amount of guanine equals the amount of cytosine, and the total number of purines equals the total number of pyrimidines
What are the three helical forms that DNA can take on?
A-, B-, and Z- forms
B-DNA is the most common
Z-DNA forms a left handed helix
nucleoid (genophore)
the bacterial genome, a single circular DNA molecule
Describe the organization of chromosomes.
DNA double helix -> beads on a string -> 30-nm fiber -> extended scaffold -> condensed scaffold -> chromosome
satellite DNAs
one type of repetitive DNA that are clustered in discrete areas such as centromeres
interspersed repeats
repetitive DNA that is distributed throughout the genome
includes SINEs, LINEs, and transposable elements
often have viral origins, transposons can cup themselves out of the genome and reinser elsewhere
nuleosome
fundamental unit of packaging DNA, contains eight histone proteins (a dimer of H2A, H2B, H3, and H4)
about 146 base pairs of dsDNA is wound around each histone with a short length inbetween histones
linker region bound by histone H1 to create 3D structure
euchromatin
transcriptionally active and contains most of the genes
light staining in an EM
heterochromatin
transcriptionally inactive DNA, stains strongly with DNA-binding dyes
constitutive heterochromatin - always inactive
facultative heterochromatin - sometimes active sometimes inactive
comes out dark in an EM
chromosome territory
the space within the nucleus where a chromosome resides
telomere
specialized DNA sequences at the ends of each chromosome that stabilize the end and help prevent linear recombination with the ends of other chromosomes
stucture contains two loops called the T-loop and the D-loop, the DNA folds back on itself and inserts the tail into the previous strands
shelterin complex
protein complex that associates with the telomere and maintains its structure
centromere
mostly highly repetitive, constitutive heterochromatin, function in chromosome segregation during mitosis
satellite DNA
repeating sequences such as those found near the centromere and the telomere
can be devided into alphoid and beta sites
ribosomal DNA are also frequently flanked by satellite DNA
:LINEs
long interspersed nuclear elements, about 6kb long, transcribed using an internal promoter
encode p40 and reverse transcriptase
SINEs
short interspersed nuclear elements, much shorter than LINEs and are tandemly rpeated within the individual sequence
alu dimers are the major formes
originated from tRNAs that got copied by reverse transcriptases and got inserted back into the DNA
most common sequences in the genome
SKY FISH
fluorescent in situ hybridization, can be used to stain each chromosome a different color
chromosome distribution
chromosome regions with very high gene density tend to be in the middle of the nucleus, regions with low gene density tend to be towards the outside of the nucleus
functional consequences of global chromatin organization
transcribe genes for a particular function at the same time
different parts of the chromosome can move a little bit and localize to form a transcription pocket
spatial regulation of large parts of a chromosome
