Chapter 10: Chromosome Organization & Molecular Structure (Exam 3) Flashcards
chromosome
structures that contain genetic material, composed of DNA and proteins
genome
comprises all genetic material an organism possesses
main function of genetic material
store information required to produce an organism:
sythesis of RNA and proteins
replication, segregation, compaction of chromosomes
nucleoid
region of bacterial cell where chromosome is found, not membrane bound
properties of bacterial chromosomes
circular, few million nucleotides in length
majority of gene sequences encode for proteins, do not have introns, nontranscribed regions referred to as intergenic regions
contain one origin of replication
compaction of bacterial chromosomes
compacted 1000-fold
formation of loop domains (microdomains) ~10k bp
nucleoid associated proteins (NAPs)
form micro and macro domains:
facilitate compaction and organization
bend DNA
facilitate segregation
help gene regulation
DNA supercoiling
second layer of DNA compaction, in bacteria negatively supercoiled (less tight than positive, creates tension that may be released by DNA strand separation)
supercoiling enzymes
DNA gyrase: introduces negative supercoils using ATP, can relax positive supercoils, untangle DNA molecules
DNA topoisomerase I: relaxed negative supercoils
eukaryotic chromosomes
contain one or more sets of chromosomes
linear
much more DNA than bacteria
located in nucleus, highly compacted
DNA-protein complex in chromosomes: chromatin
vary in size
contain repetitive DNA sequences that do not encode proteins
noncoding regions called introns
average genome 1 billion bp
types of DNA sequences in eukaryotes used for DNA replication and segregation
origins of replication, centromeres, telomeres
types of eukaryotic genome sequences
unique/ non-repetitive
moderately repetitive
highly repetitive
unique sequences
found once or twice in genome, includes structural genes and intergenic areas
41% of genome
moderately repetitive sequences
found 100s-1000s of times
includes: rRNA and histone genes, origins of replication, sequences for expression and translation, transposable elements
highly repetitive sequences
found 10s of thousands to millions of times
each copy relatively short
can be interspersed throughout genome
examples: Alu family, AATAT in drosophila
found in centromeric and telomeric regions
make up 50% of genome
nucleosome
repeating structural unit of a chromatin
composed of double stranded DNA segment wrapped around an octamer
octamer
composed of two copies each of four histone proteins
histone proteins
made of many positively charges amino acids (lysine and arginine) which bind to DNA backbone
H2A. H2B, H3, H4 make up octamer
H1 linker histone
30 nm fiber
structure of compacted nucleosomes
H1 compacts them
beads on a string morphology
shortens DNA 7 fold
loop domains in chromatin
uses proteins CTCF and SMC
contain genes cell is using, remains accessible
CCCTC binding factor (CTCF)
binds 3 regularly spaced repeats of CCCTC
structural maintenance of chromosome (SMC) proteins
wrap around themselves and 2 DNA segments to form loop
euchromatin
less condensed, transcriptionally active, made of loop domains
heterochromatin
tightly compacted, transcriptionally inactive
types of heterochromatin
constitutive and faculatative
constitutive heterochromatin
always heterochromatic
permanently inactive
highly repetitive sequences
facultative heterochromatin
regions that convert between euchromatin and heterochromatin
compaction of chromatin during cell divison
end of prophase: entirely heterochromatic
interphase: entirely euchromatic
metaphase chromosomes
loop domains highly compacted, anchored to scaffold
uses two proteins: condensin and cohesion (both SMCs)
