Ch 3: DNA & Chromosomes
Euchromatin
- less condensed - gene rich regions
heterochromatin
- most condensed - methylation of lysine 9 - genes not expressed
nuclear envelope: nuclear pores: nuclear lamina:
- two co centric lipid bilayers - allow exchange btwen the cytoplasm and nucleus - mesh of intermediate filaments that support the nucleus
each chromosome is a single molecule of ____ whose extrordinarily long length can be compacted by as much as ____-fold during _____ and tenfold more during _____ this is accomplished by binding to ____ that help package the DNA so that it can fit in the small space delimited by _____. the structure of the DNA- protein complex called ____ is highly _____ over time.
1 DNA molecule 1000 mitosis proteins nuclear envelople chromatin dynamic
gene expression code (2)
1. Lysine 4 methylation & Lysine 9 acetylation 2. Serine 10 phosphorylation & Lysine 14 acetylation
nucleosomes are further packed into 30nm fibers via what 2 things?
1. interactions btwn histone tails 2. binding of histone H1
what are the 4 main families of small organic molecules in cells
1. sugars 2. fatty acids 3. amino acids 4. nucleotides
____ % of the genome encodes codons
1.5%
double helix contains ___ bp per turn
10
each cell contains about ___ of DNA, yet the cell nucleus is only ____
2m 5-8 micrometers
how many centromeres? function? how many telomeres? function? how many origins of replication? function?
- 46; distribution of chromosomes to daughter cells - 92 protect ends of chrom and to enable complete replication of the DNA of each chromosomes all the way to its tip - >200 directs the initiation of DNA synthesis needed to replicate chromosomes
karyotype
display of the mitotic chromosomes
some forms of chromatin have a pattern of histone tail modification that causes the DNA to become so highly condensed that genes cannot be expressed to produce RNA; such condesnation occurs on all chromosomes during _________ & in the _________ of interphase chromosomes
embryonic development synthesis
T/F a DNA strand has a polarity because its two ends contain different bases
false
a ____ is often defined as a segment of DNA that contains the instructions for making a particular protein or RNA molecule
gene
the loosening of chromatin to a more decondensed state allows proteins involved in ____,____, & ____ to gain access to the necessary DNA sequences
gene expression, DNA replication & DNA repair
one of the 2 X chrom is inactivated in the cells of mammalian females by _______
heterochromatin
interphase chromosomes contain both darkly staining _________ & more lightly staining _______. genes that are being transcribed are thought to be packaged in a _____ condensed type of euchromatin.
heterochromatin euchromatin less
chromatin structure is _____ (epigenetic inheritance)
inherited
gene expression and chromosome duplication occurs during
interphase
chromosomes extended as long, thin, tangled, that cannot be easily distinguished..
interphase chromosomal DNA
nucleosome core particles coils up with the help of ______ to form the more compact structure of the ______. A ________ model described the structure of the 30nm fiber. The 30 nm chromatin fiber is further compacted by the formation of _____ that emanate from a central _____
linker histone H1 .30 nm fiber beads on string loops axis
heterochromatin formation; gene silencing code
lysine 9 methylation
chromosomes from nearly all cells are visible during mitosis, where they coil up to form much more condensed structures is called
mitotic chromosomal DNA
the 5 types of histones fall into two main groups; the ____ histones and the ____ histones
nucleosome H1
two copies of each H2A, H2B, H3, and H4 form a _______ around which the double stranded DNA helix is twice
octomer
describe the mechanism by which heterochromatin can spread, once it has been established in one region of the chromsome
once the initial H3 lysine 9 methylation is established on core histone octamers in one region the modification attracts a specific set of proteins and other histone- methylating enzymes. these snzymes create the same modification on adhacent histone octamers which continue to recruit more heterochromatin-specific proteins and enzymes, creating a wave of heterochromatin spreading along the chromosome.
homologous chromosomes (homologs)
one pair of chromosomes; one maternal & one paternal
nucleotides are linked via
phosphodiester bonds
nucleotides are comprised of
sugar (deoxyribose or ribose) nucleotide base phosphate group
nucleosomes are
the basic unit of chromatin packing consisting of 4 pairs of histones ( 8 total)
T/F G-C base pairs are more stable than A-T pairs
true
T/F Histones are relatively small proteins with a very high proportion of positively charged amino acids: negative charge helps the histones bind tightly to DNA.
true
T/F in living cells nucleosomes are packed upon one another to generate regular arrays in which the DNA is more highly condensed usually in the form of a 30 nm fiber
true
chromatin
DNA & its associated proteins
which of the following histone does not form part of the octameric core?
H1
Purines vs. Pyrimidines
Purines: A, G (2 rings) Pyrimidines: T, C (1 ring) G-C bond has 3 H bonds (higher melting temperature) A-T bond has 2 H bonds
heterchromatin example
X inactivation
a cell can regulate its chromatin structure temporarily decondensing or condensing particular regions of its chromosomes - using ___________ & enzymes that _________ histone tails in various ways
chromatin remodeling covalently modifies (methylation, acetylation, phosphorylation)
The process of sorting human chromosomes pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes "painted"?
chromosome painting relies on the specificity of DNA complimentary. Bc unique sequences for each chromosome are known, short DNA molecules matching a set of these sites can be designed for each chromosome. each set is labeled with a specific combo of fluorescent dyes and then allowed to hybridize (form base pairs) w the two homologous chrom that contain the unique sequences being tageted.
genes undergoing transcription are found in areas of chromatin with the least amount of...
condensation
nucleolus
contains genes that encode ribosomal RNA's