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