ch 10 chromosomes genetics

chromosomes

structures that contain genetic material; complexes of DNA & proteins

genome

all of the genetic material that an organism possesses

mitrochondria

additional genome in eukaryotes (13 genes)

chloroplast

additional genome in plants

2

what percentage of all RNA is mRNA?

ORI (origin of replication)

where DNA replication is initiated

intergenic regions

short regions between adjacent genes

ORI, genes, intergenic regions, repetitive sequences

the four key functional sites along a bacterial chromosome

nucleoid

the region of a bacterial cell where the chromosome is found; not membrane-bound

microdomains (loop domains)

small loops to help the DNA fold roughly 1000-fold

macrodomains

further compaction of microdomains into

NAPs (nucleoid-associated proteins)

proteins that bend DNA or act as DNA bridges to form micro- and macrodomains

nucleoid-associated proteins

NAPs

DNA supercoiling

the formation of additional coils in DNA due to twisting forces

negative supercoiling

DNA turns that unwind the helix (fewer turns); stable & present in natural bacterial DNA

positive supercoiling

DNA turns that overwind the helix (more turns); unstable

Twisted tighter forming right handed loops or crossovers(more helical twists)

topoisomers

DNA conformations that differ in supercoiling

DNA topoisomerase I

enzyme that relaxes negative supercoils

DNA gyrase (DNA topoisomerase II)

enzyme that relaxes positive supercoils while introducing two negative supercoils (requires ATP)

negative

type of supercoiling that is necessary for bacterial DNA replication & transcription

quinolones

antibiotic class that acts as a DNA gyrase inhibitor

coumarins

strong inhibitors of DNA gyrase in vitro, but weak in vivo

chromosomal loops, DNA supercoiling

two processes that make the bacterial chromosome more compact

eukaryotic chromosome

-linear

introns

noncoding, unexpressed regions of DNA

exons

coding, expressed regions of DNA

centromeres

area where two chromatids are attached

telomeres

repetitive sequences at both ends of linear chromosomes; molecular clocks

ORI, centromere, telomere

three key sites along the eukaryotic chromosome important for chromosomal replication & segregation

sequence complexity

the number of times a particular base sequence appears in the genome; three main types

unique (non-repetitive)

sequences found just a couple of times in the genome in protein-coding genes & intergenic regions

moderately repetitive

sequences found hundreds to thousands of times in the genome

highly repetitive

sequences found tens of thousands or millions of times

transposition

integration of small segments of DNA into the chromosome

TEs (transposable elements)

small, mobile DNA segments (jumping genes)

TE

critical for the sake of the immune system, because they allow for antibody & vaccine information to be incorporated into the genome

simple transpos, retro transpos

two types of transposition pathways

simple transposition

transposition where a segment of DNA just moves into a new location

Used in bacteria and eukaryotic cells

retro transposition

transposition where a segment of DNA is copied via RNA retrotranscription and then moved to a new location, so the original remains where it was

Used only in eukaryotic cells

transposase

enzyme that catalyzes simple transposition; binds at inverted repeats

retrotranscriptase, integrase

enzymes involved in retro-transposition

retrotranscriptase

enzyme that converts RNA into DNA during retro-transposition

integrase

enzyme that brings the newly retrotranscribed DNA into the genome during retro-transposition

LINEs

long interspersed elements; a kind of TE

SINEs

short interspersed elements; a kind of TE

variability, resistance

Advantages of TE

structures, interrupting

Disadvantages of TE:

breakage, rearrangement

consequences of TEs on chromosome structure

mutation, inactivation, regulation, exon

consequences of TEs on gene expression

chromatin

DNA-protein complex that allows for the compaction of eukaryotic DNA

chromosome compaction

nucleosomes --> 30 nm fibers --> loop domains --> chromosomes --> heterochromatin

nucleosome

repeating structural unit within eukaryotic chromatin

146-147

number of base pairs within a nucleosome

core histones

H2a, H2b, H3, H4

linker histone

H1

30nm fiber

nucleosomes fold on themselves to be 7x more folded

solenoid

zigzag

loop domains

chromosomal segments that are folded into loops

CCCTC-binding factor (CTCF)

CTCF; protein that binds to the CCCTC sequence in DNA to form a loop

structural maintenance of chromosomes (SMC)

SMC proteins; dimerize around 2 DNA sequences to form a loop

heterochromatin

tightly compacted regions of chromosomes

no

is heterochromatin transcriptionally active?

constituitive

type of heterochromatin in which the regions are permanently inactive (in terms of transcription)

facultative heterochromatin

type of chromosome section that can convert between heterochromatin & euchromatin

euchromatin

loosely packed regions of chromosomes that are transcriptionally active

yes

is euchromatin transcriptionally active?

metaphase

during which phase of mitosis are the chromosomes fully condensed?

condensin

proteins that play an important role in chromosome condensation (during metaphase prep)

cohesin

proteins that play an important role in aligning sister chromatids (during metaphase prep)

cytoplasm, nucleus

during interphase, condensin I is in the _ and condensin II is in the _

mitosis

condensin I enters the nucleus and the two molecules bind the chromosomes & pull the chromatin loops closer together during __

cohesin

protein that seals the sister chromatids together until it is degraded during anaphase