exam 1 nuclear and chromosomal structure Flashcards
what defines eukaryotic cells
the presence of the nucleus
what is the nucleus bounded by
a double membrane (two lipid bilayers)
how does the double membrane of the nucleus communicate with the cytoplasm
through large nuclear pores that allow things to go in and out
what does the modification of histones regulate
chromatin structure and gene expression
how are prokaryotes and eukaryotes described with kernels
eukaryote = “true kernel”
prokaryote = “before kernel”
(kernel beng nucleus)
what does the nucleus contain
genetic material of DNA within the double membrane structure, which is continuous with the ER
what is the nuclear lamina
supports the nuclear membrane - it’s a fibrous network made of proteins, which provides structural support and allows the nucleus to retain its shape
how is the nucleus compartmentalized
into dynamic subdomains - aren’t separated by membranes and can be assembled/disassembled as needed
what is the best understood subdomain of the nucleus
the nucleolus - site of ribosome assembly
how is the double membrane actually a single membrane?
it’s folded back upon itself to create a double membrane - nuclear pores are where it’s folded over
what occurs if the nuclear lamina lacks lamin A
structural support is reduced and the normal organization of chromatin is prevented - affects the ability of cells to divide
what is the nuclear lamina important for
organizing chromatin and gene expression
what does the double bilayer of the nuclear membrane present
a major barrier to the movement of material between the cytoplasm and nucleus
how is transport between the nucleus and cytoplasm regulated
large regulated nuclear pores
what are nuclear pores made up of
30 different proteins called nuclearporins
how can large macromolecules and protein complexes travel through nuclear pores
active transport
what is the DNA in the nucleus of eukaryotic cells divided into
23 pairs of chromosomes
what does chromatin do
condenses linear DNA molecules to fit within the nucleus - changes to regulate gene expression, DNA replication, and cell division
what is the basic unit of chromatin
the nucleosome
what is a histone core composed of
two copies of each of the four different histones
what do nucleosomes in chromatin look like
beads on a string
what is between the “beads” of nucleosomes
linker DNA
what is chromatin condensed into during interphase (when cells aren’t dividing)
the 30 nm fiber (formed through interactions between the N-terminal tails of histones in neighboring nucleosomes)
what does the linker histone H1 do
binds to the outside of each nucleosome and helps condense chromatin
what are the two types of interphase chromatin
heterochromatin (different chromatin) and euchromatin (true chromatin)
what is heterochromatin
DNA that is resistant to gene expression (“silences”)
includes centromeres and telomeres
what is euchromatin
less condensed that heterochromatin and remains accessible to the RNA transcript machinery
how can chromatin structure be regulated
by covalent modifications to the histone tails
what happens when histone tails get modifications
can change charge-charge interactions and lead to condensation or de-condensation
what is the most highly condensed form of chromatin
mitotic chromosomes
what is the replication origin
the site where DNA duplication is initiated (multiple in eukaryotes)
what is the centromere
the site of attachment to the mitotic spindle, which allows one copy of each duplicated chromosome to be pulled into each daughter cell during mitosis
what is a telomere
prevents the ends of chromosomes from being mistaken for broken DNA, and allows for proper duplication of the chromosomes ends
out of replication origin, centromere, and telomere, which can be found in prokaryotic cells
replication origin
what is linker DNA
DNA that is NOT wound around histones
what does linker histone do
binds the the nucleosome on the outside of histone core to help it flex the DNA to help with packing
