exam 2 info Flashcards
what is a packaging mechanism for chromosomes
chromatin
what are chromosomes
stretches of compressed DNA
whats chromatin
specific proteins interacting with DNA to form nucleoprotein
about how long is human DNA in meters
2 meters (6’6”)
how is the nucleoid formed?
specific proteins interact with DNA
what kind of fold compact is DNA in a nucleus
10,000 fold compaction
what are histones
small basic proteins
how would histones be viewed under microscopy
beads on a string. the beads being nucleosome
what is the nucleosome
basic unit of eukaryotic chromatin, formed from about 8 histones wrapped by DNA
what is chromatin remodeling
enzymes that use ATP to alter chromatin structure
what 3 mechanisms are site exposure models
repositioning
ejection
unwrapping
what 2 mechanisms are altered composition
dimer exchange
dimer ejection
closed chromatin prevents what
prevents proteins to bind to DNA
open chromatin allows what
provides access to specific DNA sequences
what is going on if a a chromatin is depleted of nucleosomes
have active regions of the genome
what goes on during nuclease digestion
digestion removes linker DNA between nucleosomes and destroys it with MNase
what is endonuclease activity
cleavage of DNA
what is exonuclease activity
chewing of DNA
how many bases of DNA typically wrap around nucleosomes
150
what is a centromere
section of chromosomes responsible for cell’s ability to properly segregate sister chromatids during cell division
how are nucleosomes arranged in chromatid
biologists don’t really know
why is chromatin modification important
recruits proteins to chromatin an regulating chromatin-based processes
how are proteins modified
through covalent attachments of various functional groups to specific amino acids
what can be attached to a proteins during modification
small chemical groups
lipids
small polypeptides
what occurs during proteolysis
split of an inactive precursor protein into an active form
what types of protein modifications are there
acetylation
methylation
phosphorylation
what are nucleosomes
8 histones proteins wrapped by about 147 base pairs
how are histones bonded
covalently
nomenclature structure of histones
name of histone +
residue one letter code +
residue number +
modification
histone lysine is acetylated by
acetyltransferases
histone lysine is deacetylated by
deacetylases
what occurs during acetylation of histone lysine
neutralizes the postitive charge of lysine’s side chain
when does lysine acetylation also occur
in citric acid cycle
functions of protein lysine acetylation
regulate interactions of histones with DNA changes interaction partners changes cellular localization controls cytoskeleton dynamics controls cell growth
histone lysine is catalyzed by? and removed by?
catalyzed- methyltransferases
removed- demethylases
lysine can have how many methyl groups
up to 3, and doesn’t ever change the charge
whats the purpose of histone lysine methylation
creates binding sites for many proteins (ex: polycomb)
what are hox genes and their purpose
organized linear structures that specify the body plan in multicellular organisms. They must be expressed in the correct environments and silenced everywhere else for proper development
mutations in the polycomb gene result in
ectopic (abnormal location) sex combs
what are ectopic sex combs
a gene is not correctly placed, causing sex spots (on legs) in places they shouldn’t be
what is a homeotic phenotype
mutational phenomenon of homeostasis, where an organ turns into another
mutations in the trihorax gene results in
sex combs are significantly reduced
whats the function of the polycomb-group protein
repress gene expression (transcription) through chromatin based mechanism
what is Zeste (E(z))?
its a polycomb-group protein enhancer, that catalyzes H3K27me3, through methylation
function of Trithorax-group proteins
activate gene expression
what does Trithorax do and catalyze?
its a histone methyltransferase, that catalyzes H3K4me3 and H3K27
