Almost all somatic cells contain very similar genetic information. Name three types of normal cells that have quite a different genetic content? How do cells that have very similar genetic information look and act so differently?
blood cells, surface skin cells, bone cells, cardiac muscle cells, skeletal muscle cells, neuron are different cell types
although they have the potential for same info, set of genes that's active/expressed in each are different
this differentiation = how a primoridal cell gets to be a certain kind of cell, by expressing certain genes and not others
long-term regulation of gene expression
Describe four steps in gene expression at which regulation can occur
1) transcription: increase transcription initiation rate, recruitment of RNA Polymerase II
2) mRNA processing: if stabilize or slow down mRNA decay rate, can make more protein, which means more enzyme --> more activity
4) post-translation: increase activity of pre-existing protein
5) protein decay: if slow down an enzyme's decay/turnover rate, have more steady state levels of protein it acts on, get more activity
what is an advantage of regulating an early step in gene expression?
advantage of regulating a late step in gene expression?
if regulate transcription (early step), it's very slow but safe
if regulate post-translationally, it's energetically expensive
what holds 2 strands of double-stranded DNA together? covalent bonds?
NO COVALENT link between 2 strands, only Hydrogen bonds
why is it easier for cellular RNA to form intramolecule double-stranded structures than it is for chromosomal DNA?
have complementarity within an RNA strand; can loop back on itself, form double strandedf RNA structure
what does it mean that genes have tissue specificity?
nearly all cells have same or v. similar coding info, but have diff structure/function due to differential gene expression
what is the flow of genetic information, from a protein-coding gene to the protein?
1) DNA is acted on by RNA Polymerase II
2) pre-mRNA is processed to mRNA
3) mRNA exported to the cytoplasm
4) mRNA is translated by ribosome into protein
how much of our genome do protein coding genes constitute?
only 1-2% of whole genome is protein coding genes
what is a pre-ncRNA? what does it become? how much of genome does it comprise?
pre-non coding RNA
product of some DNA's transcription
does not code for a protein
90% of the genome is transcribed to give a ncRNA
what is unique about RNA re: its regulatory function in humans?
many genes code for RNA only, w/ no protein produced
what are the different types of non-coding RNA (ncRNA)?
what is their function and location in the cell?
1) rRNA: ribosomal rNA, goes to nucleolus
2) tRNA: transfer RNA, used in translation, so in cytoplasm
3) miRNA: micro RNA, regulate translation, so in cytoplasm
4) lnc RNA: long non-coding RNA, regulatory function; many come back, bind to DNA, inhibit transcription
why does a liver cell's gene expression program change depending on conditions? explain
this is short term regulation
different cells do different things at different times
liver cell has many fxns: can express genes that go thru enzymes that make glucose; if eating glucose now, liver cells won't make glucose; if you're starving, will make glucose
thus its gene expression program changes depending on conditions
do all cells in the body contain all genes? why do they do different things then?
all cells in the body have insulin gene
but no cells in body make insulin except beta cells of pancreas
thus beta cells have insulin gene "on," every other cell in body has insulin gene off
this is how gene expression is regulated
what's a nucleotide? what are the components of a nucleotide?
nucleotide = basic unit of nucleic acid chain
base + sugar + phosphate
what is a nucleoside?
base + ribose sugar
what are the bases of nucleic acids?
"pure as gold, cut the pi"
how are purines numbered?
what's the ribose carbon's structure?
where does the purine/pyrimidine base link to the ribose sugar?
where does the phosphate connect to the ribose sugar?
1' position: purine/pyrimidine base
2' position: OH group RNA ONLY!
3' position: OH group
5' position: phosphate group
how are the phosphates named?
how are they re: ionization at physiological pH?
1st phosphate attached to sugar: alpha phosphate
all ionized at physiological pH
what links 2 nucleotides?
3'-to-5' phosphodiester bond between the 3' OH and 5' phosphate
what is the convention for reading DNA?
5' to 3' directionality
from 5' triphosphate to 3' OH
what varies re: DNA/RNA? what determines our DNA sequence?
phosphate-sugar chain is invariant
this determines our DNA sequence
how do strands of double stranded DNA run?
how do strands connect?
antiparallel to each other in double helix
G-C and A-T base pairs stabilize via H-bonds, base stacking, and other hydrophobic interactions
what are available H groups of double stranded DNA used for?
binding by "DNA binding partners"
what can single stranded RNA interestingly do?
single stranded RNA can form intramolecular base pairs
what is a reverse transcriptase enzyme
transcription can be reversed, w/ RNA serving as template to syntehize DNA by a reverse transcriptase enzyme
what is the intrinsic melting temperature of double stranded DNA or intramolecular double-stranded RNA?
what makes a higher melting temp? a lower melting temp?
temperature at which the 2 strands separate
higher melting temperature: higher G-C content (b/c form 3 H-bonds)
lower melting temperature: higher A-T content (b/c form 2 H-bonds)
what balances the negative charges that DNA/RNA present int he cell?
low molecular weight aliphatic cations that counteract the negative balance of the DNA
they're also important for RNA function
what is the primary structure of DNA?
the phosphate-sugar-base chain
what is the secondary structure of DNA?
what makes it happen?
complementary double-stranded DNA helix
happens b/c of complementary base pairing
what is the minor groove? the major groove?
minor groove: 3.4 A
major groove: where proteins bind DNA; 36 A
what is the basis of nucleic acid probe technology? think annealing
single stranded, "melted" DNA can "reanneal" to original double-stranded state b/c strings of "complementary" (G/C, A/T, A/U) base pairs can find themselves in solution