mbb 201 topic 5 DNA intro

primary, secondary and tertiary DNA structure \ primary- the nucleotide sequence, -secondary- any regular, stable structure taken up by some or all of the nucleotides, driven by base pairing, tertiary structure- complex 3d foldingof nuclei acids (exeukaryotic hromatin and bacterial nucleoids);

whats a phosphodiester bond \ 5’ physphate of one nucleotide unit is joined to the 3’ hydroxyl group of the next nucleotide, forms a repeating backbone;

DNA secondary structure \ double helix - h bond interactions, for a right handed double helix, the strands run in opposite directions antipralel, one 3’ to 5’, and the other 5’ to 3’ ;

dna base pairing \ A double bonds with T (or u) - g triple bonds with c, base stacking between the hydrophobic bases minimizes their contact with water and is very important for stabilizing the double helix, 10.5 bp/turn, proteins interact at grooves;

whats chormatin \ complex of DNA and protein;

chromosome \ a single strand of DNA in chromatin form;

karyotype \ an ordered display of the full set of metaphase chrojosomes ;

whats a homologous chromosome \ one maternal one paternal, 46 chormosomes;

two broad phases of the cell cylce \ interphase - when chromosomes are duplicated , hard to see using a light microscope, -mitosis m phase - when chormosomes are segregated to two daughter molecules, mitotic chormosomes are extremely compact and easy to visualize;

telomeres \ repeated sequences at the ends of chromosomes, protects from degradation and as a start site for replication of nagative strand;

replication origin \ sequence where replication begins during interphase ;

centromere \ sequence that allows dna to be separated during M phase, region of attachment to mitotic spindle;

nuclear lamina \ protein meshwork that supports the nuclear envelope that chromosomes may be attached to;

nucleosomes \ basic units of eukaryotic chromosome structure, contain DNA wrapped around a protein core of 8 histone molecules, the DNA in chromaatin is tighlty associated with these histone proteins and the cell has lots of them, nucleosomes plus the linking piece of DNA give a beads on a string appearance ;

histones \ small DNA associated proteins that ar eresponsible for the firs level of chromatin packing, major protein comonent of chromatin, the DNA is wrapped around the histone core to form the nucleosome;

what does H1 do \ holds the DNA on the histone core and is necessary for formation of the 30nm fiber, contains a pair of long flexible tails, H1 is located inthe interior of the 30nm fiber, additionally, histone tils may help pack nucleosome sinto the 30nm fiber;

what are the DNA packing levels \ 1.short region of DNA double helix 2.beads on a strong form of chromatin 3. chromatin fiber of packed nucleosomes 4. chromatin fiber folded into loops 5. entire mitotic chromosome, net result is each DNA molecule ahs been packaged into a mitotic chromosome that is 10,000 fold shorter than its fully extended length;

  1. chromatin fiber folded into loops \ further looping/coiling of solenoid DNA into highley compacted transcriptionally silent, form of chromatin occurs duringmitosis, ;

chromatin remodeling complexes \ protein machines that use ATP to change the position of DNA wrapped around nucleosomes, makes the DNA mor eor less accessible, duringmitosis many of the chromatin remodelers are inactive ;

second way to alter chromatin \ -reversible chemical modification of histones - the n terminal of each of teh core histones ar subject to covalent modifications, -protrude from the octameric disk, -highly conserved between histones, - postivively charged with many Lys and Arg residues, the pattern of modification of histone tails can dictate how a stretc of chroatin is treated by the cell;

heterochromatin \ most highly condensed form of interphase chromatin, concentrated around the centromere region adn in the telomeres’ends of the chromosomes;

euchromatin \ the rest of the interphase chromatin;

how can heterochromatin spread? \ histone tail modification can have a wave like effect, heterochromatin specific modifications can recruit proteins that makethe same modifications on adjacent nucleosomes, this casues a wave of condensed chormatin to spread, most DNA that is folded into heterochormatin doesnt contain genes, (ex deficiency of beta globin casuing anemia is situated next to a region of heterochromatin);

how is x chromosome inactivated \ -by condensing it into heterochromatin;

whats epigneetic inheritance \ transmission of a pattern of gene expression from one cell to its progeny that doesn’t involve altering the nucleotide dequence of the DNA;