W4: chapter 12

DNA Organization in Chromosomes

genetic material

responsible for passage of traits from parents → offspring

to do this, must be:

1) stable enough to store info for long periods

2) able to replicate accurately

3) capable to allow evolution

Griffith’s Transformation Experiment

1928 experiment w/ streptococcus pneumoniae in mice showed that something passed from dead bacteria → nearby living ones, allowing them to change their cell surface

Avery’s Transformation Experiment

Broke open dead cells, chemically separate components (protein & NA), determine which was capable of transforming live S. pneumoniae cells

*only NA transformed bacteria

*supports DNA or RNA as genetic material NOT protein

Hershey-Chase Bacteriophage Experiment

A 1952 experiment that used radioactively labeled bacteriophages to demonstrate that DNA, not protein, is the genetic material of viruses by showing that only DNA entered bacterial cells during infection.

*proving parents give DNA (genetic material) to offspring NOT protein to offspring

Grierer & Schramm

Tobacco mosaic virus (TMV) composed of RNA & protein

showed that when purified RNA from TMV directly applied to tobacco leaves → develop mosaic disease

*proves RNA can be genetic material NOT protein

composition & structure of DNA & RNA

monomers → nucleotides

phosphodiester linkage

nucleotide

pentose

N-base

phosphate group

pentose

DNA = deoxyribose

RNA = ribose

N-base

purines

pyrimadines

purines

A & G

dbl ring 9 membered

2 H bonds bt A & T → easier to break

pyrimidines

C, T, & U

1 ring 6 membered

(CUT PY)

3 H bonds bt C & G → harder to break

who discovered double helix?

Watson and Crick

Chargaff’s rule

States that in DNA, the amount of adenine equals thymine and the amount of guanine equals cytosine.

A - DNA

dehydrated form of DNA

B - DNA

what we talk abt

10 bp 1 turm

right-handed helix

Z - DNA

left - handed helix

existence in living cells not proven

viral chromosomes

NA, ds/ss DNA or RNA

circular or linear molecules

viral genetic material inert until released into host cell

able to package DNA into small volume

bacterial chromosomes

circular, ds DNA compacted into nucleoid

readily replicated & transcribed

plasmid = minor chromosome is dispensible to the life of the cell

both viral and bacterial chromosome (prokaryotes)

single NA molecule

largely devoid of associated proteins

much smaller than eukaryotic chromosome

contain less genetic info

topoisomerase

enzyme that cuts 1 or both strands of DNA

unwind/wind helix before resealing ends

chromatin

@ interphase → eukaryote chromosomes uncoil and decondense into chromatin

C value paradox

The C value paradox refers to the observation that the genome size (C value) does not correlate with the organism's complexity. It highlights how different species can have vastly different amounts of DNA that do not equate to the number of genes or organismal complexity.

histones

(+) proteins associated with chromosomal DNA in eukaryotes

types: H1, H2, H3, H4

contain large amounts of lysine and arginine

nucleosome

DNA wrapped around octomer of a histone

‘beads on a string’

C-banding

only centromere takes up stain

G-banding

differential staining along length of each chromosome

karyotype

heterochromatin

condensed areas mostly inactive

lacks genes/repressed genes

euchromatin

uncoiled and inactive