BIO 130 exam 2: CH 11 + 12

4 criteria for genetic material

• information

• replication

• transmission

• variation

general DNA timeline

• late 1800’s: chromosomes, biological basis of heredity

• late 1920’s: Griffith, bacterial transformation

• 1940’s: Avery, MacLeod, and McCarty, DNA is genetic material

• 1953: Watson and Crick, double stranded helix and base pairing

• late 1950’s: DNA reproduction models → Meselson and Stahl → semiconservative

Griffith’s experiment

• streptococcus pneumonidae

• smooth strains (S) secrete capsules (fatal) and rough strains (R)

• mice injected with heat killed S mixed with R died because the heat killed S transformed the type R into type S

• the transforming principle: the type S transferred genetic material into the type R, which gave them the capsule-secreting trait

Avery, MacLeod, and McCarty

• interested in biochemical basis of transformation

• added DNase, RNase, and protease → when DNase was added, no transformation took place

• found that DNA is the genetic material

nucleotides

building blocks of DNA and RNA

strand definition

linear polymer of DNA or RNA

chromosome definition

DNA associated with an array of different proteins into a complex structure

discrete unit of genetic material

genome

the complete complement of genetic material in an organism

components of DNA

phosphate group

pentose sugar (deoxyribose)

nitrogenous base

purines

double ring structure, A and G

pyrimidines

single ring structure, C, T, and U

phosphodiester bond

the covalent bond between nucleotides

phosphate group bonds to 3’ carbon of one sugar and 5’ carbon of the other

DNA backbone

formed from phosphates and sugars, bases project away from the backbone

Watson and Crick

1953

proposed the idea of the double helix structure

connected the ideas from Rosalind Franklin’s x ray diffraction and Erwin Chargoff’s base pairing

found ball and stick model to be consistent with data

Rosalind Franklin

x ray diffraction suggested helical structure of uniform diameter

Erwin Chargoff

found amount of bases to be equal, suggesting base pairing

what direction does the helix go

it is right handed

how many nucleotides per helical turn

about 10

DNA width

2 nm

minor and major grooves

alternate small and large grooves in dna helix

proteins bind to major groove to affect gene expression

models proposed for DNA reproduction

conservative, semiconservative, and dispersive

Meselson and Stahl

used light and heavy nitrogen to determine that DNA replicated according to the semiconservative model

how do you open DNA

heat or enzymes

DNA helicase

binds to DNA and travels 5’ to 3’ using ATP to separate the strands from each other

DNA topoisomerase

relieves additional coiling ahead of replication forks

single strand binding proteins

keep parental strands open to act as templates during replication

deoxynucleoside triphosphates

free nucleotides with 3 phosphate groups

breaking covalent bonds to release 2 phosphates (pyrophosphate) provides energy to connect nucleotides

two important features of DNA polymerase

cannot begin synthesis on bare strand (requires RNA primer)

only works 5’ to 3’

leading strand

DNA synthesized in as one long molecule

single RNA primer

lagging strand

DNA synthesized 5’ to 3’ but as Okazaki fragments

multiple RNA primers

DNA primase

makes RNA primer

DNA polymerase III

elongates the strand (majority of replication)

DNA polymerase I

replaces RNA primer with DNA

DNA ligase

joins Okazaki fragments together

3 mechanisms for accuracy

base complementarity

active site of DNA polymerase is unlikely to form bonds if pairs are mismatched

proofreading: polymerase can back up and digest linkages, and there are other repair enzymes

DNA polymerases in humans

(e coli has 5)

humans have 12 DNA polymerases identified by greek letters

telomeres

series of short nucleotide sequences that are repeated at the ends of chromosomes in eukaryotes

telomere at 3’ does not have a complementary strand and is called a 3’ overhang

DNA polymerase cannot copy the 3’ end of the chromosome because there is no place to put the RNA primer, so telomerase attaches the telomeres so that our DNA would not get progressively shorter and shorter

telomerase activity decreases with age

telomerase is overexpressed in cancer

senescence

biological aging, gradual deterioration of functional characteristics in living organisms

chromatin

DNA protein complex

3 levels of chromosome compation

nucleosomes, 30 nm chromatin fiber, and radial loop domains

DNA wrapping

dna wraps around histones (8) to form nucleosomes

shortens 7 fold

30 nanometer fiber

asymmetric 3D zigzag of nucleosomes

shortens another 7 fold

radial loop domains

interaction betwen 30 nm fiber and nuclear matrix

each chromosome located in discrete territory

level of compation is not uniform

euchromatin

less compacted chromatin

hetrochromatin

more compact chromatin, occurs when cells prepare to divide (metaphase)