unit 6 (topic 1 & 2)

Question 1

which scientist performed X-ray chromatography in the 1950s?

Answer 1

Rosalind Franklin

Question 2

what did Edwin Chargaff do?

Answer 2

analyzed DNA samples from different species. found that A=T (two H bonds) and C=G (three H bonds)

Question 3

nucleotide structures

Answer 3

purines and pyrimidines

Question 4

purines

Answer 4

-double ring shape
-A & G

Question 5

pyrimidines

Answer 5

-single ring structure
-T, C, and U

Question 6

how can h bonds aid in DNA replication?

Answer 6

they can break easily so this allows for DNA strands to be easily separated

Question 7

watson and crick did what?

Answer 7

combined the findings of Franklin and Chargaff to create the first 3D, double helix model of DNA

Question 8

key features of DNA

Answer 8

-double stranded helix
–>backbone: sugar-phosphate
–>center: nucleotide pairs

-antiparallel
–> 5’–>3’
–> 3’–>5’
–> 5’ end: phosphate group
–> 3’ end: hydroxyl group

Question 9

key functions of DNA

Answer 9

-primary source of heritable info
–>genetic info is stored in and passed from one generation to the next through DNA
–>EXCEPT: RNA is the primary source of heritable info for some viruses

Question 10

eukaryotic DNA

Answer 10

-Dna found in nucleus
-linear chromosomes

Question 11

prokaryotic DNA

Answer 11

-dna is in nucleoid region
-chromosomes are circular

Question 12

prokaryotes also contain

Answer 12

plasmids

Question 13

plasmids

Answer 13

-small, circular DNA molecules that are seperate from the chromosomes
-they replicate independently from chromosomal DNA
-can be manipulated in labs

Question 14

conservative model of dna replication

Answer 14

parental strands direct synthesis of an entirely new double stranded molecules
-parental strands are fully conserved

Question 15

semi-conservative model

Answer 15

two parental strands each make a copy of themselves
-after one round of rep, the two daughter mole each have one parental and one new strand
-dna rep is an example of this

Question 16

dispersive model

Answer 16

material in the two parental strands is dispersed randomly between the two daughter moles
-after one round of rep, daughter moles contain a random mix of parental and new dna

Question 17

meselson and stahl model

Answer 17

preformed exp using bacteria
-bacteria was cultured with a heavy isotope, N15
-bacteria was transferred to a medium with N14, a light isotope
-dna was centrifuged and analyzed after each rep

Question 18

steps in dna rep

Answer 18

1. begins at origins of rep; various proteins attach to the origin and open the dna to form a rep fork
2. helicase unzips dna strand at rep fork; ssbps bind to dna to keep it open; topoisomerase will help prevent strain ahead of the rep fork by relaxing supercoiling
3. enzyme primase initiates rep by adding short segments of RNA (primers) to the parental dna strand
4. antiparallel elongation; dna polymerase III attaches to each primer on the parental strand and moves in the 3’ to 5’ direction. adds nucleotides in 5’ to 3’ direction
5. leading strand is synthesized in one segment, lagging is in clumps (Okazaki fragments)
6. after dnap III forms an O fragment, DNAP I replaces rna nucleotides with dna nucleotides; dna ligase joins fragments forming a continuous dna strand

Question 19

problems at the 5’ end

Answer 19

dnap III can only add nucleotides to a 3’ end, there is no way to finish on the 5’ end of a lagging strand, so dna would get shorter. but genes are protected from this bc of telemeres: repeating units of short nucleotide sequences that dont code for genes