Chapter 16 - Molecular Basis of Inheritance

Question 1

where is DNA found in bacteria?

Answer 1

it’s supercoiled and found in the nucleoid

Question 2

how often does DNA make a full turn?

Answer 2

every 3.4 nm

every 10 layers of bases

Question 3

what are purines? what are pyrimidines?

Answer 3

purine: A/G (large)
pyrimidine: C/T (small)

Question 4

types of bonds in DNA

Answer 4

covalent bonds between sugar phosphate backbone

hydrogen bonds between bases in the center

Question 5

what’s the conservative model?

Answer 5

black DNA strand splits, makes white replicates, and then original strands come back together

N15/N15 –> N14/N14 and N15/N15 –> 3N14/N14 and N15/N15

Question 6

what’s the semiconservative model?

Answer 6

when the double helix replicated, each of the two daughter molecules will have one old strand from the parent and one newly made strand

N15/N15 –> 2N14/N15 –> 2N14/N15 and 2N14/N14

this model was correct!

Question 7

what’s the dispersive model?

Answer 7

all four strands of DNA following replication have a mixture of old and new DNA (the one with the weird fractions)

Question 8

how many DNA molecules are in a cell?

Answer 8

46 DNA molecules in a nucleus - one DNA molecules per chromosome

6 billion nucleotide pairs

Question 9

where does replication start?

Answer 9

particular sites called origins of replication, short stretches of DNA having a specific sequence of nucleotides

Question 10

what unwinds DNA?

Answer 10

helicases are enzymes that untwist the parent helix at the replication forks

Question 11

what stabilizes single stranded DNA after it’s been split apart?

Answer 11

after parental strands separate, single-strand binding proteins bind proteins bind to the unpaired DNA strands, keeping them from re-pairing until they’re used as templates

Question 12

what relieves stress from the untwisting of the double helix?

Answer 12

topoisomerase helps relieve strain by breaking, swirling, and rejoining the parental DNA ahead of the replication fork

Question 13

where is the primer located?

Answer 13

on the 5’ of the leading strand and at the end of each okazaki fragment

primase synthesizes primer: RNA chain

Question 14

where does the replication start?

Answer 14

at the 3’ end of the template strand

Question 15

which DNA polymerase adds nucleotides to the RNA primer?

Answer 15

II

Question 16

what drives the polymerization reaction?

Answer 16

as each monomer joins the DNA strand, two phosphatee groups are lost as a molecule of pyrophasphate which is then hydrolyzed into two molecules of inorganic phosphate (exergonic reactions)

Question 17

which functional groups are at the ends of DNA?

Answer 17

3’ is hydroxyl

5’ is phosphate

Question 18

characteristics of leading strand?

Answer 18

continuously being elongated in the 5’–>3’

only one primer is needed to synthesize the entire strand

Question 19

what is the lagging strand?

Answer 19

it’s elongated in the direction away from the replication fork

synthesized discontinuously as a series of okazaki fragments

Question 20

okazaki fragments

Answer 20

DNA pol II forms okazaki fragments but then DNA pol I replaces the RNA nucleotides of the adjacent primer from the 5’ end with DNA nucleotides –> DNA ligase has to actually join the Okazaki fragments into a continuous strand

Question 21

what molecule proofreads transcription?

Answer 21

DNA polymerases proofread each nucleotide against its template

Question 22

what happens when there’s damage to a complementary DNA strand during transcription?

Answer 22

the segment containing the damage is cut out by an enzyme called a nuclease –> the gap is filled with nucleotides using the undamaged strand as a template

Question 23

what is caused by UV radiation?

Answer 23

thymine dimers

Question 24

what is the name of a DNA repair system?

Answer 24

nucleotide excision repair

Question 25

shape of eukaryotic vs. prokaryotes DNA?

Answer 25

linear DNA (eukaryotes)
circular DNA (prokaryotes)

Question 26

what keeps eukaryotic DNA from shortening due to primers being located at the 5’ end?

Answer 26

eukaryotic DNA have special nucleotide sequences called telomeres at the ends which don’t contain genes - it’s just a repetition of TTAGGG

Question 27

what are the protective functions of telomeres?

Answer 27

1) prevents cell from activating cell destruction since staggered ends are usually signs of double breaks
2) act as buffer against genes shortening

Question 28

what is telomerase?

Answer 28

catalyzes the lengthening of telomeres to restore their original length and compensate for the shortening that occurs during replication

Question 29

what happens if you have too much telomerase?

Answer 29

telomerase activity is abnormally high in cancerous somatic cells

Question 30

what’s responsible for the first level of DNA packing

Answer 30

histones

lots of histone’s amino acids are positively charged so they bind tightly to negative phosphate group of DNA

Question 31

what are the levels of chromatin packing?

Answer 31

10 nm –> 30 nm –> 300nm –> 700 nm

Question 32

what is a 10 nm fiber?

Answer 32

unfolded chromatin that resembles beads on a string

each bead is a nucleosome (DNA would twice around protein core of 8 histones)

Question 33

what’s 30 nm fiber?

Answer 33

interaction between histone tails of one nucleosome and the linker DNA and nucleosomes on either side which cause fiber to fold and twist into thicker fibers

interphase!

Question 34

what is 300 nm fiber?

Answer 34

30 nm fibers form loops called looped domains attached to a chromosome scaffold

Question 35

what is 700 nm fibers?

Answer 35

metaphase chromosome: looped domains themselves fold and further compact to produce characteristic metaphase chromosome

Question 36

what is euchromatin?

Answer 36

loosely packed chromatin –> DNA is accessible go the genes in euchromatin can be transcribed

Question 37

what is heterochromatin?

Answer 37

during interphase a few regions of chromatin are highly condensed –> inaccessible to the machinery