Chapter 16 - Molecular Basis of Inheritance Flashcards

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1
Q

where is DNA found in bacteria?

A

it’s supercoiled and found in the nucleoid

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2
Q

how often does DNA make a full turn?

A

every 3.4 nm

every 10 layers of bases

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3
Q

what are purines? what are pyrimidines?

A

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

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4
Q

types of bonds in DNA

A

covalent bonds between sugar phosphate backbone

hydrogen bonds between bases in the center

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5
Q

what’s the conservative model?

A

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

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6
Q

what’s the semiconservative model?

A

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!

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7
Q

what’s the dispersive model?

A

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

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8
Q

how many DNA molecules are in a cell?

A

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

6 billion nucleotide pairs

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9
Q

where does replication start?

A

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

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10
Q

what unwinds DNA?

A

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

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11
Q

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

A

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

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12
Q

what relieves stress from the untwisting of the double helix?

A

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

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13
Q

where is the primer located?

A

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

primase synthesizes primer: RNA chain

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14
Q

where does the replication start?

A

at the 3’ end of the template strand

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15
Q

which DNA polymerase adds nucleotides to the RNA primer?

A

II

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16
Q

what drives the polymerization reaction?

A

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)

17
Q

which functional groups are at the ends of DNA?

A

3’ is hydroxyl

5’ is phosphate

18
Q

characteristics of leading strand?

A

continuously being elongated in the 5’–>3’

only one primer is needed to synthesize the entire strand

19
Q

what is the lagging strand?

A

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

synthesized discontinuously as a series of okazaki fragments

20
Q

okazaki fragments

A

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

21
Q

what molecule proofreads transcription?

A

DNA polymerases proofread each nucleotide against its template

22
Q

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

A

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

23
Q

what is caused by UV radiation?

A

thymine dimers

24
Q

what is the name of a DNA repair system?

A

nucleotide excision repair

25
Q

shape of eukaryotic vs. prokaryotes DNA?

A
linear DNA (eukaryotes)
circular DNA (prokaryotes)
26
Q

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

A

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

27
Q

what are the protective functions of telomeres?

A

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

28
Q

what is telomerase?

A

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

29
Q

what happens if you have too much telomerase?

A

telomerase activity is abnormally high in cancerous somatic cells

30
Q

what’s responsible for the first level of DNA packing

A

histones

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

31
Q

what are the levels of chromatin packing?

A

10 nm –> 30 nm –> 300nm –> 700 nm

32
Q

what is a 10 nm fiber?

A

unfolded chromatin that resembles beads on a string

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

33
Q

what’s 30 nm fiber?

A

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!

34
Q

what is 300 nm fiber?

A

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

35
Q

what is 700 nm fibers?

A

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

36
Q

what is euchromatin?

A

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

37
Q

what is heterochromatin?

A

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