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25 Cards in this Set

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  • Back
Why does DNA contain deoxyribose rather than ribose?
1. ribose makes sugar phosphate backbone reactive; branching could occur at bother 2' and 3'

2. Deoxyribose makes DNA much more stable at high pH; RNA is unstable at alklaine pH usch as 9. It makes 2'3' cyclic monophosphate derivatives at high pH.
Why does DNA contain thymine rather than uricl?
Cytosine in DNA is not very stable, it will convert to uracil by deamination. Needs folic acid for thymine for excision repair
Why does denatured DNA absorb more UV light than native DNA (hyperchromic shift)?
Base stacking in native DNA interferes with UV absorption
Why does DNA renaturation require annealing at intermediate temperatures or pH?
1. quick cooling DNA fosters inter-strand interactions

2. Intra-strand interactions occur becuase DNA contains self-complementary (snapback) regions
Why does DNA contain snapback regions?
DNA has many regions containing palidromes
Why are there palindromes in DNA?
a. RNA hairpins regulate RNA stability and structure

b. RNA hairpins regulate RNA polymerase pasuing and termination. It can also regulate ribosome binding

c. Palindromic sequences allow multi-subunit DNA binding proteins to recongnize the same DNA sequence

d. all for intrachromosomal recombination
Are linear chromsomes better than circular chromosomes?
1. linear chromosomes can accomodate much larger amounts of DNA

2. Linear chromosomes are necessary for mitosis
How do we isolate bacterial nucleoids?
Through a sucrous gradient becuase shear forces will break DNA, and DNA is very viscou
Why are there so many loops and supercoils in nucleoid DNA?
1. supercoiled loops reduce DNA entanglements, while bringing DNA in each loop close to itself

2. it makes the DNA more compact

3. negative suprecoils are needed for unwinding DNA during replication and transctipion
Why do cells need negatively supercoiled DNA?
1. it is necessary for unwinding DNA at the replication fork
2. it is necessary for RNA synthesis
2. permits certain enzymes and DNA binding proteins involved in the repair of DNA to interact with their substrates
How can histones be removed?
acetylation, methylation, or phosphorylation

chages their affinity for DNA by making the histones less basic

can activate or inhibit transcription
What were the conclusions of the Hirota study?
1. many genes are needed for DNA synthesis

2. These genes had not yet been found since all of his mutatns contained the Kornberg enzyme and they stopped growing after a certain time
Why was it so hard for Kornberg and his collaborators to find the true "DNA Polymerase"
1. DNA polymerase III is not very abundant

2. All looking for a single enzyme and such an enzyme does not exist
Primase (Dna G)
Recognizes the pre-priming complex and synthesizes a short RNA of about 30 nucleotides
What are the benefits of telomers?
1. prevent loss of informational DNA from chromosome ends during replication

2. Prevent ends of chromosomes from being fused to other chromosomes by repair enzymes

c. When too short they signal
a. arrest of growth
b. apoptosis (programmed cell death)
Why do telemeres form loops at the end?
So that other proteins can bind specifically to these loops and completely coat the telomeres which signals that the telomeres are long enough and the cell can continue living
What did the Ames test show?
chemicals that cuase mutations in bacteria, can cause cancer in rats
Why is damage to mDNA involved in aging?
has site of oxidative phosphorylation and
no recombinational repair
How are thyamine dimers formed by UV repaired?
DNA photolyase binds to dimer and breaks the cyclobutane bonds. FAD2H is cofactor

UvrABC excision repair
Why are some organisms have a higher GC content while others have a low GC content?
AT rich regions are more likely to make thymine dimers. Microorganisms that are exposed to UV light generally have a high GC content
What is Xeroderma pigmentosum?
caused by mutation in the excinuclease involved in excision repair

- causes skin caner
What are two types of plasmids?
a. small
b. multicopy
c. usually contain drug resistance genes

Conjugative plasmids
a. large
b. few copies
c. encode for conjgation functions
In rolling DNA replication, what kind of DNA is transfered?
Single stranded
Why are transposons important?
1. they are a major source of spontaneous mutations

2. provide a mechanism for genes to be transferred from one place to another

3. they are widespread
Why is there such a low frequency of transposons?
they create mutations which can kill