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46 Cards in this Set
- Front
- Back
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During which part of the cell cycle do cells spend most of their time? |
During the process called interphase |
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What happens during the S phase ? |
DNA synhesized and replicates |
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What is the G1 phase ? |
A time gap seperates S phase from preceding M phase **cell growth ** |
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What is the G2 phase ? |
The cell prepares to divide |
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What is semiconservative replication ? |
This is when half of the parent molecule is retained by each daughter molecule Helix unwinds and each parent strand serves as template for synthesis of complementary daughter strand
New DNA moleucle = 1 parent molecule +newly generated copy |
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Proof of semiconservative replication is from? |
Old and new DNA strands can be distinguished from eachother through density centrifigation which allows organelles or macromolecules with differing densites to be separated from each other by centrifugation
**Meselson and Stahl showed replication is semiconservative by using N14 and N15*** **N15 DENSER THEN N14** |
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How is circular DNA replicated ? |
Replication forks are created that move in a bidirectional fashion away from the orgion of replication (opposite directions away from ori <--> Single ori with a special DNA sequence Topoisomerase needed to disconnect two circles of DNA from eachother |
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Explain process of replication and binary fission in bacteria |
Replicating chromosomes bind to plasma membrane at their replication origins As cells grow preparing for cell division, new PM is added to region b/w chromosome attachment
**Chromosomes attached to PM** **As cells grows , new PM added btw. Atachment sites** **separation of chromosomes/each daughter cell geting copy** |
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Replication of linear DNA molecules of eukaryotic chromosomes is initiated at multiple sites, creating multpile replication units called? |
Replicons |
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What consists of a replicon? |
The center of each replicon is a DNA sequence called an orgin of replication, where synthesis is initiated **Replicon is a replication unit** **Many on a chromatid** **Each has 1 ori in center** **Replication followed by mitosis and cytokinesis**
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What is the purpose of the pre replication complex? |
-Protien known as orgin recognition compex(ORC) binds to a replication orgin -Then minichromosome maintenance (MCM) proteins are binded, which include several DNA helicase that facilitate DNA replication by unwinding double helix -MCM protiens recruitment requires helicase loaders to mediate binding of MCM to ORC
**Orgin replication complex** **MCM: DNA helicases to unwind** **Helicase loaders:MCM to ORC** |
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When is the DNA "licensed for replication"? |
After the pre-replication complex |
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What is the replication compex ? |
DNA polymerase +otherproteins |
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How is DNA synthesized ? |
Through DNA polymerase |
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How does DNA polymerase synthesize DNA ? |
-Requires a small amount of DNA to initally be present to act as a template -Guding this template DNA polymerase catalyzes elongation of DNA chains -DNA polymerase elongation occurs at 3' end and new strand is grown in a 5' --> direction
**Reqires small amount of DNA** **Copies DNA template in 3'-5'** **Synthesizes in 5'-3'** **PPi released provides energy** |
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What is significant about the leading strand? |
It is synthesized all at once |
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What happens in the lagging strand ? |
Lagging strand forms as a series of short, discontinuous okazaki fragments that are synthesized in the 5'-3' direction. which are joined together by DNA ligase to make a new 3'-5' strand
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What is the role of RNA primers ? |
They essentially initiate DNA synthesis which are synthesized from primase -DNA polymerase III adds successive deoxynucleotides to 3' end of the primer -DNA polymerase posses a 5'-3' exonuclase activity -While replacing the RNA with DNA synthesizing 5'-3'
DNA ligse sealing the gaps |
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What are some proteins that facilitate the unwinding processs of DNA ? |
DNA helicases, topoisomerase and ssDNA binding proteins |
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What is the role of DNA helicase ? |
***DNA helicase unwinds the DNA *** (Moving 3'-5' on leading strand ) (moving 5'-3' on lagging strand) |
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What is the role of single stranded DNA binding proteins (SSB) ? |
They attach to exposed single strands to keep DNA unwound and accessible to the DNA replication machinery **Stabalize the unwound DNA in an extended position** |
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What are the roles of topoisomerase ? |
After the unwinding of DNA caused by DNA helicase they creat swivel points in DNA by making and quickly resealing SSB **Form swivel ahed of the replication form**(DNA gyrase E.coli) |
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What is the replisome ? |
Various proteins involved in DNA replication are all closely associated in a large complex |
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Function of replisome? |
As replisome moves along DNA in direction of replication fork, it creats a loop that alllows DNA polymerase on both leading and lagging strand to move in same physical direction, even though two template strands are orientied with opposite polarity **Lagging strand looped --> DNA pols on both strands can move in same direction** **Set of proteins involved in DNA replication**** |
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How does DNA polymerase proofread DNA? |
If an incorrect nucleotide is incorporated DNA polymerase can move backwards and remove the incorrect base |
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What is the End-replication problem of linear DNA ? |
DNA polymerase can only add to 3' end of OH of preexisting cell -Each strand gets shourter with each cell division
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What are telomeres? |
They are highly repeated DNA sequences at terminal ends of each linear chromosome Consist of repeating sequences enriched in G **Highly repeated DNA sequences repeated at ends of chromosomes** **In humans 100-1500 tandem copies of TTAGGG sequence |
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What is telomerase? |
**Protein/RNA enzyme(RNA complementary to telomere repeats** After being lengthend by telomerase, the telomerase are protected by telomere capping proteins that bind to the exposed 3' end of the DNA **Only active in germ cells and some actively dividing cells** **reverse transcriptase RNA--DNA** **Telomere capping by capping proteins on 3'end DNA 3' loops** |
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What is associated with telomere shortening? |
***aging, too short-triggers apoptosis,** ***Degenerative diseases associated with aging*** *Mutations in telomerase -- premature aging**
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What are some types of DNA damage? |
Most common are those involving depurination and deamination reactions, which are spontaneous hydrolysis reactions ***Depurination:loss of purine*** ***Deamination: loss of -NH2 (C,G or A)*** |
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What are two ways to repair DNA damage? |
Translesion synthesis, excision repair |
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What is translesion syntehsis? |
Repair is done by DNA polymerases which forms this "translesion synthesis". This is synthesis of new DNA across regions in which the DNA template is damaged **DNA pol may 'repair DNA during replication**
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What is excision repair? |
Endonucleases recruited to DNA by proteins that recognize damage |
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What is a mismatch pair? |
-Targets errors made during DNA replication. **Corrects noncomplementary base pairs** **Which strand has wrong base? -- new DNA strands are nonmethylated
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What are function of nonhomologous end-joining ? |
Uses a set of proteins that bind to broken DNA fragments being joined to each other **Nonhomologous end joining(loss of DNA)**
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What is homologous recombination? |
intact copy of chromosomal DNA is still availble to serve as a template for guiding the repair of broken chromosome **other intact chromosome used as a template to gudie repair of broken chromo**
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What happens during M phase? |
Two copies of chromosomes made during S phase distributed into daughter cells during M phase **Includes nuclear division(mitosis ) and cytoplasmic division(cytokinesis)** **Goes through 5 stages**
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What does the cell cylce have to ensure? |
1.Correct order and appropriate time 2.Each hase completed before next one begins 3.Respond to internal/external conditions
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What are the 3 key transition points? |
1.Restriction point(late in G1) 2. G2-M transition 3.Metaphase-anaphase transition |
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How is the cell cycle regulated? |
Eukaryotic cell is controlled by several different Cdks that bind to different cyclins Cyclins required for G2-M transition and erly events of mitosis are called mitotic cyclins CDKS to which they bind are called mitotic CDK
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What is MPF (maturation promotion factor) |
Induces oocycte maturation/meiotic divison and mitosis
** A Cdk-cyclin complex found in many organisms |
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What are some cyclins responsible for during cell cylcle? |
G1 cyclins: passage thru g1 restriction point S cyclin: DNA replication |
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What does active Cdk-cyclin stimulate ? |
1)Nuclear envelope breakdown 2)Chromosome Condensation 3)Mitotic Spindle formation 4)Targeted protein degradation
**Phosphorylates APC (anaphase promoting compex) contributing to its activation |
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When is mitotic cyclin levels highest and lowest? |
During interphase(G1 S and G2) it is at its highest And fall abruptly during M phase |
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Regulation of cdk-cyclin activity is by: |
Cyclin oscillates during cell cycle Phosphorylation state of Cdks |
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What is the anaphase promoting complex(APC)? |
Targets securing and mitotic cyclin for degradation Degradation of mitotic cyclin depresses mitotic Cdk activity leading to cytokinesis chromosome decondensation and nuclear envelope reasemmbaly
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