Chapter 6: DNA Replication and Repair Flashcards
Name the three predictions of DNA replication
semiconservative, dispersive, and conservative
Semiconservative
1 old + 1 new strand in each double bond of DNA after replication
Dispersive
old + new fragments throughout each double bond of DNA after replication
Conservative
Both old or new strands in each double bond of DNA after replication
Where does DNA synthesis occur?
Y-shaped junctions called replication forks
template DNA around newly synthesized DNA
DNA strand replication process
- DNA polymerase syntehsizes DNA using parental strand as template
- parental strand splits to pair each with a newly formed strand
- needs primer; DNA polymerase cna only add nucleotides to 3’ end of double stranded segment of DNA
primers
short stretches of DNA that target unique sequences and help identify a unique part of genome
short lengths of RNA acts as primers for DNA synthesis!
Compare DNA polymerase and RNA primase
DNA polymerase can only add nucleotides to 3’ end of double stranded segment of DNA
RNA’s primase can start a new polynucleotide by joining 2 nucleotide triphosphates, without need for 3’ end start
Primase uses ribonucleoside triphosphate, rahther than deoxyribonucleoside triphosphate
Describe the DNA replication process in leading strands and lagging strands
- the leading strand is continuous and is made 5’ to 3’
- the lagging strand is not continuous and cannot be made like the leading strand
- the lagging strand is made in okazaki fragments (RNA primers form on lagging strand by primase first, and DNA polymerase then adds short strands in 5’ to 3’ direction to each primer)
What is a major issue that replication corrects during its process?
the lagging strand always comes up short
Describe the DNA replication process after DNA addition to strands
- the RNA primers are removed
- multiple DNA polymerase enzymes fill in gaps of removed RNA primers
- DNA ligase will seal up the DNA fragments here and there
What major issue does DNA replication have to correct?
The lagging strand always coming up short! If left this way, it will continue to replicate shorter and shorter
Dsecribe the process to correct a short lagging strand
- Telomerase enzyme solves this
- it detects a a G rich field (aka the telomere end of a template strand)
- using RNA, telomerase provides repeats on the strand
- the strand is then completed by DNA polymerase alpha (provides DNA primase to complete the strand)
What is PCR?
- polymerase chain reaction
- heating and cooling to make many copies of a specific region of DNA
METHOD OF SEQUENCING DNA
Describe the process of PCR
- DNA brought to boiling point to go from DNA double strand to 2 single strands
- brought to cool temp, DNA primers link on to target DNA sequence and copy the region
- higher temps help Taq polymerase bind to DNA primer to extend the nucleotides for a 2nd strand
(repeated to make many copies!)
Why is Uracil replaced with thymine in DNA?
- deamination is involved(removes an amino group)
- makes detection and repair more efficient
Describe the Meselon and Stahl experiment
What is Dideoxy Sequencing?
- makes copies of target DNA region
- depends on analysis of DNA chains terminated at every position
-relies on chain-terminating dideoxynucleoside triphosphates (ddNTPs)
Describe role of ddNTPs
These ddNTPs are derivatives of the normal deoxyribonucleoside triphosphates that lack the 3′ hydroxyl group. When incorporated into a growing DNA strand, they block further elongation of that strand.
Automated dideoxy sequencing
- relies on set of four ddNTPS, each bearing uniquely colored fluorescent tag
-To determine the complete sequence of a single-stranded fragment of DNA (gray), the DNA is first hybridized with a short DNA primer (orange). The DNA is then mixed with DNA polymerase (not shown), an excess amount of normal dNTPs, and a mixture containing small amounts of all four chain-terminating ddNTPs, each of which is labeled with a fluorescent tag of a different color. Because the chain-terminating ddNTPs will be incorporated only occasionally, each reaction produces a diverse set of DNA copies that terminate at different points in the sequence.
Importance of PCR
- can identify individual or genetic sex of individual for forensics
STRs
- PCR of short tandem repeats
- ex: chromosome number of one person is the exact same in another (2 groups of letters, with one paternal and one maternal)
- different people have diff number of repeats on their chromosomes
