Chapter 6: DNA Replication and Repair

Question 1

Name the three predictions of DNA replication

Answer 1

semiconservative, dispersive, and conservative

Question 2

Semiconservative

Answer 2

1 old + 1 new strand in each double bond of DNA after replication

Question 3

Dispersive

Answer 3

old + new fragments throughout each double bond of DNA after replication

Question 4

Conservative

Answer 4

Both old or new strands in each double bond of DNA after replication

Question 5

Where does DNA synthesis occur?

Answer 5

Y-shaped junctions called replication forks

template DNA around newly synthesized DNA

Question 6

DNA strand replication process

Answer 6

• 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

Question 7

primers

Answer 7

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!

Question 8

Compare DNA polymerase and RNA primase

Answer 8

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

Question 9

Describe the DNA replication process in leading strands and lagging strands

Answer 9

• 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)

Question 9

What is a major issue that replication corrects during its process?

Answer 9

the lagging strand always comes up short

Question 9

Describe the DNA replication process after DNA addition to strands

Answer 9

• 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

Question 9

What major issue does DNA replication have to correct?

Answer 9

The lagging strand always coming up short! If left this way, it will continue to replicate shorter and shorter

Question 10

Dsecribe the process to correct a short lagging strand

Answer 10

• 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)

Question 11

What is PCR?

Answer 11

• polymerase chain reaction
• heating and cooling to make many copies of a specific region of DNA

METHOD OF SEQUENCING DNA

Question 12

Describe the process of PCR

Answer 12

• 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!)

Question 13

Why is Uracil replaced with thymine in DNA?

Answer 13

• deamination is involved(removes an amino group)
• makes detection and repair more efficient

Question 14

Describe the Meselon and Stahl experiment

Question 15

What is Dideoxy Sequencing?

Answer 15

• makes copies of target DNA region
• depends on analysis of DNA chains terminated at every position
  -relies on chain-terminating dideoxynucleoside triphosphates (ddNTPs)

Question 16

Describe role of ddNTPs

Answer 16

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.

Question 17

Automated dideoxy sequencing

Answer 17

• 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.

Question 18

Importance of PCR

Answer 18

• can identify individual or genetic sex of individual for forensics

Question 19

STRs

Answer 19

• 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