10/22

Question 1

DNAPI 5’-3’ exonuclease activity:

Answer 1

DNAPI 5’-3’ exonuclease activity: used to remove the RNA primer and then it’s 5’-3’ polymerase activity replaces the RNA w DNA

Question 2

DNA ligase

Answer 2

DNA ligase: molecular glue. Seals nicks in between Okazaki fragments by enzymatically creating a phosphodiester bond btwn two adjacent bases. NOT an DNAP…cannot add bases

Question 3

Bloom syndrome

Answer 3

Bloom syndrome: defect in DNA ligase. Predisposition to cancer.

Question 4

Three mechanisms in place to ensure accuracy in replication:
1)
2)
3)

Answer 4

1) DNAPIII: has error rate of 1/100,000
2) DNA proofreading activity (3’-5’ exonuclease): 1/10,000,000
3) post replication DNA repair (DNAPII) 1/1 billion

Question 5

-
-

Answer 5

Eukaryotic DNA replication:

• many more origins
• more DNAPs
• slower rate of replication (due largely to the high levels of DNA packaging)

Question 6

What is the problem w replicating the ends of linear eukaryotic xsomes?

Answer 6

You lose a little bit of the ends of the linear xsomes w each round of DNA replication as a result of removing the RNA primer. The primer on the end cannot be replaced w DNA bc there is not a preexsisting 3’OH group that the DNAP can add bases to.

Question 7

Hayflick limit

Answer 7

Hayflick limit: the shrinkage of xsomes associated w cellular aging and programmed cell death

Question 8

The enzyme __________ fights back against shrinkage by binding to the ends of the xsomes and adding on tandem copies of the telomere repeat sequence.

Answer 8

The enzyme telomerase fights back against shrinkage by binding to the ends of the xsomes and adding on tandem copies of the telomere repeat sequence.

Question 9

Telomerase _____________ xsomes.

Answer 9

Telomerase elongates xsomes.

Question 10

Telomerase: ribonucleoprotein- has and RNA component and a protein component

Answer 10

Telomerase: ribonucleoprotein- has and RNA component and a protein component

Question 11

Telomerase is an _______ dependent DNA polymerase.

Answer 11

Telomerase is an RNA dependent DNA polymerase. Aka it uses its own RNA as a template to make DNA copy.

Question 12

Two types of DNA recombination:
1)
2)

Answer 12

1) homologous: common in germ lined cells in meiosis I
2) non-homologous: illegitimate recombination. Common in somatic cells
* widely accepted model is the Holliday model for homologous recombination

Question 13

The Holliday model
1)
2)
3)
4)
5)
6)

Answer 13

1) recognition and alignment
2) ssDNA breakage
3) crossing over and strand evasion
4) joining of ends by DNA ligase
5) branch migration and heteroduplex formation
6) cleavage and resolution

Question 14

Two possible resolution products for Holliday recombination:
1)
2)

Answer 14

1) horizontal: non crossover recombination, patched, on same linkage phase as parents
2) vertical: cross over recombination, spliced, opposite linkage phase

Question 15

What is DNA’s primary function?

Answer 15

DNA’s primary function is to store all genetic info in a stable form such that info is not lost when transmitted to daughter cells.

Question 16

DNA sequence is actually a code that….

Answer 16

DNA sequence is actually a code that when deciphered directs the assembly of amino acids into the formation of proteins.

Question 17

Although DNA stores the information, it is not the primary template used to direct the synthesis of proteins. It’s the _______.

Answer 17

It’s the mRNA that serves as the template for protein synthesis.

Question 18

__________________ describes the process of taking the stored info in DNA to direct the synthesis of proteins.

Answer 18

Gene expression describes the process of taking the stored info in DNA to direct the synthesis of proteins.

Question 19

Two main processes involved w gene expression:
1)
2)

Answer 19

1) transcription: the synthesis of mRNA from a DNA template to produce an mRNA molecule that is complimentary and anti parallel to the DNA template
2) translation: synthesis of a polypeptide from an mRNA template

Question 20

Transcription

Answer 20

Transcription: the synthesis of mRNA from a DNA template to produce an mRNA molecule that is complimentary and anti parallel to the DNA template

Question 21

Translation:

Answer 21

Translation: synthesis of a polypeptide from an mRNA template

Question 22

Central dogma of molecular biology: flow of genetic info w/in the cell

Answer 22

DNA -transcription—>mRNA-translation–>protein

         - DNA dep RNAPs.                               -ribosomes&tRNAs - DNA replication - DNA depen DNAPs: uses/copies DNA template

Question 23

Transcription:

Answer 23

Transcription: 5’-3’ synthesis of mRNA from a dsDNA template. Although the mRNA is transcribed from dsDNA, only ONE strand of the DNA serves as a template

Question 24

Finishing touches:
1)
2)

Answer 24

Finishing touches:

1) removal of RNA primer and replacement w DNA
2) joining of fragments, called Okazaki fragments, on lagging strand using enzyme DNA ligase