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BIOL 302 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

How fast does DNA replication occur (approximately)?

A

About 1,000 nucleotides per second

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2
Q

Finish the statement: Each DNA strand serves as a ______ for the newly formed daughter strand.

A

Template

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3
Q

Following DNA replication, what kinds of strands do you have?

A

A conserved strand and a newly synthesized strand (S strand)

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4
Q

DNA replication is _______.

A

Semi-conservative

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5
Q

T/F: The information contained in DNA is generally identical after each replication

A

True

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6
Q

Where does DNA replication begin in prokaryotes? How many origins of replication are there?

A

In one location. Replication continues around the circle until replication is complete.

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7
Q

How many origins of replications are there in eukaryotes? Why are there this many?

A

Up to 10,000. An increase in origins of replication serves as a mechanism for efficiency. Synthesis can occur simultaneously in many parts of the chromosome

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8
Q

How did Watson and Crick believe replication occur (in what manner)?

A

In a semiconservative manner.

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9
Q

What are the other ideas on how replication occurs? Explain them.

A

Dispersive replication. Certain parts of the chromosome are replicated and certain parts are maintained.

Fully conservative. Complete replication of the entire chromosome.

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10
Q

Which experiment proved that DNA is the genetic material? Explain the experiment.

A

Messelson and Stahl. Used stable isotopic nitrogen to evaluate heavy or light incorporation into bacterial cultures. They then isolated the cells and grew them in heavy nitrogen rich medium and light nitrogen (nitrogen 15 and 14). Using a cesium chloride density gradient, they were able to separate out the DNA from each environmental condition. They found the material was intermediate to the heavy and light form; this did not confirm semiconservative, as replication could be dispersive. Once the DNA was separated, they evaluate the weight of each strand, and found 1 was heavy and 1 was light, confirming semiconservative replication.

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11
Q

Why are regions of AT density more prone to be the region where DNA replication starts?

A

They are generally less dense in hydrogen bonds regions of GC density (AT has 2 H-bonds between them, GC has 3). They require less energy to break apart.

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12
Q

Detail the process of DNA replication.

A
  1. Regions of AT density open up, allowing a small primer to be inserted by RNA primase
  2. DNA polymerase attaches to the primer, initiating new synthesis of daughter DNA material
  3. Once DNA polymerase reaches an RNA primer, the RNA bases are degraded by nuclease
  4. A repair DNA polymerase comes in and continues to synthesize DNA compliment to the parent strand
  5. Fragments are joined by DNA ligase
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13
Q

Because there is a leading and lagging strand, replication is known to be _______.

A

Discontinuous

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14
Q

What does the lagging strand consist of?

A

Okazaki fragments

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15
Q

How does DNA polymerase proofread?

A

There should always a purine bound to a pyrimidine. The location of hydrogen bonding serves as a first check (molecular distance)

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16
Q

How much does proofreading reduce the occurrence of errors in DNA replication?

A

Errors occur about once every 10^9 placements.

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17
Q

What unwinds the genome?

A

DNA helicase

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18
Q

What is the function of helicase (what does it prevent)?

A

It prevents supercoiling

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19
Q

DNA primase inserts (DNA, RNA) nucleotides so polymerase can start in that location

A

RNA

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20
Q

What is the function of single-stranded DNA-binding protein?

A

Enhances the lengthening or straightening of material that needs to be replicated

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21
Q

In eukaryotic chromosomes, what region does not get completely replicated?

A

The telomeres

22
Q

Explain the function of telomerase.

A

Telomerase has an RNA template that will allow for the addition of new deoxyribose nucleotides to the end of the eukaryotic chromosome

23
Q

Telomerase adds what kinds of sequences?

A

Short lengths of repeated sequences.

24
Q

What is the short length of nucleotides that is repeated and extended off the end of the eukaryotic chromosome?

A

GGGTTA

25
Q

What is the significance of incorrect nucleotide insertion?

A

It can lead to altered protein structure. Disease like sickle cell can arise

26
Q

STRUCTURE DICATES _______

A

FUNCTION

27
Q

What is the Central Dogma?

A

DNA is replicated to make more DNA, then transcribed into RNA (mRNA, rRNA, tRNA), which is then translated into a protein (translated from nucleic acid into an amino acid language)

28
Q

At what step are mutations more likely to occur? DNA replication, transcription, or translation?

A

DNA replication. Mutations in mRNA are shorter-lived, less significant

29
Q

Mutations are often _________.

A

Spontaneous

30
Q

Mutations are often the result of __________.

A

Environmental factors

31
Q

Mutations within DNA often do what?

A

Change the structure of the nitrogenous base.

32
Q

What are 3 major kinds of mutation? Explain each.

A
  1. Depurination. The entire nitrogenous base is removed from the purine. Completely erases any sort of chemical information about that nucleotide, all that’s left is a sugar and phosphate backbone
  2. Deamination. The nitrogenous base goes through a removal of an amine group, changing the structure (cytosine → uracil after deamination)
  3. Thymine dimers. After exposure to UV radiation, adjacent pyrimidines (primarily thymines) may undergo spontaneous dimerization
33
Q

What is the significance of a spontaneous thymine dimerization?

A

The polymerase reads the dimer as a single nucleotide (instead of ATTAT, polymerase would read ATAT)

34
Q

When DNA damage exists but is only slight, damage can be identified and removed with _______ and _________ will go down the chromosome to be placed in the gap.

A

Nuclease, a secondary repair polymerase

35
Q

How can a single nucleotide error be easily corrected?

A

Using template information

36
Q

What are the 2 kinds of large scale repair?

A
  1. Non-homologous end-joining

2. Homologous recombination

37
Q

Why is a double strand break very problematic?

A

Nucleases present in the cell have the opportunity to easily degrade the exposed nucleotides that are essential to cell function

38
Q

Which method of large scale repair is known as the “quick and dirty” method of repair? Explain why.

A

Non-homologous end joining. The ends of DNA are processed by nuclease, and the ends are joined by DNA ligase. The break is repaired with some loss of nucleotides at the repair site. Could be a significant loss of nucleotides.

39
Q

Explain why homologous recombination is the preferred method of double stranded break repair.

A

When a homologous chromosome is nearby, the homologous chromosome can serve as the template to repair the break. Broken ends are processed by a special nuclease. The break is accurately repaired using undamaged DNA as a template. Break is repaired with only slight loss of nucleotides at the repair site.

40
Q

A consequence of homologous recombination is possible _________.

A

Loss of genetic variability.

41
Q

What are the 3 kinds of polymerases present in eukaryotes?

A

Pol I, Pol II, and Pol III

42
Q

What is the system by which prokaryotes express genes?

A

Operons

43
Q

Define an operon.

A

A series of related genes that are controlled and expressed together. All the genes form proteins that are significant for the same function.

44
Q

In prokaryotes, what directs the synthesis of multiple proteins?

A

The mRNA transcript.

45
Q

Is there any modification of the mRNA transcript in prokaryotes? Explain why or why not.

A

No. The mRNA transcripts are extremely short-lived (between 2-5 minutes). They are only synthesized when the proteins synthesized by those genes are necessary for the cell at that moment.

46
Q

Where does transcription occur in prokaryotes?

A

In the cytoplasm.

47
Q

Where does transcription occur in eukaryotes?

A

In the nucleus.

48
Q

Explain the beginning of transcription in eukaryotes, describing the order of each transcription factor.

A
  1. Transcription factor 2D attaches after an AT dense region called the TATA box
  2. TF2B comes and binds to TF2D
  3. Transcription starts downstream of these transcription factors
49
Q

In eukaryotes, nothing begins until what happens?

A

The RNA polymerase becomes phosphorylated.

50
Q

What happens when RNA polymerase is phosphorylated?

A

When the tail is phosphorylated, the structure of the RNA polymerase changes, and the polymerase begins transcribing.

BIOL 302 (2 decks)

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