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Genetics > Exam 2 > Flashcards

Exam 2 Flashcards

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1
Q

In sea urchin, which is double stranded, 17.5% of the bases were shown to be cytosine What percentage of the bases would you expect to be adenine (A).

A

32.5%

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2
Q

The experiment by Avery, MacLeod, and McCarty ruled out which genetic material?

A

RNA and proteins

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3
Q

Negative control of transcription involves which of the following?

a. binding of a repressor protein to a regulatory DNA sequence to turn off transcription
b. Inactivation of an activator protein by binding an inhibitor to turn off transcription
c. Release of an activator protein from a regulatory DNA sequence to turn off transcription
d. Inactivation of a repressor protein by binding an inducer to turn off transcription

A

binding of a repressor protein to a regulatory DNA sequence to turn off transcription

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4
Q

During DNA replication, the leading and lagging strands differ in that

A

the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction

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5
Q

What polypeptide product would you expect from poly-A mRNA that is 15 adenosines in length?

A

a pp made up of 5 lysine amino acids

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6
Q

The first level of packaging of eukaryotic DNA involves proteins called

A

histones

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7
Q

Which condition will result in the greatest levels of transcription of the lac operon?

A

lactose present, glucose absent

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8
Q

Place the following events in the synthesis of a polypeptide in the proper order.

  • The large ribosomal subunit attaches to the small subunit, with the initiator tRNA in the P site.
  • An aminoacyl tRNA base pairs with the codon in the A site
  • A peptide bond forms
  • tRNAs translocate from the A site to the P site and from the P site to the E site.
  • A small amount of ribosomal subunit binds to an mRNA and an initiator tRNA
A
  1. An aminoacyl tRNA base pairs with the codon in the A site
  2. A small amount of ribosomal subunit binds to an mRNA and an initiator tRNA
  3. A peptide bond forms
  4. The large ribosomal subunit attaches to the small subunit, with the initiator tRNA in the P site.
  5. tRNAs translocate from the A site to the P site and from the P site to the E site.
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9
Q

A tRNA with the sequence 3-UAU-5 would base pair with which of the following codons?

A

5-AUA-3

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10
Q

The reaction that attaches an amino acid to a tRNA molecule is catalyzed by what group of enzymes?

A

aminoacyl-tRNA-synthetases

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11
Q

Although RNA is typically single stranded, some RNA molecules (such as tRNA) have regions of base pairing. What pairing is possible to A?

A

A-U

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12
Q

Which type of RNA is involved in the splicing of pre-mRNA molecules in eukaryotes?

A

snRNA

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13
Q

Which of the nucleotides found in a completed mRNA were not transcribed from the DNA sequence?

A

the A nucleotides in the poly A tail

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14
Q

The strands of DNA molecules can be separated by heating. It has been shown that AT base pairs are less thermostable than GC base pairs. What is the reason for this difference?

A

AT base pairs form 2 hydrogen bonds whereas GC pairs form 3 hydrogen bonds

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15
Q

The proofreading activity of DNA polymerase removes incorrect nucleotides from the ___end of a strand

A

3’

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16
Q

Peptidyl transferase activity covalently joins the growing polypeptide chain attached to the tRNA in the P site to the amino acid attached to the tRNA in the A site. This catalytic activity is associated with which ribosomal component?

A

the 23S rRNA

17
Q

Which of the following statements about siRNAs and miRNAs is false?

  • They both can cause cleavage and degradation of target mRNAs
  • They are both incorporated into the RISC complex
  • They both bind to target cellular mRNAs by complementary base pairing
  • They are both encoded by specific genes
A

-They are both encoded by specific genes

18
Q 
Which step in translation initiation is unique to eukaryotes?
scanning 
ribosome assembly
joining of the 60s
translocation
A

scanning

19
Q

In prokaryotes describe what happens to mRNA while RNA polymerase is synthesizing the mRNA from the template DNA strand of a protein coding gene.

A

mRNA is also translated at the same time because there is no compartmentalization in prokaryotic cell

20
Q

In eukaryotes, describe one specific thing that happens to the precursor mRNA while RNA polymerase II is synthesizing it from the template DNA strand of a protein coding gene.

A

the 5’cap is added, the polyA tail is added and the introns are removed

21
Q

Describe the effects of high glucose concentrations in a bacterial cell on transcription of the lac operon genes

A

If glucose levels are high there are lower levels of cAMP, so the transcription of the operon is not stimulated. The cell would rather produce energy from glucose than lactose.

22
Q

If you are producing a human protein in E. Coli and the mRNA strand is almost twice as long as you expected, why would this have happened?

A

E. coli does not have a spliceosome so mature RNA is never produced, the intron sequences would still be in the mRNA strand making it much longer than in humans.

23
Q

Early proposals regarding the genetic code considered the possibility that DNA served directly as the template for polypeptide synthesis. List one difficulty this system would pose in eukaryotes.

A

There would not be an opportunity to remove the introns, this would leave behind genetic information that is not needed and would not allow for genetic diversity.

24
Q

The Beta polypeptide chain of a hemoglobin is composed of 146 AAs what is the minimum number of nucleotides in a mature mRNA coding for this pp chain?

A

146X3= 438
- 3 for the stop codon
435

25
Q

Did the Hershey and chase experiment rule out the possibility that RNA is the genetic material of bacteriophage T2? Explain. If not how could you modify the experiment to show that DNA and not RNA is the genetic material of T2?

A

No, it distinguished between DNA and proteins, not RNA. I would tag the Uracil in the RNA to distinguish between DNA and RNA

26
Q

If single stranded binging proteins were not present during DNA replication what would you expect to happen?

A

The separated Single strands of DNA would try to reanneal or H bond to each other again, closing the replication fork and stopping DNA replication

27
Q

within a protein, certain amino acids are positively charged, some are negatively charged, some are nonpolar. If you knew that a DNA binding protein was recognizing the DNA backbone rather than the base sequences, which specific amino acids in the protein would be good candidates for interacting with the DNA?

A

The backbone of the DNA chain is negatively.

positively charged polar amino acids

Genetics (8 decks)

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