Bio 115 unit 4

1. In the process of translation, _____.
A) DNA is replicated
B) RNA is synthesized
C) proteins are synthesized
D) mRNA attaches to ribosomes

Proteins are synthesized

2. In the process of transcription, _____.
A) DNA is replicated
B) RNA is synthesized
C) proteins are synthesized
D) mRNA attaches to ribosomes

RNA is synthesized

3. According to the central dogma, what molecule should go in the blank? DNA → _____ → Proteins
A) mtDNA
B) rRNA
C) mRNA
D) tRNA

mRNA

4. Codons are part of the molecular structure of _____.
A) a protein
B) mRNA
C) tRNA
D) rRNA

mRNA

5. Once researchers identified DNA as the unit of inheritance, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. What is the mechanism of information transfer in eukarotes?
A) DNA from a single gene is replicated and transferred to the cytoplasm, where it serves as a template for protein synthesis.
B) Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.
C) Proteins transfer information from the nucleus to the ribosome, where protein synthesis takes place.
D) Transfer RNA takes information from DNA directly to a ribosome, where protein synthesis takes place.

Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.

6. Translation requires _____.
A) mRNA, tRNA, DNA, and rRNA
B) mRNA, DNA, and rRNA
C) mRNA, tRNA, and rRNA
D) mRNA, tRNA, and DNA

mRNA, tRNA and rRNA

7. A nonsense mutation in a gene _____.
A) changes an amino acid in the encoded protein
B) has no effect on the amino acid sequence of the encoded protein
C) introduces a premature stop codon into the mRNA
D) alters the reading frame of the mRNA

introduces a premature stop codon into the mRNA

8. The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in _____.
A) a base-pair substitution
B) a frameshift mutation
C) a polypeptide missing an amino acid
D) a nonsense mutation

a polypeptide missing an amino acid

9. How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene, and why? (1pt)

It might cause a different protein to be expressed due to the change of the amino acid sequence, causing the phenotype of the organism to change. One letter change can cause a completely different protein to be produced.

10. Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?
A) a deletion of a codon
B) a deletion of two nucleotides
C) a substitution of the third nucleotide in an ACC codon
D) a substitution of the first nucleotide of a GGG codon

A deletion of two nucleotides

11. What does it mean when we say that the genetic code is redundant and unambiguous? (2pts)

It means that all amino acids except methionene and tryptophan are coded by more than one codon and that a single codon never codes for more than one amino acid.

12. List the 3 distinct characteristics of the genetic code and explain why they are important. (3pts)

1) It is non-overlapping: once the ribosome locks onto the first codon, it then reads each separate codon one after another 2) The code is nearly universal: all codons specify the same amino acids in all organisms 3) The code is conservative: when several codons specify the same amino acid, the first two bases in those codons are most always identical

13. In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its cap and poly-A tail. Which of the following would you expect her to find?
A) The mRNA is quickly converted into a ribosomal subunit.
B) The cell adds a new poly-A tail to the mRNA.
C) The mRNA attaches to a ribosome and is translated, but more slowly.
D) The molecule is digested by enzymes because it is not protected at the 5′ end.

The molecule is digested by enzymes because it is not protected at the 5′ end

14. Which molecule or reaction supplies the energy for polymerization of nucleotides in the process of transcription?
A) the interaction between RNA polymerase and the promoter
B) the phosphate bonds in the nucleotide triphosphates that serve as substrates
C) the energy released when hydrogen bonds are broken as the DNA molecule is unwound
D) ATP only

The phosphate bonds in the nucleotide triphosphates that serve as substrates

15. What ensures that the correct amino acid is added during translation?
A) the anticodon of a properly formed aminoacyl tRNA
B) the methyl-guanosine cap of a properly modified mRNA
C) the poly-A tail of a properly modified mRNA
D) the twisting number of a properly supercoiled DNA

The anticodon of a properly formed aminoacyl tRNA

16. A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA, while a primary transcript in a prokaryotic cell is _____ the functional mRNA.
A)the same size as; smaller than
B)larger than; the same size as
C)larger than; smaller than
D)the same size as; larger than

Larger than; the same size as

17. Which of the following contradicts the one-gene, one-enzyme hypothesis?
A)A mutation in a single gene can result in a defective protein.
B)Alkaptonuria results when individuals lack a single enzyme involved in the catalysis of homogentisic acid.
C)Sickle-cell anemia results in defective hemoglobin.
D)A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally

A single antibody gene can code for different related proteins, depending on the splicing that takes place post transcriptionally

18. How does termination of translation take place?
A) The end of the mRNA molecule is reached.
B) A stop codon is reached.
C) The cap is reached.
D) The poly-A tail is reached

A stop codon is reached

19. Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?
A)Prokaryotic codons usually contain different bases than those of eukaryotes.
B)Prokaryotic codons usually specify different amino acids than those of eukaryotes.
C)The translation of codons is mediated by tRNAs in eukaryotes, but translation requires no intermediate molecules such as tRNAs in prokaryotes.
D)Codons are a nearly universal language among all organisms.

Codons are a nearly universal language among all organisms

20. Which of the following is the first event to take place in translation in eukaryotes?
A)elongation of the polypeptide
B)base pairing of activated methionine-tRNA to AUG of the messenger RNA
C)binding of the larger ribosomal subunit to smaller ribosomal subunits
D)covalent bonding between the first two amino acids
E)the small subunit of the ribosome recognizes and attaches to the cap of mRNA

The small subunit of the ribosome recognizes and attaches to the cap of mRNA

21. A particular triplet of bases in the template strand of DNA is 5′ AGT 3′. The corresponding codon for the mRNA transcribed is _____.
A) UCA
B) UGA
C) TCA
D) ACU

UCA

23. Which of the following levels of gene expression allows the most rapid response to environmental change?
A) transcriptional control
B) translational control
C) post-translational control
D) DNA control

Post translational control

24. The reason for differences in the sets of proteins expressed in a nerve and a pancreatic cell of the same individual is that nerve and pancreatic cells contain different _____.
A) genes
B) regulatory sequences
C) sets of regulatory proteins
D) promoters

Sets of regulatory proteins

25. In negative control, a gene is switched off when _____.
A) a kinase adds a phosphate to DNA
B) lactose is transported into the cell
C) a regulatory protein binds to DNA and shuts down transcription
D) a regulatory protein is removed from DNA and shuts down transcription

a regulatory protein binds to DNA and shuts down transcription

26. The trp repressor blocks transcription of the trp operon when the repressor _____.
A) binds to the inducer
B) binds to tryptophan
C) is not bound to tryptophan
D) is not bound to the operator

binds to tryptophan

27. Tumor-suppressor genes _____.
A) are frequently overexpressed in cancerous cells
B) are cancer-causing genes introduced into cells by viruses
C) encode proteins that help prevent uncontrolled cell growth
D) often encode proteins that stimulate the cell cycle

encode proteins that help prevent uncontrolled cell growth

28. Altering patterns of gene expression in prokaryotes would most likely serve an organism’s survival by _____.
A) organizing gene expression, so that genes are expressed in a given order
B) allowing each gene to be expressed an equal number of times
C) allowing an organism to adjust to changes in environmental conditions
D) allowing environmental changes to alter a prokaryote’s genome

allowing organisms to adjust to changes in environmental conditions

29. E. coli can alter its production of amino acids based on the availability of those amino acids in the environment. The trp repressor blocks transcription of the trp operon for producing the amino acid tryptophan when the repressor _____.
A) binds to the inducer
B) binds to tryptophan
C) is not bound to tryptophan
D) is not bound to the operator

…

30. Not long ago, it was believed that a count of the number of protein-coding genes would provide a count of the number of proteins produced in any given eukaryotic species. This is incorrect, largely due to the discovery of widespread _____.
A) chromatin condensation control
B) transcriptional control
C) alternative splicing
D) translational control

alternative splicing

31. Steroid hormones produce their effects in cells by _____.
A) activating key enzymes in metabolic pathways
B) activating translation of certain mRNAs
C) promoting the degradation of specific mRNAs
D) binding to intracellular receptors and promoting transcription of specific genes

binding to intracellular receptors and promoting transcription of specific genes

32. Imagine that you have set up a genetic screen to identify E. coli mutants that cannot metabolize the amino acid tryptophan for energy. Beginning with a master plate containing many colonies, you prepare replica plates on medium with glucose or tryptophan as the only energy source. You would look for colonies that _____.
A) cannot grow on either type of media
B) can grow on both types of media
C) can grow only on the plates with tryptophan
D) can grow only on the plates with glucose

can grow only on the plates with glucose

34. Compare and contrast transcription and DNA replication (2 ways they are similar, and 2 ways they are different). (2pts)

Similarities: Template-directed synthesis by polymerases in a 5′ to 3′ direction Differences: RNA polymerase doesn’t require a primer Sigma guides RNA polymerase to specific locations while transcription is happening

Explain the ‘central dogma’ of biology

DNA–transcription–>RNA–translation–>PROTEIN

Identify different types of mutations and how they can affect gene expression

Beneficial, Neutral, Deleterious

Explain the three possible mechanisms of gene expression regulation in prokaryotes

1) Transcriptional control: 2) Translational control: 3) Post-translational control:

Compare and contrast negative and positive control

Negative control causes transcription to stop due to repressor proteins; Positive control triggers transcriotion due to activator proteins and regulatory proteins.

Transcription

The process of copying hereditary information in DNA to RNA

Translation

The process of using the information in nucleic acid to synthesize proteins

Missense mutation

A point mutation that causes a change in the amino acid expression of the organism

Silent mutation

A point mutation that does not cause a change in the amino acid expression of the organism

Frameshift mutation

Addition or deletion of a codon that alters the meaning of all subsequent codons

Nonsense mutation

A point mutation that causes the expression of an amino acid to be changed to a stop codon

Initiation of Translation

Holoenzymes (RNA polymerase and sigma in bacteria; a combination of basal transcription factors) bind to promoters; DNA is separated and NTPs are added so that mRNA is polymerized and extended from the site of transcription.

Elongation of Translation

Prominent channels and grooves in the enzyme are filled

Termination of Transcription

RNA polymerase transcribes a DNA sequence that functions as a termination signal; a hairpin loop forms and causes the mRNA to separate from RNA polymerase

Intron

Portion of RNA that is spliced out because it doesn’t code for any information

Exon

Portion of RNA that is joined together after introns are spliced out; codes for necessary information

RNA processing

Happens in eukaryotic cell transcription; includes: 1) Addition of 5′ cap on mRNA 2) Splicing of introns 3) Addition of 3′ poly-A tail on mRNAs

Translational control

Allows the cell to quickly change which proteins are produced

Post-translational control

Folding: Sped up by "molecular chaperones" Chemical modifications: Chemical groups added in the Golgi and ER, alteration by enzymes

Compare and contrast transcription and translation

Transcription: -Synthesis of RNA -Uses genes as a template -Located in the nucleus Translation: -Synthesize proteins -Uses mRNA as a template -Located in the ribosomes

tRNA

It is the type of RNA that translates between mRNA and proteins. It has a specific hairpin loop structure, and at the end of one of the loops contains an anticodon that recognizes and decodes mRNA so that it can be made into proteins.

rRNA

The assembly plant where everything comes together to synthesize proteins from mRNA

Given the template strand: 5’AGT3′
What is the mRNA codon? What is the tRNA anticodon?

mRNA: 3’UCA5′ or 5’ACU3′ tRNA: 3’UGA5′

What does RNA polymerase do?

It synthesizes mRNA by catalyzing the reaction that cleaves off 2 phosphates and forms a phosphodiester bond between the 3′ end of the mRNA chain and the new ribonucleoside monophosphate.