BIOL 222 Lecture Notes - Lecture 21: Helicase, Dna Replication, Sigma Factor

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4 Nov 2016

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Outline: transcription in bacteria: structure of genes, bacterial promoter, rna polymerase structure and function, start and end of termination. Bacterial cell structure and transcript: bacteria have no nucleus, both transcription and translation occurs in the cytoplasm, dna more accessible to rna polymerase. Organization of bacterial genes: many bacterial genes are organized into operons. Transcribed into a single (polyeistronic) transcript: not all bacterial genes are in operons (most aren"t) Eukaryotes: operons = 2+ genes that have the same reg. sequence transcribed into a single mrna, monocistrinic = encodes one protein, polycistronic = encodes more than one protein. Promoters: recruit rna polymerase, identi ed by: Bacterial rna polymerase: 5 subunits (=core enzymes, sigma factor = necessary for recognition of promoter (helix-turn-helix motif, 5 subunits + sigma factor = holoenzyme. Sigma factors: different sigma factors turn on different sets of genes, sigma factors are named based on their size, some sigma factors can turn on only during stressful conditions.

Related Questions

1. There are viruses, called bacteriophage, that infectbacterial cells. Following viral entry, the cell begins tosynthesize viral DNA and viral proteins, leading to the productionof mature virus and the death of the bacterial cell. During thecourse of viral infection, transcription of bacterial genes isturned off so that transcription of viral genes predominates. Whichof the following is the most likely explanation for how the virusmanages to shift transcription from bacterial genes to its owngenes?

a. it synthesizes a viral RNA polymerase that recognizes onlyviral promoters

b. it synthesizes a viral DNA polymerase that recognizes onlyviral origins

c. it synthesizes a viral sigma subunit that directs thebacterial RNA polymerase to viral promoters

d. it has special viral ribosomes that only translate viralproteins

2. Unlike bacterial transcripts, eukaryotic RNA transcripts arechemically modified because:

a. Chemical groups help protect the mRNAs from degradation inthe eukaryotic cytoplasm, bacterial mRNAs are not degraded

b. Chemical groups facilitate the transport of eukaryotic RNAsfrom the nucleus to the cytoplasm, bacterial RNAs are synthesizedin the cytoplasm

c. Eukaryotic RNA polymerases cannot transcribe genes unlessthey are chemically modified, bacterial RNA polymerases transcribeunmodified genes

d. Transcripts in eukaryotic cells contain non coding regionsthat must be removed, bacterial transcripts contain only codingsequence

e. b and d

3. Termination of transcription in both E. coli and eukaryoticcells occurs because

a. there is a termination signal in the DNA following the genesequence.

b. there is a hairpin structure followed by a string of U

copperturtle968

1 DNA sequences found in introns provide [A] amino acid sequence information.

[B] regulatory information.
[C] no known useful information.

[D] structure for the gene.
[E] alternative DNA splicing possibilities.

3. The TATA box is a(n)
[A] sequence close to the promoter region of many genes.
[B] square-shaped sequence.
[C] enhancer consensus sequence.
[D] activator sequence necessary for proper translation.
[E] None of the above

5. Regarding genes and gene expression, which of the following is not a difference between prokaryotes and eukaryotes
[A] Eukaryotic DNA does not contain a TATA box close to the initiation site as does prokaryotic DNA.

[B] In eukaryotes, RNA polymerase requires

'transcription factors'or initiation.

[C] Prokaryotic genes are often grouped together in

operons.

[D] In eukaryotes, the regulation of several genes at once requires common control elements in each of the genes.
[E] There is a diversity of eukaryotic polymerases that is reflected in the diversity of eukaryotic promoters.

10) In eukaryotic cells, a repressor

[A] is made of DNA.
[B] binds to the enhancer region to block transcription. [

C] is located both upstream and downstream from the promoter.
[D] binds to the operator to block RNA polymerase.

[E] binds to a silencer to reduce transcription rates.

Coordinated regulation of genes in eukaryotic cells [A] is the result of positioning the same regulatory sequence in front of each gene.
[B] results from all of those genes being under the control of one promoter.

[C] occurs because related genes all have the same

operons.
[D] occurs because enhancers cause DNA to bend.

Which of the following is NOT characteristic of bacterial operons?

Question 20 options:

an operon may be switched "off" and "on" by concentrations of molecules in the cell

a single mRNA transcript from an operon encodes multiple polypeptides

enhancers and transcription factors play key roles in switching each gene of an operon "on" and "off"

genes within one operon have related functions

one promoter serves multiple genes

Suppose an individual is born into a population with a novel mutation. Is the new mutation an evolutionary change, and why?

Question 21 options:

	yes, because new mutations are always adaptive
	yes, because the appearance of a new genetic variant is a genetic change in a population
	no, because it is not a big enough change to count
	no, because most mutations are not adaptive
	no, because not enough individuals have the mutation for it to matter

BIOL 222 Lecture Notes - Lecture 21: Helicase, Dna Replication, Sigma Factor

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