Microbio Bacterial Genetics Week 4

The anticodon for asparagine is

AAU --> UUA

What is the bacterial "start codon"?

AUG

What molecule is the inducer for the negative regulation of the lac operon?

Allolactose

What is quorum sensing?

At a high density of bacteria, sufficient quantities of signaling molecules (autoinducers) are available for binding to the signaling receptors on the bacterial surface (Gram-positive bacteria) or in the cytoplasm (Gram-negative bacteria), and the quorum sensing genes that enable the bacteria to act as a population become activated.

What does the nuclear area of a bacterial cell contain?

CHROMOSOMES: contain the genes (hereditary info) PLASMIDS: conjugative plasmids (sex pili) & R factors (antibiotic resistance)

On average, RNA polymerase makes one error for every 10,000 nucleotides it incorporates in RNA. By contrast, only one base pair error remains for every ten billion base pairs during DNA replication. Explain why the accuracy of RNA transcription is not as critical as the accuracy of DNA replication.

DNA is the permanent repository of the genetic information of an organism, thus changes to the DNA result in permanent changes in the genetic code. RNA is a temporary copy of the genetic code, therefore errors in RNA do not have lasting effect.

Which enzyme is responsible for synthesizing the growing (new) daughter strand by reading the template strand and incorporating the appropriate nucleotide?

DNA polymerase

Why is deleting 1 nucleotide more detrimental than deleting 3 nucleotides?

Deleting 1 nucleotide results in frame shift mutations, resulting in a change of all amino acids translated beyond the deletion. Deleting 3 nucleotides results in only thedeletion of 1 amino acid

The sugar found in DNA is:

Deoxyribose

When does translation end?

Elongation continues until ribosome reaches stop codon and falls off mRNA, UAG, UGA, UAA

True/False: A silent mutation causes an amino acid change in the synthesized protein.

False

True/False: When many cells are present in a bacterial population, the concentration of signaling molecules is low.

False.

True/False: Repressors enhance transcription. Activators block transcription.

False; reverse is true

What can be found at the 5' end of a nucleic acid strand?

Free phosphate group

If there are equal concentrations of glucose and lactose in the environment outside of an E. coli cell, which will be transported in to use as an energy source?

Glucose

The strands of ds (double-stranded) DNA are:

Held together by H bonds; antiparallel

Which enzyme is responsible for separating the DNA during replication?

Helicase

The necessary ingredients for DNA synthesis can be mixed together in a test tube. The DNA polymerase is from Thermus aquaticus, and the template is from a human cell. The DNA synthesized would be most similar to which of the following?

Human DNA

What is the function of DNA?

Information storage 1. Replication 2. Expression: A. Transcription 3. Translation

Which of the following statements is correct?

Replication of a new DNA strand (daughter strand) occurs in the 5'3' direction & During replication, two new DNA strands are created (Both A and B are correct)

Which gene is turned off when it is not needed?

Repressed

Which of the following are possible outcomes of a base substitution?

Silent mutation, Missense mutation, Nonsense mutation (all)

What might happen if a mutation occurs in the promoter sequence of a gene such that a segment of the bases are deleted?

So how likely you will see no protein being made depends on how many regulatory sequences your promoter has and how big your deletion is.

The best definition of a gene is:

A segment of DNA that encodes a functional product, usually a protein

Agents in the environment that directly or indirectly bring about mutations are called

mutagens

What are some ways that chemicals can cause mutations in DNA?

nucleotide substitution, +/- of nucleotides, insertional inactivation

Making new copies of DNA from old copies of DNA is known as:

replication

How does the Ames test help to determine if a chemical is mutagenic?

use a petri dish which only allows mutants to grow and if many colonies, chemical is a powerful mutagen

Which of the following is the best definition for transcription?

The synthesis of a complementary strand of RNA from a DNA template

Could two mRNAs have different nucleotide sequences and yet code for the same protein? Explain.

Yes, different mRNA sequences can encode for the same protein but be different genetic sequences.

What molecule is the inducer for the POSITIVE regulation of the lac operon?

cAMP

False: nucleic acid strands are synthesized via hydrolysis

dehydration synthesis

Which of the following is NOT part of an operon?

(operator, gene, promoter) ORIGIN

Two daughter cells are most likely to inherit which one of the following from the parent cell? (why/why not for each) -a change in a nucleotide in mRNA -a change in a nucleotide in tRNA -a change in a nucleotide in rRNA -a change in a nucleotide in DNA -a change in a protein

-a change in a nucleotide in DNA

During replication, what would the correct sequence be for a newly synthesized strand, if the template strand read 5' G C A T T 3'

3' C G T A A 5'

During transcription what would the correct sequence be for a newly synthesized strand, if the template strand read 5' G C A T T 3'

3' C G U A A 5'

What is degeneracy?

64 possible codons; 20 amino acids

Which nucleotides pair together in DNA?

A & T -- C & G

Which nucleotides pair together in RNA?

A & U -- C & G

What is a mutation?

Mutations are random, inheritable changes in the sequence of DNA Mutations may be neutral, beneficial, or harmful Mutations are important because they are the ultimate source of genetic variability in a species -error by DNA polymerase, UV light, chemicals

The "building block" (molecular structural units) of nucleic acids are:

Nucleotides

DNA replication:

Occurs bidirectionally & Is semiconservative & Begins at the origin of replication (All of the above)

An enzyme that copies DNA to make a molecule of RNA is

RNA polymerase

When does transcription end?

RNA polymerase reaches terminator sequence

True/False: Bacteria are able to repair thymine dimers using energy from visible light.

True

True/False: most mutations are corrected by a repair system before being passed on as a mutation.

True

What mutagen causes thymine dimers?

Ultraviolet light

When does transcription begin?

When RNA polymerase binds to the promoter

When does translation begin?

When the ribosome locates the AUG codon

A sequence of nucleotides formed during replication of the lagging DNA strand is

an Okazaki fragment

What is the function of RNA primase?

enzyme that synthesizes short RNA sequences called primers, which serve as starting points for DNA synthesis

Erythromycin is used to treat microbial infections by binding to the front of the A site on the 50S subunit of a ribosome. What step in protein synthesis is inhibited by this drug? Will this drug affect the host's (human) cell? Why or why not? Will this drug be effective against bacteria, viruses* or both? (*remember that viruses are acellular; not made of cells and do not contain the cellular components that bacteria do)

erythromycin binds in front of the A site on the 50s subunit of the ribosome it inhibits aminoacyl translocation by interfering with the transfer of trna from a site to the p site therefore elongation of the polypeptide chain is inhibited; does not effect viruses because the single strands of DNA and RNA of viruses would not require unwinding of ssDNA for transcription and ssRNA already have mRNA for protein synthesis; does not effect host cell because acts specifically on bacterial ribosome

Under which of the following conditions will transcription of the lac operon occur?

lactose present/glucose absent

During replication, which strand is synthesized continuously (choose the most specific one)?

leading strand

Which of the following is involved in translation?

mRNA, tRNA, rRNA (all)

Use the following information to answer the questions below: Codon on mRNA and the corresponding amino acid AUG - methionine UAA - nonsense CCG - proline GCA - alanine AAG - lysine GUU - valine AAU - asparagine UGC - cysteine UCG, UCU - serine What is the sequence of amino acids coded for by the following DNA sequence: 3' T A C T T A G G C A G C

methionine - asparagine- proline- serine

Where is an anticodon located?

tRNA

Hydrogen bonds between complementary nucleotides are crucial to the structure of dsDNA because they hold the two strands together. Why couldn't the two strands be effectively linked by covalent bonds? What process(es) would this inhibit if they were?

the amont of energy required to separate covalently bonded strands, which would be necessary for transcription and replication, would be prohibitive