Chapter 11 microbiology

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Questions and Answers

Which base pairs with adenine in the DNA structure?

Cytosine

Guanine

Uracil

Thymine (correct)

What direction does DNA replication occur?

5’ to 3’ (correct)

2’ to 3’

3’ to 5’

No specific direction

Which of the following statements is true about DNA strands?

DNA strands can be interconnected

The 3’ end of one strand is opposite the 5’ end of the other strand (correct)

Strand orientation does not affect replication

Both strands are parallel

What is the function of primase in DNA replication?

To synthesize RNA primers Signup and view all the answers

Which term describes the method of DNA replication?

Semiconservative Signup and view all the answers

What role does DNA helicase play in DNA replication?

It unwinds the DNA strands Signup and view all the answers

Which protein is primarily responsible for adding DNA nucleotides during elongation?

DNA polymerase Signup and view all the answers

Which protein is responsible for reducing supercoiling ahead of the replication fork?

Topoisomerase Signup and view all the answers

What is the role of aminoacyl tRNA synthetase in translation?

It charges tRNA with the appropriate amino acid. Signup and view all the answers

What happens at the P site of the ribosome during translation?

The growing amino acid chain is held by tRNA. Signup and view all the answers

Which site requires energy for the translocation of tRNA?

E site Signup and view all the answers

During translation initiation, which component binds to the start codon AUG?

Charged tRNA Signup and view all the answers

Which statement is true about the elongation phase of translation?

Energy is not required for tRNA binding. Signup and view all the answers

Which of the following correctly describes the exit (E) site of the ribosome?

Newly-uncharged tRNA is released from this site. Signup and view all the answers

How many main steps are involved in the translation process?

Three Signup and view all the answers

What feature of ribosomes helps facilitate the binding of charged tRNA during elongation?

Ribosomal RNA's catalytic properties Signup and view all the answers

Which method of horizontal gene transfer is primarily used by researchers to alter bacterial genomes?

Transposition Signup and view all the answers

What is the first step in the process of transcription?

Initiation Signup and view all the answers

Which of the following molecules is essential for the elongation phase of transcription?

RNA Polymerase Signup and view all the answers

During transcription, how many strands of RNA are synthesized from a DNA template?

One strand Signup and view all the answers

What is the process called when genes are expressed continuously without regulation?

Constitutive expression Signup and view all the answers

Which nucleotide triphosphate (NTP) is used during transcription instead of deoxyribonucleotide triphosphates (dNTPs)?

UTP Signup and view all the answers

Which strand of DNA serves as the template for mRNA synthesis during transcription?

Antisense strand Signup and view all the answers

What is the relationship between the template strand of DNA and the corresponding mRNA sequence?

Complementary sequences Signup and view all the answers

What effect does UV radiation have on DNA?

It causes thymine to bond with adjacent bases. Signup and view all the answers

Which repair mechanism involves the recognition and removal of mismatched base pairs?

Proofreading Signup and view all the answers

After mismatch repair (MMR), what is the rate of mistakes in new nucleotides?

1 error per 10^9 nucleotides Signup and view all the answers

What does the Ames Test measure?

The mutagenic potential of chemical compounds Signup and view all the answers

What is horizontal gene transfer (HGT)?

The absorption of a gene from one species into another's genome. Signup and view all the answers

Which of the following mutations leads to the formation of thymine dimers?

UV radiation Signup and view all the answers

What is the primary function of excision repair in DNA management?

To remove bulky lesions from DNA. Signup and view all the answers

In which organisms is horizontal gene transfer (HGT) especially common?

Microorganisms Signup and view all the answers

Under what conditions is the Lac Operon transcribed?

When lactose is present and glucose is absent. Signup and view all the answers

What occurs if sucrose-digesting structural genes are placed downstream of the Lac promoter?

They would be transcribed when lactose is present and glucose is absent. Signup and view all the answers

What is the role of reporter genes in genetic research?

To monitor transcriptional activity by performing a known function. Signup and view all the answers

Which of the following best describes how eukaryotic Pre-mRNA differs from prokaryotic mRNA?

Eukaryotic Pre-mRNA undergoes processing, while prokaryotic mRNA is translated directly. Signup and view all the answers

How do researchers manipulate genomes to create inducible systems?

By mixing and matching regulatory regions with structural genes. Signup and view all the answers

Which of the following is a famous reporter gene that causes fluorescence?

Green Fluorescent Protein Signup and view all the answers

What is the primary function of regulatory regions in operons?

To determine whether structural genes are transcribed. Signup and view all the answers

What characterizes the Central Dogma of molecular biology in prokaryotes and eukaryotes?

The same overall processes are involved, but the structures differ. Signup and view all the answers

Study Notes

Aminoacyl tRNA Synthetase

Each aminoacyl tRNA synthetase is specific to a single amino acid and tRNA
No other amino acid can bind to the synthetase
No other tRNA can bind to the synthetase

Ribosomes and Translation

Ribosomes are made up of two subunits, a large and a small subunit
The large subunit has three binding sites: the A site, the P site, and the E site
The A site binds to the anticodon of the charged tRNA
The P site binds to the tRNA holding the growing polypeptide chain
The E site is where the uncharged tRNA exits the ribosome

Translation

Translation involves three steps: initiation, elongation, and termination
Initiation requires a charged tRNA, a small ribosomal subunit, and an mRNA molecule
In prokaryotes, the small ribosomal subunit binds to the Shine-Dalgarno sequence on the mRNA
In eukaryotes, the small ribosomal subunit binds to the 5' cap of the mRNA
The start codon is AUG, which codes for methionine
The first tRNA always binds to the P site
Elongation requires energy, which is used to bring a new charged tRNA into the A site
The rRNA in the large subunit catalyzes the transfer of the growing polypeptide chain from the tRNA in the P site to the tRNA in the A site
Elongation does not require energy
The newly-uncharged tRNA translocates to the E site, while the tRNA with the growing polypeptide chain translocates to the P site
Elongation requires energy
Termination occurs when a stop codon is encountered, which signals the release of the polypeptide chain from the ribosome

DNA Replication

DNA replication is semi-conservative, meaning that each new DNA molecule contains one old strand and one new strand
DNA replication occurs in the 5' to 3' direction
DNA replication involves three steps: initiation, elongation, and termination
Initiation involves unwinding the double helix to create two template strands
Elongation involves the sequential addition of complementary nucleotides linked by phosphodiester bonds
Termination occurs when all regions of the DNA have been replicated
The origin of replication is the site where DNA replication begins
Prokaryotes have a single origin, while eukaryotes have multiple origins
Topoisomerase reduces supercoiling in the DNA
DNA helicase unwinds the DNA using energy from ATP hydrolysis
Single-strand binding proteins (SSBs) prevent the separated DNA strands from re-annealing
Primase synthesizes short RNA primers, which are required for DNA polymerase to initiate DNA synthesis
DNA polymerase is the main enzyme that catalyzes elongation of DNA
DNA polymerase has an active site for adding nucleotides and finger-like domains that recognize nucleotide bases

DNA Repair

DNA repair mechanisms are crucial for maintaining the integrity of the genome
Proofreading occurs during DNA replication where DNA polymerase recognizes mismatched pairs and removes incorrectly paired bases
Mismatch repair (MMR) involves other proteins scanning newly replicated DNA for mismatches and correcting them
Excision repair involves enzymes scanning DNA for bulky lesions, excising them, and replacing them with undamaged nucleotides
The Ames test uses bacteria to screen for carcinogenic potential of new chemical compounds.

Horizontal Gene Transfer

Horizontal gene transfer (HGT) involves the transfer of genes between organisms that are not directly related, such as through transformation, transduction, or conjugation
HGT is common in microorganisms, but less so in eukaryotes
HGT can make it difficult to determine evolutionary relationships between organisms

Gene Expression

Gene expression involves two steps: transcription and translation
Transcription copies a DNA sequence into a complementary RNA sequence
Translation uses the RNA sequence as a template to synthesize a polypeptide (protein) sequence
The central dogma of molecular biology describes how information flows from DNA to RNA to protein
Transcription is similar to DNA replication, but uses RNA polymerase instead of DNA polymerase
Transcription occurs in three steps: initiation, elongation, and termination
RNA polymerase needs the help of a sigma factor to bind to the DNA
Transcription involves the use of NTPs instead of dNTPs.
Transcription produces many different small mRNA molecules, unlike DNA replication which produces a single large DNA genome
Transcription does not require primers

Template and Non-Template Strands

The template strand of DNA is used as a base to build mRNA
The template strand is complementary to the mRNA sequence
The non-template strand is identical to the mRNA sequence (except it has T's instead of U's)
The non-template strand is not actually involved in transcription

Constitutive Expression

Constitutive expression is when genes are always expressed, or transcribed and translated, all the time
Some genes, such as those involved in energy production, are constitutively expressed
Not all genes are constitutively expressed

The Lac Operon

The Lac Operon is a group of genes that are involved in the metabolism of lactose
The lac operon is only transcribed when lactose is present and glucose is absent
The regulatory region of the lac operon controls whether or not the genes are transcribed
The structural genes of the lac operon are the genes that are actually transcribed
The lac operon is an example of an inducible system, which is a system where the expression of genes is controlled by an inducer

Reporter Genes

Reporter genes can be used to monitor the expression of other genes
Reporter genes are often designed to monitor transcription and are called transcriptional fusions or operon fusions
Examples of reporter genes include Green Fluorescent Protein, LacZ, Luciferase, and Red Fluorescent Protein

Eukaryotic Pre-mRNA Processing

Eukaryotic pre-mRNA transcripts are processed prior to translation
The overall Central Dogma works the same in prokaryotes and eukaryotes
There are differences in gene structure and whether or not the nucleus separates transcription and translation, between prokaryotes and eukaryotes

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