Microbiology Chapter 8 Flashcards

Questions and Answers

What is genetics?

The study of what genes are, how they carry information, how information is expressed, and how genes are replicated.

Define a gene.

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

What is a genome?

All the genetic material in a cell.

Define genomics.

The molecular study of genomes. Signup and view all the answers

What is a genotype?

The genes of an organism. Signup and view all the answers

What is a phenotype?

Expression of the genes. Signup and view all the answers

What is genetic information expression?

Genetic information is used within a cell to produce the proteins needed for the cell to function. Signup and view all the answers

Define genetic information recombination.

Genetic information can be transferred between cells of the same generation. Signup and view all the answers

What is genetic information replication?

Genetic information can be transferred between generations of cells. Signup and view all the answers

What is semi-conservative DNA synthesis?

Half old and half new. Signup and view all the answers

Define transcription.

Synthesis of a complementary strand of RNA from the code found in DNA. Signup and view all the answers

What does transcription require?

RNA nucleotides and the enzyme RNA polymerase. Signup and view all the answers

What are repressible enzymes?

Enzymes that assist in the process by which a protein can stop the synthesis of another protein. Signup and view all the answers

What are inducible enzymes?

Enzymes that assist in the process of the inducer that causes transcription of specific genes. Signup and view all the answers

Define translation.

The conversion of the DNA codes from protein production into the protein. Signup and view all the answers

MRNA is translated in ____.

codons (three nucleotides). Signup and view all the answers

What is degeneracy in genetics?

Alternative codons for most amino acids provides coverage against possible mutation. Signup and view all the answers

Translation of mRNA begins at the __:.

start codon: AUG. Signup and view all the answers

Translation of mRNA ends as __:.

nonsense codons: UAA, UAG, UGA. Signup and view all the answers

What is the genetic code?

64 sense codons on mRNA encode the 20 amino acids. Signup and view all the answers

Define tRNA.

Carries the complementary anticodon; complementary to a codon; base-pairs with its associated codon. Signup and view all the answers

What is the site of translation?

The ribosome of RNA. Signup and view all the answers

____ direct the building of tRNA and mRNA codon.

Ribosomes. Signup and view all the answers

What starts the protein synthesis?

When the start codon is released from the ribosome unit and then additional RNA units attach. Signup and view all the answers

When can prokaryotic cells start translation?

Prior to the completion of transcription. Signup and view all the answers

Where is mRNA transcribed in eukaryotes?

In the cytoplasm rather than the nucleus. Signup and view all the answers

When are start codons exposed?

Even before the remaining codons are completed. Signup and view all the answers

For what are enzymes needed?

Practically all cell metabolism; some to a greater extent than others. Signup and view all the answers

What are constitutive enzymes?

Enzymes expressed at a fixed rate with genes turned on continuously. Signup and view all the answers

Define catabolite repression.

Inhibits the use of alternative carbon sources when glucose is available. Signup and view all the answers

What is an operon?

In bacteria, a group of coordinately regulated structural genes with related metabolic functions. Signup and view all the answers

In the operon model for an inducible system, what does a regulatory gene code for?

The repressor protein. Signup and view all the answers

What happens when the inducer is absent in an operon?

The repressor binds to the operator, and no mRNA is synthesized. Signup and view all the answers

What happens when the inducer is present in an operon?

It binds to the repressor so that it cannot bind to the operator. Signup and view all the answers

Define mutation.

A change in genetic material; may be neutral, beneficial or harmful. Signup and view all the answers

What is a mutagen?

An agent that causes mutation or permanent change in DNA. Signup and view all the answers

What is a spontaneous mutation?

Mutation that occurs in the absence of a mutagen. Signup and view all the answers

Define missense mutation.

Alteration in DNA that causes amino acid substitutions. Signup and view all the answers

What is a nonsense mutation?

A stop codon is created in the midst of synthesis. Signup and view all the answers

Define frameshift mutation.

Insertion or deletion of one or more nucleotide pairs. Signup and view all the answers

Give examples of mutations.

Resistance to antibiotics or altered pathogenicity. Signup and view all the answers

What is a mutation rate?

The probability that a gene will mutate when a cell divides. Signup and view all the answers

What is the spontaneous mutation rate?

1 in 10^9 replicated base pairs or 1 in 10^6 replicated genes. Signup and view all the answers

Mutagens increase the mutation rate to what values per replicated gene?

10^-5 or 10^-4. Signup and view all the answers

How do mutations occur?

Randomly along a chromosome. Signup and view all the answers

What is a low rate of spontaneous mutation beneficial for?

Providing the genetic diversity needed for evolution. Signup and view all the answers

What are chemical mutagens?

Include base-pair mutagens, nucleoside analogs, and frameshift mutagens. Signup and view all the answers

What are the effects of ionizing radiation on mutation?

Causes the formation of ions and free radicals that react with DNA, leading to mutations. Signup and view all the answers

What are the effects of ultraviolet (UV) radiation on mutation?

Causes bonding between adjacent thymines; damage can be repaired. Signup and view all the answers

Define nucleotide excision repair.

Enzymes cut out and replace the damaged portion of DNA. Signup and view all the answers

What is light repair?

Enzyme repairs thymine dimers in the presence of visible light. Signup and view all the answers

How can mutations be detected?

By selecting or testing for an altered phenotype. Signup and view all the answers

What is positive selection?

Involves the selection of mutant cells and rejection of nonmutated cells. Signup and view all the answers

Define replica plating.

Used for negative selection; detects cells that have nutritional requirements not possessed by the parent. Signup and view all the answers

What is positive (direct) selection?

Detects mutant cells because they grow or appear different. Signup and view all the answers

What is negative (indirect) selection?

Detects mutant cells because they do not grow differently. Signup and view all the answers

What is the Ames test?

A non-expensive and rapid test for identifying possible chemical carcinogens. Signup and view all the answers

Define vertical gene transfer.

Occurs during reproduction between generations of cells. Signup and view all the answers

What is horizontal gene transfer?

The transfer of genes between cells of the same generation. Signup and view all the answers

Define genetic recombination.

Rearrangement of genes from separate groups of genes. Signup and view all the answers

What is a recombinant?

The resultant cell when some of the donor's DNA has been integrated into the recipient's DNA. Signup and view all the answers

What is transformation vs recombination?

Transformation involves no cell-to-cell contact; recombination uses plasmid. Signup and view all the answers

What is conjugation?

A process that requires contact between living cells. Signup and view all the answers

What type of cells are F+ and F-?

F+ cells are genetic donor cells; recipient cells are F-. Signup and view all the answers

What happens when a plasmid becomes incorporated into the chromosome?

The cell is called an Hfr (high frequency of recombination) cell. Signup and view all the answers

What can an Hfr cell do during conjugation?

Transfer chromosomal DNA to an F- cell. Signup and view all the answers

Define transduction.

The DNA is passed from one bacterium to another in a bacteriophage. Signup and view all the answers

What are plasmids?

Self-replicating circular molecules of DNA carrying genes that are not usually essential for cell survival. Signup and view all the answers

What are the types of plasmids?

Conjugative plasmids, dissimilation plasmids, bacteriocins, and resistance factors. Signup and view all the answers

Define transposons.

Jumping genes; small segments of DNA that can move from one region of a DNA molecule to another. Signup and view all the answers

What are insertion sequences (IS)?

Simplest transposons; they contain only a gene that codes for an enzyme transposase. Signup and view all the answers

What are complex transposons?

Transposons that carry other genes not connected with the transposition process. Signup and view all the answers

Why can transposons spread between cells?

They may be carried between cells on plasmids or viruses. Signup and view all the answers

Study Notes

Genetics Overview

Genetics is the study of genes, their information storage, expression, and replication.
A gene is a DNA segment encoding functional products, primarily proteins.
The genome includes all genetic material within a cell.
Genomics focuses on the molecular analysis of genomes.

Genetic Concepts

Genotype refers to the genetic makeup of an organism, while phenotype is the observable expression of these genes.
Genetic information is expressed through protein production needed for cell function.
Recombination allows genetic information transfer between cells during the same generation.
Replication ensures genetic information is passed between generations.

Transcription and Translation

Transcription is the process of synthesizing RNA from DNA, involving RNA polymerase and starting at the promoter.
mRNA is translated in codons, with a total of 64 combinations encoding 20 amino acids.
Translation initiates at the start codon (AUG) and terminates at nonsense codons (UAA, UAG, UGA).
tRNA carries anticodons complementary to mRNA codons and plays a vital role in translation.
Ribosomes act as the site for translation, assembling proteins by decoding mRNA.

Regulatory Enzymes and Operons

Repressible enzymes stop protein synthesis when excessive material is present, while inducible enzymes initiate transcription upon activation.
A catabolite repression inhibits the use of alternative carbon sources when glucose is available.
The operon model describes groups of structurally related genes regulated together, including promoter and operator cites.
The presence of an inducer causes the repressor to detach from the operator, leading to mRNA synthesis.

Mutation and Its Effects

Mutation refers to changes in genetic material, which can be neutral, beneficial, or harmful.
Mutagens are agents that directly cause mutations, while spontaneous mutations occur without mutagen involvement.
Various types of mutations include missense (amino acid substitution), nonsense (premature stop codon), and frameshift (insertion or deletion of nucleotides).
The mutation rate is the probability a gene will mutate during cell division, represented as a negative exponent.

Mutation Detection and Selection

Positive selection identifies mutant cells that grow or differ visibly, while negative selection detects mutants that fail to grow.
The Ames test is a method for screening potential chemical carcinogens based on the reversion of mutant cells.

Gene Transfer Mechanisms

Vertical gene transfer occurs during reproduction, passing genes to offspring.
Horizontal gene transfer involves gene exchange between cells of the same generation, enhancing genetic diversity.
Transformation involves DNA uptake without cell contact, while conjugation requires direct contact between living cells.
Transduction is the gene transfer mediated by bacteriophages, incorporating DNA into recipient bacteria.

Plasmids and Transposons

Plasmids are self-replicating circular DNA molecules with genes that are typically non-essential for survival.
Types of plasmids include conjugative, dissimilation, bacteriocin, and resistance factors.
Transposons, or jumping genes, can move across DNA regions, facilitating gene transfer between chromosomes and organisms.

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Dive into the essential terms of Microbiology with this Chapter 8 flashcard quiz. Each card explores pivotal concepts in genetics, from the definition of genes to the complete genetic makeup of an organism. Perfect for students looking to reinforce their understanding of genetic principles.