Exam 3: Chapter 8 & 15

What is the definition of genetics?

Genetics is the science of heredity; it studies genes, how they carry information, how they replicate, and how that information is expressed.

Describe DNA replication.

DNA replication is the process in which one parental DNA molecule is copied to produce two identical daughter DNA molecules. The DNA strands separate, each original strand acts as a template, and complementary nucleotides are added to form new strands.

What does transcription do?

Transcription produces mRNA by copying DNA information into a complementary RNA strand.

What does RNA use instead of thymine?

RNA uses uracil (U) instead of thymine (T).

What is initiation in transcription?

Initiation is the beginning of the gene, where RNA polymerase binds to the promoter and starts RNA synthesis.

What is elongation in transcription?

Elongation is the growing mRNA stage, where RNA nucleotides are added to lengthen the RNA strand.

What is termination in transcription?

Termination is the end of the gene, where RNA polymerase reaches the terminator and releases the completed mRNA strand.

What is the role of the promoter?

The promoter is the DNA region where transcription begins; it is where RNA polymerase binds.

What is the role of the terminator?

The terminator is the DNA sequence that signals the end of transcription.

What is the role of mRNA?

mRNA carries the genetic message copied from DNA to the ribosome for protein synthesis.

What does translation do?

Translation produces proteins by using the mRNA message to build an amino acid chain.

What is initiation in translation?

Initiation is the beginning of protein synthesis, when the ribosome attaches to mRNA and the first amino acid is added.

What is elongation in translation?

Elongation is the lengthening of the amino acid sequence as amino acids are added one by one.

What is termination in translation?

Termination is the end of the amino acid sequence and completion of the protein.

Where does translation occur?

Translation occurs at the ribosome in the cytoplasm.

What is a codon?

A codon is a sequence of three mRNA nucleotides that codes for one amino acid.

What is the genetic code?

The genetic code is the set of rules that determines how codons specify amino acids.

What is the start signal in the genetic code?

The start signal is AUG, which codes for methionine.

What are the stop signals?

The stop codons are UAA, UAG, and UGA.

How does mRNA production in eukaryotes differ from the process in prokaryotes?

In eukaryotes, transcription occurs in the nucleus and the mRNA is processed before leaving the nucleus. In prokaryotes, transcription occurs in the cytoplasm and translation can begin before transcription is finished.

What are introns and exons?

Introns are noncoding regions removed from pre-mRNA, while exons are coding regions that remain and are joined together.

What is gene expression?

Gene expression is the process by which the information in DNA is used to make a functional product, usually a protein, through transcription and translation.

What are constitutive genes?

Genes that are always turned on and continuously expressed at a fixed rate because the cell always needs their products.

What are non-constitutive genes?

Non-constitutive genes are genes that are not always active and are turned on or off depending on the cell’s needs and environmental conditions.

What is the difference between constitutive and non-constitutive genes?

Constitutive genes are expressed all the time, while non-constitutive genes are regulated and expressed only when needed.

In pre-transcriptional control, what does repression mean?

Repression means to turn off transcription, preventing mRNA from being made.

In pre-transcriptional control, what does induction mean?

Induction means to turn on transcription, allowing mRNA to be made.

What is a repressor?

A repressor is a protein that binds to DNA, usually the operator, to block RNA polymerase and stop transcription.

What is an inducer?

An inducer is a molecule that inactivates the repressor, allowing transcription to occur.

What is an operon?

An operon is a group of genes that are transcribed together and controlled by the same promoter and operator.

What is the role of the regulatory gene in an operon system?

The regulatory gene codes for the repressor protein that controls whether the operon is on or off.

What is the role of the promoter in an operon?

The promoter is the site where RNA polymerase binds to begin transcription.

What is the role of the operator in an operon?

The operator is the DNA region where the repressor binds to control transcription.

What happens in the lac operon when lactose is absent?

The repressor binds to the operator and transcription is turned off.

What happens in the lac operon when lactose is present?

Lactose (allolactose) binds the repressor, making it inactive, so transcription is turned on.

Is the lac operon inducible or repressible?

The lac operon is an inducible operon because it is normally off and turns on when lactose is present.

What genes are produced in the lac operon?

The lac operon produces enzymes needed for lactose metabolism, including β-galactosidase, permease, and transacetylase.

What happens in the trp operon when tryptophan is absent?

The repressor remains inactive, so transcription is turned on and tryptophan synthesis enzymes are produced.

What happens in the trp operon when tryptophan is present?

Tryptophan acts as a corepressor, activating the repressor, which binds the operator and turns transcription off.

Is the trp operon inducible or repressible?

The trp operon is a repressible operon because it is normally on and turns off when tryptophan is present.

What is the role of cAMP in regulating gene expression?

cAMP binds to CAP (catabolite activator protein) and helps RNA polymerase bind more effectively to the promoter, increasing transcription.

What is positive regulation by cAMP?

Positive regulation by cAMP occurs when low glucose causes high cAMP levels, allowing CAP-cAMP to activate transcription, especially in the lac operon.

What happens to cAMP levels when glucose is high?

When glucose is high, cAMP levels are low, so CAP cannot activate transcription.

What happens to cAMP levels when glucose is low?

When glucose is low, cAMP levels are high, which promotes transcription of alternative sugar metabolism genes.

Is a mutation always a negative event?

No. A mutation is not always negative. Some mutations are harmful, some are neutral, and some can be beneficial.

What is the molecular definition of a mutation?

A mutation is a change in the nucleotide sequence of DNA.

Why can mutations have different effects?

Because a change in DNA may alter a protein, have no effect, or create a new trait depending on where the mutation occurs.

What is a human example of a harmful mutation?

Sickle cell anemia is a harmful mutation in which a change in the hemoglobin gene causes red blood cells to become sickle-shaped.

How are people expressing sickle cell mutation different from those who do not express it?

They may have abnormally shaped red blood cells, reduced oxygen transport, pain crises, and anemia.

Is the sickle cell mutation harmful, beneficial, or neither?

It can be harmful, but in some environments it can also be beneficial because it provides resistance to malaria.

What is a base substitution mutation?

A base substitution is when one nucleotide is replaced by another nucleotide.

What is a missense mutation?

A missense mutation is a base substitution that changes one amino acid in the protein.

Why can missense mutations affect protein function?

Because changing one amino acid may alter the shape or function of the protein.

What is a nonsense mutation?

A nonsense mutation is a base substitution that changes a codon into a stop codon, causing protein synthesis to end early.

What happens to proteins made from nonsense mutations?

They are usually shortened and often nonfunctional.

What is a frameshift mutation?

A frameshift mutation is caused by the insertion or deletion of nucleotides, shifting the reading frame of the genetic code.

Why are frameshift mutations usually severe?

Because they change every codon after the mutation site, often drastically changing the protein.

How can a mutation be beneficial?

A mutation can be beneficial if it gives an organism a survival advantage, such as resistance to disease, antibiotics, or environmental stress.

How can mutations be repaired?

Mutations can be repaired by DNA repair enzymes that detect and correct damaged or mismatched nucleotides.

What is the role of DNA repair enzymes?

They help maintain DNA integrity by fixing errors caused during replication or by mutagens.

How do mutagens affect the mutation rate?

Mutagens increase the frequency of mutations by damaging DNA or causing errors in replication.

What are mutagens?

Mutagens are physical or chemical agents that induce mutations.

How can chemicals act as mutagens?

Chemicals can damage DNA bases or interfere with DNA replication, increasing mutation rate.

Why do chemical products often include safety guidelines?

Because some chemicals can be mutagenic and harmful to cells.

How does radiation act as a mutagen?

It causes DNA strand breaks and base damage.

Why do dentists place an apron over your torso during X-rays?

To reduce radiation exposure and protect tissues from DNA damage.

How does UV light act as a mutagen?

UV light damages DNA by causing abnormal bonds between adjacent bases, such as thymine dimers.

Why is sunblock recommended?

Because it helps protect skin cells from UV-induced DNA mutations.

Can mutagens affect organisms other than humans?

Yes. Mutagens can affect all living organisms, including bacteria and other microbes.

What is meant by the frequency of mutation?

The frequency of mutation is how often mutations occur within a population or DNA sequence.

What increases the frequency of mutation?

Exposure to mutagens and errors during DNA replication increase mutation frequency.

What is genetic recombination?

Genetic recombination is the exchange of genes between DNA molecules to form new combinations of genes.

Why is genetic recombination important in bacteria?

It allows bacteria to acquire new genes for traits they do not already have, such as antibiotic resistance or the ability to metabolize new substances.

What are plasmids?

Plasmids are small, circular fragments of DNA that exist outside the bacterial chromosome and can replicate independently.

How are plasmids transferred between bacteria?

Plasmids are commonly transferred through conjugation using a conjugation pilus (sex pilus).

What types of genes do plasmids carry?

Plasmids may carry genes for antibiotic resistance, heavy metal resistance, toxin production, bacteriocin production, attachment factors, metabolic enzymes, and conjugation functions.

What is vertical gene transfer?

Vertical gene transfer is the passing of genes from parent cells to offspring during reproduction.

What is an example of vertical gene transfer?

A bacterial cell dividing by binary fission and passing its chromosome to daughter cells.

What is horizontal gene transfer?

Horizontal gene transfer is the transfer of genes between cells of the same generation rather than from parent to offspring.

What are the three major types of horizontal gene transfer?

Transformation, conjugation, and transduction.

What is the main difference between vertical and horizontal gene transfer?

Vertical transfer is parent to offspring, while horizontal transfer is between unrelated cells of the same generation.

What are transposons?

Transposons are small segments of DNA that can move from one location in DNA to another.

Why are transposons sometimes called “jumping genes”?

Because they can move within a chromosome, between plasmids, or from one DNA molecule to another.

What enzyme is involved in transposon movement?

Transposase.

What is transformation in bacteria?

Transformation is the transfer of naked DNA from one bacterium to another.

Who first demonstrated bacterial transformation?

Frederick Griffith in 1928.

What organism did Griffith use in his experiment?

Streptococcus pneumoniae.

What happened when Griffith injected live encapsulated bacteria into mice?

The mice died.

What happened when Griffith injected live nonencapsulated bacteria into mice?

The mice remained healthy.

What happened when Griffith injected heat-killed encapsulated bacteria into mice?

The mice remained healthy.

What happened when Griffith injected live nonencapsulated bacteria mixed with heat-killed encapsulated bacteria?

The mice died, and living encapsulated bacteria were recovered.

What did Griffith conclude from his experiment?

Some hereditary material from the dead encapsulated bacteria transformed the live nonencapsulated bacteria.

What is conjugation?

Conjugation is the direct transfer of genetic material from one bacterial cell to another through direct cell-to-cell contact.

What structure is used during conjugation?

A sex pilus (conjugation pilus).

What genetic material is usually transferred during conjugation?

Usually plasmids, especially the F factor plasmid.

What is an F⁺ cell?

A bacterial cell that contains the fertility factor (F plasmid).

What is an F⁻ cell?

A bacterial cell that lacks the F plasmid.

What happens when an F⁺ cell conjugates with an F⁻ cell?

The F plasmid is copied and transferred, converting the F⁻ cell into an F⁺ cell.

What is an Hfr cell?

A cell in which the F factor has become integrated into the bacterial chromosome.

What is transduction?

Transduction is the transfer of bacterial DNA from one bacterium to another by a bacteriophage.