GENETICS EXAM 3

What is the genetic code?

A sequence of three-nucleotide codons to specify amino acids or stop signals during protein synthesis.

What is a frameshift mutation?

A mutation caused by inserting or deleting nucleotides that changes how codons are read.

What is a reading frame?

A process how nucleotides are grouped into sets of three during translation.

What is a nonoverlapping code?

Each nucleotide belongs to only one codon in a given reading frame.

What is degeneracy of the genetic code?

Multiple codons can specify the same amino acid.

What is the wobble hypothesis?

Flexible pairing at the third codon position allows one tRNA to recognize multiple codons.

What is the initiation codon?

The start codon, usually AUG, signals where translation begins and codes for methionine.

What are the termination codons?

UAA, UAG, and UGA signal the end of translation.

What is a missense mutation?

A mutation that changes a codon so that a different amino acid is incorporated into a protein.

What is a nonsense mutation?

A mutation that changes an amino-acid codon into a stop codon.

What are open reading frames?

Nucleotide sequences that can be translated from a start codon to a stop codon without an intervening stop codon.

What is transcription?

The process of copying DNA information into RNA.

What do RNA polymerases do?

Synthesize RNA from a DNA template, with different types performing specialized functions in cells.

What is the Pribnow box?

A bacterial promoter region near position −10 that helps initiate transcription.

What is the TATA box?

A promoter sequence in many eukaryotic genes that helps position the transcription machinery.

What are the three stages of transcription?

Initiation begins RNA synthesis, elongation extends the RNA strand, and termination ends transcription.

What do enhancers and silencers do?

Enhancers increase transcription, while silencers decrease transcription.

What are cis and trans elements?

Cis-regulatory elements are DNA sequences that regulate nearby genes, while trans-acting elements are diffusible molecules, such as regulatory proteins, that interact with those sequences.

What are transcription factors?

Proteins that regulate gene expression by helping activate or repress transcription.

What is RNA capping?

A modified guanine cap is added to the 5′ end of eukaryotic mRNA to protect it and help translation begin.

What is RNA splicing?

Removes introns and joins exons together.

What is RNA tailing?

A poly-A tail is added to the 3′ end of most eukaryotic mRNAs to improve stability and aid processing and export.

What are introns and exons?

Introns are usually removed from pre-mRNA, while exons are retained in mature RNA.

What is translation?

Uses the information in mRNA to assemble amino acids into a protein.

What is tRNA?

Carries specific amino acids to the ribosome and uses its anticodon to recognize mRNA codons.

What is mRNA?

Carries genetic instructions from DNA to the ribosome for protein synthesis.

What is rRNA?

Forms part of the ribosome and helps catalyze peptide bond formation.

What is codon-anticodon pairing?

An mRNA codon pairs with a complementary tRNA anticodon to ensure the correct amino acid is added.

What is tRNA charging (aminoacylation)?

Aminoacyl-tRNA synthetases use energy to attach the correct amino acid to its corresponding tRNA.

What are the stages of Initiation, elongation, termination?

Translation begins when the ribosome assembles at the start codon, continues as amino acids are added, and ends when a stop codon is reached.

What is peptidyl transferase?

Catalyzes peptide bond formation between amino acids during translation.

How does translation occur in eukaryotes?

on ribosomes in the cytoplasm or on the rough ER and involves initiation, elongation, and termination.

What is the Kozak sequence?

A eukaryotic mRNA sequence surrounding the start codon that helps the ribosome initiate translation efficiently.

What is a point mutation?

A mutation that changes a single nucleotide in DNA.

What is a missense mutation?

A mutation that changes a codon so that a different amino acid is produced.

What is a nonsense mutation?

A mutation that changes an amino-acid codon into a stop codon.

What is a silent mutation?

A mutation that changes a codon without changing the amino acid it encodes.

What are transitions and transversions?

A transition replaces a purine with another purine or a pyrimidine with another pyrimidine, while a transversion replaces a purine with a pyrimidine or vice versa.

What is a frameshift mutation?

A mutation that results from inserting or deleting nucleotides in numbers not divisible by three, changing the downstream reading frame.

What is a loss-of-function mutation?

A mutation that reduces or eliminates the normal activity of a gene product.

What is a null mutation?

A mutation that eliminates the function of a gene product.

What is a dominant mutation?

A mutation that produces a phenotype when only one copy of the affected allele is present.

What is a dominant gain-of-function mutation?

A mutation that gives a gene product increased, new, or abnormal activity.

What is a lethal mutation?

A mutation that causes death under the conditions in which it is expressed.

What is a lethal conditional mutation?

A mutation that causes death under specific environmental conditions but permits survival under others.

What is a neutral mutation?

A mutation that has no significant effect on an organism's fitness or observable phenotype.

How can DNA replication cause spontaneous mutations?

DNA replication errors can introduce incorrect nucleotides into newly synthesized DNA.

What is replication slippage?

Occurs when DNA polymerase loses its place on repetitive DNA, causing insertions or deletions.

What are tautomers and tautomeric shifts?

Tautomeric shifts temporarily change the structure of DNA bases, potentially causing incorrect base pairing.

What is depurination?

Removes a purine base, adenine or guanine, from DNA.

What is deamination?

Removes an amino group from a base, potentially changing its base-pairing properties.

What is oxidative damage?

Occurs when reactive oxygen species alter DNA bases or the DNA backbone.

What are transposable elements?

DNA sequences that can move to new locations in the genome and disrupt genes or their regulation.

What are mutagens?

Agents that cause changes or mutations in DNA.

What are base analogs?

Resemble normal DNA bases and can be incorporated into DNA, causing incorrect base pairing.

What are alkylating agents?

Add alkyl groups to DNA bases, potentially altering their pairing.

What are intercalating agents?

Insert between DNA base pairs and can cause insertions or deletions during replication.

What are UV-light-induced pyrimidine dimers?

Ultraviolet light can cause adjacent pyrimidines, especially thymine bases, to form dimers that distort DNA.

What are free radicals?

Damage DNA bases and the sugar-phosphate backbone through oxidation.

What are polygenic and monogenic diseases?

Monogenic diseases result primarily from mutations in a single gene, while polygenic diseases involve multiple genes and often environmental factors.

What are proofreading and mismatch repair?

Proofreading corrects replication errors as DNA is synthesized, while mismatch repair corrects errors that remain afterward.

What is strand discrimination?

Identifying the newly synthesized DNA strand so replication errors can be corrected.

What is DNA methylation?

Adds methyl groups to DNA and can help certain bacteria distinguish parental DNA from newly synthesized DNA.

What does adenine methylase (Dam methylase) do?

In E. coli, methylates adenine in GATC sequences, helping mismatch repair identify the newly synthesized strand before it becomes methylated.

What is the E. coli SOS repair system?

Activates DNA damage-response genes, allowing damage repair and survival but potentially increasing mutations.

What is post-replication repair?

Helps cells tolerate or bypass DNA lesions left unresolved during replication.

What is photoreactivation repair?

Uses light-dependent photolyase enzymes to directly reverse certain UV-induced pyrimidine dimers in organisms that possess this mechanism.

What is base excision repair (BER)?

Removes individual damaged bases using DNA glycosylases and repairs the resulting DNA site.

What is nucleotide excision repair (NER)?

Removes a short stretch of DNA containing bulky, helix-distorting damage and replaces it with new DNA.

What is homologous recombination repair?

Uses a homologous DNA template, usually a sister chromatid, to repair double-strand breaks accurately.

What is nonhomologous end joining?

Reconnects broken DNA ends without requiring a homologous template and can introduce small mutations.

What is the Ames test?

Uses specially selected bacterial strains to determine whether a chemical causes mutations, often measuring the return of bacteria to the ability to grow without a required nutrient.