DNA Metabolism part 2

What is the primary consequence of DNA mutations escaping repair systems?

The incorrect base serves as a template in replication, resulting in a changed sequence in both strands of the daughter DNA.

What is the correlation between DNA mutations and cancer?

The accumulation of mutations in eukaryotic cells is strongly correlated with cancer, and most carcinogens are also mutagens.

What causes pyrimidine dimers in DNA?

Exposure to UV light.

What is the function of Dam methylase in E. coli?

It fully methylates DNA at GATC sites before replication.

How does methylation help distinguish DNA strands during repair?

The parent (template) strand is methylated, while the newly synthesized strand remains unmethylated for a short period, allowing the cell to identify the strand containing potential errors.

Which proteins are involved in the methyl-directed mismatch repair system in E. coli?

MutS and MutL bind to the mismatched base pairs, and MutH cleaves the unmethylated strand at GATC sites.

What is the function of DNA glycosylases in Base-Excision Repair?

They recognize and remove damaged bases, creating an abasic (AP) site.

When is Nucleotide-Excision Repair typically utilized?

For DNA lesions that cause large distortions in the helical structure.

How do DNA photolyases repair cyclobutane pyrimidine dimers?

They use absorbed light and specific cofactors to reverse the dimerization reaction.

What is the role of O6-methylguanine-DNA methyltransferase?

It transfers a methyl group from O6-methylguanine to one of its own Cysteine residues to repair the damage.

Which enzyme catalyzes the oxidative demethylation of 1-methyladenine or 3-methylcytosine?

AlkB.

What is the translesion DNA synthesis (TLS) pathway?

An error-prone repair strategy used in response to severe DNA damage that allows replication to continue despite high mutation rates.

What is the SOS response in bacteria?

A bacterial response to severe DNA damage that includes the activation of the error-prone translesion DNA synthesis (TLS) pathway.

What are the three main types of DNA recombination?

Homologous genetic recombination, site-specific recombination, and DNA transposition.

What are transposons?

Segments of DNA that can move from one location in a chromosome to another, often referred to as 'jumping genes'.

What is the difference between simple and complex transposons?

Simple transposons (insertion sequences) contain only the genes for transposition, while complex transposons contain additional genes, such as those for antibiotic resistance.

What is the primary function of homologous genetic recombination during meiosis?

It facilitates the exchange of genetic material between homologous chromosomes, enhancing genetic diversity.

What are 'Holliday intermediates' in homologous recombination?

Crossover structures formed when a single-strand extension from one chromosome invades the intact duplex of a homologous chromosome.

How does recombination contribute to antibody diversity?

Immunoglobulin genes are assembled by the recombination of various V and J gene segments, creating a vast array of unique variable regions.

What is the role of DNA ligase in Nucleotide-Excision Repair?

It seals the nick in the DNA backbone after the gap has been filled by DNA polymerase.

Why is transposition considered a 'molecular parasite'?

Because it moves randomly and can potentially kill the host cell if it jumps into an essential gene.

What defines homologous genetic recombination?

Genetic exchange between two DNA molecules that share an extended region of nearly identical sequence.

What is the result of O6-methylguanine pairing with Thymine instead of Cytosine?

It causes GC to AT mutations.

What is the purpose of terminal repeats at the ends of transposons?

They hybridize with complementary regions of the target DNA during the insertion process.

What are the two driving forces of evolution in sexually reproducing organisms?

Recombination and mutations.