DNA Replication and Genetics

What is the central dogma of genetics?

DNA is transcribed into mRNA, which is translated into protein.

What is a gene?

A length of DNA that generally encodes a protein.

What is a genome?

The full complement of DNA for an organism.

What are the three components of a nucleotide?

A nitrogenous base, a sugar, and phosphate groups.

What is the difference between DNA and RNA sugars?

Deoxyribose has a hydrogen at the 2' carbon instead of a hydroxyl (OH) group.

What are the two types of nitrogenous bases?

Purines (two rings) and Pyrimidines (single ring).

What direction are DNA strands oriented relative to each other?

Antiparallel orientation.

What bonds hold the DNA sugar-phosphate backbone together?

3'-5' phosphodiester covalent bonds.

What are the complementary base pairs and their hydrogen bond counts?

A-T (2 H bonds) and G-C (3 H bonds).

Which region of DNA is more thermodynamically stable?

A GC-rich region, due to three hydrogen bonds per base pair.

What is the strongest non-covalent force in DNA structure?

Base-stacking via Van der Waals interactions.

What is a karyotype?

The constitution and number of chromosomes in an organism.

What is a nucleosome?

DNA wound around an octamer core of eight histone proteins plus an H1 protein.

What is the effect of histone acetylation?

It changes positive lysine charges to neutral, promoting a looser DNA structure and aiding transcription.

What is the function of histone acetyl transferases (HATs)?

They acetylate histones, leading to chromatin decondensation and transcription activation.

What is the function of HDAC inhibitors like Vorinostat?

They inhibit histone deacetylases, decondensing chromatin to reactivate silenced genes in cancer therapy.

What is the function of telomeres?

They cap chromosome ends, act as a buffer, and maintain structural integrity.

What is heterochromatin?

Highly condensed, dark-staining, transcriptionally inactive, and gene-poor chromatin.

What is euchromatin?

Extended, light-staining chromatin that is actively transcribed and gene-rich.

What is semiconservative replication?

Daughter DNA molecules consist of one parental strand and one newly synthesized strand.

What are the four requirements for DNA replication?

Single-stranded template, dNTPs with Mg2+, replisome, and a primer with a free 3' OH.

Where does DNA replication begin in eukaryotes?

At multiple origins of replication containing AT-rich consensus sequences.

What is the function of DNA helicase?

It breaks hydrogen bonds between DNA strands to unwind the double helix during replication.

What does single-strand binding (SSB) protein do?

It stabilizes open single-stranded DNA.

What is the role of topoisomerase (gyrase)?

It prevents supercoiling during DNA unwinding.

In what direction does DNA polymerase read the template strand?

From 3' to 5'.

In what direction does DNA polymerase synthesize new DNA?

From 5' to 3'.

What is the function of the sliding clamp?

It encircles the DNA template to keep DNA polymerase closely associated during rapid synthesis.

How does DNA polymerase proofread?

Using 3' to 5' exonuclease activity to remove mismatched nucleotides.

Why is lagging strand replication discontinuous?

Because DNA polymerase can only synthesize in the 5' to 3' direction.

What are Okazaki fragments?

Short segments of DNA synthesized on the lagging strand.

What enzyme joins Okazaki fragments together?

DNA ligase.