Lecture 1
What is the central dogma of molecular biology?
DNA → RNA → Protein
What type of bond explains water’s cohesion and many of its unique properties?
Hydrogen bonds.
What base pairs with A, and what base pairs with G in DNA?
A pairs with T; G pairs with C.
Which base is found in RNA instead of thymine?
Uracil (U).
What is a codon?
A 3-nucleotide sequence in mRNA that codes for an amino acid or a stop signal.
What is an operon?
A group of genes controlled by a single promoter/operator and transcribed together as one mRNA (common in bacteria).
What does “differential gene expression” mean?
Different cells can turn different genes on/off, so they make different RNAs/proteins even though they have the same DNA.
What are the four main classes of biological macromolecules?
Carbohydrates, lipids, proteins, nucleic acids.
In what direction can DNA polymerase synthesize new DNA?
5′ → 3′ only.
Why can RNA fold into hairpins/structures more easily than DNA?
RNA is usually single-stranded and can base-pair with itself.
What is the most common start codon, and what amino acid does it code for?
AUG; methionine (Met).
What is the difference between an activator and a repressor?
Activators increase transcription; repressors decrease transcription
Why can a neuron and a liver cell have the same genome but different functions?
They express different sets of genes, producing different proteins.
What does it mean if a molecule is amphipathic?
It has both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.
What does “semi-conservative replication” mean?
Each daughter DNA molecule has one old (template) strand and one newly synthesized strand.
In what direction does RNA polymerase synthesize RNA?
5′ → 3′.
What is a reading frame?
The grouping of nucleotides into triplets (codons) that determines the amino acid sequence.
In the trp operon, what role does tryptophan play in regulation?
Tryptophan acts as a corepressor: when tryptophan is high, it activates the repressor to shut transcription off.
Why was genome sequencing a major turning point for biology/medicine?
It allowed rapid identification of genes/variants linked to traits and disease and enabled modern diagnostics and targeted research.
What is pH and what does it measure?
pH is a measure of hydrogen ion concentration; pH = −log10[H⁺].
What is the job of helicase during DNA replication?
It unwinds/separates the DNA strands at the replication fork.
What is the key sugar difference between DNA and RNA?
RNA has ribose with a 2′-OH; DNA has deoxyribose with a 2′-H.
What happens if you insert or delete 1 nucleotide early in a coding sequence?
It usually causes a frameshift, changing all downstream codons and often creating an early stop codon.
In the lac operon, what does lactose (allolactose) do?
It inactivates the lac repressor, allowing transcription (if glucose conditions also allow it)
Why are model organisms often useful for studying human biology?
Many core genes and pathways are evolutionarily conserved across species.
How does a buffer resist pH change?
It contains a weak acid and conjugate base that can absorb or release H⁺ to stabilize pH.
What is chromatin, and what is a nucleosome?
Chromatin is DNA packaged with proteins; a nucleosome is DNA wrapped around histone proteins.
What is the relationship between transcription and protein levels (in general)?
More transcription usually increases mRNA and often increases protein (though regulation can occur later too).
What do stop codons do, and name the three stop codons.
They terminate translation; UAA, UAG, UGA.
Why is glucose important in lac operon control?
Low glucose increases cAMP and activates CAP, which helps strongly turn on lac transcription when lactose is present.