Biology Unifying Concepts & Molecular Genetics: DNA Structure, Function, and Evolution

Evolution

Explains diversity.

Structure & function

How form matches job.

Information flow

DNA → RNA → protein.

Energy & matter

Life needs constant input.

Systems

Parts interact to form a whole.

Galapagos finches

Their beaks evolved by natural selection — structure linked to function, showing evolution in action.

ALX1 gene & beaks

Scientists compared DNA of finches with different beaks and found ALX1 variants linked to shape differences.

Central Dogma

DNA → RNA → Protein.

DNA vs amino acids

DNA/RNA = nucleotides (A, T/U, G, C); proteins = amino acids. DNA sequence determines amino acid sequence.

DNA structure for its functions

Double helix is stable (storage), complementary strands (copying), sequence codes proteins (information).

Gene structure

Promoter (control), coding region (info for protein), terminator (stop).

Template strand choice

The promoter direction shows which strand RNA polymerase uses.

Transcription factors

Proteins that bind DNA to turn genes on/off.

Transcriptional profiles & microarrays

Scientists measure which genes are "on" in different cells. Microarrays compare expression — bright spots show high expression differences.

Darwin's theory

Individuals with helpful traits survive/reproduce more → those traits spread.

DNA packaging

DNA wraps around histones → chromatin → chromosomes.

Genome differences

Changes in ploidy (extra/missing sets), sequence mutations, copy number changes (duplications, deletions, gene families).

DNA mutation

Any change in DNA (substitution, insertion, deletion). Can affect protein or not.

Flow of change

DNA mutation → protein change → trait change → natural selection decides if it spreads.

Descent with Modification

Species pass on DNA (continuity) but mutations allow adaptation (modification).

DNA structure & replication

Complementary strands ensure accurate copying, but mutations allow variation.

Origin of Replication

Specific DNA spot where replication starts.

DNA strand growth

New nucleotides added 5′ → 3′.

Five challenges of replication

Getting started → primase makes RNA primer; Both strands replicated → leading (continuous) & lagging (Okazaki fragments); Tangling → topoisomerases relieve stress; Ends copied → telomerase fixes chromosome ends; Accuracy → DNA polymerase proofreads & repair systems correct errors.