DNA, RNA, Transcription, and Translation

DNA vs RNA

• DNA is double-stranded with deoxyribose sugar and the bases adenine (A), thymine (T), cytosine (C), and guanine (G).
• RNA is single-stranded with ribose sugar and the bases adenine (A), uracil (U), cytosine (C), and guanine (G).
• Uracil (U) in RNA replaces thymine (T) found in DNA.

Gene Expression Pathway

• The central pathway of gene expression is DNA → RNA → Protein.
• This process involves two main steps: transcription and translation.

Transcription

• Transcription occurs in the nucleus.
• RNA polymerase, an enzyme, binds to DNA at the promoter region.
• The template strand of DNA is used to make a complementary RNA molecule.
• During transcription, adenine (A) pairs with uracil (U), and cytosine (C) pairs with guanine (G).

Translation

• Translation occurs at the ribosomes in the cytoplasm.
• The small ribosomal subunit binds to mRNA first, followed by the large subunit.
• Transfer RNA (tRNA) molecules bring amino acids to the ribosome.
• Each tRNA has an anticodon that matches a specific mRNA codon and an amino acid attachment site.
• The start codon AUG initiates translation and codes for methionine.
• The translation process continues until a stop codon is encountered.

Codon Table

• Each 3-base codon corresponds to one amino acid.
• Redundancy is present, meaning multiple codons can code for the same amino acid.

Mutations

• A substitution mutation may or may not change the protein sequence.
• Frameshift mutations, caused by insertion or deletion, have a big impact on the protein sequence.

Gene Regulation

• Repressors inhibit transcription.
• Activators enhance transcription.
• Gene regulation occurs at multiple levels, affecting the amount, timing, and location of gene expression.

rBGH and GMOs

• Recombinant Bovine Growth Hormone (rBGH) is produced by inserting a cow gene into bacteria using a plasmid.
• A plasmid is a circular bacterial DNA molecule used for genetic engineering.
• GRAS stands for "Generally Recognized As Safe," a designation for food modifications.
• Ti plasmids are used in plants, while gene guns shoot DNA into plant cells.
• A GMO is an organism with altered genes.

Stem Cells

• Totipotent stem cells can become any cell type.
• Therapeutic cloning is used to create specific tissues.
• Germ-line therapy involves changes to sperm or egg cells and is heritable.
• Somatic therapy involves changes only in the individual and is not heritable.

Dolly the Sheep

• Dolly was the first cloned mammal created via somatic cell nuclear transfer.

Evolution Controversy

• Human culture and religious beliefs contribute to mixed acceptance of evolution.

Lice and Pesticide Resistance

• Lice evolving resistance to pesticides is an example of microevolution.
• Microevolution is defined as changes in allele frequencies within a population over time.

Microevolution vs. Macroevolution

• Microevolution involves small changes within a species.
• Macroevolution involves large changes, leading to the emergence of new species.

Natural Selection Examples

• Examples include pesticide resistance in insects, antibiotic resistance in bacteria, and viral resistance in rabbits.

Darwin and Wallace

• Both Charles Darwin and Alfred Russel Wallace developed the theory of natural selection.
• Wallace's letter prompted Darwin to publish "On the Origin of Species."

Common Descent

• All life shares a common ancestor.

Seven Lines of Evidence for Evolution

• Biological classification (taxonomy).
• Comparative anatomy (homologous structures).
• Vestigial traits (useless features).
• Comparative embryology (similar development).
• DNA similarities.
• Biogeography (organism distribution).
• Fossil evidence.

Classification Hierarchy

• Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Four Models Regarding Descent

• Static model (unchanging species), transformation (species change but no new ones), and separate types (different origins for groups) are all rejected.
• Common descent is the supported model.

TB and Evolution

• Tuberculosis (TB) bacteria have evolved resistance to drugs.

Darwin's 4 Observations

• Variation exists in populations.
• Some variation is heritable.
• Overproduction of offspring occurs.
• Survival and reproduction are not random.

Fitness

• Fitness is relative to the environment.

Important Examples of Natural Selection

• Bill depth in finches during drought (deep bills = survival advantage).
• Panda's "thumb" (imperfect adaptations).

Artificial vs. Natural Selection

• Artificial selection involves human-chosen traits like dog breeding.
• Natural selection involves environment-selected traits like fruit flies in an alcohol environment.

Modern Synthesis

• Combines genetics with Darwinian evolution.

Three Patterns of Selection

• Directional selection favors one extreme.
• Stabilizing selection favors the average.
• Diversifying selection favors both extremes.

Antibiotic Resistance

• It's crucial to always finish prescriptions.
• Combination drug therapy kills more variants of bacteria.

Binomial Nomenclature

• It consists of a two-part scientific naming system: Genus species.

Biological Species Concept

• A species is defined as an interbreeding population that produces fertile offspring.

Pre-fertilization Barriers

• Spatial isolation.
• Behavioral isolation.
• Mechanical isolation.
• Temporal isolation.
• Gametic incompatibility.

Post-fertilization Barriers

• Hybrid inviability.
• Hybrid sterility (e.g., mules).

Speciation Steps

• Isolation of populations.
• Evolution of differences.
• Reproductive isolation.

Founder Effect

• A small group starts a new population, potentially leading to rapid speciation.

Allopatric vs. Sympatric Speciation

• Allopatric speciation involves physical separation (e.g., snapping shrimp).
• Sympatric speciation occurs without physical separation (e.g., apple maggot flies).

Polyploidy

• Instant speciation in plants occurs by doubling the chromosome number.

Gradualism vs. Punctuated Equilibrium

• Gradualism is slow change.
• Punctuated equilibrium involves sudden bursts of change.

Race and Genetics

• "Race" lacks biological validity as genetic differences are not consistent with "races."

Human Origins

• Africa has the highest genetic diversity.

Hardy-Weinberg Principle

• Predicts allele frequencies in non-evolving populations.

Convergent Evolution

• Traits evolve similarly in unrelated groups (e.g., dolphin and shark).

Genetic Drift

• Founder effect.
• Bottleneck effect.
• Chance events.

Sexual Selection

• Traits evolve to increase mating success.

Assortative Mating

• Individuals mate with similar others.