Single-Stranded Binding Protein: Prevents strands from re-annealing.
Topoisomerase: Relieves tension in the strands.
RNA Primase: Lays down RNA primers to start replication.
DNA Polymerase: Adds nucleotides.
DNA Polymerase I: Removes RNA primers and replaces them with DNA.
Ligase: Seals the gaps between Okazaki fragments.
Semi-Conservative Replication: Each new DNA molecule contains one original strand and one new strand.
Protein Synthesis
Central Dogma: DNA → RNA → Protein.
Transcription:
Initiation: RNA polymerase binds to a promoter region on a gene.
Elongation: RNA polymerase adds RNA nucleotides.
Termination: A polyadenylation signal halts transcription.
RNA polymerase is used to make mRNA.
After mRNA is built, it exits the nucleus and goes to the cytoplasm.
RNA Processing (Eukaryotes only): Takes place in the nucleus and before translation in eukaryotes.
Spliceosomes: Remove introns and join exons together.
Ribosomes: Large and small subunits that translate mRNA into proteins.
Proteins made by free ribosomes go to the cytoplasm.
Key Players:
mRNA: Copies DNA instructions.
tRNA: Brings amino acids to the ribosome.
rRNA: Ribosomes are made of rRNA and proteins.
Translation:
Initiation: mRNA binds to the ribosome.
Elongation: tRNA brings amino acids to the ribosome, forming a polypeptide chain.
Termination: A stop codon signals the end of translation.
Eukaryotic vs. Prokaryotic Cells
Eukaryotes have a nucleus, so RNA processing must occur before translation can begin in the cytoplasm
Gene Expression
Promoter: A piece of DNA where RNA polymerase binds.
Operons (Prokaryotes): Control region of DNA for multiple genes, found in bacteria.
Promoter: Where RNA polymerase binds.
Operator: Part of the promoter where a repressor binds.
Repressor: Turns the operon off.
Corepressor: Changes the repressor to activate it.
Inducer: Causes the repressor to fall off the operator, turning the operon on.
Outcomes: Gene expression can be turned on or off.
*Natural Causes of mutations: errors during DNA replication.
Eukaryotic Transcription Regulation
RNA Polymerase: Binds to mRNA.
Promoter: Where RNA polymerase binds to start of the gene.
TATA Box: Where specific transcription factors bind.
Transcription Factors: Regulate transcription.
Enhancer: Where activators bind. Activator binds to the enhancer of DNA, upstream to the gene.
Activators: Start transcription.
Mediator Proteins: Help RNA polymerase bind to the promoter region.
Bending Proteins: Fold DNA to allow activators to interact with the promoter region.
Activators, mediator proteins, transcription factors & RNA polymerase are all involved in initiation and beginning transcription.
In eukaryotes, repressors block activators from binding to the promoter.
Chromatin Structure
Heterochromatin: DNA tightly wound around histone proteins (condensed).
Euchromatin: DNA loosely wound around histone proteins (less condensed, more accessible for transcription).
Mutations
Silent Mutation: Codes for the same amino acid.
Missense Mutation: Codes for a different amino acid.
Nonsense Mutation: Codes for a stop codon.
Viruses
Can insert DNA into genes, leading to disorders.
Chemical mutagens or carcinogens can disrupt DNA replication or damage it.
Tumor suppressor genes and proto-oncogenes are genes that when mutated, can lead to cancer.
Transformation: Bacterium picks up plasmids left behind
Conjugation: Bacterium exchange plasmids with another
Transduction: Viruses inject DNA instructions in the host Cell, then the DNA gets mixed in the cell & gets seperated into a new Virus. Different combinations of materials making a new Virus.
Further Mutation Causes and Outcomes
Environmental Factors:
Radiation, chemicals, and viruses can cause mutations.
Outcomes:
Mutations cause genetic variation.
Natural selection favors beneficial mutations, but harmful mutations can be eliminated over time through natural selection.
Biotechnology
Genetic Engineering: The process of directly altering DNA.
Recombinant DNA Molecule: DNA molecule used to carry foreign genetic material; plasmids are commonly used.
Transformation organism takes up recombinant plasmid DNA from the environment.
Products used to produce proteins or be cloned to study genes.
PCR (Polymerase Chain Reaction): Copy specific DNA sequences in large quantities from a sample.
Cell Cycle
Chromosomes: Store genetic information, ensure DNA is copied, and organize DNA for cell division.
Purpose: To allow cells to grow, replicate DNA, and divide into two new cells.
Purpose of Mitosis: To separate the homologous pairs.
Prophase: Spindles form.
Metaphase: Homologous pairs line up in the middle.
Anaphase: Homologous pairs separate.
Telophase: The cells separate.
Makes identical diploid cells
*Chromosomes Store genetic info, ensure DNA is copied & Seperated during cell division, Regulate gene expression & inher-tence.
*Haploid Gamete = Egg & Sperm
*Diploid = Body cell. Sometic cell
*Law of Segeration Each gamete recives I Allele of each gene
*Law of independent Assortment: Homologous Chromosomes align independently at the metaphase plate.
Meiosis
Crossing Over: Creates new combinations of genes on each chromosome.
Independent Assortment: Occurs during meiosis I. Homologous chromosomes align independently at the metaphase plate.
Cell Communication
Cells need to communicate for growth and response to changes.
Process:
A ligand binds to a receptor on a target cell.
A signal transduction pathway relays the signal into the cell.
The cell responds by changing gene expression.
Amplification: One signal molecule activates many molecules, amplifying the response.
Hydrophilic Ligands: Bind to surface receptors.
Hydrophobic Ligands: Cross the membrane and bind to internal receptors.
Protein Hormones: Hydrophilic and cannot pass through the membrane by themselves.
Steroid Hormones: Hydrophobic and can pass through the membrane (slower response).
Kinase: An enzyme that adds a phosphate group.
Phosphorylation Cascade: A series of kinases activate each other by phosphorylation, leading to a cellular response.
Purpose: Amplifies the signal and allows for regulation of the response.
Energy and Enzymes
Exergonic Reaction: A chemical reaction where energy is released.
Endergonic Reaction: A chemical reaction where energy is absorbed.
Enzymes
Active Site: Where the substrate binds to create a chemical reaction.
Allosteric Site: Allows molecules to activate/inhibit the enzyme.
Activation Energy: The minimum amount of energy required to start a reaction or process.
Inhibitors:
Competitive Inhibitor: Blocks the substrate from binding to the active site.
Non-Competitive Inhibitor: Molecule binds to allosteric site to change the shape of the active site.
Feedback Inhibition: A mechanism where the end product of a metabolic pathway inhibits an enzyme early in that pathway.
Ecology
Photoautotrophs: Use sunlight for energy.
Chemoautotrophs: Use chemical energy.
Energy Flow: Flows one way (sun → heat).
Nitrogen Cycle:
Nitrogen-Fixing Bacteria: Converts atmospheric nitrogen (N<em>2) to ammonia (NH</em>3).
Nitrifying Bacteria: Convert ammonia (NH<em>3) into nitrite (NO</em>2) and then into nitrate (NO3).
Denitrifying Bacteria: Convert nitrate (NO<em>3) back into atmospheric nitrogen gas (N</em>2).
Nitrogen is used to make proteins and nucleic acids.
Population Dynamics:
Growth: Births, immigration.
Decline: Deaths, emigration.
Density-Dependent Factors: Affect a population's size/growth based on the population density; examples include disease and predation.
Density-Independent Factors: Affect populations regardless of their density; examples include natural disasters.
Population Growth Curves:
J-curve = exponential growth.
S-curve = logistic growth.
Carrying Capacity: The maximum population size an environment can sustain.
Symbiotic Relationships:
Mutualism: Both benefit.
Parasitism: One benefits, one is harmed.
Commensalism: One benefits, the other is neither harmed nor benefitted.