AP BIOLOGY RECAP! ALL TOPICS CONCISELY EXPLAINED! (Shorts Compilation) 2025
Water and Hydrogen Bonding (Topic 1.1)
Water is essential for life.
Living organisms are about 70% water.
Water is polar, with slight negative and positive sides due to polar covalent bonds between hydrogen and oxygen atoms.
Each water molecule acts like a small magnet.
Hydrogen bonds are the attractions and repulsions between these "magnets".
These bonds give water its unique properties.
Water sticks to itself (cohesion) and other polar surfaces (adhesion).
High energy is required for evaporation.
Strong force is needed to break the surface tension.
Water's stickiness helps plants defy gravity and move water upwards.
Organisms can float on water surfaces due to surface tension.
Water is an excellent solvent for polar substances, making it suitable for metabolic reactions.
Elements of Life (Topic 1.2)
Living things need to take in nutrients and remove waste as organic molecules.
Organic means from a living thing and carbon-based.
Essential elements for life include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
Carbon is the most important because it forms the backbone of all organic molecules.
Carbon atoms can form up to four covalent bonds, making them versatile for building complex molecules.
Four main groups of biomolecules: carbohydrates, proteins, lipids, and nucleic acids.
Elements in each biomolecule type:
Carbohydrates: C, H, O
Proteins: C, H, O, N, S
Lipids: C, H, O
Nucleic Acids: C, H, O, N, P
Isomers: Molecules with the same atoms arranged differently.
Geometric isomers: Different arrangements around a double bond.
Enantiomers: Mirror image isomers around a central carbon atom.
Introduction to Biological Macromolecules (Topic 1.3)
Four main groups of biological molecules are carbohydrates, proteins, lipids, and nucleic acids.
Polymers are large molecules made of repeating subunits called monomers.
Proteins are polymers of amino acids.
Dehydration synthesis: Linking monomers by removing water.
Example: Two amino acids, one with -OH and the other with -H, combine to form water and a new covalent bond.
The enzyme removes these two groups from each other, it's going to form a water molecule and a new covalent bond between those two monomers.
Hydrolysis: Breaking down polymers into monomers by adding water.
The enzyme adds an on one monomer and an on the other monomer using a water molecule , and then splits the covalent bond between those two.
Hydrolysis breaks down, while dehydration synthesis builds up.
Monomers of Biomolecules (Topic 1.4)
Monomer of carbohydrates: Monosaccharide (usually rings of carbon and oxygen).
Major source of cellular energy.
Two rings form a disaccharide, linked by glycosidic linkages.
Monomer of proteins: Amino acids.
All amino acids have an amino group, a carboxyl group, and an R group (variable side chain).
R group can be positive, negative, polar, or non-polar.
R group properties determine protein structure and function.
Amino acids are linked by peptide bonds.
Lipids: Non-polar with monomer as fatty acid.
Fatty acids: Long chains of carbon and hydrogen.
Double bond: Chain is bent (unsaturated).
No double bond: Chain is straight (saturated).
Nucleotides will be discussed in further detail in Topic 1.6.
Biological Polymers (Topic 1.5)
Polysaccharides are long chains of monosaccharides.
Can be linear or branched.
Used for energy storage or structure.
Polypeptides are chains of amino acids; multiple polypeptides can form a protein.
Protein structure and function are determined at four levels:
Primary structure: Sequence of amino acids.
Secondary structure: How chains fold or coil (hydrogen bonds between amino acid backbones).
Tertiary structure: Shape due to side chain interactions (coils and folds combined).
Quaternary structure: Polypeptides combine into a functional protein.
Nucleic acids (DNA and RNA) are made of long chains of nucleotides.
Nucleic Acids (Topic 1.6)
DNA and RNA are polynucleotide strands made of nucleotides (monomers).
Nucleotides have a phosphate, a pentose sugar, and a nitrogenous base.
DNA sugar: Deoxyribose; RNA sugar: Ribose.
Five nitrogenous bases: A, C, G, T (DNA), and U (RNA).
Purines (A and G): Two-ring nitrogenous base.
Pyrimidines (C, T, and U): One-ring nitrogenous base.
Nucleotides are linked via sugars and phosphates.
DNA: Two long chains form a ladder shape with opposite orientations.
A pairs with T; C pairs with G.
RNA: Single strand with U instead of T.
Cell Structure and Subcellular Components (Topic 2.1)
All life is made of cells.
Cells can be categorized based on compartmentalization and DNA location (nucleus or no nucleus).
All cells have:
Ribosomes (protein synthesis).
Plasma membrane (controls entry and exit).
Cytosol (jelly-like substance).
Eukaryotic cells (plant and animal) have more components:
Nucleus (DNA).
Rough and smooth ER (protein and lipid production, transport via vesicles).
Golgi apparatus (cellular product sorting).
Mitochondria (powerhouse).
Lysosomes and peroxisomes (breakdown).
Centrioles (mitosis).
Plant cells additionally have:
Chloroplasts (photosynthesis).
Central vacuole (larger than other vacuoles).
Cellulose-based cell wall.
Mitochondria and Chloroplasts (Topic 2.2)
Form meets function: structure is designed for a specific job.
Mitochondria and chloroplasts are compartmentalized with membranes.
Mitochondria have two membranes:
Outer membrane (smooth).
Inner membrane (folded).
ATP production requires different reactions in different places.
Krebs cycle (matrix).
Oxidative phosphorylation/electron transport chain (inner membrane).
Chloroplasts produce glucose using sunlight.
Light reactions (thylakoids).
Calvin cycle (stroma).
Cell Size (Topic 2.3)
Cells need to exchange materials with their environment (nutrients in, waste out).
Cells depend on diffusion: Movement from high to low concentration.
Cells with a larger surface area to volume ratio are better at exchanging materials.
, the larger the cell, the smaller the ratio
AP Biology asks to calculate the surface area to volume ratio of a cube and a sphere.
Specialized cells increase surface area through microvilli (e.g., intestinal lining cells).
Plasma Membranes (Topic 2.4)
Plasma membranes control what enters and exits the cell.
Membranes are selectively permeable.
Fluid mosaic model: Phospholipid bilayer with embedded proteins, glycoproteins, and sterols.
Phospholipid bilayer:
Two layers of phospholipids.
Amphipathic: Polar head and non-polar tails.
Non-polar fatty acid tails face inward; polar regions face outward.
Membrane fluidity is influenced by the saturation of fatty acid tails.
Membrane Permeability (Topic 2.5)
Plasma membranes are selectively permeable; non-polar regions face the middle.
Non-polar = hydrophobic.
Small, non-polar molecules (oxygen, carbon dioxide) pass through easily.
Polar molecules have difficulty unless very small (water sometimes).
Large molecules, large polar molecules, and charged molecules cannot pass through the bilayer.
Proteins facilitate the transport of large polar molecules (glucose) or charged ions (sodium, chloride).
Cell wall provides structure and rigidity (not selective permeability).
Membrane Transport (Topic 2.6)
Diffusion: Moves substances from high to low concentration (passive transport).
Concentration gradient: More of a substance on one side.
Example: Oxygen moves into the cell if there's more outside than inside.
Active transport: Moves substances from low to high concentration (requires ATP).
Vesicles move large particles:
Endocytosis: Bringing substances in.
Exocytosis: Taking substances out.
Facilitated Diffusion (Topic 2.7)
Facilitated diffusion is passive transport using proteins.
Ions require ion channels; water requires aquaporins.
Concentration gradient of ions causes a charge difference (membrane potential or voltage).
Electrochemical gradient: Combination of concentration gradient and membrane potential (acts like a battery).
Resting potential is regulated by:
Sodium-potassium pump (uses ATP to pump out sodium ions and pump in potassium ions).
Proton pumps (same, but with hydrogen ions).
Osmosis (Topic 2.8)
Osmosis: Diffusion of water.
Water moves from high to low concentration.
In a solution, more water means less solute (dissolved substances).
Concentration of solutes determines the direction of water flow.
More solute in the cell: Water flows in.
More solute outside the cell: Water flows out.
Equal solute concentrations: Osmosis is balanced.
Water follows the solutes.
Tonicity is important for cells:
Plant cells prefer hypotonic solutions (turgid).
Animal cells prefer isotonic solutions (avoid shriveling or bursting).
No cells like hypertonic solutions.
Overview of Membrane Transport (Topic 2.9)
Passive transport: Diffusion from high to low concentration (no energy required).
Active transport: Uses ATP to move molecules against the gradient (low to high concentration).
Facilitated diffusion: Passive transport for molecules that can't pass the bilayer (channel proteins required).
Cells can use charge differences (membrane potential) to move substances.
Electrogenic pumps: Use ATP to move ions and create a gradient.
Co-transport: Gradient created by pumps is used to bring in other molecules.
Endocytosis and exocytosis: Use vesicles to move large particles in or out (active transport).
Compartmentalization (Topics 2.10 and 2.11)
Compartmentalization: Eukaryotic cells have internal membranes that divide cellular processes.
Each membrane set has a different job (organelles).
Eukaryotic cells are compartmentalized; prokaryotic cells are not.
Endosymbiotic theory: Explains the origin of compartmentalization.
One large prokaryotic cell engulfed another.
The small cell made ATP using oxygen and glucose.
The cells become the first eukaryotic cell.
The smaller cell became the mitochondria.
Chloroplasts evolved from cyanobacteria via the same process.
Evidence: Mitochondria and chloroplasts have double membranes, their own DNA, ribosomes, and divide independently.
Enzyme Structure (Topic 3.1)
Metabolism is all of the reactions that happen within an organism.
Life is a network of chemical reactions where atoms are rearranged to form new molecules.
Requires organisms to use and obtain energy.
Metabolism occurs through pathways: series of steps where one molecule is altered to become another.
Catabolic pathways break down molecules; anabolic pathways build them up.
Enzymes are biological catalysts (proteins) that speed up biological reactions.
Enzymes act upon a substrate; shape and charge are specifically built for one substrate.
Example: Lactase enzymes only bind with lactose.
Enzyme Catalysis (Topic 3.2)
Enzymes enable reactions for living things.
Biological reactions happen on their own eventually, but not at the rate or when and where living things specifically need them.
Enzymes reduce the energy required to contort and change substrates (lower activation energy).
Saving energy is important because living things should ensure not to expend more than they take in.
Substrates bind to the active site, which enables the substrate to become a product.
The product detaches, and the enzyme can be used again.
Example: Lactose binds to the active site of lactase, which lowers the activation energy to hydrolyze lactose into glucose and galactose.
Factors Affecting Enzyme Function (Topic 3.3)
Enzymes have optimal pH and temperatures for efficient function.
Too low or high pH/temperature drastically changes reaction rates.
Enzymes in the stomach function in acidic conditions, not in neutral intestines.
Higher temperature increases reaction rate, but enzymes can denature at too high temperatures or too low pH levels.
Increasing enzyme and substrate concentrations increases reaction rate up to a point.
Too much substrate and not enough enzymes will limit how fast reactions happen, and vice versa.
Inhibitors prevent enzyme function to regulate reactions.
Competitive inhibitors block substrate binding to the active site.
Allosteric inhibitors bind elsewhere and change the active site shape.
Cellular Energy (Topic 3.4)
Living things depend on chemical reactions that require more energy taken in than is used.
Energy cannot be reused or recycled; it is converted and lost as heat.
Energy coupling: A metabolic pathway where the net energy release from one reaction is used to drive another.
Exergonic reaction: Releases energy.
Endergonic reaction: Requires extra energy and absorbs energy from its surroundings to begin.
The first reaction's energy can power the second if an exergonic reaction comes before an endergonic one.
Photosynthesis (Topic 3.5)
Process by which plants and algae convert sunlight into chemical bonds and glucose, releasing oxygen.
Light-dependent reactions:
Chlorophyll and photosystems on thylakoid membranes use photons to split water, separating hydrogen and oxygen (H_2O ">" 2H + O).
Releases high-energy electron, which passes along proteins to make ATP.
Electrons absorb a second photon, and that energy is used to make NADPH.
Calvin cycle:
Carbon dioxide molecules are fixed (put together).
Uses enzymes, ATP, and NADPH to assemble into glucose .
Cellular Respiration (Topic 3.6)
Process by which cells produce ATP (cellular energy molecule).
All life needs ATP.
Can be aerobic or anaerobic, meaning that it uses oxygen molecules or doesn't use it.
Phosphorylating ADP into ATP begins with glycolysis: Glucose is broken down into two pyruvate molecules.
For prokaryotes, the process stops here, but if you have some oxygen , pyruvate gets converted into acetyl CoA and enters the Krebs cycle.
The Krebs cycle produces electron carriers NADH and FADH2 (electron carriers that initiate the electron transport chain).
Electron transport chain: Electrons get passed around to proteins along the inner mitochondrial membrane to produce a proton gradient.
ATP synthase uses the proton gradient to add a phosphate onto ADP to make ATP (over 30 ATP molecules).
Oxygen accepts these electrons, which makes the cellular respiration super efficient.
Fitness (Topic 3.7)
Variation improves fitness: More variety in living systems is better.
The more kinds of molecules that cells have, the better they are at responding to environmental changes.
Variety of enzymes enables a wide variety of reactions.
Variations in the same kind of molecules improve an organism's odds, even variations in enzymes.
Different chlorophylls absorb different wavelengths of light.
Different phospholipids alter membrane fluidity.
Different hemoglobins absorb and carry oxygen at different developmental stages.
Cell Communication (Topic 4.1)
Organisms made of multiple cells must communicate and respond to signals.
Cells communicate through chemicals; issues arise when there's a problem transmitting, receiving, or responding to the signals.
One way is by direct contact, where one cell's surface proteins, called antigens, interact with another's.
Paracrine signaling: Receiving cells are nearby.
Endocrine signaling: Receiving cells are far away, uses hormones, and are sent through the blood or the lymph.
Autocrine signaling: A cell picks up its own chemical message.
Synaptic signaling: A neuron transfers electrical impulses from one to another or to a target cell through neurotransmitter molecules like serotonin or dopamine.
Introduction to Signal Transduction (Topic 4.2)
Cell communication has three stages:
Reception: A messenger molecule called a ligand binds to a receptor protein (plasma membrane) that is specifically made for it.
Transduction: Takes the message and brings it inside so that the cell can produce the proper response to the signal.
Kinases phosphorylate others to turn them on, forming phosphorylation cascades.
Phosphatases turn off proteins.
Second messengers amplify signals and activate many proteins at once.
Response: The cell can grow, secrete molecules, produce proteins through gene expression, or die.
Specifics about Transduction Pathways (Topic 4.3)
Some receptors it is helpful to know are:
Ligand-gated ion channels: Do what their name suggests.
Intracellular receptors: Initiate a gene expression response.
An important pathway to be familiar with for a bio test uses a G-protein-coupled receptor or GPCR.
Epinephrine receptors are GPCRs where epinephrine binds and activates a G-protein, which activates adenylate cyclase; this enzyme produces cyclic AMP (second messenger).
Cyclic AMP phosphorylates different proteins, including glycogen phosphorylase, and that is where it hydrolyzes glycogen in order to produce glucose.
Changes in Signal Transduction Pathways (Topic 4.4)
Mutations can alter the receptors, enzymes, kinases, phosphatases, or any other protein thus resulting in a cell over-responding to one signal and not responding at all to another.
Example: Mutated p53 (tumor suppressor protein) cannot stop cell division, leading to cancer; mutated insulin receptors prevent cells from storing glucose, leading to diabetes.
Chemicals like medicines or poisons can block a receptor, inhibit a kinase or enzyme, among a whole bunch of other things.
Poisons shut down key enzymes like adenylate cyclase or ion channels or pumps.
Feedback (Topic 4.5)
Cells give feedback to one another on whether or not a change in your internal environment should continue or if it should be stopped.
Maintaining this internal balance is called maintaining homeostasis, and all living things do this through feedback loops.
Negative feedback loops maintain internal balance.
The sensor detects a change in the internal environment.
A control center establishes a set point where a certain factor should be at, for example, blood sugar or temperature.
An effector gets told what to do by the control center in response to the initial change in the internal environment.
Positive feedback loops accelerate change.
E.g., childbirth; cells respond with more of the change.
Cell Cycle (Topic 4.6)
Cells need to divide for multicellular organisms to grow, repair tissues, or continue existing.
Eukaryotic cells spend most of their lives in interphase:
Gap 1: Cell carries out normal functions and prepares for DNA replication.
S: DNA gets copied.
Gap 2: Cell gets ready to divide into two copies of itself.
M (Mitosis): Division of the nucleus.
Phases of Mitosis:
Prophase: DNA condenses into chromosomes, centrosomes form the mitotic spindle, and the chromosomes get moved towards the middle of the cell.
Metaphase: Chromosomes align, spindle attaches to centromeres, DNA is copied, and it needs to be split evenly between two daughter cells so that they are identical.
Anaphase: Begins and splits apart the chromosomes, which elongates the cell once all the chromosomes are properly aligned and the spindle is attached to the centromeres of all the chromosomes.
Telophase: New nuclei form, spindles are broken down.
Cytokinesis: Cell contents get divided during and after telophase.
Regulation of the Cell Cycle (Topic 4.7)
Cell division is controlled to prevent too much or not enough division (division needs to be an optimal amount).
Cells control when they progress through the cell cycle through checkpoints.
Certain requirements must be met before progressing to the next phase.
Cyclins and cyclin-dependent kinases are proteins involved in these transduction pathways.
For example, one type of cyclin activates the enzymes responsible for DNA replication.
If there is something wrong with one of the genes to which it helps to continue or stop the progression of the cell cycle, then the cell division can become uncontrolled.
Cells typically self-destruct (apoptosis) if division is uncontrolled.
Failure to respond to the apoptosis signal results in cells dividing rapidly (cancer).
A clump of cells that can't control how much they divide is called a tumor which can be either:
Benign: If it stays in one place.
Malignant: If it finds a way to metastasize (move to another place in the body).
Meiosis (Topic 5.1)
All living things must pass down their genes (molecular instructions) to their offspring.
Heredity is the study of how this happens.
Mitosis is an example of asexual reproduction: One cell copies its DNA and splits into two clones.
Multicellular life produces offspring with unique gene combinations from two parents (sexual reproduction).
Gametes (sex cells) transmit unique genes from each parent and then fuse to form a new organism with a brand new combination of genes.
Meiosis shuffles genes and chromosomes to produce four haploid cells (gametes) with one set of chromosomes each.
Two haploid cells combine via fertilization to form a diploid cell with two sets of chromosomes.
Humans have sperm and egg cells with 23 chromosomes that combine into 23 sets of homologous pairs (46 total).
Genetic Variation (Topic 5.2)
Meiosis produces four non-identical haploid gametes, a process that needs two divisions.
Meiosis I: Homologous pairs split (one chromosome inherited from each parent); ends with two haploid cells with duplicated chromosomes.
Meiosis II: Sister chromatids split; ends with four haploid cells with unduplicated chromosomes.
Meiosis ensures genetic variation through the following:
Independent assortment: Homologous chromosomes are randomly divided between the four gametes, so long as each gamete has at least one of each chromosome.
Crossing over: Homologous chromosomes swap genes with each other, thereby increasing the number of combinations of genes on each chromosome.
Mendelian Genetics (Topic 5.3)
Genetics is using heredity to analyze the inheritance of traits and make predictions.
Gregor Mendel discovered that traits get masked from others during inheritance.
Masked traits are produced by inheriting two recessive alleles (one from each parent), while dominant traits only require one allele to be expressed.
Alleles are versions of the same gene.
Genotype: Alleles an organism inherits.
Phenotype: Physical traits determined by genotype.
Punnett squares use Mendel's laws to predict the outcome of a genetic cross:
Non-Mendelian Genetics (Topic 5.4)
Exceptions to Mendelian laws include:
Both alleles for a characteristic are dominant, or neither are dominant.
One gene affects multiple phenotypes, or multiple genes impact one phenotype.
The inheritance of one gene alters the phenotype produced at another gene.
Some genes aren't part of nuclear DNA, but are inherited through mitochondrial DNA.
Genes are located on a sex chromosome (X or Y).
Thomas Hunt Morgan found that some sets of genes are more likely to be inherited together because they are located on the same chromosome or linked.
Genes that are closer together on a chromosome are less likely to get flip-flopped during crossing over.
Genes that are further apart tend to get swapped, breaking Mendel's law of segregation, which said that genes are inherited independently of one another.
Environmental Effects on Phenotype (Topic 5.5)
Environment plays a large role in phenotypic variations.
Phenotypic plasticity is when a phenotype is altered by the environment.
In humans, things like skin color, height, weight, and intelligence are multifactorial.
Examples include:
The sex of reptiles when they're born is determined by the temperature at which their eggs are incubated.
In orchids, the color of the petals is determined by the pH of the soil that flowers are planted in.
Chromosomal Inheritance (Topic 5.6)
Chromosomes are assorted independently during meiosis, where each sex cell gets a unique set of chromosomes.
Studying how chromosomes are inherited has led to a better understanding of genetic diseases.
Some disorders result from a mutation in a gene located on a chromosome or from the inheritance of too many or not enough chromosomes.
Are the genes mutated allele dominant? Recessive? Autosomal? Sex-Linked? Some disorders are caused by a nondisjunction of chromosomes during meiosis, where chromosomes do not properly separate from one another.
When chromosomes do not properly separate from one another it leads to one gamete having too many chromosomes and another not having enough.
Aneuploidy is having an odd number of chromosomes.
Examples: Down syndrome or Trisomy 21.
DNA and RNA Structure (Topic 6.1)
Gene expression: Process by which genes (DNA segments) are used to make specific proteins.
DNA: Carries molecular instructions from parents to build proteins.
DNA is packaged into chromosomes made of chromatin (DNA wound around histones).
Plasmids: Circular DNA pieces that are not packaged into chromosomes and are copied separately.
DNA is a double helix comprised of two antiparallel polynucleotide strands bound together by phosphodiester bonds and by hydrogen bonds between the nitrogenous bases A and T and C and G.
RNA is one polynucleotide strand, with U instead of T.
DNA Replication (Topic 6.2)
DNA replication is semiconservative: Each new molecule has one template strand and one newly synthesized strand.
Helicase splits open the two DNA strands, while the Single-strand binding proteins make sure that they stay open.
Topoisomerase makes sure that the DNA strands don't supercoil upstream of the replication fork.
Primase places an RNA primer on both DNA template strands to serve as a starting point for DNA polymerase, which starts to synthesize new DNA nucleotides that match up with those templates.
DNA polymerases can only make new strands in the 5' to 3' direction.
Because DNA is antiparallel, one new strand is built in the forward direction, but the other strand needs to be built backwards, so only a piece of the new strand can be built at a time. These pieces are referred to as Okazaki fragments.
Ligase seals Okazaki fragments together.
Transcription and RNA Processing (Topic 6.3)
Transcription: Production of mRNA from DNA (temporary gene copy).
RNA polymerase produces a complementary mRNA strand based off of a DNA template strand and is by prying open the double helix and adjoining RNA nucleotides together as it slides down the template strand. It begins at the sequence called a promoter and ends at the terminator.
Transcription factors control whether RNA polymerase will bind to make sure that the mRNA makes it safely out of the nucleus and into the ribosome so that the right part of the gene is translated.
Primary mRNA transcript is processed, and thus:
A 5' prime GTP cap and a 3' prime poly A tail are added.
Splicing, which is where the unused, or non-coding regions, are removed and the coding regions are linked together, kind of like editing a video.
Translation (Topic 6.4)
Translation: mRNA gets brought to a ribosome (RNA and protein complex) that decodes the mRNA to assemble the correct amino acid sequence to make a polypeptide.
mRNA gets fed through the subunits of a ribosome, like putting originals into a copy machine.
Three nucleotides of mRNA form a codon, and it binds with the ribosome at a time, while another RNA called transfer RNA or tRNA matches its complementary anticodon to the mRNA in order to bring one amino acid to the ribosome.
Example: codon AUG matches anticodon UAC, and tRNA transfers methionine to the ribosome.
The ribosome continues reading the mRNA three nucleotides at a time, and tRNA puts together a chain of amino acids based on the mRNA code until a stop codon is reached, and it gets cut off.
Viruses (Topic 6.4)
The central dogma of molecular biology says that all living things have DNA as their genetic material, transcribe individual genes into RNA, and then translates that RNA into a chain of amino acids in order to build a specific protein.
Viruses are just capsules of protein and DNA/RNA that take control of a cell's gene expression in order to spread more of themselves from cell to cell.
Viruses are not living things, so they are not considered living things by the scientific community.
Retroviruses (e.g., HIV) use reverse transcriptase to convert viral RNA into DNA.
The viral DNA is incorporated into the host cell's genome, which can then lay dormant and get copied every time a cell decides to divide.
Regulation of Gene Expression (Topic 6.5)
No cell needs to express every one of those genes.
Prokaryotes control gene expression through the use of operons, where the transcription of one gene is turned on or off by the presence or absence of a repressor protein, which binds itself to a segment of DNA upstream of a transcribed region called the operator.
Eukaryotes control gene expression in a variety of ways:
Modification of histones in chromosomes allows the cell to choose which genes to express on a chromosome.
Negative and positive transcription factors control binding RNA polymerase.
Different ways mRNA can be spliced.
Translation can be blocked with microRNAs.
Stop and break already finished proteins.
Gene Expression and Cell Specialization (Topic 6.6)
Multicellular organisms are made of tissues, organs, and organ systems.
Each cell typically does one job only; cells are highly specialized.
The function of a cell is determined by its regulation of gene expression in the body.
Each cell has a copy of DNA but uses only some of it.
Signal tells stem cells which combinations of genes to express, determining their cell type. A neuron will express a combination of genes to send signals, while a red blood cell will express genes that allow it to carry oxygen.
Mutations (Topic 6.7)
Mutations are random changes to genetic information.
Change in DNA results in a change in a protein, which leads to a change in a phenotype or a trait.
Point mutation: When a single nucleotide is changed, which can alter an mRNA codon or affect the protein structure and function if it changes an amino acid.
Frameshift mutation: Extra nucleotides are inserted or deleted, changing the groups of three nucleotides. Ribosomes read, which ultimately leads to different amino acids being used.
Bacteria pass mutations down vertically or horizontally with plasmids.
Biotechnology (Topic 6.8)
Restriction enzymes are derived from bacteria that scientists cut DNA in specific locations.
Bacterial transformation inserts a gene into a plasmid, which is absorbed into bacteria to be expressed in large quantities.
Polymerase chain reactions copy a target gene in high speed, making billions of copies using a special heat-resistant DNA polymerase.
Gel electrophoresis uses restriction enzymes to compare DNA from two sources.
Introduction to Natural Selection (Topic 7.1)
Evolution explains why living things are the way they are.
Species change and become new species.
A scientific theory answers the questions that begin with why.
Evolution explains why all life is so diverse and related, and also why living things are so well adapted to their environments.
Darwin's contribution to science is that his work provided the main reason for why species change, which is natural selection.
Natural Selection (Topic 7.2)
Individual organisms do not evolve; populations do.
Genetic variation amongst members of a species creates a variety of phenotypes and genetic traits.
Those that have an easier time surviving and reproducing have more fitness and are following survival of the fittest.
The environment in which a population lives determines which genes and traits are more likely to be passed down than others.
As generations pass, and those with the genes giving a leg up on the competition reproduce more frequently, those genes become more common.
Artificial Selection (Topic 7.3)
Natural selection occurs when the environments select traits based on advantage for survival and reproduction.
Artificial selection: When traits that are beneficial to people are more likely to be passed down because
humans selectively breed the organisms with their desired traits.Humans control evolution through selecting which organisms reproduce, and it has shaped how human society has developed over thousands of years.
For example, dogs wouldn't exist without people only allowing particular ones to breed based on traits that are preferable to us.
Generations of farmers only used seeds from the best harvest and using that to plant for the next harvest.
Population Genetics (Topic 7.4)
Microevolution is when a gene pool changes from one generation to the next.
Little changes over a long time become big changes.
Microevolution happens for these five reasons:
Natural selection
Gene flow, where members of a population move in or out of it, taking their genes with them and altering gene pools.
Mutations that create new alleles.
Sexual
Genetic Drift
Hardy Weinberg Equilibrium
p² + 2pq + q² =1
p + q = 1