AP Bio Midterm

Unit One: Chemistry of Life

1.1 Structure of Water and Hydrogen Bonding

Objective: Explain how the properties of water that result from
its polarity and hydrogen bonding affect its biological function.

Key Terms:

• Polarity: the sharing of electrons within a compound

• Hydrogen bonding: when H is bonded to NOF. Intramolecular (ex. between DNA strands) and intermolecular (ex. between two H2O molecules). Keep proteins folded.

• Cohesion: hydrogen bonds hold water molecules together, resulting in high surface tension.

• Adhesion: an attraction between different substances (ex. water and plant wall) that helps counter gravitational down pull

• Electronegativity: water is a polar covalent molecule because the oxygen is more electronegative than hydrogen (electronegativity is the tendency of an atom or a functional group to attract electrons toward itself)

• Hydrophilic vs. Hydrophobic: hydrophobic materials are 'water-fearing', and do not mix with water, whereas hydrophilic materials are 'water-loving' and have a tendency to be wetted by water

• Specific heat of water: specific heat is the amount of heat that must be absorbed or lost for 1g of a substance by 1 degree celsius. Water is resistant to changes in temperature because of its high specific heat (heat is absorbed when H bonds break and vise versa) 

• pH scale: more H+ = lower pH

• Acid: pH between 1-7

• Base: pH between 7-14

• Buffer: substances that minimize changes in concentration to maintain a constant pH

• 4 Emergent properties of water: cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent

1.2 Elements of Life

Objective: Describe the composition of macromolecules required by living organisms.

Key Terms:

• Carbon: Carbon is the basis for biological molecules. It can form 4 bonds and create a ‘carbon skeleton’. 

• Carbon skeletons: Variation in carbon skeletons is an important source of molecular complexity/diversity (vary in length, double bond position, and rings)

• Organic molecules: contain carbon and hydrogen (the first to by synthesized was urea)

• Isomers: compounds with the same molecular formula but different structure

• Structural isomers: differ in covalent arrangement

• Cistrans isomers: differ in spatial arrangement

• Enantiomers: mirror images of eachother but differ because of an asymmetrical carbon (important in pharmaceuticals)

• Main Elements of Life: Carbon, Hydrogen, Nitrogen, Phosphorus, and Sulfur

• Carbohydrates: made of CHO, a source of energy and provide structural support

• Lipids: hydrophobic molecules of CHO, provide energy, make up cell membrane, and hormones

• Protein: made of CHON, catalyze reactions, transport, support, etc.

1.3 Intro to Biological Macromolecules

Objective: Describe the properties of the monomers and the type of bonds that connect the monomers in biological macromolecules.

Key Terms:

• Hydrolysis: breaking down a polymer by add a molecule of water (H attaches to one monomer and OH to the other)

• Dehydration synthesis: synthesizing a polymer by removing a molecule of water (each reactant contribute part of the H2O being removed to form a bond)

• Covalent bond: bond resulting from two atoms sharing an electron

• Aldoses: A carbohydrate with the carbonyl group at the end

• Ketoses: A carbohydrate with the carbonyl group within the skeleton

• Glucose: a type of sugar. Alpha glucose and beta glucose are enantiomers, differing in the location of their hydroxyl group (enzymes that hydrolyze alpha linkages can't do beta linkages)

• Glycosidic linkage: covalent bond formed between monosaccharides in dehydration synthesis

1.4 Properties of Biological Macromolecules

Objective: Describe the properties of the monomers and the type of bonds that connect the monomers in biological macromolecules.

Key Terms:

• Peptide bond: covalent bond between the carboxyl group on one amino acid to the group on the other

• Amino acid: monomers of proteins, have R groups that give them characteristics/shape

• R-group: a side chain specific to each amino acid that confers particular chemical properties to that amino acid (ex. if the R-group is a hydrocarbon the amino acid is non-polar)

• Amino terminus: 

• Carboxyl terminus:

• Phospholipids: make up the membrane, two fatty acids and a phosphate (hydrophilic head and hydrophobic tail)

• Chitin: a hard to break compound that's embedded in some proteins (found in the exoskeleton of arthropods and fungi cell walls)

• Cellulose: the structural polysaccharide of plant walls, consists of glucose joined by beta linkages (humans cannot digest cellulose, it works as an insoluble fiber in our bodies)

1.5 Structure and Function of Biological Macromolecules

Objective: Explain how a change in the subunits of a polymer may lead to changes in structure or function of the macromolecule.

Key Terms:

• Hydrogenation: process of converting unsaturated fats to saturated fats

• Trans fats: result of hydrogenating vegetable oils - an unsaturated fat with trans double bonds

• Steroids: cyclical chemical compounds made up of 4 rings of carbon atoms, distinguishable by the chemical group attached (ex. cholesterol)

• Primary structure: the sequence of amino acids (determined by DNA)

• Secondary structure: beta pleated or alpha helix (hydrogen bonded)

• Tertiary structure: caused by bond between R groups (disulfide bridge is the strongest and reinforces the protein)

• Quaternary structure: results when a protein consists of multiple polypeptide chains

• Denaturation: protein loses its shape (gets rid of all but the primary structure)

• Plaque deposits: build up of fatty substances, cellular waste, etc (clogs arteries) 

1.6 Nucleic Acids

Objective: Describe the structural similarities and differences between DNA and RNA.

Key Terms:

• DNA: deoxyribose nucleic acid - double helix, stays in the nucleus

• RNA: ribonucleic acid - single strand, thymine is replaced by uracil, directs synthesis (mRNA)

• Nucleotide: made of a nitrogenous base, a pentose sugar, and one or more phosphate groups. Nucleotides are bonded by phosphodiester bonds and antiparallel strands are bonded by hydrogen bonds at the nitrogenous bases

• Phosphate group: PO4

• Nitrogenous bases: Adenine, Thymine (Uracil in RNA), Guanine, Cytosine

• 5’ to 3’:Nucleic acid sequences are written from the 5' phosphate end to the 3' hydroxyl end 

• Pyrimidines: a family of nitrogenous bases including cytosine, thymine and uracil

• Purines: a family of nitrogenous bases including adenine and guanine

• Transcription: the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA)

• Translation:the process by which a cell makes proteins using the genetic information carried in messenger RNA (mRNA)

Unit Two: Cell Structure and Function

2.1 Cell Structure: Subcellular Components

Objective: Describe the structure and/ or function of subcellular components and organelles.

Key Terms:

• Ribosomes: responsible for protein synthesis in the E.R and cytoplasm. Attaches to mRNA to build a protein.

• Rough E.R: makes secretory proteins and membrane phospholipids. Works with membrane bound ribosomes to take polypeptides and amino acids from the cytosol, threading it through the lumen (pores) to make secretory proteins (usually glycoproteins)

• Smooth E.R: synthesizes lipids, metabolizes carbs, detoxes drugs, and stores calcium ions.

• Golgi apparatus: modifies, stores, and routes products of the E.R. Cis face receives products and trans face exports them using transport vesicles.

• Mitochondria: site of cellular respiration. Enclosed by two phospholipid bilayers.

• Lysosomes: used to digest (hydrolyze) macromolecules. Acidic inner condition to suit lysosomal enzymes (hydrolytic) which break down material. Lysosomes can use their enzymes for autophagy, which is the recycling of the cell's own material.

• Vacuole: large vesicles derived from the E.R. (ex. contractile vacuole pumps excess water out of the cell and the central vacuole helps plants grow)

• Chloroplast: site of photosynthesis, contains chlorophyll, thylakoids, and stroma.

• Cytoskeleton: provides mechanical/structural support to cells and enables cell motility. Consists of microtubules, centrosomes, centrioles, cilla, flagella, microfilaments, and intermediate filaments.

2.2 Cell Structure and Function

Objective: Explain how subcellular components and organelles contribute to the function of the cell. Describe the structural features of a cell that allow organisms to capture, store, and use energy.

Key Terms:

• Thylakoid: flattened membranous sacs stacked into grana inside the chloroplast. Location of the light dependent reactions of photosynthesis.

• Stroma: fluid within the inner chloroplast membrane (outside the thylakoid). Contains ribosomes, enzymes, etc.

• Endomembrane system: a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins. Includes the nuclear membrane, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles and the plasma membrane.

• Carbon fixation: part of photosynthesis. Occurs in the stroma.

• Mitochondrial matrix: krebs cycle occurs here

• Inner mitochondrial membrane: electron transport chain and ATP synthesis occurs here

2.3 Cell Size

Objective: Explain the effect of surface area-to-volume ratios on the exchange of materials between cells or organisms and the environment.

Key Terms:

• Surface area-to-volume ratio: as cells increase in volume, the relative surface area decreases and the demand for internal resources increases. Thus ​​more complex cellular structures (e.g., membrane folds) are necessary to adequately exchange materials with the environment.

• Cristae: infolding of the outer mitochondrial membrane to give it a larger surface area

• Plasma Membrane: acts as a physical barrier between the external environment and the inner cell organelles. The plasma membrane is a selectively permeable membrane, which permits the movement of only certain molecules both in and out of the cell.

2.4 Plasma Membrane

Objective: Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the cell. Describe the Fluid Mosaic Model of cell membranes.

Key Terms:

• Phospholipid bilayer: made of two layers of phospholipids. The hydrophilic phosphate head is oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid tails face each other within the interior of the membrane.

• Integral proteins: penetrate the hydrophobic interior of the lipid bilayer

• Transmembrane proteins: integral proteins that span the entire membrane

• Peripheral proteins: loosely bound to the surface of the membrane, not embedded at all

• Integrins: type of transmembrane proteins that combine to give animal cells a stronger framework

• Fluid mosaic model: describes the plasma membrane structure as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.

2.5 Membrane Permeability 

Objective: Explain how the structure of biological membranes influences selective permeability. Describe the role of the cell wall in maintaining cell structure and function.

Key Terms: 

• Selective permeability: Selective permeability is a direct consequence of membrane structure, as described by the fluid mosaic model.

• Cell wall: external layer of plant cells that is specifically designed to provide structural support and rigidity

2.6 Membrane Transport

Objective: Describe the mechanisms that organisms use to maintain solute and water balance. Describe the mechanisms that organisms use to transport large molecules across the plasma membrane.

Key Terms:

• Passive transport: does not require ATP

• Active transport: requires ATP

• Exocytosis: bulk transport out of the cell using a vesicle from the golgi apparatus that fuses to the plasma membrane and spills its contents to the outside

• Endocytosis: bulk transport into the cell. Three types: phagocytosis (in amoeba and bacteria, vacuole fuses with lysosomes to digest), pinocytosis (smaller, coated pit, used by humans for cholesterol), and receptor-mediated (specific)

2.7 Facilitated Diffusion

Objective: Explain how the structure of a molecule affects its ability to pass through the plasma membrane.

Key Terms:

• Aquaporins: assist passive movement of water

• Channel proteins: create a “hole” in membrane for things to passively move through 

• Transport proteins: help large hydrophobic mqs pass through the layer

2.8 Tonicity and Osmoregulation

Objective: Explain how concentration gradients affect the movement of molecules across membranes. Explain how osmoregulatory mechanisms contribute to the health and survival of organisms.

• Osmosis: The movement of water molecules across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration.

• Diffusion: The process by which molecules spread from an area of higher concentration to an area of lower concentration until equilibrium is reached.

• Water potential: The potential energy of water in a system, driving the movement of water, influenced by solute concentration and pressure. (Ψ=Ψp +Ψs)

• Pressure potential: The component of water potential that refers to the physical pressure exerted on water within a cell or vessel.

• Solute potential: The component of water potential that is determined by the concentration of dissolved solutes in the solution. (Ψs =−iCRT)

• Lysed: The condition where a cell bursts due to excessive water intake, typically in a hypotonic environment.

• Plasmolysis: The process in which a plant cell's plasma membrane pulls away from the cell wall due to water loss in a hypertonic environment.

• Isotonic: A solution with the same solute concentration as another solution, resulting in no net movement of water.

• Hypertonic: A solution with a higher solute concentration compared to another solution, leading to water loss from a cell.

• Hypotonic: A solution with a lower solute concentration compared to another solution, leading to water intake into a cell.

2.9 Mechanisms of Transport

Objective: Describe the processes that allow ions and other molecules to move across membranes.

Key Terms:

• Cotransport: A process in which the transport of one substance across a membrane is coupled with the transport of another substance, often in the same direction (symport) or opposite direction (antiport).

• Ion pumps: Membrane proteins that actively transport ions across a membrane against their concentration gradient, typically using energy from ATP.

2.10 Cell Compartmentalization

Objective: Describe the membrane- bound structures of the eukaryotic cell. Explain how internal membranes and membrane- bound organelles contribute to compartmentalization of eukaryotic cell functions.

2.11 Origins of Cell Compartmentalization

Objective: Describe similarities and/or differences in compartmentalization between prokaryotic and eukaryotic cells.

Key Terms:

• Endosymbiotic theory: The hypothesis that certain organelles, such as mitochondria and chloroplasts, originated from free-living prokaryotes that were engulfed by a host cell in a symbiotic relationship.

• Prokaryotes: Single-celled organisms that lack a membrane-bound nucleus and other membrane-bound organelles, such as bacteria and archaea.

• Eukaryotes: Organisms whose cells contain a membrane-bound nucleus and organelles, including plants, animals, fungi, and protists.

Unit Three: Cellular Energetics

3.1 Enzyme Structure

Objective: Describe the properties of enzymes.

Key Terms:

• Enzyme: a protein that acts as a catalyst for reactions. Work by lowering the activation energy of a reaction.

• Active site: place that holds the substrate

• Substrate: the substance an enzyme acts upon

• Cofactors: Cofactors are non protein helpers that bind to the enzyme permanently, or reversibly with the substrate. Inorganic cofactors include metal atoms such as zinc, iron, and copper in ionic form. Organic cofactors are called coenzymes

• Induced fit model: the enzyme and substrate undergo structural changes to achieve an optimal fit

• Lock-and-key model: portrays an enzyme as conformationally rigid and able to bond only to substrates that exactly fit the active site.

• Enzyme specificity: enzymes are specific to one reaction or substrate

3.2 Enzyme Catalysis

Objective: Explain how enzymes affect the rate of biological reactions.

Key Terms:

• Competitive inhibition: a molecule binds to the active site, blocking the substrate from binding (can be combatted by adding more substrate)

• Non-competitive inhibition: a molecule binds to another area of the enzyme, changing its shape

• Allosteric regulation: any form of regulation where the regulatory molecule (an activator or inhibitor) binds to an enzyme someplace other than the active site

• Activation energy: minimum energy required to start a reaction

3.3 Environmental Impact on Enzyme Function

Objective: Explain how changes to the structure of an enzyme may affect its function.

Key Terms:

• pH: Environmental pH can alter the efficiency of enzyme activity, including through disruption of hydrogen bonds that provide enzyme structure.

• Temperature: Higher environmental temperatures increase the speed of movement of molecules in a solution, increasing the frequency of collisions between enzymes and substrates and therefore increasing the rate of reaction. However, temperatures outside the optimal range can cause changes to the enzyme's structure.

• Denaturation: Denaturation of an enzyme occurs when the protein structure is disrupted, eliminating the ability to catalyze reactions.

• Optimal conditions: conditions in which the efficiency of the enzyme-substrate complex is maximized

• Substrate concentration: The relative concentrations of substrates and products determine how efficiently an enzymatic reaction proceeds. More substrate = higher chance of collision

3.4 Cellular Energy

Objective: Describe the role of energy in living organisms.

Key Terms:

• ATP (Adenosine triphosphate): high energy molecule used to power cell work. When the terminal phosphate bond of ATP is broken through hydrolysis it releases a lot of energy that can be used

• Energy coupling: use of energy released from an exergonic reaction to fuel an endergonic reaction

• Endergonic reactions: change in free energy (G) is zero or positive, meaning energy was consumed (anabolic)

• Exergonic reactions: change in free energy (G) is negative, meaning energy was released (catabolic)

• Phosphorylation: attachment of a phosphate to a molecule, making it less stable with more free energy

• Redox reactions: chemical reaction that involves the transfer of electrons between reactants

• 2nd Law of Thermodynamics: Energy input must exceed energy loss to maintain order and to power cellular processes. Cellular processes that release energy may be coupled with cellular processes that require energy. Loss of order or energy flow results in death.

3.5 Photosynthesis

Objective: Describe the photosynthetic processes that allow organisms to capture and store energy.

Key Terms:

• Chlorophyll: Chlorophyll is the pigment that absorbs light energy for photosynthesis. Found in the thylakoid membranes of chloroplasts. Chlorophyll absorbs light (primarily in the blue and red wavelengths) to excite electrons.

• Photosystem I : in the thylakoid. Photosystem I receives electrons from Photosystem II and uses light to reduce NADP+ to NADPH.

• Photosystem II: in the thylakoid. Photosystem II captures light to split water molecules, generating oxygen and high-energy electrons.

• Light-dependent reactions: These reactions require light to generate ATP and NADPH, which are used in the light-independent reactions (Calvin Cycle). Oxygen is released as a byproduct.

• Light-independent reactions (Calvin Cycle): in the stroma of the chloroplast. The Calvin Cycle uses ATP and NADPH (from the light-dependent reactions) to fix CO₂ into organic molecules, ultimately producing G3P, a sugar precursor.

• ATP synthase: in the thylakoid membrane. ATP synthase is an enzyme that synthesizes ATP from ADP and inorganic phosphate (Pi) using the energy from a proton gradient created by the electron transport chain.

• NADPH: Electron carrier in photosynthesis

• Carbon fixation: during the calvin cycle. Carbon fixation is the process of incorporating carbon dioxide from the atmosphere into an organic molecule (RuBP) in the Calvin Cycle. This is the first step in forming glucose.

• RuBP (Ribulose bisphosphate): RuBP is a 5-carbon molecule that combines with CO₂ during carbon fixation in the Calvin Cycle to form two molecules of 3-PGA.

• G3P (Glyceraldehyde-3-phosphate): G3P is a 3-carbon sugar produced during the Calvin Cycle. It can be used to form glucose and other carbohydrates.

• Electron transport chain: The electron transport chain is a series of protein complexes in the thylakoid membrane that transfer electrons from Photosystem II to Photosystem I. This process pumps protons into the thylakoid lumen, generating a proton gradient used by ATP synthase to produce ATP.

• Carbon dioxide: enters leaf through stomata

3.6 Cellular Respiration

Objective: Describe the processes that allow organisms to use energy stored in biological macromolecules.

Key Terms:

• Glycolysis: occurs in the cytoplasm

  • Energy investment phase: 2 ATP split glucose into two carbon sugars

  • Energy payoff phase: 4 ATP synthesized (net 2 ATP), 2 NAD+ reduced to NADH, sugars oxidized to form 2 pyruvate and 2 H2O

• Citric acid cycle (Krebs cycle): occurs in the mitochondrial matrix

  • Products: oxidizes organic fuel from pyruvate. Generates 1 ATP, NADH and FADH2 per turn, as well as 2 CO2 as waste (2 turns per glucose molecule)

• Electron transport chain (ETC): electrons from NADH and FADH2 pass through carrier molecules down a chain. Carriers alternate between reduced and oxidized as they accept and donate electrons, breaking down the drop in free energy into smaller steps. The final acceptor is O2.

• Chemiosmosis: energy released during the ETC is used to pump H+ from the mitochondrial matrix to the intermembrane space. The H+ then moves down the gradient through ATP synthase, causing it to catalyze the phosphorylation of ADP

• Oxidative phosphorylation: the synthesis of ATP from ADP and inorganic phosphate by chemiosmosis

• Aerobic respiration: most efficient catabolic pathway. Requires oxygen 

• Anaerobic respiration: harvests energy without oxygen

• Lactic acid fermentation: no oxygen. After glycolysis NADH reduces pyruvate to lactic acid. Used by fungi and bacteria to make cheese and by muscle cells.

• Alcohol fermentation: CO2 is released from pyruvate, then NAD+ and ethanol are produced. Used by yeast.

3.7 Fitness

Objective: Explain the connection between variation in the number and types of molecules within cells to the ability of the organism to survive and/or reproduce in different environments.

Key Terms:

• Adaptation: Adaptation is the process by which organisms become better suited to their environment through genetic changes, improving survival and reproduction. These changes often involve molecular variations in cells, like enzymes or pigments, which help organisms thrive in specific environments.

• Wavelengths: Wavelengths refer to the different lengths of light waves, which organisms can use or detect (e.g., for photosynthesis or vision). The ability to absorb or perceive certain wavelengths is crucial for survival and reproduction.

Unit Four: Cell Communication and Cell Cycle

4.1 Cell Communication

Objective: Describe the ways that cells can communicate with one another. Explain how cells communicate with one another over short and long distances.

Key Terms:

• Cell signaling: The process by which cells communicate through chemical signals, triggering responses inside the cell.

• Cell communication: The exchange of information between cells, allowing them to coordinate activities.

• Local signaling: Communication between nearby cells, including paracrine (nearby cells), autocrine (self-signaling), and synaptic signaling (nerve cell signaling)

• Long-distance signaling: Communication between distant cells, typically via hormones traveling through the bloodstream (endocrine signaling).

• Receptor proteins: Proteins on or inside cells that bind to signaling molecules (ligands), initiating a response.

• Ligands: Signaling molecules that bind to receptor proteins to trigger a cellular response.

• Signal molecules: Molecules involved in cell signaling, such as hormones or neurotransmitters, that convey messages between cells.

4.2 Intro to Signal Transduction

Objective: Describe the components of a signal transduction pathway. Describe the role of components of a signal transduction pathway in producing a cellular response.

Key Terms:

• Signal transduction: The process of converting an external signal into a cellular response

• G-protein coupled receptors (GPCRs): Membrane receptors that activate G-proteins to trigger an intracellular signaling pathway.

• Second messengers: Small molecules like cAMP that relay and amplify signals inside the cell.

• cAMP (Cyclic AMP): A second messenger that activates protein kinases to amplify signals.

• Protein kinases: Enzymes that add phosphate groups to proteins, regulating their activity.

• Phosphorylation cascade: A series of protein activations through phosphorylation, amplifying the signal.

• Signal amplification: The process where a small signal leads to a large cellular response.

4.3 Signal Transduction

Objective: Describe the role of the environment in eliciting a cellular response. Describe the different types of cellular responses elicited by a signal transduction pathway.

Key Terms:

• Cellular Response: The series of events that occur in a cell after it receives a signal, resulting in a change in cell behavior, such as gene expression or cell division.

• Gene Expression: The process by which information from a gene is used to synthesize a functional gene product, typically proteins, that carry out cellular functions.

• Apoptosis: Programmed cell death, a controlled process that eliminates damaged or unnecessary cells in an organism.

• Cell Division: The process by which a cell divides into two daughter cells, including mitosis (for growth and repair) and meiosis (for reproduction).

• Metabolic Changes: Alterations in the cell’s metabolic processes, such as energy production or consumption, in response to external signals.

• Transcription Factors: Proteins that regulate the transcription of specific genes by binding to DNA and influencing RNA production.

• Cell Differentiation: The process by which a cell becomes specialized to perform a specific function, often during development.

• Growth Factors: Signaling molecules that stimulate cell growth, division, and differentiation.

• Stress Response: The cell’s reaction to stress (e.g., damage or environmental changes), including repair mechanisms or activation of apoptosis.

• Inhibition of Cellular Processes: The suppression or downregulation of certain cellular functions, often as a regulatory mechanism in response to signals or stress.

• Cellular Communication: The exchange of signals between cells, enabling them to coordinate activities and responses to environmental or internal cues.

4.4 Changes in Signal Transduction Pathways

Objective: Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway.

Key Terms:

• Mutation: A change in the DNA sequence of a gene that can result in a change in the protein produced, potentially altering cellular functions or behaviors.

• Signal Molecule Alteration: Changes in the structure or function of signaling molecules (ligands), which may affect how they bind to receptors and trigger cellular responses.

• Receptor Mutation: A mutation in the gene encoding a receptor protein that may alter the receptor’s structure, function, or ability to bind to its ligand, potentially disrupting normal signaling.

• Signal Pathway Disruption: Interruption or alteration of the normal sequence of events in a signal transduction pathway, which can result from mutations in receptors, enzymes, or other components, leading to abnormal cellular responses.

4.5 Feedback

Objective: Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway. Explain how negative feedback helps to maintain homeostasis. Explain how positive feedback affects homeostasis.

Key Terms:

• Negative Feedback: A regulatory mechanism in which a change in a variable triggers a response that counteracts or reduces that change, helping to maintain stability (e.g., body temperature regulation).

• Positive Feedback: A mechanism in which a change in a variable triggers a response that amplifies or increases that change, often leading to a dramatic outcome (e.g., blood clotting or childbirth contractions).

• Homeostasis: The process by which living organisms maintain a stable internal environment (e.g., temperature, pH, and glucose levels) despite external changes.

• Feedback Loop: A cycle in which the output of a system is fed back into the system as input, influencing the system's activity. It can be either positive or negative.

• Feedback Inhibition: A form of negative feedback where the product of a process inhibits its own production by acting on an earlier step in the process, preventing overproduction (e.g., regulation of enzyme activity)

4.6 Cell Cycle

Objective: Describe the events that occur in the cell cycle. Explain how mitosis results in the transmission of chromosomes from one generation to the next.

Key Terms:

• Interphase: The cell grows; in preparation for cell division, the chromosomes are duplicated, with the genetic material (DNA) copied precisely.

• G1 phase: metabolic growth and activity

• S phase (Synthesis): metabolic growth, activity, and DNA synthesis

• G2 phase: chromosomes duplicated but uncondensed, prep for cell division

• Mitosis: The chromosome copies are separated from each other and moved to opposite ends of the cell.

• Cytokinesis: splitting of the cell. Cleavage furrow in animal cells, cell plate in plant cells.

• Prophase: The first stage of mitosis, where chromosomes become visible as they condense, the nuclear envelope starts to break down, and the spindle apparatus begins to form.

• Metaphase: The stage of mitosis where chromosomes align at the cell's equator, or metaphase plate, ensuring they are positioned for proper separation.

• Anaphase: The stage of mitosis where sister chromatids are pulled apart to opposite poles of the cell, ensuring that each daughter cell will receive an identical set of chromosomes.

• Telophase: The final stage of mitosis, where the separated chromosomes begin to decondense, and nuclear envelopes reform around each set of chromosomes, resulting in two distinct nuclei.

• Chromosomes: Condensed

• Spindle Apparatus: A structure made up of microtubules that forms during mitosis, helping to align and separate chromosomes by attaching to the centromeres and pulling the chromatids apart.

• Centrosomes: Organelles that organize the microtubules of the spindle apparatus during mitosis. Each centrosome contains a pair of centrioles that play a role in organizing the spindle fibers.

• Chromatin: loose (condenses to form a chromosome during mitosis)

4.7 Regulation of Cell Cycle

Objective: Describe the role of checkpoints in regulating the cell cycle. Describe the effects of disruptions to the cell cycle on the cell or organism.

Key Terms:

• Cell cycle checkpoints

• Cyclins: Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks). 

• Cyclin-dependent kinases (CDKs): when cyclin binds to CDKs it triggers a phosphorylation cascade. The CDK becomes phosphorylated by ATP and then transfers phosphate groups to other proteins and molecules to activate a cellular response that drives the cell cycle forward.

• Cell cycle arrest: cell stops replicating and dividing

• Cell division regulation

• M checkpoint: internal signal in M. Anaphase wont start til all the chromosomes are attached to the spindle.

• G1 checkpoint: If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2 and M phases and divide. If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0

• Cancer: does not require growth factors.

• MPF (maturation promoting factor): a cyclin-CDK complex that triggers a cell's passage from G2 to M. Peak MPF activity = peak cyclin concentration.