AP Biology Unit 4 Cell Communication PDF

AP Biology Unit 4: Cell Communication and Cell Cycle  Topic 4.1/2/3/4  Cell Communication Cell-to-cell communication is critical for the function and survival of cells Responsible for the growth and development of multicellular organisms  Cells communicate through...

AP Biology Unit 4: Cell Communication and Cell Cycle  Topic 4.1/2/3/4  Cell Communication Cell-to-cell communication is critical for the function and survival of cells Responsible for the growth and development of multicellular organisms  Cells communicate through three general ways How Do Cells 1. Direct Contact Communicate? 2. Local Signaling 3. Long-distance signaling  Direct Contact Direct contact: communication through cell junctions Signaling substances and other material dissolved in the cytoplasm can pass freely between adjacent cells Animal cells: gap junctions Plant cells: plasmodesmata Direct Contact Example: Immune cells Antigen presenting cells (APCs) communicate to T cells through direct contact  Local regulators: a secreting cell will release chemical Local Regulators messages (local regulators/ligands) that travel a short distance through the extracellular fluid The chemical messages will cause a response in a target cell Examples: Paracrine signaling Synaptic signaling  Local Regulators Paracrine signaling: secretory Target cell cells release local regulators Local regulator (ie growth factors) via exocytosis to an adjacent cell Secretory cell that acts on nearby cells  Local Regulators Axon Synaptic signaling: Occurs in animal nervous systems Neurotransmitters Neurons secrete neurotransmitters Diffuse across the synaptic cleft- space Synaptic cleft between the nerve cell and target cell Target cell  Long Distance Signaling Animals and plants use hormones for long distance signaling Plants release hormones that travel in the plant vascular tissue (xylem and phloem) or through the air to reach target tissues Animals use endocrine signaling Specialized cells release hormones into the circulatory system where they reach target cells  Long Distance Signaling Example: Insulin Insulin is released by the pancreas into the bloodstream where it circulates through the body and binds to target cells  What type of communication involves 01 a cell secreting a substance to an adjacent target cell? Quick Check Plant cells in direct contact with each 02 other can diffuse substances through these structures to communicate. What are they?  What type of communication involves 01 a cell secreting a substance to an adjacent target cell? Answer: paracrine signaling Quick Check Plant cells in direct contact with each 02 other can diffuse substances through these structures to communicate. What are they?  What type of communication involves 01 a cell secreting a substance to an adjacent target cell? Answer: paracrine signaling Quick Check Plant cells in direct contact with each 02 other can diffuse substances through these structures to communicate. What are they? Answer: plasmodesmata Practice Problems Card Sort How do you think cells process signals?  Cell Signaling: Overview Cell-to-cell messages can be divided into three stages 1. Reception Ligand binds to receptor  Cell Signaling: Overview Cell-to-cell messages can be divided into three stages 1. Reception Ligand binds to receptor 2. Transduction Signal is converted  Cell Signaling: Overview Cell-to-cell messages can be divided into three stages 1. Reception Ligand binds to receptor 2. Transduction Signal is converted 3. Response A cell process is altered A C B  Stage 1: Reception Reception: the detection and receiving of a ligand by a receptor in the target cell Receptor: macromolecule that binds to a signal molecule (ligand) All receptors have an area that interacts with the ligand and an area that transmits a signal to another protein Binding between ligand and receptor is highly specific  Stage 1: Reception When the ligand binds to the receptor, the receptor activates (via a conformational change) Allows the receptor to interact with other cellular molecules Initiates transduction signal Receptors can be in the plasma membrane or intracellular  Stage 1: Reception Plasma Membrane Receptors Intracellular Receptors Most common type of Found in the cytoplasm or receptor involved in signal nucleus of target cell pathways Bind to ligands that can pass Bind to ligands that are: through the plasma Polar, water-soluble membrane Large Ie hydrophobic molecules Examples: Steroid and thyroid G protein coupled hormones receptors (GPCRs) Gasses like nitric Ligand-gated ion channels oxide  Stage 1: Reception Note: the AP exam will not expect you to be able to classify any given molecule as hydrophobic, usually they will either tell you it is hydrophobic, or they will say the molecule is a steroid hormone Intracellular receptors  Stage 2: Transduction Transduction: the conversion of an extracellular signal to an intracellular signal that will bring about a cellular response Requires a sequence of changes in a series of molecules known as a signal transduction pathway Intracellular signaling molecules  Stage 2: Transduction The signal transduction pathway regulates protein activity through: Phosphorylation by the enzyme protein kinase Relays signal inside cell Dephosphorylation by the enzyme protein phosphatase Shuts off pathways Intracellular *Remember: a change in signaling molecules shape means a change in function  Stage 2: Transduction During transduction the signal is amplified Second messengers: small, non-protein molecules and ions help relay the message and amplify the response Intracellular Cyclic AMP (cAMP) is a signaling common second molecules messenger © Getting Down With Science  Stage 3: Response Response: the final molecule in the signaling pathway converts the signal to a response that will alter a cellular process Examples: a. Protein that can alter membrane permeability b. Enzyme that will change a metabolic process c. Protein that turns genes on A B C or off Quick Review 01 02 03 What are the three What is the actual How is this “signal” stages of cell “signal” being passed from outside signaling? transduced in a to inside the cell? signal transduction pathway? Quick Review 01 02 03 What are the three What is the actual How is this “signal” stages of cell “signal” being passed from outside signaling? transduced in a to inside the cell? Answer: reception, signal transduction transduction, reponse pathway? Quick Review 01 02 03 What are the three What is the actual How is this “signal” stages of cell “signal” being passed from outside signaling? transduced in a to inside the cell? Answer: reception, signal transduction transduction, reponse pathway? Answer: a ligand Quick Review 01 02 03 What are the three What is the actual How is this “signal” stages of cell “signal” being passed from outside signaling? transduced in a to inside the cell? Answer: reception, signal transduction Answer: through transduction. transduction, reponse pathway? During transduction the signal is relayed by protein kinases Answer: a ligand and amplified by second messengers  Signal Transduction Pathways Signal transduction pathways can influence how a cell responds to its environment They can result in changes in gene expression and cell function Can alter phenotypes or result in cell death  Mutations to receptor proteins or to any component of the signaling pathway will result in a change to the transduction of the signal Changes in Signal Transduction Pathways  Some diseases, such as cancer and diabetes, are caused by defective protein Practice FRQ phosphatases. Explain how such a defective protein would affect a signal transduction pathway. Important Receptors In eukaryotic organisms there are two main categories of cell membrane receptors: G protein coupled receptors (GPCRs) Ion channels  GPCRs G protein coupled receptors (GPCRs): Largest category of cell surface receptors Important in animal sensory systems Binds to a G protein that can bind to GTP, which is an energy molecule similar to ATP  GPCRs The GPCR, enzyme, and G protein are inactive until ligand binding to GPCR on the extracellular side Inactive ligand enzyme Inactive G protein Inativate GPCR  GPCRs Ligand binding causes cytoplasmic side to change shape Allows for the G protein to bind to GPCR Activates the GPCR and G protein GDP becomes GTP  GPCRs Part of the activated G protein can then bind to the enzyme Activates enzyme Amplifies signal and leads to a cellular response Ion Channels Ligand gated ion channels: Located in the plasma membrane Important in the nervous system Receptors that act as a “gate” for ions When a ligand binds to the receptor, the “gate” opens or closes allowing the diffusion of specific ions Initiates a series of events that lead to a cellular response Ion Channels Topic 4.5 © Getting Down With Science  Overview The body must be able to monitor its internal conditions at all times Set points: values for various physiological conditions that the body tries to maintain This set point has a normal range for which it can fluctuate Example: body temperature Set point: 98.6℉ Normal range: 97℉ to 99℉  Overview Homeostasis: the state of relatively stable internal conditions Organisms detect and respond to a stimulus Think: balance The body maintains homeostasis through feedback loops  Feedback loops There are two types of feedback loops: negative and positive Terms to know: Stimulus: a variable that will cause a response Receptor/sensor: sensory organs that detect a stimulus. This information is sent to the control center (brain) Effector: muscle or gland that will respond Response: changes (decreases or increases) the effect of the stimulus  Negative Feedback The most common feedback mechanism This type of feedback reduces the effect of the stimulus Examples: Sweat Blood sugar Breathing rate  Example: Negative Feedback Body temperature regulation Stimulus: heat Stimulus: cold Receptor: temperature Receptor: temperature receptors in skin receptors in skin Effector: sweat glands Happy Effector: muscles Patrick Response: sweat Response: shivering Sweaty Patrick Shivering Patrick  Positive Feedback This type of feedback increases the effect of a stimulus Examples: Child labor Blood clotting Fruit ripening  Example: Positive Feedback Stimulus: baby pushes on cervix Childbirth Receptor: nerve cells in Response: Oxytocin cervix send signal to stimulates contractions brain Effector: pituitary gland releases oxytocin  Homeostatic Imbalances There are many reasons for why the body may not be able to regulate homeostasis For example: Genetic disorders Drug or alcohol abuse Intolerable conditions (ie extreme heat or cold)  Homeostatic Imbalances Disease: when the body is unable to maintain homeostasis Examples: Cancer: the body cannot regulate cell growth Diabetes: the body cannot regulate blood glucose levels  Cell Signaling as a Means of Homeostasis In order to maintain homeostasis, the cells in a multicellular organism must be able to communicate Communication occurs through signal transduction pathways  Topic 4.6/7 © Getting Down With Science  Cell Cycle The cell division process is an integral part of life Allows for the reproduction of cells, growth of cells, and tissue repair Cell cycle: the life of a cell from its formation until it divides  Organization of DNA Cells must organize and package their DNA before division DNA associates with and wraps around proteins known as histones to form nucleosomes Strings of nucleosomes form chromatin When a cell is not actively dividing, chromatin is in a non- condensed form After DNA replication, chromatin condenses to form a chromosome Chromosomes are densely packed to allow for easier division  Organization of DNA Since the DNA was replicated, each chromosome has a duplicated copy The copies join together to form sister chromatids Centromere: the region on each sister chromatid where they are most closely attached Kinetochore: proteins attached to the centromere that link each sister chromatid to the mitotic spindle  Genome Genome: all of a cell’s genetic information (DNA) Prokaryotes: singular, circular DNA Eukaryotes: one or more linear chromosomes Every eukaryote has a specific number of chromosomes Humans: 46 Chimps: 48 Elephants: 56  Genome Homologous chromosomes: two chromosomes (one from mom and one from dad) that are the same length, have the same centromere position, and carry genes controlling the same characteristics  Practice FRQ Biological structures tend to be composed of smaller units that assemble into more complex structures. Using eukaryotic chromosomes as an example, a) describe the smaller units and their assembly that leads to the larger, more complex structure of a chromosome. b) Identify one major function of chromosomes.  Types of Cells Somatic Cells Gametes Body cells Reproductive cells Diploid (2n): two sets of (eggs/sperm) chromosomes, one set Haploid (n): one set of from each parent chromosomes Divide by mitosis Divide by meiosis Humans: 2n=46 Humans: n=23 23 from mom 23 from dad Cell Cycle  Cell Cycle The cell cycle consists of alternating phases of interphase and mitosis G₁→ S→ G₂ → mitosis → cytokinesis Interphase  Cell Cycle Interphase The longest portion of the cell cycle (90%) G1 “first gap” phase The cell grows and carries out normal functions S “synthesis” phase DNA replication and chromosome duplication occurs G2 “second gap” phase Final growth and preparation for mitosis M Phase Mitosis: nucleus divides Cytokinesis: cytoplasm divides Mitosis results in 2 identical diploid daughter cells  Phases of Mitosis Mitosis is broken down into 5 stages: 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase and cytokinesis Key events: Prophase Chromatin condenses Nucleoli disappear Duplicated chromosomes appear as sister chromatids Mitotic spindle begins to form Centrosomes move away from each other  Prometaphase Key events: Nuclear envelope fragments Microtubules enter nuclear area and some attach to kinetochores  Metaphase Key events: Centrosomes are at opposite poles Chromosomes line up at the metaphase plate Microtubules are attached to each kinetochore  Anaphase Key events: Sister chromatids separate and move to opposite ends of the cell due to the microtubules shortening Cell elongates  Telophase and Cytokinesis Key events: Two daughter nuclei form Nucleoli reappear Chromosomes become less condensed  Telophase and Cytokinesis Cytokinesis occurs Animals: a cleavage furrow appears due to a contractile ring of actin filaments Plants: vesicles produced by the Golgi travel to the middle of the cell and form a cell plate  Tracking Chromosomes Maternal chromosomes Paternal chromosomes 2n=2 daughter cells Parent cell 2n=2 2 chromosomes 2 chromosomes After S phase 2 chromosomes 4 chromatids Anaphase © Getting Down With Science 4 chromosomes Human Cells: Tracking Chromosomes Can you identify stages of mitosis in the image below? © Getting Down With Science  Practice Multiple Choice 1. Movement of the chromosomes during anaphase would be most affected by a drug that prevents A) nuclear envelope breakdown. B) cell wall formation C) elongation of microtubules. D) shortening of microtubules. E) formation of a cleavage furrow  Practice Multiple Choice 1. Movement of the chromosomes during anaphase would be most affected by a drug that prevents A) nuclear envelope breakdown. B) cell wall formation C) elongation of microtubules. D) shortening of microtubules. E) formation of a cleavage furrow  Practice Multiple Choice 2. Eukaryotic chromatin is composed of a. condensed DNA only b. DNA and RNA c. DNA and carbohydrates d. DNA and proteins e. DNA and ribosomes  Practice Multiple Choice 2. Eukaryotic chromatin is composed of a. condensed DNA only b. DNA and RNA c. DNA and carbohydrates d. DNA and proteins e. DNA and ribosomes  Practice Multiple Choice 3. If a sperm cell contains 12 chromosomes, it comes from an animal that has ______ chromosomes. a. 4 b. 8 c. 12 d. 16 e. 24  Practice Multiple Choice 3. If a sperm cell contains 12 chromosomes, it comes from an animal that has ______ chromosomes. a. 4 b. 8 c. 12 d. 16 e. 24  Practice FRQ A cell has 50 chromosomes. After mitosis and cell division, you find that one daughter cell has 49 chromosomes and the other daughter cell has 51 chromosomes. Predict one way that this could have happened. Regulation of the Cell Cycle Throughout the cell cycle there are checkpoints Control points that regulate the cell cycle Cells receive stop/go signals  Major Checkpoints G₁ Checkpoint Most important checkpoint Checks for cell size, growth factors, and DNA damage Stop/Go signals “Go”- cell completes the whole cell cycle “Stop”- cell enters a nondividing (quiescent) state known as G₀ phase  Major Checkpoints G₀ Some cells stay in G₀ forever (muscle/nerve cells) Some cells can be called back into the cell cycle  Major Checkpoints G₂ Checkpoint Checks for completion of DNA replication and DNA damage “Go”--cell proceeds to mitosis “Stop”-- cell cycle stops and the cell will attempt to repair damage If damage cannot be repaired the cell will undergo apoptosis Programmed cell death  Major Checkpoints M (Spindle) Checkpoint Checks for microtubule attachment to chromosomes at the kinetochores at metaphase “Go”--cell proceeds to anaphase and completes mitosis “Stop”-- cell will pause mitosis to allow for spindles to finish attaching to chromosomes  Internal Cell Cycle Regulators Regulation of the cell cycle involves an internal control system that consists of: 1. Proteins known as cyclins Concentration of cyclins varies Cyclins are synthesized and degraded at specific stages of the cell cycle 2. Enzymes known as cyclin-dependent kinases (CDKs) Concentration remains constant through each phase of the cell cycle Active only when its specific cyclin is present  Internal Cell Cycle Regulators Each cyclin-CDK complex has a specific regulatory effect Active CDK complexes phosphorylate target proteins, which help regulate key events in the cell cycle Notice: varying levels of different cyclins in each stage  External Cell Cycle Regulators Growth factors: hormones released by cells that stimulate cell growth Signal transduction pathway is initiated CDKs are activated leading to progression through the cell cycle Contact (or density) inhibition: Cell surface receptors recognize contact with other cells Initiates signal transduction pathway that stops the cell cycle in G₁ phase Anchorage dependence: cells rely on attachment to other cells or the extracellular matrix to divide Cancer: Evasion of the Cell Cycle Normal cells become cancerous through DNA mutations DNA mutations: changes in the DNA Cancer cells on average have accumulated 60 or more mutations on genes that regulate cell growth  Normal Cells vs Cancer Cells Normal Cells Cancer Cells Follow checkpoints Do not follow Divide on average checkpoints 20-50 times in Divide infinitely when culture (in petri in culture dishes) Considered to be Go through “immortal” apoptosis when Evade apoptosis and there are significant continue dividing even errors with errors  Cancer Cells The uncontrollable growth of cancer cells can lead to a tumor A mass of tissue formed by abnormal cells Benign tumor: cells are abnormal, but not considered to be cancerous (yet) Cells remain at only the tumor site and are unable to spread elsewhere in the body Malignant tumor: mass of cancerous cells that lose their anchorage dependency and can leave the tumor site Metastasis: when cells separate from the tumor and spread elsewhere in the body  Cancer Prevention Unfortunately, cancer can affect anyone. However, there are various things that you can do that will minimize your risk of developing cancer: Do not smoke (cigarettes, vape products) Nicotine causes mutations in cells at high rates Eat healthy and drink water Fatty foods and dehydration can affect the functions of cells Protect your skin from the sun by using SPF Sun is damaging to skin cells and can cause mutations to occur after exposure If possible, ask your family about any history of cancer and receive regular cancer screenings  Practice FRQ Vinblastine is a chemotherapeutic drug often administered to patients suffering from Hodgkin’s lymphoma, lung cancer, and bladder cancer. Vinblastine works by entering cancer cells and binding to tubulin, which is a protein that forms microtubules. Once Vinblastine has bound to tubulin, it inhibits the assembly of microtubules and proper formation of the mitotic spindle. This causes the cell cycle to arrest. a) Identify and explain two phases of the cell cycle most affected by Vinblastine. b) Identify the checkpoint that is most likely responsible for arresting the cell cycle.