AP Biology Unit 4 Reading Guide PDF

Name: ________________________ Period: ________ Unit 4: Cell Communication & Cell Cycle Reading Guide Topics: 1. Cell Communication 2. Signal Transduction 3. Homeostasis and Feedback Loops 4. The Cell Cycle 5. Cell Cycle Regulation and Cance...

Name: ________________________ Period: ________ Unit 4: Cell Communication & Cell Cycle Reading Guide Topics: 1. Cell Communication 2. Signal Transduction 3. Homeostasis and Feedback Loops 4. The Cell Cycle 5. Cell Cycle Regulation and Cancer Annotation Key All students are expected to complete annotations for the readings below. ❖ Pink highlighter → Vocabulary words ❖ Yellow highlighter → Key equations/formulas ❖ Underline → Definitions ❖ Circle→ Unfamiliar words ❖ Star → Key ideas/facts ❖ Write a question mark (?) → Next to anything that is confusing you ❖ Write down notes in the margins → Any questions you have or thoughts/comments you have about what you read Topic #1: Cell Communication What is Cell Communication? Cell communication refers to the processes through which cells can detect and respond to signals in their environment. This communication is crucial for coordinating various functions, including growth, development, and maintaining homeostasis. 1 Name: ________________________ Period: ________ How Do Cells Communicate? Cells communicate through three main types of signaling: direct contact, local signaling, and long-distance signaling. See the table on the next page that depicts these signaling types. 1. Direct Contact ○ Gap Junctions (Animals): Protein channels that connect adjacent cells. They enable the transfer of ions, small molecules, and electrical impulses directly between cells. i. For example, in cardiac muscle cells, gap junctions ensure that the heart contracts in a coordinated manner by allowing ions to flow quickly between cells. ○ Plasmodesmata (Plants): Microscopic channels that traverse the cell walls of plant cells. ○ Juxtacrine Signaling: Involves direct contact between immune cells and their target cells. i. NK cells bind to infected or cancerous cells through receptor-ligand interactions on their surfaces. 2. Local Signaling: ○ Autocrine Signaling: A cell targets itself. i. Cancer cells often use autocrine signaling to stimulate their own growth and proliferation. ○ Paracrine Signaling: A cell targets a nearby cell. i. This type of signaling is often seen in tissue repair and immune responses. ii. Example: growth factors signal nearby target cells to grown and divide ○ Synaptic Signaling: This is a specific type of local signaling used by neurons. i. Neurotransmitters are released from the synaptic terminal of a neuron and diffuse across the synaptic cleft to bind to receptors on the adjacent neuron, muscle cell, or gland, facilitating rapid communication across synapses. 3. Long-Distance Signaling: ○ Hormone Signaling in Plants: Plants use hormones to communicate over long distances through their vascular tissues, such as the phloem and xylem. ○ Endocrine Signaling in Animals: In animals, hormones are released into the bloodstream by endocrine glands and travel to target cells throughout the body. i. An example is insulin, which regulates blood sugar levels by signaling cells to uptake glucose. 2 Name: ________________________ Period: ________ Summary of Cell Signaling Types: 3 Name: ________________________ Period: ________ Topic #2: Signal Transduction Pathways Overview of Cell Signaling Cell signaling is a complex process that allows cells to communicate with each other and respond to their environment. This process is vital for numerous cellular functions, including growth, differentiation, and metabolism. Signal transduction involves three main stages: reception, transduction, and response. 1. Reception Reception is the first stage of cell signaling, where a signaling molecule, known as a ligand, binds to a receptor on the target cell's surface or inside the cell. Ligands and Receptors: ○ Ligands: These are signaling molecules that can be proteins, peptides, amino acids, steroids, or other types of molecules. They bind specifically to receptors. ○ Receptors: These are proteins that receive the signaling molecules. They can be located on the plasma membrane or within the cell (intracellular receptors). Types of Receptors: ○ Plasma Membrane Receptors: These receptors are embedded in the cell membrane and bind to ligands that cannot cross the membrane. Examples include G protein-coupled receptors (GPCRs) and ion channel receptors. GPCRs: These are a large family of receptors that work with the help of a G protein. When a ligand binds to a GPCR, it causes a conformational change that activates the G protein, starting the signal transduction pathway. 4 Name: ________________________ Period: ________ Ion Channels: These receptors act as gates that open or close in response to a ligand, allowing ions to flow into or out of the cell. ○ Intracellular Receptors: These receptors are found inside the cell, in the cytoplasm or nucleus. They bind to ligands that can cross the cell membrane, such as steroid hormones. When the ligand binds, the receptor-ligand complex can directly influence gene expression. Conformational Change: When a ligand binds to its receptor, it causes a change in the receptor's shape (conformational change). This change is crucial as it initiates the signal transduction cascade, setting off a series of events inside the cell. 2. Transduction Transduction is the process by which the signal is converted into a form that can bring about a specific cellular response. Conversion of Signal: The extracellular signal (ligand binding) is converted into an intracellular signal through a series of steps often involving multiple molecules. Phosphorylation and Dephosphorylation: ○ Phosphorylation: Adding a phosphate group to a protein, typically using enzymes called kinases. This usually activates the protein. ○ Dephosphorylation: Removing a phosphate group, typically using enzymes called phosphatases. This usually deactivates the protein. Amplification via Second Messengers: Second messengers are small molecules that propagate the signal inside the cell. An example is cyclic AMP (cAMP), which is produced in response to a signal and activates other proteins to amplify the signal. 3. Response Response is the final stage, where the transduced signal triggers a specific cellular activity. 5 Name: ________________________ Period: ________ Altering Cellular Processes: The signal can lead to various cellular responses such as changes in gene expression, enzyme activity, or cell behavior. ○ Examples: A signal might cause a cell to divide, differentiate, or initiate apoptosis (programmed cell death). It could also lead to the secretion of hormones or other signaling molecules. Changes in Signaling Pathways: The pathways can be altered by changes in the environment, mutations in the signaling components, or the presence of other signaling molecules. Important Receptors in Signal Transduction G Protein-Coupled Receptors (GPCRs): These receptors interact with G proteins to transmit signals. ○ The ligand binding causes the GPCR to activate a G protein. ○ GDP becomes GTP. ○ The part of the activated G protein can bind and activate the enzyme. ○ Signal is amplified and can lead to a cellular response. Ion Channel Receptors: These open or close in response to a ligand binding, allowing ions to move across the cell membrane, which can change the cell’s electrical potential and trigger a response. ○ Location: Plasma membrane ○ Important in: Nervous system 6 Name: ________________________ Period: ________ Topic #3: Homeostasis and Feedback Loops Introduction to Homeostasis Homeostasis is the process by which living organisms maintain a stable internal environment despite changes in external conditions. This balance is crucial for the proper functioning of cells and, consequently, the entire organism. Some key words you should know are: Set Points: These are the ideal values or ranges that the body tries to maintain for various physiological conditions, such as temperature, pH, and glucose levels. Stimulus: Any change in the environment that can trigger a physical or behavioral response. For example, an increase in body temperature due to exercise. Receptor/Sensor: A receptor detects the stimulus. For instance, temperature sensors in the skin detect changes in external temperature. Effector: The effector is the organ or cell that acts to correct the deviation from the set point. For example, sweat glands act to cool the body. Response: The action taken by the effector to restore homeostasis. In our example, sweating helps to reduce body temperature. Feedback Loops Feedback loops are mechanisms that help maintain homeostasis. There are two main types: negative feedback loops and positive feedback loops. Negative Feedback Loops Negative feedback loops work to counteract changes that move conditions away from the set point, thereby maintaining equilibrium. What Happens: When a change is detected, the body initiates a response to reverse the change and bring conditions back to the set point. 7 Name: ________________________ Period: ________ Example: Thermoregulation in humans. When body temperature rises, receptors in the skin and brain detect the increase. The brain signals sweat glands to release sweat, which cools the body down, bringing the temperature back to the set point. ○ Stimulus: Increase in body temperature. ○ Receptor/Sensor: Receptors in the skin and brain. ○ Effector: Sweat glands. ○ Response: Release of sweat and subsequent cooling of the body. Positive Feedback Loops Positive feedback loops amplify changes, moving the system further from the set point. These are usually associated with processes that need to be pushed to completion. What Happens: When a change is detected, the body initiates a response that increases the change. Example: Childbirth. During labor, contractions of the uterus are intensified by the release of oxytocin, which increases the strength and frequency of contractions until the baby is born. ○ Stimulus: The baby pressing against the cervix. ○ Receptor/Sensor: Stretch receptors in the cervix. ○ Effector: Release of oxytocin from the pituitary gland. ○ Response: Intensified contractions of the uterus. Homeostatic Imbalances Homeostatic imbalances occur when the body is unable to maintain homeostasis, leading to diseases or disorders. Examples include diabetes, where blood glucose levels are not properly regulated and hyperthermia or hypothermia, where body temperature is not maintained within the normal range. Cell Signaling and Homeostasis Cell signaling plays a crucial role in maintaining homeostasis. It involves the transmission of signals between cells to coordinate actions and responses. 8 Name: ________________________ Period: ________ Topic #4: Cell Cycle The Cell Cycle The cell cycle is a series of stages that a cell goes through to grow and divide. This process is crucial for growth, tissue repair, and reproduction in living organisms. The cell cycle ensures that genetic material is accurately replicated and distributed to the daughter cells. DNA Organization 1. DNA Double Helix: The most relaxed form of DNA is the double helix, where the DNA molecule is coiled into a spiral shape. This structure allows the DNA to carry genetic information in the sequence of its bases (adenine, thymine, cytosine, and guanine). 2. Histones and Nucleosomes: In order to fit inside the cell nucleus, the DNA double helix wraps around special proteins called histones. When DNA is wrapped around histones, it forms structures called nucleosomes. Each nucleosome is made up of a segment of DNA wound around eight histone proteins, like beads on a string. This packaging helps to organize the DNA and regulate its accessibility for processes like transcription and replication. 3. Chromatin: The nucleosomes further coil and stack together to form chromatin. Chromatin is a more compact and organized form of DNA but still relatively relaxed compared to chromosomes. 4. Chromosomes: The most compact form of DNA organization occurs when chromatin further condenses during cell division to form chromosomes. Each chromosome is a single, continuous thread of DNA that has been tightly coiled and folded to ensure that it can be efficiently and accurately separated during cell division. This high level of compaction is necessary to prevent tangling and breakage of the DNA strands. 9 Name: ________________________ Period: ________ Chromosome Replication and the Formation of the X Shape 1. DNA Replication: Before a cell divides, during the S phase of interphase, the entire DNA molecule is duplicated. This ensures that each new cell will have the same genetic material as the original cell. 2. Sister Chromatids: After DNA replication, each chromosome consists of two identical DNA molecules called sister chromatids. These sister chromatids are joined together at a central region called the centromere, forming the characteristic X shape of a replicated chromosome. a. Attached to the centromere is a protein complex called the kinetochore, which plays a crucial role during cell division by linking the chromosomes to the spindle fibers. These spindle fibers help to pull the sister chromatids apart to opposite ends of the cell during mitosis, ensuring that each new cell receives an identical set of chromosomes. 3. Homologous Chromosomes (Homo- = same): Pairs of chromosomes in a diploid organism that have the same genes at the same loci but may have different alleles, one inherited from each parent. For example, chromosome 1 that you inherit from your mother and from your father are homologous chromosomes. The Genome The genome of an organism is its complete set of DNA, including all of its genes. Prokaryotic Genome: Typically consists of a single, circular chromosome located in the nucleoid region. Eukaryotic Genome: Consists of multiple, linear chromosomes contained within the nucleus. The number of chromosomes varies between species (e.g., humans have 46 chromosomes, while fruit flies have 8). Types of Cells Somatic Cells: These are body cells that undergo mitosis to produce genetically identical daughter cells. They are diploid (2n), meaning they have two sets of chromosomes—one from each parent. 10 Name: ________________________ Period: ________ Gametes: These are reproductive cells (sperm and eggs) that undergo meiosis to produce genetically unique cells. They are haploid (n), meaning they have one set of chromosomes. The Cell Cycle Stages The cell cycle is broken up into three main stages, (1) Interphase, which is when the cell is growing and preparing for division, (2) Mitosis, when the cell is dividing its genetic material and nucleus, and (3) Cytokinesis, which is the division of the cytoplasm and physical cell. 1. Interphase: This is the longest phase of the cell cycle, where the cell grows and prepares for division. It includes three sub-phases: ○ G1 Phase (First Gap): The cell grows and performs its normal functions. This phase ensures the cell is ready for DNA replication. ○ S Phase (Synthesis): DNA replication occurs, doubling the genetic material. Each chromosome is replicated to form two sister chromatids. ○ G2 Phase (Second Gap): The cell continues to grow and prepares for mitosis by producing the necessary proteins and organelles. 2. M Phase (Mitosis): This is the phase where the nucleus divides. It includes several stages: ○ Prophase: Chromatin condenses into visible chromosomes. The nucleoli disappear. The mitotic spindle, made of microtubules, begins to form. 11 Name: ________________________ Period: ________ ○ Prometaphase: The nuclear envelope breaks down, and spindle fibers attach to the kinetochores of chromosomes. ○ Metaphase: Chromosomes align at the cell’s equatorial plane, known as the metaphase plate. Microtubules are attached to each kinetochore. ○ Anaphase: Sister chromatids are pulled apart to opposite poles of the cell by the spindle fibers. The cell elongates. ○ Telophase: Nuclear envelopes reform around each set of separated sister chromatids, now individual chromosomes, and the chromosomes begin to decondense back into chromatin. 3. Cytokinesis: This is the process of dividing the cytoplasm to form two distinct daughter cells. ○ In Animals: A cleavage furrow forms, pinching the cell in two. 12 Name: ________________________ Period: ________ ○ In Plants: A cell plate forms down the middle of the cell and develops into a new cell wall, separating the two daughter cells. The summary table below shows the number of chromosomes present after each phase in mitosis. It is also helpful to be able to identify cells in different stages of mitosis under a microscope. An example of this is shown below. 13 Name: ________________________ Period: ________ Topic #5: Cell Cycle Regulation and Cancer Cell Cycle Regulation What is Cell Cycle Regulation? Cell cycle regulation ensures that cells divide correctly, preventing errors that could lead to problems like cancer. It involves various mechanisms that control the timing and sequence of events in the cell cycle, making sure cells only divide when they are ready and conditions are suitable. Checkpoints in the Cell Cycle Checkpoints are control points in the cell cycle where the cell assesses whether to proceed with division. The major checkpoints include: 1. G1 Checkpoint: This checkpoint checks for cell size, nutrients, growth factors, and DNA damage. If conditions are not right, the cell may enter a resting state (G0) or undergo apoptosis (programmed cell death). 2. G2 Checkpoint: This checkpoint ensures that DNA replication has been completed without damage. If errors are found, the cell cycle is halted for repairs or the cell undergoes apoptosis. 3. M Checkpoint: This checkpoint, also known as the spindle checkpoint, checks that all chromosomes are properly attached to the spindle fibers before proceeding with mitosis. Internal Cell Cycle Regulators Internal cell cycle regulators are molecules inside the cell that control the cell cycle's progression: 1. Cyclins: These are proteins whose levels fluctuate throughout the cell cycle. Different cyclins are produced at specific stages to regulate progression. 2. Cyclin-Dependent Kinases (CDKs): These enzymes become active when bound to cyclins. Active CDKs phosphorylate target proteins to drive the cell cycle forward. 14 Name: ________________________ Period: ________ External Cell Cycle Regulators are signals from outside the cell that influence cell division: 1. Growth Factors: These are proteins released by other cells that stimulate cell division by binding to receptors on the cell surface. 2. Contact Inhibition: Cells stop dividing when they come into contact with other cells, preventing overgrowth. 3. Anchorage Dependence: Cells must be attached to a solid surface to divide, ensuring they only grow in appropriate locations. Cancer Cancer is the result of uncontrolled cell division due to failures in cell cycle regulation. It can be caused by mutations in genes that regulate the cell cycle. Here's how cancer develops and progresses: 1. Normal vs. Cancerous Cells: ○ Normal Cells: Follow strict control mechanisms for division, stop dividing when necessary, and undergo apoptosis if damaged. ○ Cancerous Cells: Ignore regulatory signals, divide uncontrollably, do not respond to apoptosis signals, and can invade other tissues. 2. Mutations and Oncogenes: ○ Mutations: Changes in DNA that can activate oncogenes or inactivate tumor suppressor genes. ○ Oncogenes: Genes that, when mutated, promote uncontrolled cell division. ○ Tumor Suppressor Genes: Genes that normally prevent uncontrolled cell growth; mutations in these genes can lead to cancer. 15 Name: ________________________ Period: ________ 3. Tumors: ○ Benign Tumors: Non-cancerous growths that remain localized. ○ Malignant Tumors: Cancerous growths that invade nearby tissues and can spread to other parts of the body (metastasis). 4. Metastasis: The process by which cancer cells spread from the original site to other parts of the body, forming new tumors. Cancer Prevention Unfortunately, cancer can affect anyone; however there are ways to minimize your risk of developing cancer or catching it early, including: 1. Healthy Lifestyle: Avoiding tobacco, maintaining a healthy diet, exercising regularly, and protecting skin from excessive sun exposure. 2. Regular Screenings: Early detection through screenings like mammograms, colonoscopies, and skin checks can catch cancer early when it is most treatable. 3. Vaccinations: Vaccines like the HPV vaccine can prevent cancers caused by certain infections. 16