Exam # 3 Study Guide Chapters: 9 – 13, 43 Chapter 9: Cell Communication. Terms and Definitions: - Ligand: a signaling molecule that is required in cell communication. - Receptor protein: a molecule to which the signal binds. Why do cells communicate? Cells communicate in several ways in order to influence one another and create a certain action. Interaction occurs between ligands and receptor proteins to initiate signal transduction, which converts the signal information into a cellular response. What molecules can be used as signals? The molecules that can be used as signals include: -large proteins -amino acids -peptides -nucleotides -steroids and other lipids. What are the four basic kinds of cell signaling? 1. Direct Contact: -Cells that are in direct contact may send signals through gap junctions. -When cells are close to one another, some of the surface molecules (proteins, carbohydrates, and lipids) on one cell can be recognized by receptors on the other cell. BIO 183 1st Edition2. Paracrine signaling: -Secretions from one cell affect only the cells in the immediate area. -Signal molecules released by cells diffuse through extracellular fluid to another cell. -Paracrine signals are local and short-lived. 3. Endocrine signaling: -Signal molecules found in the extracellular fluid enter the circulatory system and travel throughout the body. -These signals called ‘hormones’ are long-lived and they affect distant cells.4. Synaptic signaling: -Neurotransmitters (signal molecules) are transmitted from a neuron to a target cell. -The association of a neuron and its target cell is called ‘chemical synapse’. What is a ‘signal transduction’? What is the function of a signal transduction pathway? -Signal transduction is the event that occurs in the cell on receipt of a signal. This event forms discrete pathways that lead to a cellular response to the signal received. -The function of a signal transduction pathway is to change the nature of a cell in response to a signal. This action requires changing the composition of proteins in the cell (ie. activating or deactivating proteins).Protein function can be controlled by adding or removing phosphate groups by phosphorylation or dephosphorylation, respectively. Phosphorylation: addition of phosphate group to a protein using the enzyme protein kinase. Dephosphorylation: removal of phosphate group from a protein using the enzyme phosphatase. What are the different types of receptors? -Cells must have a specific receptor to be able to respond to a particular signaling molecule. -Receptor types: - Intracellular receptors: -Many signals are lipid-soluble or very small that can pass through the plasma membrane of the target cell, where they interact with intracellular receptors found in the cytoplasm or nucleus. -Steroid hormone is an example of a nonpolar structure that can cross the membrane and bind to intracellular receptors. -Steroid hormone receptors function as regulators of gene expression. These receptors have three domains: (1) hormone-binding domain, (2) DNA-binding domain, and (3) a domain that can interact with coactivators. -Coactivators are proteins that increase gene expression by binding to activators which contain a DNA binding domain. - Membrane/ Cell surface receptors: -Membrane receptors include three subclasses: 1. Channel-linked receptors: -Chemically gated ion channels allow the passage of ions through pores that open and close by chemical signals (ligands).2. Enzymatic receptors: -Ligands activate the enzyme when they bind to receptors. When the enzymes become activated, they transmit the signal across the membrane. 3. G protein-coupled receptors (GPCR): -GPCR bind to ligands outside the cell and to G proteins inside the cell. The G protein activates an enzyme or ion channel (GTP and α bind to enzyme) transmitting signals to the interior of the cell. The G protein is composed of three subunits α, β, and ɣ called heterotrimeric G proteins.  The G protein provides a link between a receptor that receives signals and effector proteins that produce cellular responses. These proteins are inactive when bound to GDP and active when bound to GTP.  When the G protein becomes activated, it exchanges GDP for GTP and dissociates into Gα bound to GTP that turns on the effector proteins. The hydrolysis of GTP to GDP turns off the process. The effector proteins produce a second messenger. The most common effectors are adenylyl cyclase and phospholipase C that produce cyclic adenosine monophosphate ‘cAMP’ (a second messenger). The cAMP binds to and activates the enzyme protein kinase A (PKA) which adds phosphate (phosphorylation) to proteins in the cell. Chapter 10: How Cells Divide. Terms and Definitions: - Chromosome: a threadlike structure of nucleic acids and protein found in the nucleus that carries genetic information in the form of genes. - Karyotype: a picture of a person's chromosomes. It describes the number of chromosomes, and what they look like under a light microscope. - Diploid cells: somatic/body cells containing 2 sets of chromosomes (2n). - Haploid cells: sex cells (sperm and egg cells) containing 1 set of chromosomes (n). How do bacteria divide? Bacteria divide by a process called “Binary fission”. Bacteria have a genome made up of a singular, circular DNA molecule. DNA is not located in the nucleus, but in the nucleoid, a region that is distinct from the cytoplasm. -Steps of Binary fission: 1. Bacterial double-stranded DNA molecule replicates. This replication begins at a specific site called ‘origin of replication’. 2. The replication enzymes move out in both directions and make copies of DNA strands. These enzymes meet at a specific site called ‘terminus of replication’. 3. The cell elongates as the DNA is replicated and partitioned in the cell such that the termini are oriented toward the middle.4. A new membrane and cell wall begin to grow forming a septum at the midpoint of the cell. The protein FtsZ facilitates this process. 5. The cell divides into two daughter cells, each containing a bacterial DNA molecule. Structure of Chromosome: -Kinetochore are specialized protein complexes assembled on the centromere that connect to spindle microtubules and mediate proper chromosome segregation during cell division.-Sister chromatids are two replicas of a chromosome held together at the centromere. -Homologous chromosomes are the