Ch.11 Cell Communication

Question 1

describe the basic signal-transduction pathway used for mating in yeast.
Explain the evidence that these pathways evolved before the first multicellular organisms appeared on Earth.

Answer 1

each yeast cell secretes a mating factor that binds to receptors on the other cell type. Binding of the factors to receptors induces changes in the cells that lead to their fusion. The nucleus of the fused cell includes all the genes from the a and alpha cells.

Question 2

explain the evidence that these pathways evolved before the first multicellular organisms appeared on Earth.

Answer 2

the similarities in animal, plant, and bacteria cell signaling provide proof the pathways evolved before organisms became multicellular.

Question 3

explain how plant and animal hormones travel to target cells

Answer 3

• plant: travel in vessels, move through cells,
  diffuse through air as a gas
• animal: circulatory system (bloodstream)

Question 4

list the three stages of cells signaling

Answer 4

1. reception
2. transduction
3. response

Question 5

describe the reception step of the cell signaling process

Answer 5

the target cell detects a signal from outside the cell by the signal binding to a receptor on the target cell’s plasma membrane or inside the cell

Question 6

describe the transduction step of the cell signaling process

Answer 6

the binding of the signal changes the receptor protein’s shape and initiates transduction, this is where the signal is converted to a form that brings about a specific cell response `

Question 7

describe the response step of the cell signaling process

Answer 7

the transduced signal triggers a specific cellular response: catalysis of enzymes, rearrangement of cytoskeleton, transcription of genes

Question 8

describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system

Answer 8

signaling molecule(ligand) shape is specific to the binding site of its receptor. binding causes a receptor protein to undergo a change in shape which either activates the receptor, enabling it to interact with other molecules. Or, causes the aggregation of two or more receptor molecules leading to further molecular events inside the cell

Question 9

state where signal receptors may be located in target cells

Answer 9

in/on the plasma membrane or inside cell(cytoplasm)

Question 10

compare and contrast G-protein-linked receptors, tyrosine-kinase receptors, and ligand-gated ion channels

Answer 10

G-protein-linked receptors: plasma membrane receptor that works with the help of a G-protein. G protein uses energy of GTP to activate, and then activate an enzyme that triggers a cellular response
Tyrosine-kinase receptor: dimerize upon ligand-binding, and use ATP to activate tyrosine kinase regions. Multiple relay proteins act upon the regions and become activated, leading to a cellular response.
Ligand-gated ion channels: ligand binds and a gate opens or closes, allowing or blocking the flow of ions through a channel across the membrane. Change in concentration leads to a cellular response

Question 11

list two advantages of using a multistep pathway in the transduction stage of cell signaling

Answer 11

1. greatly amplifies the signal
2. provides more opportunities for coordination and regulation than simpler systems

Question 12

explain how an original signal molecule can produce a cellular response when it may not even enter the target cell

Answer 12

the original signal molecule information is passed on through the relay molecule pathway

Question 13

describe how phosphorylation propagates signal information

Answer 13

The signal is transmitted by a cascade of protein phosphorylations, each causing a shape change because of the interaction of the newly added phosphate groups with charge or polar amino acids on the protein being phosphorylated. The change in shape alters the function of the protein, most often activating it. The added phosphates amplify the signal by the end

Question 14

explain why a single cell may require hundreds of different protein kinases

Answer 14

each kinase is specific for a different substrate protein

Question 15

explain how protein phosphates turn off signal-transduction pathways

Answer 15

remove phosphate groups from proteins, deactivating the protein kinases so no initial signal is present

Question 16

define second messenger. briefly describe the role of these molecules in signaling pathways

Answer 16

second messengers are small, non-protein, water-soluble molecules that can spread easily by diffusion. They participate in pathways that are initiated by both G protein-linked receptors and receptor tyrosine kinases. The two most widely used are cyclic AMP and calcium ions

Question 17

describe how cyclic AMP is formed and how it propagates signal info in target cells

Answer 17

cyclic AMP is formed from the binding of epinephrine to the plasma membrane of a liver which elevates the cytosolic concentration of cyclic AMP. When it is created cAMP broadcasts the signal to the cytoplasm

Question 18

describe how the cytosolic concentration of Ca2+ can be altered and how the increased pool of Ca2+ is involved with signal transduction

Answer 18

in plant cells, a wide range of hormonal and environmental stimuli can cause brief increases in cytosolic Ca2+ concentration, triggering various signaling pathways. In response to a signal relayed by a signal transduction pathway, the cytosolic calcium level may rise, usually by a mechanism that releases calcium from the cell’s ER. The pathways leading to calcium release involve two other second messengers, IP3 and DAG

Question 19

describe how signal info is transduced into cellular responses in the cytoplasm and in the nucleus

Answer 19

pathways of reactions, one protein binds to another, which binds to another, and so on, until it reaches its target and produces a cellular response in nucleus

Question 20

describe how signal amplification is accomplished in target cells

Answer 20

elaborate enzyme cascades amplify the cell’s response to a signal. At each catalytic step in the cascade, the number of activated products can be much greater than in the preceding step

Question 21

explain why different types of cells may respond differently to the same signal molecule

Answer 21

the particular proteins a cell possesses(relay,receptor,and response) determine what signaling molecules it responds to and the nature of the response. The proteins are different because they code for different genes

Question 22

explain how scaffolding proteins help to contribute a cell’s response to incoming signals

Answer 22

scaffolding proteins are large relay proteins to which several other relay proteins are attached. It carries all these proteins with it when binding to a receptor, thus facilitating the transduction of these molecules

Question 23

describe the roles of ced-3, ced-4, and ced-9, in apoptosis during embryonic development in Caenorhabditis elegans

Answer 23

ced-3 and ced-4 are two key apoptosis genes that encode proteins essential for apoptosis. ced-3 a protease triggers a cascade of reactions leading to activation of nucleases and other proteases.
ced-9:a protein in the outer mitochondrial membrane acts as a brake in the absence of a signal promoting apoptosis.
When a death signal is received by the cell, Ced-9 is inactivated and ced-3/4 are uninhibited

Question 24

describe the events that may trigger signals from within a cell to trigger apoptosis

Answer 24

1. signal is generated from the nucleus when the DNA is has suffered irreparable damage
2. ER signals when excessive protein misfolding occurs

Question 25

describe the role of apoptosis in normal development and degenerative disease in vertebrates

Answer 25

cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components. The cell shrinks and becomes loved and the cell’s parts are packaged up in vesicles that are engulfed and digested by specialized scavenger cells. This is needed because it is essential for normal development of the nervous system, normal operation of the immune system, and for normal morphogenesis of hands and feet in humans and paw in other mammals.