Unit 4: Cell Communication & Cell Cycle

multicellular: used to maintain homeostasis and survival of organism

unicellular: organisms communicate with each other and change behavior based on pop. density (quorum sensing)

signaling molecules that bind to receptors to alter activities of cell

protein on cell membrane that the ligand binds to

sequence of molecular events within a cell that leads to cell’s response to signal

1. reception: signal binds to ligand

2. transduction: receptor is activated by signal binding + amplifies signal

3. response

increasing the response to a signal, done through secondary messengers that distribute signal

cell signals itself and makes signal that binds to its own receptors

signals diffuse to and affect nearby cells (local signaling)

requires direct cell contact between signaling and responding cells, uses gap junctions (animal cells) and plasmodesmata (plant cells)

hormones travel to distant cells through bloodstream (long-distance)

intracellular: receptor is inside the cell so ligand diffuses across membrane

intercellular: ligand binds to receptor on cell membrane

intercellular receptor; helps ions move in when a ligand binds to receptor and opens channel

intercellular receptor

1. receptor binds to signal

2. receptor changes shape, which transmits signal to cytoplasm

3. signal activates receptor’s protein kinase domain in the cytoplasm

4. pk domain adds phosphate groups to targets, triggering response

intercellular receptor

1. hormone binds to receptor and activates G protein, and GTP replaces GDP

2. part of activated G protein activates an effector protein that converts reactants to products, amplifying response

3. GTP on G protein becomes GDP but remains bound to G protein

remove phosphate from target proteins to stop response

epinephrine (ligand) binds to:

• heart cells- activates uptake in glucose for muscle contractions

• digestive cells- inhibits so energy can be used for fight/flight instead

when you eat, blood glucose rises, so insulin binds to protein kinase receptor to initiate insertion of glucose transport proteins into cells

if glucose low, insulin binds to liver cells and cells break down glycogen into glucose

if calcium low, parathyroid hormone acts on kidneys to increase calcium reabsorption

positive- signals become amplified after signaling system is activated

negative- responds to a change in a system by returning system to set point

receive signals

where action potential starts

transmit signal to the next neuron

contains nucleus and organelles

gaps where action potential jumps along

make myelin

carries the action potential to the end of the neuron

covering along the axon, helps transmit signal faster

1. action potential arrives at the axon terminal

2. calcium channels open + calcium enters

3. calcium triggers a synaptic vesicle to surround acetylcholine (ligand)

4. vesicle fuses to membrane + acetylcholine is released

5. acetylcholine binds to receptors on dendrites of next neuron

6. transduction begins, another action potential is started

7. extra acetylcholine reabsorbed/broken down by enzymes

unicellular- reproduction

multicellular- growth/replacing dead or injured cells

binary fission; duplicates its genetic material and then divides into two parts

ensures that each daughter cell gets a copy of the genome

1. G1- cell grows and duplicates organelles

2. S- cell synthesizes copy of DNA

3. G2- cell grows, makes organelles, reorganizes DNA

DNA condenses, chromosomes become visible, centrioles move towards opposite sides of cell

nuclear envelope dissolves, chromosomes line up at metaphase plate, spindle fibers connect centromeres to centrioles

chromosomes move along spindles to opposite ends of cell, cell develops cleavage furrow

chromosomes spread out into chromatin, nuclear envelope reforms, spindle fibers break down

plant- cell plate becomes 2 cell membranes, cell wall forms between two membranes

animal- membrane draws inwards, cytoplasm pinched

G1- checks for cell size, nutrients, growth factors

S- checks for proper replication of DNA

G2- checks for DNA damage

protooncogene- codes for proteins that stimulate forward movement of cell cycle (MPF, cyclins)

tumor suppressor gene- codes for proteins that stop forward movement of cell cycle (P53, RB)

protein enzyme that controls cell cycle, always present but not active until connected to cyclin

cyclin-CDK complex that allows cells to pass G2 and go to M phase

disorder in which cells lose ability to control growth by not responding to regulation, causes tumors (benign/malignant) and metastasis (movement of cancer cells)