Show Menu
Cheatography
  1. Home >
  2. Education >

AP Biology: Unit 4 Cheat Sheet (DRAFT) by

Cell Communication & Cell Cycle

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Cell Signals

1. Direct Contact
↳ plasmo­desmata of plants~
open channels through the cell wall connecting adjacent cells allowing substances to pass between
↳ cell-cell recogn­ition~
intera­ction between molecules protruding from their surfaces (immune cells)
2. Local Signaling
↳ paracrine signaling~
secreting cell acts on nearby target cells by discha­rging growth factor molecules
↳ synaptic signaling~
nerve cells release neurot­ran­smitter molecules into synapse
3. Long Distance
↳ animal hormones~
cells secrete hormones into body fluids to target cell
↳ plant hormones~
hormones move through the cells (by xylem) or diffuse through the air as a gas

Step 1: Reception

- ligand:
molecule that binds specif­ically to another molecule
- plasma membrane receptors:
transmit inform­ation from extrac­ellular enviro­nment to inside of the cell by changing shape or aggreg­ating when a ligand binds
↳ cell surface receptors~
1. G protei­n-c­oupled receptors (GPCRs)
 
2. receptor tyrosine kinases (RTK)
 
3. ligand gates ion channels
↳ intrac­ellular receptor proteins

G Protei­n-C­oupled Receptor (GPCR)

- functi­on/­act­ivity: 1. embryonic develo­pment 2. sensory reception (smell, vision, etc.)
*GPCR Sequence*
↳ receptor is activated & changes shape
↳ binds to inactive G protein = GTP to replace GDP (activ­ating G protein)
↳ G protein binds to an enzyme (change in shape/­act­ivity)
↳ enzyme triggers next step for response
↳ G protein inacti­vates by hydrol­yzing bound GATP to GDP

Receptor Tyrosine Kinases (RTK)

- kinase: enzyme that catalyzes the transfer of phosphate groups
- differs from GPCR by triggering many pathways
*RTK Sequence*
↳ binding of signal causes 2 receptor monomers to come together = dimer
↳ tyrosine kinase region activated by ATP (adds a phosphate group)
↳ receptor recognized by relay proteins
↳ proteins bind (change shape) & activates protein
↳ transd­uct­ion­/re­sponse triggered

Ligand Gated Ion Channels

- for larger­/hy­dro­philic molecules
- can be controlled by electrical conditions -- voltag­e-gated ion channels
*Ligand Channel Sequence*
↳ signal molecule causes receptor gate to open/close
↳ ions flow through (NA+ or Ca+)

Intrac­ellular Receptor Proteins

2 areas present~
cytoplasm
 
nucleus of target cells
3 signal molecule types~
1. steroid hormones
 
2. thyroid hormones
 
3. nitric oxide
- once receptor protein is activated the signal molecules enter the nucleus and turn on specific genes

Step 2: Transd­uction

molecular intera­ctions relay signals from receptors to target molecules in the cell
 
ex) phosph­ory­lation cascade; second messengers
- signal amplif­ica­tion:
molecules in a pathway transmit the signal to many molecules at the next step
- advantage of multistep pathway responses~
more coordi­nation & regulation (fine-­tuning of response)

Protein Phosph­ory­lation

- protein phosph­atases: enzymes that remove phosphate groups (depho­sph­ory­lation)
- acts as a molecular switch to turn activities on/off or up/down
*Phosp­hor­ylation Sequence*
↳ a molecules receive phosphate group from ATP (serine & threonine) = phosph­ory­lation
↳ next molecule is activated in the pathway
↳ process continues to trigger response

Second Messengers

- second messenger: small, nonpro­tein, water-­soluble molecu­le/ion in transd­uction pathways
ex) cAMP, Ca2+
- cAMP level rise when epinep­hrine binds to liver membrane receptors
↳ causing a break down of glucose
↳ levels go back down from phosph­odi­est­erase (cAMP to AMP)
- 3 possible responses to calcium =
↳ 1. muscle cell contration 2. secretion of substances 3. cell division
↳ calcium released from ER when signal molecule (IP3) binds to cell

Step 3: Response

- cell signaling leads to regulation of transc­ription/cytop­lasmic activities
- many pathways regulate protein synthesis by turning specific genes on/off
4 FINE TUNING RESPONSE
1. signal amplif­ica­tion~
# of activated products gets increa­singly bigger
 
proteins process many molecules
2. specif­icity of signaling & coordi­nation of response~
different kinds of cells have different collec­tions of proteins (diff. responses from same signal)
3. effici­ency~
scaffo­lding proteins: large relay proteins w/ several relay proteins attached
 
creates more than one pathway
4. termin­ation of signal~
reverse change from prior signal to receive new one
 
by dephos­pho­riz­ation of relay proteins
 

Apoptosis

" programmed cell death"
- general process~
↳ DNA chopped up & organelles fragmented
↳ cell shrinks & becomes lobe shaped
↳ cell's parts are packaged into vesicles
↳ cell parts engulfed & digested by scavenger cells
- processes this is needed for~
1. develo­pment of nervous system
2. operation of immune system
3. morpho­genesis of hands/­fee­t/paws

Cell Cycle Background

- what two organism have cell division the same as reprod­uction?
1. prokar­yotes 2. unicel­lular eukaryotes
- what are the roles of cell division?
↳ growth, repair, reprod­uction, & replac­ement
- how do the genomes of prokar­yotes & eukaryotes differ?
↳ eukary­otes~ # of DNA molecules; larger; linear DNA; lots of non-coding DNA
 
↳ prokar­yotes~ single DNA molecule; smaller; looped DNA; more coding DNA
- somatic cell:
any cell in an organism except reprod­uctive cells (body cells)
- sister chromo­some:
2 copies of a duplicated chromosome attached at the centromere
- mitosis:
process of nuclear division (P, PM, M, A, T)
- cytoki­nesis:
division of the cytoplasm to form 2 separate daughter cells
- centro­meres
produce microt­ubules (in plants & animals)
- centrioles
microt­ubules that spindle fibers attach to (in animals only)
- binary fission:
asexual reprod­uction by "­div­ision in half" (proka­ryotes & unicel­lular eukary­otes)
- origin of replic­ation:
site where replic­ation of DNA molecule begins
- densit­y-d­epe­ndent inhibi­tion:
cell stop dividing when in contact with one another
- anchorage depend­ence:
cell must attach to a substance in order to divide

Cell Cycle Diagram

Interphase

- 3 sub phases of interp­hase~
↳ G
1
phase (first gap)=
cell growth
↳ S phase (synth­esis)=
DNA replic­ation
↳ G
2
phase (second gap)=
cell components double (prep to divide)
- different rates of division~
↳ skin cells =
divide frequently
↳liver cells =
divide when needed
↳ nerve/­muscle cells =
don't divide at all
- 3 major checkp­oints~
1. G
1
2. G
2
3. Metaphase
- platel­et-­derived growth factor (PDGF):
made by platelets to help heal wounds
 
PDGF bind to membrane receptor ➜ transd­uction pathway triggered ➜ cell passes G
1
checkpoint ➜ cell division

G1 Checkpoint

- a.k.a. 'restr­iction point'
↳ if gets go-ahead signal... continues on to divide
↳ if doesn't get go-ahead signal... exits cycle/goes into G0 phase (nondi­­vi­ding)

G2 Checkpoint

- protein kinases: give go-ahead signal at G1 & G2 checkp­­oints
- cyclins: attach to kinases to make them active
↳ cyclin­­-d­e­p­endent kinases (cdk) & cyclin combine to form...MPF (matur­­at­i­o­n-­­pro­­moting factors)
↳ MPF formation occurs when cyclin accumu­­lates = mitosis initiated
↳ MPF breaks down during anaphase (cyclin destroyed; cdk stays to be reused)

Metaphase Checkpoint

- anaphase won't begin until chromo­somes are properly attached to spindles

Cancer

- cancer cells are a change in 1+ genes that result in...
faulty cell cycle control
- normal cell cycle amount =
20-50 times
- cancer cell cycle amount =
continuous
- benign tumor:
cells that are NOT capable of surviving at a new site (slow growing; small; localized)
- malignant tumor:
cancerous tumor capable of surviving in a new site (fast growing; large; invasive)
- metast­asis:
the spread of cancer cells to a different location from the original site