Unit 4 : Cell Communication & Cell Cycle Flashcards
Animal Cells communicate by:
Direct contact (gap junctions)
Secreting local regulators (growth
factors, neurotransmitters)
Long distance (hormones)
3 types of cell signaling
Reception
Transduction
Response
Reception
Detection of a signal molecule (ligand) coming from outside the cell
Transduction
Convert signal to a form that can bring about a cellular response
Response
Specific cellular response to the signal molecule
Reception (Full concept)
Binding between signal molecule (ligand) + receptor is highly
specific.
Types of Receptors: Plasma membrane receptor & Intracellular receptors
Ligand binds to receptor protein→protein changes SHAPE →initiates transduction signal
Plasma Membrane Receptor
water-soluble ligands
Intracellular receptors
(cytoplasm, nucleus)
small or hydrophobic ligand molecules
Eg. testosterone or nitric oxide (NO)
Transduction (full concept)
Cascades, Protein kinase, Phosphorylation cascade
Cascades…
of molecular interactions relay signals from receptors → target molecules
Protein kinase
enzyme that phosphorylates and
activates proteins at next level
Phosphorylation cascade
enhance and amplify
signal
Second Messengers
small, nonprotein molecules/ions that can relay signal inside cell
Ex: cyclic AMP (cAMP), calcium
ions (Ca2+), inositol triphosphate
(IP3)
cAMP
cAMP = cyclic adenosine monophosphate
GPCR → adenylyl cyclase (convert ATP → cAMP) → activate protein kinase A
Response (full concept)
Regulate protein synthesis by turning on/off genes in nucleus (gene expression)
Regulate activity of proteins in cytoplasm
Signal Transduction Pathway
Problems/Defects
Diabetes
Cholera
Autoimmune disease
Cancer
Neurotoxins, poisons, pesticides
Drugs (anesthetics, antihistamines, blood pressure meds)
Cholera
Disease acquired by drinking contaminated water (w/human feces)
Bacteria (Vibrio cholerae) colonizes lining of small intestine and **produces toxin which modifies G-protein involved in regulating salt & water secretion
G protein stuck in active form → intestinal cells secrete salts, water
Infected person develops
profuse diarrhea and could die
from loss of water and salts
Viagra
Used as treatment for erectile dysfunction
Inhibits hydrolysis of cGMP → GMP
Prolongs signal to relax smooth muscle in artery walls; increase blood flow to penis
Apoptosis
CELL SUICIDE
Cell is dismantled and digested
Triggered by signals that activate cascade of “suicide” proteins (caspase)
WHY? Protect neighboring cells from damage
Animal development & maintenance
May be involved in some diseases (Parkinson’s, Alzheimer’s)
Cell Cycle
life of a cell from its formation until it
divides into 2 cells
Functions of Cell Division
Reproduction, Growth &
Tissue Repair
Genome
all of a cell’s genetic info (DNA)
Prokaryote
single, circular chromosome
Eukaryote
More than one linear chromosomes
Eg. Human:46 chromosomes, mouse: 40, fruit fly: 8
Each chromosome must be duplicated (replicated) before cell division
Duplicated chromosome = 2 sister chromatids attached by a centromere
Somatic Cells
Body cells
Diploid (2n): 2 of each type of
chromosome
Divide by mitosis
Humans: 2n = 46
Gametes
Sex cells (sperm/egg)
Haploid (n): 1 of each type of
chromosome
Divide by meiosis
Humans: n = 23
Phases of the Cell Cycle
The mitotic phase alternates with interphase: G1 → S → G2 → mitosis → cytokinesis
Interphase
(90%+ of cell cycle)
G1 Phase
cell grows and carries out normal functions
S Phase
duplicates chromosomes (DNA replication)
G2 Phase
prepares for cell division
M Phase
(mitotic)
Mitosis + PMAT
nucleus divides
prophase, metaphase, anaphase, telophase
Cytokinesis
cytoplasm divides
More on Mitosis
Continuous process with observable structural features:
Chromosomes become visible (prophase)
Alignment at the equator (metaphase)
Separation of sister chromatids (anaphase)
Form two daughter cells (telophase & cytokinesis)
IMPORTANT *** Checkpoint if theres a mutation it’ll cause cancer ESPECIALLY IN G2 bc its last one in interphase before mitosis so NO CHANGING DNA before that
Cytokinesis
Cytoplasm of cell divided
Animal Cells: cleavage furrow
Plant Cells: cell plate forms
During anaphase
Chromosomes walked to poles by motor proteins
Kinetochore microtubules shorten at ends as they depolymerize
Bacterial cells divide by..
Binary Fission
*** Checkpoint
Control point where stop/go signals
regulate the cell cycle
If theres a mutation it’ll cause cancer ESPECIALLY IN G2 bc its last one in interphase before mitosis so NO CHANGING DNA before that
Major Checkpoints
G1 checkpoint (Most important!)
Controlled by cell size, growth factors, environment
“Go” → completes whole cell cycle
“Stop” → cell enters nondividing state (G0 Phase)
Nerve, muscle cells stay at G0; liver cells called back from G0
G2 checkpoint
Controlled by DNA replication completion, DNA mutations, cell size
M-spindle (Metaphase) checkpoint
Check spindle fiber (microtubule) attachment to chromosomes at kinetochores (anchor sites)
Internal Regulatory Molecules
Kinases, Cyclins, MPF
Kinases
(cyclin-dependent kinase, Cdk): protein enzyme controls cell cycle; active when connected to cyclin
Cyclins
proteins which attach to kinases to activate them; levels fluctuate in the cell cycle
MPF
maturation-promoting factor
specific cyclin-Cdk complex which allows cells to pass G2 and go to M phase
External Regulatory Factors
Growth Factor, Density-Dependent Inhibition, Anchorage Dependence,
Growth Factor
proteins released by other cells
to stimulate cell division
Density-Dependent Inhibition
crowded cells normally stop dividing; cell-surface protein binds to adjoining cell to inhibit growth
Anchorage Dependence
cells must be attached to another cell or ECM (extracellular matrix) to divide
Cancer
Disorder in which cells lose the ability to control growth by not responding to regulation.
Multistep process of about 5-7 genetic changes (for a human)
for a cell to transform
Loses anchorage dependency & density-dependency regulation
Transformation
Process that converts a normal cell to a cancer cell
Tumors
mass of abnormal cells
Benign tumor
lump of cells remain at original site
Malignant tumor
invasive - impairs functions of 1+ organs (called cancer)
Metastasis
cells separate from tumor and travel to other parts of body
Cancer Cells
Some have abnormal #’s of chromosomes
Metabolism disabled
Lose attachment to ECM → spread to other tissues
Signaling molecules cause blood vessels to grow toward tumor
Treatment
Surgery, radiation, chemotherapy
Personalized Medicine:
Breast Cancer: 20-25% tumors show high HER2 receptors → use Herceptin to block HER2 protein
Cancer Prevention
Anyone can get cancer but there are ways to minimize risk:
Don’t smoke, legal or illegal (includes hookahs, chew,
2nd-hand smoke)
Use sun protection
Exercise and keep weight at ideal level
Eat 5-7 servings of fruit and veggies a day
Use screening/preventative measures-breast/testicle/mole
checks
Practice abstinence or use condoms
Vaccines (eg. HPV)
WHAT IS HOMEOSTASIS?
Organisms stay alive by maintaining a stable internal environment.
Depends on the interactions of body
systems to maintain balance.
Homeostasis is in jeopardy when
internal and external conditions
becomes too extreme
NEGATIVE FEEDBACK
Keeping the body in balance (homeostasis) to limit extreme conditions
Most body responses are controlled by negative feedback
3 Components of Negative
Feedback
Sensor, control center, effector
Sensor
Detects the change (body is
getting too warm)
Control Center
Receives signal (usually the brain) from sensor and sends message to effector
Effector
Reverses the initial change (skin
pores begin to perspire and blood vessels dilate)
EXAMPLES of Negative Feedback
Low body core temperature caused by cold temperature, High blood CO2 levels (carbon dioxide) caused by intense exercise, High blood glucose levels caused by eating a
candy bar
Low body core temperature caused by cold temperature
our skin pores stop perspiring and
muscles contract (shiver) to generate heat
High blood CO2 levels (carbon dioxide) caused by
intense exercise
our body increases respiration and
heart rate to remove excess CO2 and deliver more oxygen rich blood to our muscles.
High blood glucose levels caused by eating a candy bar
our body releases insulin to remove the blood sugar into our cells
POSITIVE FEEDBACK
Continual increasing of a response
until a final product is reached
This response occurs faster to
guarantee the product
Example of Positive Feedback
During pregnancy, the uterus
contracts as soon as labor begins,
which pushes the baby’s head against the cervix.
This causes the body to release
oxytocin, a hormone, to increase
the contractions until baby is born.
