unit 4 cell communication and cell cyle Flashcards
cell to cell communication is critical for
function and survival of cells
cells communicate through 3 ways
direct contact, local signaling, and long distance signaling
direct contact
communication through cell junctions
- signaling substances can pass freely between adjacent cells
in direct communication animal cells communicate through ____ and plants communicate through _____
animals: gap junctions
plants: plasmodesmata
what is an example of direct contact?
immune cells: antigen presenting cells communicate to T-cells through direct contact
local regulators
a secreting cell will release chemical messages (local regulators) that travel a short distance through the extracellular fluid
paracrine vs synaptic signaling
paracrine: secrete cells release local regulators via exocytosis to an adjacent cells
synaptic: animals nervous system
-nuerons secrete neurotransmitter
- diffused across synaptic cleft (space between the nerve cell and target cell)
long distance signaling
both animals and plants use hormones for long distance
plants vs animals long distance signaling
plants: release hormones that travel in the plant (xylem or phloem) to reach target issues
animals: use endocrine signaling
- cell releases hormones in the circulatory system where they reach target cells
insulin
released from the pancreas into the bloodstream and bind to target cells
- tells liver cells to take out excess sugar
what communication involves a cell secreting a substance to an adjacent cell
paracrine signaling
cell-to-cell stages
reception, transduction, response
describe reception, transduction, and response
reception: ligand binds to receptor
transduction: signal is converted
response: a cell process is altered
what is a receptor.
macromolecule that binds to a signal molecule (ligand)
any ligand can bind to any receptor T or F
false
when the ligand binds to receptor, the receptor…
activates (via a conformational change) which allows the receptors to interact with other cell molecules
plasma membrane receptors are identified as
polar, water- hydrophilic, large
ex: G protein coupled receptors
ligand-gated ion channels
intracellular receptors are identified as
in the cytoplasm, hydrophobic, steroid and thyroid hormone, gasses like nitric oxide
what is transduction and what does it require
the conversion of an extracellular signal into a intracellular signal that will bring about cellular response and requires changes in a series of molecules (signal transduction pathway)
transduction regulates protein activity though
- phosphorylation by the enzyme protein kinase (help relay signals inside the cells)
- dephosphorylation by the enzyme protein phosphatase (shuts down pathway)
during transduction the signal is _____
amplified
what are second messengers?
small, non-protein molecules help relay the message and amplify the signal
-cyclic AMP (gets signal stronger)
stage 3: response
converts signal to a response that will alter a cellular process
ex:
a. protein that can alter membrane permeability
b. enzyme that will change metabolic process
c. protein that will turn genes off and on
how is the signal passed from outside the cell to inside?
during transduction the signal is relayed by protein kinase and amplified by second messengers
signal transduction pathways can result in
gene expression, cell function, alter phenotypes or result in death
____ to receptors proteins will result in a ____ to the transduction of the signal
mutations, change
GPCR’s
- binds to g protein that can bind to GTP
- ligand binds to extracellular side, activating the G protein and GPCR (GDP–GTP). After g protein binds to enzyme which will amplify signals and lead to a cellular response
ion channels
nervous system , receptors act as a gate for ions.
- when a ligand binds to the receptor, the “gate” opens or closes allowing the diffusion of ions –> cellular response
set points
values for various physiological conditions that the body tries to maintain
ex; body temp
homeostasis
the state of relatively internal conditions
- organisms detect and respond to a stimulus
stimulus
a variable that will cause a response
receptor/sensor
sensory organs that detect a stimulus (sent to the brain)
effector
muscle or gland that will respond
response
changes the effect of the stimulus
negative feedback
reduces the effect of the stimulus
-sweat, blood sugar (insulin), breathing rate
positive feedback
increases the effect of the stimulus
- child labor, blood clotting, fruit ripening
why would do the body not regulate homeostasis?
genetic disorders, drug or alcohol, intolerable conditions (cold or heat)
disease
when the body is unable to maintain homeostasis
- cancer: the body cannot regulate cell growth
- diabetes: the blood cannot regulate blood glucose levels
during transduction the signal is _____
amplified
in order to maintain homeostasis, cells must ____
communicate through signal transduction pathways
describe the response that a cell can have to a signal
Once a receptor protein receives a signal, it undergoes a conformational change, which in turn launches a series of biochemical reactions within the cell.
what does it mean when genes are turn off and on?
off: no longer able to provide directions for creating proteins
on: the gene is being transcribed into mRNA which then translates into a protein.
what would happen to the signal transduction pathway of protein phosphatase was mutated
A malfunctioning protein phosphatase would not be able to dephosphorylate a particular receptor or relay protein. Would not be able to terminate
what would happen to the signal transduction pathway of protein kinase was mutated
it will disrupt the entire signal pathway.
cell cycle
the life of a cell from its formation until it divides
DNA associates around _____ known as ______ to form ______
proteins, histones, nucleosomes
strings of nucleosomes form ____
chromatin
After DNA replication, ___ condenses to form a ____
chromatin, chromosomes
centromere
the region on each sister chromatid where they are most closely attached
kinetochore
proteins attached to the centromere that link each sister chromatid to the mitotic spindle
genome
all of a cell’s genetic information (DNA)
prokaryote vs eukaryote genome
prokaryotes: singular, circular DNA
eukaryote: one or more linear chromosomes
Humans: 46
Chimps:48
Elephants: 56
homologous chromosomes
2 chromosomes that are the same length , have the same centromere position, and carry genes controlling the same characteristics
somatic vs gamete cells
somatic: body cells, diploid (2n)- 2 sets. of chromosomes, one from each parent, divide by mitosis, 46 chromosomes
Gametes: reproduction cells (egg/sperm), haploid cells (n)- one set of chromosomes, divide by meiosis, n=23, only contain moms or dad genetic material
G1 phase
the cells grows and carries out functions
s phase
DNA replication and chromosome duplication occurs
g2 phase
final growth and preparation for mitosis
mitosis
nucleus divides
cytokinesis
cytoplasm divides
mitosis results in
2 identical diploid daughter cells
Prophase
- chromatin condenses
- nucleoi disappear
- duplicate chromosomes appear as sister chromatids
- mitotic spindle will begin forming
- centrosomes move away from each other
prometaphase
- nuclear envelope fragments
- microtubules enter nuclear area and some attach to kinetochores
metaphase
-centrosomes are at opposite poles
- chromosomes line up at the metaphase plate
- microtubules are attached to each kinetochore
anaphase
-sister chromatids separate and move to opposite ends of the cell due to the microtubules shortening
- cell elongates
telophase
- two daughter nuclei form
-nuclei reappear - chromosomes become less condensed
cytokinesis
animal: cleavage furrow appears due to a contractile ring of actin filaments
plants: vesicles produced by the Golgi travel to the middle of the cell and form a cell plate
G1 checkpoint
- checks for cell size, DNA damage, and growth factors
- Go- cell completes the whole cycle
-Stop- cell enters a nondividing (quiescent) state known as G0
G0
-some cells stay in G0 (muscle/nerve cells)
-some cells will go back into the cell cycle
G2 checkpoint
checks for completion of DNA replication and DNA damage
- Go- cells proceeds to mitosis
- Stop- cell cycle stops and the cell will attempt to repair damage (if damage cannot be repaired the cell will undergo apoptosis)
M (spindle) checkpoint
- check for microtubule attachment to chromosomes at kinetochores at metaphase
- go- cell proceeds to anaphase. and completes mitosis
- stop- cell will pause mitosis to allow spindles to finish attaching to chromosomes
cyclins as an internal cell cycle regulator
- concentration of cyclins varies
-cyclins are synthesized and degraded at specific stages of the cell cycle
cyclin dependent kinases (CDK’s) -cycle regulator
- concentration remains constant through each phase of the cell cycle
- active only when a specific cyclin is present
each cyclin-CDK complex has a _____ regulatory effect
specific
- active CDK complexes phosphorylate target proteins which help regulate key events in the cell cycle.
growth factors
hormones released by cells that stimulate cell growth
- signal transduction pathway initiated
- CDK’s are activated leading to progression through the cell cycle
contact (or density) inhibition
cell surface receptors recognize contact with other cells
- initiates the signal transduction pathway that stops the G1 phase in the cell cycle
anchorage dependence
cells rely on attachment to other cells or extracellular matrix to divide
normal cells become cancerous through ____
DNA mutations (changes in DNA)
- cancer cells on average have accumalated 60 or more mutations on genes that regulate cell growth
normal. vs cancer cells
normal:
-follow checkpoint
- divide on average 20-50 times in culture (petri dish)
- go through apoptosis when there are significant errors
Cancer:
-doesn’t follow a checkpoint
- divide infinitely when in culture
- considered to be immortal
- evade apoptosis and continue dividing even with errors
the uncontrollable growth of cancer cells can lead to ___
tumor (a mass of tissue formed by abnormal cells)
benign tumor
cells are abnormal but not considered to be cancerous
- cells remained at only the tumor site and are unable to spread elsewhere in the body.
malignant tumor
mass of cancerous cells that lose their anchorage dependency and can leave the tumor site
