AP Bio Ch 4

direct contact

communications through cell junctions, passing freely through adjacent cells (gap junctions, plasmodesmata)

local regulators

secreting cells releasing chemical messages (ligands/local regulators) that travel a short distance through extracellular fluid and cause a response in a target cell

paracrine signaling

secretory cells release local regulators (ie growth factors) via exocytosis to an adjacent cell

synaptic signaling

neurons secreting neurotransmitters that diffuse across the synaptic cleft (aka the space between the nerve cell and target cell)

long distance signaling

hormones, endocrine signaling through circulatory system

cell signaling steps

reception (ligand binds to receptor), transduction (signal is converted), response (cell process is altered)

reception

detection and receiving of ligand by target cell

• one area of receptor interacts with ligand and one area transmits a signal to another protein, highly specific bonding

plasma membrane receptors

most common receptor in signal pathways, binds to polar large water soluble ligands (ex: peptide hormones, GPCRs)

intracellular receptors

found in the cytoplasm or nucleus of target cell, binds to hydrophobic ligands passed through plasma membrane (ex: steroid and thyroid hormones)

transduction

conversion of an extracellular signal to an intracellular signal that will bring about a cellular response, requires changes in the signal transduction pathway

phosphorylation

adding phosphate via ATP or enzyme protein kinase to relay signal inside cell (part of transduction)

dephosphorylation

removing phosphate by enzyme protein phosphatase, shuts off pathways (part of transduction)

second messengers

small, nonprotein molecules and ions help relay the message and amplify the response during transduction

response

final molecule in signaling pathway converts the signal to a response that will alter a cellular process (ex: proteins or enzymes)

G protein coupled receptors (GPCRs)

largest category of cell surface receptors, important for animals’ sensory systems, binds to a G protein that can bind to GTP (molecule similar to ATP), inactive until ligand binds to it

• ligand binding changes cytoplasmic side’s shape

• activates/binds to enzyme, amplifying signals

ion channels

receptors in plasma membrane that open or close for diffusion of specific ions to start off cellular response events

negative feedback loop

reduces the effect of the stimulus (ex: heat —> skin receptors —> sweat glands —> sweat), stops when problem is solved

positive feedback loop

increases the effect of a stimulus (ex: blood clotting, fruit ripening), stops when problem is solved

centromere

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

chromatin

formed by strings of nucleosomes. in a non-condensed form when not dividing, but condenses into a chromosome after DNA replication

homologous chromosomes

one chromosome from each parent that are the same length, have the same centromere position, and carry genes controlling the same characteristics

somatic cells

diploid (2n): 2 sets of chromosomes, one set from each parent, divides by mitosis, humans have 46 total (23 from each parent)

gametes

reproductive cells, haploid (n): one set of chromosomes, divides by meiosis, humans have 23

interphase

longest portion of cell cycle

G1 (first gap) phase

cell grows, carries out normal function

S (synthesis) phase

DNA replication, chromosome duplication occurs

G2 (second gap) phase

final growth and preparation for mitosis

mitosis

division of nucleus, results in 2 identical diploid daughter cells

cytokinesis

cytoplasm divides

prophase

chromatin condenses, nucleoli disappear, duplicated chromosomes appear as sister chromatids, mitotic spindle forms, centromeres 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 metaphase plate, microtubules are attached to each kinetochore

anaphase

sister chromatids separate and move to opposite ends of the cell due to microtubule shortening, cell elongates

telophase

2 daughter nuclei form, nucleoli reappear, chromosomes decondense

cytokinesis

cleavage furrow appears due to a contractile ring of actin filament in animals, and vesicles produced by the Golgi travel to the middle of the cell and form a cell plate in plants

G1 checkpoint

most important, checks for cell size, growth factors, and DNA damage, gives go/stop signal

G2 checkpoint

checks for completion of DNA replication and DNA damage

apoptosis

programmed cell death

M (spindle) checkpoint

checks for microtubule attachment to chromosomes at the kinetochores at metaphase

cyclins

regulatory proteins that control the cell cycle by binding to and activating cyclin-dependent kinases

cyclin-dependent kinases

enzymes that are only active when its specific cyclin is present, constant concentration throughout cell cycle

growth factors

hormones released by cells that stimulate cell growth, initiates signal transduction pathway

contact (or density) inhibition

cell surface receptors recognize contact with other cells, initiates signal transduction pathway that stops the cell cycle in G1 phase

anchorage dependence

cells rely on attachment to other cells or the extracellular matrix to divide

cancer cells

don’t follow checkpoints, divide infinitely, evade apoptosis and continue dividing with cell errors