ap biology | cell communication + cell cycle

ligand

a chemical signal that triggers a specific cellular response

three main steps of signal transduction

reception, transduction, response

autocrine signaling

the cell that secreted the ligand binds to a receptor + triggers a response on the same cell

juxtacrine signaling

direct contact between the cell sending the ligand and the cell receiving the ligand

paracrine signaling

ligand travels a short distance

effects cells in the immediate area

endocrine signaling

ligands (hormones) travel a long distance between the sending and receiving cells

ligands that travel a long distance are

hormones

hydrophilic ligands ___ cross the phospholipid bilayer

cannot

hydrophilic ligands bind to the

cell membrane receptors

target cells

cells that respond to the presence of the ligand

hydrophobic ligands bind to

intracellular receptors in the cytosol

reception

ligand binds to a specific receptor on or in the target cell

(receptor must be specific to the ligand)

receptor changes shape upon binding

transduction

series of chemical reactions that help the cell choose the appropriate response

possible components of transduction

signal amplification

kinases

phosphatases

secondary messengers

signal amplification

a series of chemical reactions where one molecules activates multiple molecules, amplifying the cell’s response to a signal

kinases

enzyme that transfer phosphate groups to other molecules (activates those molecules)

phosphatases

enzymes that remove phosphate groups from other molecules (inactivates those molecules)

secondary messangers

other molecules that relay signals

produced by enzymes

adenylyl cyclase

producesthe secondary messenger cyclic AMP (cAMP) from ATP

response

final stage of signal transduction and ultimate result generated by the ligand

signal transduction pathways

series of chemical reactions that mediate the sensing and processing of stimuli

feedback mechanisms

help living organisms respond to changes in the environment while maintaining homeostasis

homeostasis

the maintenance of an organism’s stable stae

negative feedback

returns a system to its original condition

cell signaling causes a person to release sweat when they become to hot, which helps them cool back down. what kind of feedback mechanism is this?

negative

the pancreas releases insulin when blood levels are too high. insulin is a ligand that triggers a series of chemical reactions upon binding that causes cells to absorb glucose from the blood. what kind of feedback mechanism is this?

negative

the pancreas releases glucagon when blood levels are too low. insulin is a ligand that triggers a series of chemical reactions upon binding that causes liver cells to break down glycogen into glucose, releasing glucose into the blood. what kind of feedback mechanism is this?

negative

positive feedback

magnifies cell processes

the hormone oxytocin stimulates contraction of the uterine muscle in labor interaction during childbirth. the contractions triggers production of even more oxytocin, which increases the contracts of the uterine muscles further. what kind of feedback mechanism is this?

positive

positive feedback ____ deviation from homeostasis

increases

negative feedback ___ deviation from homeostasis

decreases

three phases of the cell cycle

interphase

mitosis

cytokinesis

what are the stages of interphase?

g1, s, g2

what is stage g0?

the stage nondividing cells enter after leaving the cell cycle

what’s the longest phase of the cell cycle?

interphase

what happens during interphase?

the cell grows so that it has enough material to divide between two daughter cells

(replicates dna)

what happens during g1?

the cell grows and prepares for dna replication

some cell organelles are replicated

what happens during the s (synthesis) stage?

dna is replicated

contains double the dna but the same amount of chromosomes

each chromosome ; one chromatid → two identical chromatids held together by one centromere

what happens during the g2 stage?

the cell continues to grow and prepares the materials needed for mitosis

stages of mitosis

prophase

metaphase

anaphase

telophase

what happens during mitosis?

two identical daughter cells are created from one parent cell

what happens during prophase?

nuclear membrane dissolves

chromosomes condense + become visible

spindle fibers begin to form

what happens during metaphase?

the spindle fibers have fully attached to the centromeres of each chromosome

chromosomes align at the “equator” of the cell

what is the center of the mitotic spindle called?

metaphase plate

what happens during anaphase?

each chromosome splits at its centromere as opposing spindle fibers begin to shorten

the identical chromatids are pulled towards opposite ends of the cell

what happens during telophase?

two new nuclear membranes form

each of the nuclei now contain the same number of chromosomes + the same genetic information as the parent cell

cytokinesis

division of the cytoplasm, a long with all of its cellular contents, between the two daughter cells

how does cytokinesis occur in animal cells?

a cleavage furrow forms which partitions the cytosol and its contents between the two new cells

how does cytokinsis occur in plant cells?

a cell plate is built within the dividing cell, providing new cell wall material for each daughter cell

when may cell stop dividing?

when they reach their fully differentiated state or when environmental conditions are not favorable for continued growth

how is progress during the cell cycle regulated?

checkpoints

where are the checkpoints of the cell cycles located?

g1 checkpoint

s checkpoint

g2 checkpoint

m (metaphase/spindle) checkpoint

some checkpoints are controlled by the interactions between

cyclins and cyclin-dependent kinases

cyclin-dependent kinases are present at ____ levels throughout the cell cycle

constant

the levels of cycling proteins __ during the cell cycle

vary

when does the amount of cycling proteins reach it’s maximum?

just before mitosis starts

mitosis-promoting factor (MPF)

formed when cycling are bound to cyclin-dependent kinases

triggers the start of mitosis

somatic (body) cells

all of the cells in an organism that are not involved with sexual reproduction

density-dependent inhibition

may occur in somatic cells

when the density of cells is too high, they will stop dividing

anchorage dependence

may occur in somatic cells

cells need to be attached to a surface in order to divide

are cancer cells regulated by density-dependent inhibition or anchorage dependence?

no

proto-oncogenes

propel cell division at a specific rate

oncogenes

mutated proto-oncogenes that promote abnormally high rates of cell division

causes the formation of tuomrs

tumor suppressor genes

code for proteins that detect mutations in cells that may cause tumors to develop

what happens to a tumor suppressor gene if there is a single mutation in one allele?

the unmutated tumor suppressor allele will still continue to function

apoptosis

programmed cell death

what stage of the cell cycle is this?

interphase

what stage of the cell cycle is this?

prophase

what stage of the cell cycle is this?

metaphase

what stage of the cell cycle is this?

anaphase

what stage of the cell cycle is this?

telophase

what stage of the cell cycle is this?

cytokinesis