ap bio unit 4: cell communication and cell cycle

direct contact

cell communication via cell to cell contact, juxtacrine

direct channels of communication

gap junctions (animals), plasmodesmata (plants)

gap junctions

form of direct contact between animal cells

plasmodesmata

form of direct contact between plant cells

paracrine signaling

when signaling cells release chemical messages that travel a short distance, creates a response in nearby target cell

synaptic signaling

occurs in animal nervous systems, neurons, a type of paracrine signaling

autocrine signaling

a cell signals to itself

releases ligands that bind to receptors on the same cell

self regulation

endocrine signaling

long distance cell signaling

mostly for hormones, release into the circulatory system and reach target cells that are far away

ligand

chemical messengers (signals)

binds to receptors

can be a peptide (protein) or a small molecule (hormones, gasses, neurotransmitters)

receptors

proteins that recognize and bind to specific chemical messengers (ligands)

initiate signaling cascades and reactions, highly specific

receptors can be found in the cell membrane or inside a cell

cell surface receptors

most common type of receptors

embedded in cell membrane

binds to ligands that are polar, large, and/or water soluable

3 domains: ligand-binding, transmembrane, and intracellular

ligand-binding domain

area of a receptor that interacts with the ligand that is outside of the cell

pokes outside of the cell for cell-surface receptors

transmembrane domain

area of a cell-surface receptor that is hydrophobic and is inside the cell membrane

intracellular domain

area of a cell-surface receptor that is inside of the cell and transmits a signal

intracellular receptors

receptors found in the cytoplasm or nucleus of a cell

binds to ligands that already can pass through the cell membrane (small hydrophobic molecules)

interacts inside of the cell, most are used for DNA transcription

2 domains: ligand-binding and DNA-binding

DNA-binding domain

area of an intracellular receptor that interacts with regions of target genes

reception

1st step of cell-to-cell signaling

ligand binds to the receptor

for intracellular receptors, the ligand must cross the cell membrane first

transduction

2nd step of cell-to-cell signaling

information from the signal is converted into a cell response

cell-surface receptors initiate signaling cascade, while DNA-binding area of intracellular receptors activate

response

3rd step of cell-to-cell signaling

the result where a cell process is finally altered

cell growth, secretion of molecules, or genes turned on or off

protein kinases

enzymes that relay and amplify the message or signal by transferring a phosphate group from ATP to a protein temporarily

the addition of a negatively charged phosphate group changes the proteins shape, thus its function as well

more kinases will lead to greater amplification, more reaction steps more power

turns on

protein phosphatases

enzymes that remove phosphate groups from proteins, returning the protein back to its original state

regulates protein kinase activity and certain pathways or processes

turns off

second messengers

small, non-protein molecules and ions that relay and amplify the initial message (ligand)

helper molecules, rapidly diffuse across cell membrane and send more signals

ex: cAMP and Ca2+

cross talk

when pathways communicate and interact with each other

ex.) a protein kinase can phosphorylate proteins in multiple pathway, transcription can sometimes require multiple signals

signal transduction pathways

the series of reactions in transduction, influences how a cell responses to its environment

mutation in receptor proteins —> change of transduction of a signal

a change can alter gene expression, cell function, phenotypes, or cause cell death

GPCRs

largest category of cell surface receptors, important in animal sensory systems

activate a group of regulatory G proteins, binds to effectors and releases second messengers which activates protein kinases

leads to cellular response

inactive until signal is received

ion channels

located in the plasma membrane, important for nervous system

receptors act as a gateway for ions

when a ligand binds to the receptor, the “gate” opens and ions diffuse

leads to cellular response

cell cyle

the life of a cell from its formation until it divides

histones

proteins that DNA associates with and wraps around

nucleosomes

DNA wrapped around histones

chromatin

DNA in its non-condensed form

chromosomes

DNA in a more organized, condensed form

organized chromatin

sister chromatids

replicated DNA

two copies of a chromosome joined together

centromere

the region on each sister chromatid where they are most closely attatched

kinetochore

proteins attached to the centromere that link each sister chromatid to the mitotic spindle

genome

all of a cell’s genetic information

homologous chromosomes

two chromosomes (one from mom and one from dad) that are the same length, have the same centromere position, and carry genes controlling the same characteristics

the two that go together

somatic cells

body cells

diploid

divides via mitosis

46 chromosomes: 23 from mom and 23 from dad

gametes

reproductive cells

haploid

divide via meiosis

only 23 chromosomes

diploid

two sets of chromosomes, one set from each parent

haploid

one set of chromosomes

interphase

longest portion of cell cycle

G1, S, G2

G1 phase

the cell is metabolically active and carries out normal functions

duplicates organelles and cytoslic components

S phase

dna is replicated

chromatin —> sister chromatids

G2 phase

final growth and preparation for mitosis

protein synthesis occurs

ATP produced in large quantities

prophase

nuclear envelope breaks down

chromosomes condense

centrosomes move away from each other, mitotic spindle fibers grow

metaphase

sister chromatids line up at metaphase plate (center of the cell) and mitotic spindle fibers attach to sister chromatids

anaphase

mitotic spindle fibers pull sister chromatids apart to opposite ends

cell elongates

telophase

two seperate nuclei form

chromosomes become less condensed

mitotic spindle fibers break down

cytokinesis

divison of the cytoplasm

G1 checkpoint

between G1 and S

most important checkpoint in cell cycle

checks for proper cell size and growth

checks for DNA damage

G0 phase

resting cell that is diversified and/or nondividing

can re enter cell cycle

G2 checkpoint

between G2 and mitosis

checks for proper DNA replication and if there is any DNA damage

M checkpoint

between metaphase and anaphase

checks that spindles are attached to sister chromatids

CDK complex

cyclin and cyclin-dependent kinase binded together

regulates events in cell cycle by pushing cell into next stage when ready

growth factors

external cell cycle regulator

hormones released by cells that stimulate cell growth

contact / density inhibition

external cell cycle regulator

cell surface receptors recognize contact with other cells

anchorage dependence

external cell cycle regulator

cells rely on attachment to other cells to divide

cancer cells

cells that avoid apoptosis, divide infinitely, “immortal”, doesn’t follow checkpoints

benign tumor

abnormal cells that aren’t considered cancerous yet

only at tumor site and unable to spread to other locations in the body

malignant tumor

mass of cancerous cells with no anchorage dependence that can leave the tumor site

metastasis

when cells separate from the tumor and spread elsewhere in the body

proto-oncogenes

genes that code for proteins to push cells to divide a normal amount

oncogenes

mutated genes that code for mutated proteins to push cells to divide an abnormal amount

tumor suppressor genes

genes that code for proteins that regulate cell division (not too much)