biol 1201 final - gregg

local signaling

animal cells may communicate by direct contact, or cell-cell recognition (paracrine and synaptic signaling)

cell junctions

Animal and plant cells; directly connect the cytoplasm of adjacent cells

paracrine signaling

the target cells lie near the secreting cells

synaptic signaling

a nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell

endocrine (hormonal) signaling

Specialized endocrine cells secrete hormones into body fluids, often blood. Hormones reach virtually all body cells, but are bound only by some cells.

cell-cell recognition

two cells in an animal may communicate by interaction between molecules protruding from their surfaces

three stages of cell signaling

reception, transduction, response

reception

The target cell's detection of a signal molecule coming from outside the cell.

transduction

the binding of the signaling molecule alters the receptor and initiates a signal transduction pathway; occurs in a series of steps

response

the transduced signal triggers a specific response in the target cell

signal transduction pathway

A series of steps linking a mechanical or chemical stimulus to a specific cellular response

ligand

Signal molecule that binds to the receptor

three main types of membrane receptors

-G protein-coupled receptors

-Receptor tyrosine kinases

-Ion channel receptors

G protein-coupled receptors (GPCRs)

cell-surface transmembrane receptors that work with the help of a G protein

Receptor Tyrosine Kinases (RTKs)

membrane receptors that transfer phosphate groups from ATP to another protein

ligand-gated ion

acts as a gate that opens and closes when the receptor changes shape

intracellular receptors

receptors located inside the cell rather than on its cell membrane

phosphorylation

the addition of a phosphate group to a molecule

dephosphorylation

removal of a phosphate group from a molecule

second messengers

Small, non-protein water soluble molecules or ions that send messages throughout the cells by diffusion.

common second messengers

cyclic AMP and calcium ions

cyclic AMP (cAMP)

A compound formed from ATP that acts as a second messenger; one of the most commonly used

adenylyl cyclase

an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal

phosphorylation cascade

a sequence of events where one enzyme phosphorylates another, causing a chain reaction leading to the phosphorylation of thousands of proteins

protein phosphates

Enzymes that can rapidly remove phosphate groups from proteins.

calcium ions (Ca2+)

more widely used as a second messenger than cAMP; concentration in the cytosol is much lower than the concentration outside the cell

pathways leading to the release of calcium involve ____ and ____ as additional second messengers

inositol triphosphate (IP3) and diacylglycerol (DAG)

output response

cell's response to extracellular signal

four aspects of signal regulation

amplification, specificity, efficiency, termination

signal amplification

Enzyme cascades amp the cell's response to a signal. At each step in the cascade, the number of activated products is much greater than the prev step

specificity of cell signaling

different kinds of cells have different collections of proteins

Signaling Efficiency

scaffolding proteins and signaling complexes

scaffolding proteins

large relay proteins to which several other relay proteins are attached

termination of the signal

a specific sequence of nucleotides that marks the end of a gene

operator

on-off switch is a segment of DNA

operon

the entire stretch of DNA that includes the operator, the promoter, and the genes that they control

The operon can be switched off by

protein repressor

corepressor

a molecule that cooperates with a repressor protein to switch an operon off

regulatory genes

genes that control gene expression

repressible operon

one that is is usually on; binding of a repressor to the operator shuts of transcription

example of repressible operon

trp operon

inducible operon

one that is usually off; a molecule called an inducer inactivates the repressor and turns on transcription

lac operon

the operon that controls the metabolism of lactose

inducible enzymes usually function in

catabolic pathways

inducible enzymes synthesis is induced by

a chemical signal

repressible enzymes usually function in

anabolic pathways

repressible enzymes synthesis is repressed by

high levels of the end product

when glucose is scarce

CAP is activated by binding with cyclic AMP

differential gene expression

the expression of different genes by cells with the same genome

histone acetylation

acetyl groups are attached to an amino acid in a histone tail

DNA methylation

adding a methyl group to DNA

genomic imprinting

methylation regulates expression of either the maternal or paternal alleles of certain genes at the start of development

epigenetic inheritance

Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence

proximal control elements

located close to the promoter

distal control elements

may be far away from a gene

activator

a protein that binds to an enhancer and stimulates transcription of a gene

control elements

segments of noncoding DNA that serve as binding sites for transcription factors that help regulate transcription

alternative RNA splicing

different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

the initiation of translation of selected mRNAs can be blocked by _________ _________ that bind to sequences or structures of the mRNA

regulatory proteins

nervous system

network of specialized cells (neurons) that transmit signals along dedicated pathways

animal hormones

chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

endocrine system

hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream

communication between animal cells through secreted signals can be classified by two criteria:

-the type of secreting cell

-the route taken by the signal in reaching its target

autocrine signaling

the target cell is also the secreting cell

synapses

secreted molecules called neurotransmitters diffuse short distances and bind to receptors on target cells

neuroendocrine signaling

specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream

local regulators such as the prostaglandins are

modified fatty acids

Prostaglandins

Modified fatty acids that are produced by a wide range of cells

the response to a lipid soluble hormone is usually a

change in gene expression

When a steroid hormone binds to its cytosolic receptor...

a hormone receptor complex forms that moves into the nucleus

endocrine cells are often grouped in ductless organs called _________ ______, such as the thyroid and parathyroid glands and testes or ovaries

endocrine glands

exocrine glands

have ducts to carry secreted substances onto body surfaces or into body cavities

hormones are released from an

endocrine cell

neurosecretory cells

secrete a neurohormone, which enters the bloodstream and travels to target cells

hypothalamus

coordinates endocrine signaling

pituitary gland

at the base of the hypothalamus; composed of the posterior pituitary and anterior pituitary gland

posterior pituitary

stores and secretes hormones that are made in the hypothalamus

pheromones

diffuse from nerve cell endings into the bloodstream

nitric oxide (NO)

a gas that functions in the body as both a local regulator and a neurotransmitter

signal transduction

chain of events that converts the extracellular chemical signal to a specific intracellular response

anterior pituitary

makes and releases hormones under regulation of the hypothalamus

posterior pituitary hormones

neurosecretory cells of the hypothalamus synthesize the two posterior pituitary hormones; oxytocin and ADH

antidiuretic hormone (ADH)

regulates physiology and behavior

oxytocin

regulates milk secretion by the mammary glands

negative feedback

the response reduces the initial stimulus

positive feedback

reinforces a stimulus, leading to an even greater response

prolactin

stimulates milk production

hormone cascade

sets of hormones from the hypothalamus, the anterior pituitary, and a target endocrine gland

tropic hormones

stimulate certain endocrine glands to secrete hormones

thyroid-stimulating hormone (TSH)

stimulates release of thyroid hormone by the thyroid gland

growth hormone

secreted by the anterior pituitary; stimulates growth through both tropic and non-tropic effects

the liver is a major target and responds to GH by

releasing insulin-like growth factors

insulin-like growth factors (IGFs)

circulate in the blood and directly stimulate bone and cartilage growth

parathyroid hormone and vitamin D

control blood calcium

parathyroid hormone (PTH)

in mammals; released by the parathyroid glands when Ca2+ levels fall below a set point

PTH

increases blood calcium levels

Calcitonin

decreases blood calcium levels

parathyroid glands

a set of four small structures embedded in the posterior surface of the thyroid

adrenal hormones

located atop the kidneys

adrenal gland

tissue located on top of the kidneys that releases adrenaline and cortisol during states of emotional arousal