AP Bio Unit 4

Juxtacrine communication

cells communicate through direct contact

paracrine communication

cells communicate over short distances by releasing ligands that travel to nearby cells

ex: neural communication

endocrine communication

cells communicate over long distances by releasing ligands that target particular cells

endocrine communication allows…

responses that are widespread but specific

• hormones travel whole body but only cells w/ matching receptors respond

signal transduction pathway parts

1. receptor binds ligand

2. all of the processes within the cell that relay the signal to a response

3. cellular response

most signal receptors are found at..

the cell’s surface

where does the ligand bind

extracellular ligand-binding domain

types of surface receptors

• ligand-gated ion channels

• enzyme linked receptors

• g protein coupled receptors

ligand-gated ion channels

open or close when ligand binds

enzyme linked receptors

catalyze reaction when ligand binds

3 processes of signal transduction

1. secondary messengers

2. phosphorylation cascades

3. amplification

secondary messengers

small molecules that relay the signal within the cell

phosphorylation

adding a phosphate group to a protein

• changes protein’s structure → activation or deactivation

kinases

add phosphates

phosphatases

remove phosphates from a target protein

phosphorylation cascades

one kinase activates 1+ kinases in the pathway in a series of phosphorylation events

signal amplification

secondary messengers & phosphorylation cascades work together to take a relatively small input & amplify it to a large cellular response

negative feedback systems…

return a system back to its target set point when disrupted → homeostasis

positive feedback systems…

amplify responses to produce a change or transformation (further from set point)

Stages of cell cycle

• G0

• G1

• M phase

• G2

G1 phase of interphase

• cell maintains normal metabolic activities

• cell grows & duplicates organelles & cytosolic components

S phase of interphase

DNA replication

• DNA replicated

• not yet condensed

G2 phase of interphase

preparation for division

• centrosomes replicate

• protein synthesis occurs

• ATP produced in large quantities

G0 phase of Interphase

nondividing cells can exit cell cycle or stay in G0 where it no longer divides & re-enter later in response to approptiate cues

mitosis (M phase)

cell rep

stages of mitosis

PMAT

prophase metaphase anaphase telophase

cell cycle alternates…

interphase with mitosis

what regulates cell cycle

cyclins

checkpoints

make sure cell doesn’t advance through cell cycle too quickly

as cell goes through cell cycle …

different cyclins build in concentration

to pass a checkpoint…

the right kind of cyclins must be concentrated enough to trigger cyclin-dependent kinases which trigger checkpoint pathways

when a cell looses control over its checkpoints/cell cycle →

signal for apoptosis if doesn’t work → cancer