AP Bio Unit 4 - Cell Communication & Cell Division

Cell Communication and Cell Cycle

What are the three stages of cell communication?

1. Reception

2. Transduction

3. Response

What is usually the same of a signal that binds to the receptor on a cell?

ligand

Most signals are water soluable, so can they cross the cell membrane? Thus, where are most signal receptors located?

• They cannot cross the membrane of the target cell

• The cells are on the membrane (membrane bound receptor)

What happens to the shape of the receptor protein on the inside of the cell when a ligand binds to the receptor?

it changes shape, which means some chemical reactions happen

How do G-coupled protein receptors work?

1. Receptor is linked to G-protein

2. Ligand binds, causing the G-protein to change shape

3. This change in shape causes the GDP in the G-protein to be replaced by GTP

4. The G protein turns on and migrates inside the membrane to activate other proteins or enzymes

5. Finally, G protein returns to its normal position

How do receptor tyrroscen kinsases work?

1. Two monomer forms of the kinsases bind together and to two ligands (dimerize)

2. The new TRK grab phosphates from ATP and deliver them to their target proteins to activate them

What is a kinase?

a protein that add phosphate groups to its target substrate

How do ligand gated ion channels work?

they are either opened or close depending on whether a signaling molecule is attached to it

What is transduction?

the passing on of the message from the receptor to the target to get the desired response by the cell

What is a second messenger? Give two examples

what brings the receptor to the actual transduction phase

• Cyclic AMP

• Calcium ions

What is cyclic AMP?

Adenisine mono-phosphate with its one phosphate attached in a special way

How does transduction work?

1. The ligand activates the protein (likely a G protein) and GTP attaches

2. The protein activates another enzyme

3. This enzyme creates Cyclic AMP (second messenger)

What is a phosphorylation cascade? How does it work?

• Cyclic AMP (the activated relay molecule) activates a protein by giving it a phosphate group using ATP

• This goes down and down and down in a cascade until it reaches the actual target protein

Why does phosphorylation happen in a cascade, and not just by one?

Because its not just the last enzyme sending the message, all of the enzymes that were activated send it together to amplify the message

Can hormones go through the membrane? How?

yes, they diffuse

What is apoptosis?

programmed cell death

What is the order of the cell cycle? Which phases are under interphase?

• G1

• S. > Interphase (G1, S, G2)

• G2

• M

What happens in the G1 phase?

• Growth

• Gathering materials

• Performs regular cell duties

What happens in the S phase?

• DNA synthesis

• All of DNA is copied

What happens in the G2 phase?

• organelles are duplicated

• checks to ensure the DNA was replicated correctly

What are the steps of the M phase?

What is the molecule that controls much of the cell cycle?

cyclin

What is formed during the cell cycle when cyclin binds to cyclin-dependent kinase? What step in the cell cycle does this initiate?

MPF - Maturation promotion factor

this signals the M phase

What kinds of things stimulate cell division?

• PDGF - platelet derived growth factor

• injury, blood needing to clot, etc.

What is the main important thing about cancer when it comes to AP Biology?

it is UNinhibited cell division

(at a time when division is supposed to be inhibited)

What are the 2 ways cell division is inhibited?

• Anchorage dependence - cells can only divide if they are in a place where they are anchored to a tissue

• Density dependent inhibition - cells will not divide if they see that there are lots of other cells around them

How does cell communication tie to density-dependent inhibition of cell division?

membrane bound proteins on close-together cells send signals to each other, causing inhibition of divison