AP Biology Unit 4

4.1 Cell Communication & Cell Cycle

Why do cells need to communicate?

1) To adjust to changes

2) To keep us functioning properly

3) To maintain homeostasis

What are the two ways for cell communication?

1) Direct contact

2) Cell signaling

State an example of direct contact

The immune system

How does a T-cell become a killer cell?

An infected cell binds to it, causing it to become an active killer

Short distance vs Long distance chemical signaling

Neurons vs Estrogen/Testosterone

Neurons (short distance signaling)

Communicate with other cells via chemical signals

Estrogen and Testosterone

Communicate with other cells through the body (ex: through bloodstream)

What do signal transduction pathways do?

Convert signals into cellular responses

3 stages of cell signaling

1) Reception

2) Transduction

3) Response

Reception

1) Happens on the cell surface (plasma membrane)

2) Target cell detects ligand, (from sending cell)

3) Ligan binds to the receptor

T or F ligands bind specifically to a receptor and changes the receptor’s shape

True

What are examples of ligands?

1) Hormones

2) Neurotransmitters

3) Lipids

4) Gas molecules

Three types of reception

1) GPCR

2) Tyrosine Kinase

3) Ligand gated ion channels

G protein coupled receptor

1) Ligand activates GPCR

2) G protein binds to GPCR, and the GDP is replaced by GTP

3) GTP on G protein move to adenylyl cyclase and activates it

4) Phosphate disassociates, and GDP is now formed again on G protein

* process repeats*

T or F: The Tyrosine Kinase Receptor can only signal one signaling pathway at a time.

False; It can signal multiple signaling pathways at once

Tyrosine Kinase Receptor

1) Ligand activates each of two tyrosine kinase protein

2) Tyrosine Kinase proteins form a dimer

3) Cross phosphorylation occurs

4) Inactive relay proteins bind to phosphates

5) Phosphates become active and evoke a response

Ligand Gated ion channels

1) Ligand activates LGICR, which has a closed gate prior to the binding

2) Ions are floating around------ gate opens and ions (such as Na+ and Ca+) pour through

3) Ligand unbinds (deactivates LGICR) and the gate closes

Where are intracellular receptors typically found? are they hydrophillic or hydrophobic?

They are typically found in the cytosol or nucleus, and they are hydrophobic

Hormone Receptor Complex

1) Hormone (ligand) binds to receptor, and forms this complex

2) Can act as a transcription factor, turning on specific genes

Transduction

1) Converts the signal

2) Relay molecules are now activated

3) Relay molecules change shape as they are phosphorylated

Protein Kinase vs Protein Phosphotase

Protein Kinase- phosphorylates by adding a phosphate

Protein Phosphotase- dephosphorylates by removing a phosphate

Describe a phosphorylation cascade

1) Ligand binds to receptor

2) Receptor forms into relay molecule

3) Relay molecule activates PK1

4) PK1 activates PK2

5) PK2 gets phosphate and phosphate activates PK3

6) PK3 gets phosphate and activates a protein----- 7) Cellular response is formed

What are second messengers? What do they do?

1) They are small, nonprotein, water-soluble molecules that diffuse into the cell.

2) They activate intracellular signaling pathways, relaying and amplifying those signals.

Examples of second messengers

1) cAMP (activates PKA; from ATP)

2) Ca2+

Response

Gene transcription in the nucleus

What type of synthesis is happening during response? What’s being done?

Enzyme synthesis, where genes are either turned on or off in the nucleus

Examples of response

1) Inflammation

2) Cell growth

3) Apoptosis

4) Protein activation

5) Cell metabolism

6) Change in gene expression

Apoptosis

Programmed cell death

What are some apoptosis triggers?

1) DNA damage in the nucleus

2) Protein misfolding in the ER

3) Death signalling ligand

What happens during apoptosis?

Cells are packaged into vesicles that are digested by scavenger cells

Stem cells

Cells that can make cells like themselves or completely different ones

Feedback mechanisms

1) Maintains an organism's internal environment and helps to respond to environmental changes

Positive feedback vs Negative feedback

Positive: brings us away from homeostasis

ex: ripening of fruit

Negative: brings us toward homeostasis

ex: glucose in blood

3 stages of the cell cycle

Interphase- G1, S, G2 (G0)

Mitosis- nucleus division

Cytokinesis- cytoplasm division

Mitosis ensures the transfer of…

a complete genome from a parent cell to two genetically identical daughter cells

4 Steps of Mitosis

1) Prophase

2) Metaphase

3) Anaphase

4) Telophase

What are the regulatory proteins that are involved in the cell cycle?

Cyclins and Cdks

What is the role of p53?

It acts as a tumor suppresor

Characteristics of a cancer cell

1) They make their own growth factor

2) They have an abnormal cell cycle