Exam 4: Chp 7, 11, 12

Bulk transport

The engulfing of receptors to get a bulk of a specific substance

Amphipathic

Both hydrophobic and hydrophilic regions

Why are phospholipids amphipathic?

A stable boundary between two compartments because of the molecular arrangement

Fluid Mosaic Model

The membrane is a mosaic of protein molecules in and around the bilayer

Membrane fluidity

Even in low temperatures, due to the kinks in the unsaturated fats in the membrane, it will not solidify

How does cholesterol affect the membrane fluidity?

It is a fluidity buffer.

• At high temperatures, it makes it less fluid by retaining movement

• At low temperatures, it lowers the temperature for solidifying because it hinders the phospholipids to pack closely together

Intergral protein

Proteins that are within the membrane (can be partly in, or fully extend to both sides) that can have both hydrophobic and hydrophilic regions

Peripheral proteins

Proteins on the surface of the membrane

6 Functions of Membrane proteins

Transport, Enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to cytoskeleton and ECM

Transport protein

A protein that helps with the transport of a solute from one side of the membranes to another.

• Types: finding a specific solute, changing solute shape, or using ATP to move solute

Enzymatic activity proteins

An enzyme protein with an active site that helps with membrane reactions

Signal transduction protein

A protein that changes shapes with a signaling molecule that binds to it. This change can relay a message inside the cell membrane.

Cell-cell recognition protein

Identification between cells

Intercellular joining proteins

Proteins on cells that hook onto each other

Protein attached to cytoskeleton and ECM

A protein where microfilament or elements of the cytoskeleton bind onto, helping with cell shape and stabilization of certain membrane proteins

2 Examples of cell-cell recognition

• White blood cells: Membrane protein to communicate and identify foreign invaders

• No CCR5 receptors, HIV will not affect the cells

Glycolipid

A carb binded to a lipid

Glycoprotein

A carb binded to a protein

Where is the Glycolipid?

The green chain on the phospholipid head

Where is the Glycoprotein?

The green chain on the protein

Where is the integral protein?

Any purple protein that is within the membrane

Where is the Peripheral Protein?

Any purple only on the surface of the membrane

Where is Cholesterol?

The yellow chains in the hydrophobic part of the membrane

Where are the ECM fibers?

The green fibers around the outside of membrane

Where are the Cytoskeleton microfilaments?

The orange chains in the cytoplasm

Channel protein

A hydrophilic channel that allows certain molecules or ions to use as a tunnel through membrane

Carrier protein

Changes the shape of proteins to move them across the membrane

Are transport protein specific?

Yes.

• If the protein is not available for a certain molecule, it will not pass into the membrane

• This only allows certain ions and molecules to pass through the membrane

Aquaporin

A channel protein that helps move water through the membrane

Diffusion

The movement of particle of any substance so that they spread out into the available space (no energy), high to low gradient

Concentration gradient

The region along which the density of a chemical substance increase or decreases (each substance has its own concentration gradient)

Passive transport

The diffusion of a substance across a biological membrane

Osmosis

The diffusion of free water (water that has the ability to move/has no solute; regular water) across the membrane

Turgid

A cell is firm (normal in plant cells, bursting in animal cell)

Flaccid

A cell is limp (Normal in animal cells)

Plasmolysis

Due to being placed in a hypertonic solution, the plasma membrane pulls away from the cell wall

How does diffusion work with two solutes?

Each of the two solutes will diffuse down its own gradient; they do not effect one another

Why does a plant cell not burst in a hypotonic solution?

A plant cell has a cell wall that will exert pressure back onto the cell, that will refuse more water intake

Facilitated diffusion

A protein that helps pass polar molecules and ions through the membrane with no energy

Ex. Channel protein, carrier protein

Active transport

Solutes moving against their gradient concentration (low to high) with energy

• Only carrier proteins

• ATP will give a phosphate group in order to change protein’s shape for ion

What is happening in 1?

Na+ from the cytoplasm binds to the sodium-potassium pump/transport protein

What is happening in 2?

The binding of all 3 Na+ ions stimulates phosphorylation by a kinase, using ATP (Phosphate is added to pump; ATP to ADP)

What is happening in 3?

Phosphorylation leads to a change in protein shape, and releases Na+ to the other side

What is happening in 4?

With the new shape, it attracts K+ and binds to the protein. The binding of the 2 K+ causes the phosphate group to be released

What is happening in 5?

The loss of the phosphate group restores the protein back to its shape, which does not attract K+

What is happening in 6?

The 2 K+ are released into the cytoplasm, the cycle repeats

Which one is simple diffusion?

1/Purple

Which one is facilitated diffusion with a channel protein?

2/Orange

Which one is facilitated diffusion with a carrier protein?

3/Blue

Which one is active transport with a carrier protein?

4/Multi colored ions

Membrane potential

The voltage across a membrane

Which side of the membrane will have a positive charge?

The outside membrane, the membrane favors the passive transport of cations

What are the two forces that drive diffusion of ions across the membrane?

Chemical force and Electrical force

Chemical force

The ion’s concentration gradient

Electrical force

The effect of the membrane potential on the ion’s movement

Cotransport

A transport protein can couple the downhill diffusion of a solute and uphill transport of a second substance against its own gradient

How is Cotransport used in the treatment of diarrhea?

An animal cell uses Na+ and glucose together in intestinal cells.

Diarrhea expels water so rapidly, the colon cannot reabsorb sodium

• Treatment: A drink containing Na+ and glucose together allows Na+/Glucose transporters on the surface of intestinal cells and pass through the cells into the blood

Exocytosis

A vesicle with proteins/substances merges with the cell membrane, releasing those proteins/substances out of the cells

Endocytosis

The cell takes in molecules and particles, forming new vesicles to take them into the cell

Receptor-mediated endocytosis

The engulfing of receptors to acquire bulk quantities of specific substances

Phagocytosis

Type of endocytosis; A cell a particle by extending around it and packing it within a membranous sac

Pinocytosis

A cell brings in extracellular fluid with solutes from outside of the membrane into the cell by engulfing around it

What type of transport is endocytosis, exocytosis, phagocytosis, and pinocytosis?

Active transport

Electrogenic pump

A transport protein that generates voltage across a membrane (Ex. Protein pump, translocates H+ out of the cells with the ATP)

Quorum sensing

Bacteria being able to sense each other from the signaling molecules they send out

Biofilms

A group of bacteria cells that combine into one once a certain density is met

• Usually bacteria lacking nutrients

How are quorum sensing and biofilm lead to disease?

The communication and merge in of bacteria with antibiotic resistance can cause issue with fight the bacteria

What are the three steps in signal transduction pathway?

1. Signal reception

2. Signal transduction

3. Cellular response

How can chemical signals pass through adjacent animal cells?

Gap junctions

How can chemical signals pass through plant cells?

Plamosdesmata

2 more ways chemical signals pass through animal cells?

Local signaling and Long-distance signaling

Local signaling

Signaling molecules are secreted by the signaling cell (Short distance)

Long-distance signaling

Special cells that secrete hormones and bind to specific cells

3 ways of animal signaling molecules

Paracrine signaling, Synaptic signaling, Endocrine (hormonal) signaling

Paracrine signaling

A signaling cell acts on nearby target cells by secreting molecules of a local regulator

Synaptic signaling

An electrical signal along a nerve cell triggers the secretion of neurotransmitter molecule

Endocrine (hormonal) signaling

Specialized endocrine cells that secrete hormones into body fluid

Why are chemical signals received by specific cells?

The receptors of specific chemical signals are on/within the cell, that is how a response is enabled

Compete the signal transduction pathways

1. Signal reception

2. Signal transduction

3. Cellular response

Signal reception

The binding of a signaling molecule to the receptor on the cell’s surface

Signal transduction

converting the signal to form a specific cellular response (can be one or more steps)

Cellular response

The transducer signal finally trigger a specific cellular response

Ligand

The signaling molecule

3 categories of receptors

G protein-coupled receptors (GPCRs), Receptor Tyrosine Kinases (RTKs), and Ion channel receptors

How does a G-protein receive a signal?

The GPCR receives a single from the signaling molecule that binds from the outside of the cell. The GPCR binds to the G-Protein and is activated

What is happening here? (1)

All proteins are inactive

What is happening here? (2)

• Signaling molecule binds to GPCR

• GPCR will bind to G-protein

• GPCR will displace GDP into GTP on the G-protein, activating the protein

What is happening here? (3)

• G-protein will dissociate from the GPCR and move to the enzyme, binding to it and chasing it shape and activity

• The enzyme will trigger the cellular response

• At the same time, the signaling molecule will dissociate from GPCR

What is happening here? (4)

• G-protein will hydrolyze its bound GTP to GDP and P, deactivating it

• The enzyme will not longer be active

• This allows the pathways to rapidly shut down

Why is it important that the G-protein is also a GTPase enzyme?

It hydrolyze GTP to GDP and P, deactivating it

Kinase enzyme