Membrane Transport & Cell Signaling

Vocabulary flashcards covering key terms and concepts from Chapter 5: Membrane Transport & Cell Signaling.

What is the main idea of the cell membrane?

It is a selective barrier that controls what enters and leaves the cell while allowing the cell to communicate with its environment.

Amphipathic

Describing a molecule, such as a phospholipid or membrane protein, that contains both hydrophobic and hydrophilic regions.

Why are phospholipids called amphipathic?

They have two different regions: Hydrophilic head that interacts with water and Hydrophobic tails that avoid water.

Fluid Mosaic Model

A model of cell membrane that is a fluid phospholipid bilayer with proteins embedded in it that can move around. Fluid= parts can move; mosaic= different proteins/lipids are arranged together

Why do phospholipids form a bilayer?

Because their hydrophilic heads face the watery environments while their hydrophobic tails hide together away from water.

Why is membrane fluidity important?

It allows membrane components to move and helps the membrane function properly instead of becoming too stiff or too loose.

Which membrane is more fluid and why?

The right is more fluid because its kinked tails prevent phospholipids from packing tightly.

What happens to unsaturated phospholipids at freezing temperatures compared with saturated ones?

They stay fluid longer because their kinked tails prevent tight packing and lower the freezing point.

Why does cholesterol affect membrane fluidity?

Cholesterol helps regulate how tightly phospholipids can move/pack, helping stabilize membrane fluidity.

Can membrane lipids move?

Yes. Most lipids can move laterally within the membrane.

Why can membrane lipid composition be considered an adaptation?

Organisms can adjust lipid composition to maintain proper membrane fluidity under specific condtions.

How do organisms adapt their membranes to temperature?

They change their membrane lipid composition. Cold-water fish have more unsaturated fats, while thermophilic bacteria have lipids that prevent excessive fluidity.

Why do thermophilic bacteria have special lipids?

Their lipids prevent excessive membrane fluidity at high temperatures.

What mainly holds membranes together?

Hydrophobic interactions

Are the interactions holding membranes together strong or weak?

Weak, which contributes to membrane fluidity

Can membrane proteins move laterally?

Some can, but some are restricted by the cytoskeleton or extracellular matrix

What can direct some membrane proteins?

Cytoskeleton

What can hold many proteins immoblie?

Cytoskeleton or ECM

Why can O₂ and CO₂ cross the membrane easily?

They are small and nonpolar, so they can dissolve in the hydrophobic interior of the lipid bilayer.

Glycolipid

A membrane carbohydrate covalently bonded to a lipid, located on the outer extracellular bilayer.

Glycoprotein

A membrane carbohydrate covalently bonded to a protein, playing a vital role in cell-cell recognition.

Where are membrane carbohydrates located?

On the outer surface of the membrane

What are the six functions of integral membrane proteins?

1. Transport

2. Enzymatic activity

3. Attachment to cytoskeleton/ECM

4. Cell-cell recognition

5. Intercelluar joining

6. Signal transduction

What does an integral protein involved in transport do?

Helps substances cross the membrane.

What does an integral protein involved in signal transduction do?

Helps the cell receive and transmit signals.

What is a major function of membrane carbohydrates aka glycoproteins?

Cell-Cell recognition

Why is cell-cell recognition important?

Serves as I.D tags by helping organisms identify cells in your body and tell them apart from foreign cells.

How do membrane carbohydrates help the immune system?

They act like cell ID tags, helping the immune system recognize the body's own cells and distinguish them from foreign cells.

Give examples where cell recognition is important.

Embryo development, immune system recognition, and ABO blood typing.

What happens at intercellular joining?

Proteins from tight and gap junction

Why is cell recognition important during embryo development?

Developing cells must recognize the right cells around them so they can organize into the correct tissues and structures.

Does a membrane have identical sides?

No, it has two distinct sides.

What are the two sides of a membrane?

Cytosol side and lumen/extracellular side.

What is the cytosol side of a membrane?

The side that faces the cytosol (inside the cell)

What is the lumen side/ECM of a membrane

Outside of cell

Can the two lipid layers have different lipid compositions?

Yes

Do membrane proteins have a specific orientation?

Yes. Each protein has a directional orientation.

When is membrane asymmetry established?

As the membrane is being built by the Er & Golgi

Whats the order of Protein Synthesis?

Er then Golgi then Vesicle then plasma membrane

Where are membrane proteins and lipids synthesized?

Endoplasmic reticulum

What happens to proteins in the ER?

Carbohydrates may be added, forming glycoproteins, and proteins are modified.

What happens to carbohydrates in the Golgi?

They are further modified.

How are glycolipids formed?

Some membrane lipids acquire carbohydrates.

What transports glycoproteins, glycolipids, and secretory proteins?

Vesicles

What happens when a vesicle reaches the plasma membrane?

The vesicle fuses with the plasma membrane.

What happens to the vesicle's outside face when it fuses with the plasma membrane?

It becomes the inside face of the plasma membrane.

What does selective permeability mean?

The membrane allows some substances to cross more easily than others based on their properties.

Do molecules constantly move across the plasma membrane?

Yes. Small molecules and ions can move across in both directions.

What happens to nutrients in muslce cells?

Sugars, amino acids and other nutrients enter the cell.

What happens to Metabolic wastes when these sugars, amino acids and nutrients enter the cell.

They leave the cell.

What happens to O2 and CO2?

O2 enters for celluar respiration and CO2 leaves

What does inorganic mean?

A substance that is generally not based on carbon.-hydrogen bonds. It usually does not contain carbon.

Which ions does the cell regulate acrss the membrane?

Na+, K+, Ca2+ and Cl-

What type of molecules cross the lipid bilayer easily?

Nonpolar molecules

Why can nonpolar molecules cross easily?

They are hydrophobic and can dissolve in the membrane's lipid interior.

Give examples of molecules that cross easily.

O2, CO2, and hydrocarbons

Why are ions blocked by the lipid bilayer?

They are hydrophilic, while the membrane interior is hydrophobic.

Why do polar molecules have difficulty crossing?

The hydrophobic interior creates a barrier.

Can glucose cross the lipid bilayer?

Yes, but very slowly because it has both hydrophobic and hydrophilic regions.

Can water cross the membrane?

Yes, but even water crosses the lipid bilayer slowly.

Why are transport proteins needed?

They allow hydrophilic substances to cross without directly contacting the hydrophobic lipid interior.

What is a channel protein?

A protein containing a hydrophilic channel that allows certain molecules or ions through.

Think of a channel protein as what?

A tunnel thrugh the membrane.

Are channel proteins nonspecific?

No. They allow certain molecules or ions through.

Aquaporin

A channel protein that allows water to cross the cell membrane.

Why does the cell need aquaporins?

Water is polar, so it doesn't easily cross the hydrophobic membrane. Aquaporins give water an easier pathway.

What does a carrier protein do?

It binds to its specific passenger and changes shape to move that substance across the membrane.

How is a carrier protein different from a channel protein?

Channel protein is a membrane protein that forms a hydrophilic passageway through the membrane for specific ion or molecule to move through it, while a carrier protein binds to a substance, changes shape, and moves it across the membrane.

What causes a carrier protein to change shape?

Binding and release of the transported molecule can trigger the change.

Are carrier proteins specific?

Yes

Which type of transport protein is shown?

Carrier protein

Which type of transport protein is shown?

Channel Protein

Can a transport protein transport every molecule?

No. A transport protein is specific for the substance it transports.

Example of transport protein specificity?

A protein might allow a glucose but not fructose to cross.

Why are molecules constantly moving?

They have thermal energy.

What is diffusion?

The net movement of molecules down their concentration gradient.

What direction does a substance move when it travels down its concentration gradient?

High to low concentration

Do individual molecules all move high to low?

No. Their movement is random, but the net movement of the population is from high to low.

Why is diffusion considered spontaneous?

Because molecules naturally move from high to low concentration due t their random motion without using ATP.

Does one substance's concentration gradient determine another substance's movement?

No. Each substance diffuses according to its own concentration gradient.

What is osmosis?

Diffusion of free water across a selectively permeable membrane.

What substance moves during osmosis?

Water

Why is osmosis a type of diffusion?

Water moves down its concentration gradient without using energy.

Is osmosis passive or active transport?

Passive transport

What happens when there is more solute in one area?

There is less free water in that area.

What does “free water” mean?

Water that is available to move across the membrane.

How are solute and free water related?

More solute equals to less free water

What direction does water move during osmosis?

From higher water concentration to lower water concentration

Why does water move from lower to higher solute concentration?

Higher solute means less free water, so water moves toward the side with less free water.

What causes water to move during osmosis?

A difference in water concentration across a membrane.

What type of membrane is needed for osmosis?

A selectively permeable membrane that allows water through.

Tonicity

The ability of a solution to cause a cell to gain or lose water.

What does isotonic mean?

No net water movement

What does hypertonic mean?

The solution causes the cell to lose water.

What happens to a cell in a hypertonic solution?

It loses water causing the cell to shrivel and possibly die.

What does Hypotonic mean?

The solution causes water to enter the cell.

What happens to a cell in a hypotonic solution?

It gains water, causing the cell to swell and potentially burst/lyse.

A cell is placed in a solution with more solute outside the cell than inside.

Hypertonic

A cell is placed in a solution with less solute outside the cell than inside.

Hypotonic

Inside the cell: 25% solute
Outside the cell: 5% solute

What is the outside solution and will water move into or out of the cell?

Outside is hypotonic and water is moving into of the cell.