BIO 1210-W4-Membrane Structure and Function

In general, what is the structure of a plasma membrane?

Phospholipid Bilayer

The animal cell, plasma membrane consist of a type of steroid, what is it?

Steroid

In animal cell’s plasma membrane, where is the steroid, cholesterol located?

Located between the phospholipids in the bilayer

Ture or False: Proteins are also found in plasma membrane

True

What are the two types of proteins that can be found on a plasma membrane?

1. Integral protein

2. Peripheral protein

Define Integral protein

• Embedded in the lipid bilayer by their hydrophobic region

• Can also be Transmembrane proteins thus they may also have hydrophilic region extending on both sides of membrane

Define Transmembrane protein

Refers to a protein that is embedded and also extends through the cell membrane

Define Peripheral protein

Do not penetrate the lipid bilayer instead, are loosely associated on either end of the plasma membrane—inner or outer side.

Why would a hydrophobic amino acid like valine be most likely present in the transmembrane domain of integral membrane protein?

• A hydrophobic amino acid like valine is found in the transmembrane domain because the interior of the lipid bilayer is hydrophobic, and hydrophobic amino acids (like valine) are nonpolar and repel water.

• They form strong non-polar bonds from within — anchoring it in place

What are the two types of fibers that may held a protein in place?

1. ECM — Extracellular matrix (From outer)

2. Cytoskeleton (From within)

What are the 6 functions of membrane proteins?

1. Transport

2. Enzymatic activity

3. Signal transduction

4. Cell-to-cell recognition

5. Intercellular joining

   1. Attachment to the cytoskeleton and ECM

Plasma membrane also consist of carbohydrates, what are the forms that are mostly found and forms that are “some”

Mostly in forms of glycoprotein and some in forms of glycolipid

What is the structure of a glycoprotein?

Protein with carbohydrate chain attached

What is the structure of a glycolipid?

Lipid with carbohydrate chain attached

What is the fluid mosaic model?

Current model used to describe the structure of a plasma membrane

What does the mosaic part of a fluid mosaic model refer to?

Refers to different types of proteins present within the phospholipid bilayer

What does the fluid part of a fluid mosaic model refer to?

The phospholipids and proteins can move freely about the membrane

What are the two ways that affect membrane fluidity?

1. Temperature

2. The type of lipid that the membrane is composed of

If temperature in plasma membrane decrease, will the fluidity increase or decrease?

Decrease

If temperature in plasma membrane increase, will the fluidity increase or decrease?

Increase

What are the three components of lipid composition that affect membrane fluidity?

1. Length of the fatty acid side chain 

2. Degree of unsaturation

3. Presence of sterols

If membrane have longer fatty acid chain, compared to smaller fatty acid chain, will the fluid be less or more?

Less

If plasma membrane contains more unsaturated fatty acids, will the fluid be less or more?

More — more kinks make more empty gaps thus more room for fluidity

How does cholesterol influence fluidity?

It acts as temperature buffer—it exerts different effects at different temperature

At high temperature, does the cholesterol make the plasma membrane less fluid or more?

Less—Restrains movement of phospholipids

At low temperature, does the cholesterol make the plasma membrane less fluid or more?

More—Interacts with the hydrocarbon chain so they do not fit as tightly together when temperature is low

Define Homeoviscous adaptation

Cellular mechanism where organisms adjust their cell membrane lipid composition, particularly the degree of saturation of fatty acids, to maintain consistent membrane fluidity and function despite changes in external temperature

What are examples where Homeoviscous Adaptation occur?

• Bacteria

• Yeast

• Plants

• Ectotherms

• Archaea

Why are plasma membrane considered asymmetrical?

The two monolayer of plasma membrane contain different kinds of lipids and proteins that are randomly distributed.

Define Active Transport

• Energy is required

• Movement is against the concentration gradient

• Transport proteins are always involved

What are the functions of Active transport that make it an important process?

• Allows the cell to uptake essential nutrients from the environment when they are lower outside the cell than inside the cell.

• Allows secretory or wastes products to be removed even when the concentration is higher outside the cell

• Allows constant, non-equilibrium concentration of certain ions inside the cell

Example of constant, non-equilibrium concentration of certain ions inside the cell in animal cells

Sodium-potassium pump

Example of constant, non-equilibrium concentration of certain ions inside the cell in plant, bacteria, and fungi cells

Proton pump

Example of electrogenic pump in animal cells

Sodium-potassium pump

Example of electrogenic pump in plant, bacteria, and fungi cells

Proton pump

Where there is more Na+ and K+ ion concentration in animal cells?

• There are more K⁺ inside the cell than outside

• There are more Na⁺  outside the cell than inside

Which ways are Na⁺ and K⁺ pumped in an animal cell?

• More K⁺  inside a cell, thus potassium is pumped into the cell

• More Na⁺ outside a cell, thus sodium is pumped out of the cell

Are Na⁺ and K⁺ pumped down the concentration gradient or against their concentration gradient in a cell?

Pumped against their concentration gradient

How is Sodium and Potassium ions transported across the membrane in a animal cell?

Through the active transport mechanism, they are transported by a transport protein called Sodium-potassium pump

List steps of the sodium-potassium transport in an animal cell

______  Na+ are pumped out for every _____ K+ brought into the cell. 

3 Na⁺ are pumped out for every 2 K⁺ brought into the cell

Since 3 Na+ are pumped out for every 2 K+ brought into the cell, what does it mean for the charge outside and inside the cell

• More Na⁺ pumped out → Positive charge outside

• Less K⁺ pumped into the cell → Negative charge inside the cell

Why do the cells have voltage after sodium-potassium pump?

Due to the difference in charges after the active transport of sodium-potassium ions.

What is voltage of an animal cell referred to as?

Voltage is referred to as the membrane potential

Define Electrogenic Pumps

Pumps that generate a voltage due to charge imbalance

Why is proton pump useful?

It utilizes active transport, creating an charge imbalance thus voltage across membranes. Generating a voltage across membranes, the pumps help the cell to store energy that can be use for future cellular work.Ex

Example of proton pump being useful, in general.

Transport of materials across the membrane

What do plants utilize proton pump for?

Used to transport sucrose into a sieve tube cell

When does co-transport occur?

Occurs when a pump transporting a specific solute across the membrane is responsible for indirectly help pump another solute across the membrane against its concentration gradient

In general, how do large molecules enter and exit the cell?

Large molecules generally cross the membrane by a mechanism involving vesicles

Examples of large molecules that may need vesicles to get it across the membrane

• Large proteins

• Polysaccharides

Define exocytosis

Mechanism by which large molecules exit

Define endocytosis

Mechanism by which large molecules enter. The cell takes in molecules by forming new vesicles from the plasma membrane

List the three types of Endocytosis

1. Phagocytosis

2. Pinocytosis

3. Receptor-mediated cytosis

Describe phagocytosis

Folds of the plasma membrane called pseudopods surround a particle, forming a phagocytic vacuole. The vacuole fuses with a lysosome and the material is digested.

Describe pinocytosis

Results from the inward folding of the plasma membrane to form a pocket, forming a vesicle/ The vesicle fuses with a lysosome for breakdown of the internalized materials

Describe Receptor-mediated endocytosis

On the plasma membrane there are receptors for certain substances. Receptor binds to its ligand forming a complex which moves to a special region called “coated pit.” This forms a vesicle and the vesicles fuses with a lysosome.