Chapter 5 Bio 111 Exam 2

Membranes

A 'collage' of different proteins embedded in the fluid matrix of the lipid bilayer

Flexible but maintains structure

Membranes are flexible but maintain their structure

Plasma membrane

The dynamic and ever-changing boundary that separates the living cells from its nonliving surroundings

Selective permeability

The property of the plasma membrane that allows some substances to cross more easily than others

Functions of the plasma membrane

The plasma membrane functions to define the outer border of cells and organelles, manage what enters and exits the cell, receive external signals and initiate cellular responses, and adhere to neighboring cells

Fluid mosaic model

A model that describes the plasma membrane as a fluid structure with a 'mosaic' of various components embedded in it, including phospholipids, cholesterol, proteins, and carbohydrates

Carbohydrates on the membrane

Carbohydrates are only found on the exterior surface of the membrane, attached to proteins or lipids

What are phospholipids?

Major component of plasma membranes

What are the characteristics of phospholipids?

Amphipathic, containing both hydrophobic and hydrophilic regions; Can move around within the bilayer; Movement makes it impossible to form a completely impenetrable barrier

How does temperature affect the fluidity of the membrane?

Colder temperature restricts movement and leaves smaller gaps between phospholipids; Warmer temperature separates phospholipids and leaves larger gaps

What is the role of cholesterol in the fluidity of the membrane?

Acts as a buffer, keeping membranes fluid when cold and not too fluid when hot; Increases fluidity at low temperatures and decreases fluidity at high temperatures

How does fatty acid composition affect the fluidity of the membrane?

Saturated fats are straight and pack tightly, making the membrane less fluid; Unsaturated fats have double bonds that create kinks, making the membrane more fluid

What are the functions of proteins in the membrane?

Transportation, receptors, enzymatic activity, binding

What are integral proteins?

Proteins that span the entire bilayer and move things in and out of the membrane

What are peripheral proteins?

Proteins that are located on the exterior or interior surface of the membrane, usually enzymes or structural attachments

What is the role of carbohydrates in the membrane?

Cell-to-cell recognition and attachment; Located on the exterior surface of the plasma membrane; Bound to proteins (glycoproteins) or lipids (glycolipids)

What are viral receptors?

Glycoproteins used by most viruses to attach to a host cell

What is the viral receptor of HIV?

gp120 (glycoprotein 120) that adheres to the human immune cell CD4 receptor

What is the function of CD4 receptor?

Cell adhesion molecule that keeps other immune cells close by when immune response is generated

Are plasma membranes symmetric?

No, the inner surface differs from the outer surface

Give an example of asymmetric membranes.

I

What do interior proteins do?

Anchor fibers of the cytoskeleton to the membrane.

What do exterior proteins do?

Bind to the extracellular matrix.

What do glycoproteins do?

Bind to the substances the cells need to import.

What affects the movement of proteins synthesized in the endomembrane system?

Distinct faces.

What does the orange color indicate?

Facing the cell (cytoplasmic).

What does the blue color indicate?

Facing outside the cell (extracellular).

What is the endomembrane system?

Group of membranes & organelles that work together to synthesize, modify, package, and transport proteins and lipids.

What are the components of the endomembrane system?

Nuclear envelope, plasma membrane, endoplasmic reticulum (ER), Golgi apparatus, vesicles, lysosomes.

What is the function of the endomembrane system?

Synthesize, modify, package, and transport proteins and lipids.

What is the result of membrane structure?

Selective permeability.

What is the role of the plasma membrane?

Control the exchange of materials between the cell and its surroundings.

What type of molecules can pass easily through the lipid bilayer?

Small, nonpolar molecules (ex: O2 & CO2).

What type of molecules have a more difficult time crossing the lipid bilayer?

Small, polar molecules (ex: H2O).

Can large, nonpolar molecules pass through the lipid bilayer?

Yes, but it is a slow process.

Why is it difficult for large, polar molecules and ions to pass through the lipid bilayer?

Their size and charge make it difficult to pass through the nonpolar region of the phospholipid membrane without help.

What is the purpose of transport across the plasma membrane?

To allow materials to enter and exit the cell.

What is the asymmetrical membrane?

The difference in cytosol (inside the cell) solutions and extracellular (outside the cell) fluids.

What is passive transport?

The movement of solute from areas of high concentration to areas of low concentration.

What is diffusion?

The passive transport of substances moving down a concentration gradient.

Passive Transport

Special type of diffusion

Osmosis

Movement of water across a semipermeable membrane

Solute concentration

Determines the direction of water movement in osmosis

Water potential

Tendency of water to move from one place to another

Tonicity

Ability of a solution to cause a cell to gain or lose water

Isotonic solution

Solution with the same concentration inside and outside the cell

Hypotonic solution

Solution with a lower solute concentration than the cell

Hypertonic solution

Solution with a higher solute concentration than the cell

Equilibrium

No net movement of water in an isotonic solution

Hypoglycemia

Low blood glucose levels

Hyperthyroid

Excessive production of thyroxine

Osmoregulation

Regulation of water flow in organisms

What is the function of contractile vacuoles in freshwater protists?

To pump water out of the cell and prevent bursting.

How do marine invertebrates maintain internal salt concentrations?

Their internal salt concentrations match their environment.

How do fish excrete excess water or salts?

They excrete diluted urine.

What do osmoreceptors in the brain cells monitor?

Solute concentrations in the blood.

What is the effect of osmoreceptors releasing hormones?

It affects kidney function.

How do cell walls help maintain water balance in plants?

They help balance the uptake of water by pushing back on the cell.

In what type of environment are plant cells healthiest?

Hypotonic environment.

What is the process of moving substances down their concentration gradients called?

Facilitated diffusion.

What are the two types of transmembrane proteins used in facilitated diffusion?

Channel proteins and carrier proteins.

What types of molecules use facilitated diffusion?

Ions and large polar molecules.

What is the function of channel proteins?

To allow the passage of appropriate molecules into and out of the cell.

What are the two types of channel proteins?

Those that are open all the time and those that are gated.

What determines whether a channel protein is open or closed?

Receiving a signal.

What factors determine which molecules can pass through channel proteins?

Size and charge of the molecule.

What is the function of aquaporins?

To allow for the bulk transport of water across the plasma membrane.

What is an example of a transmembrane receptor?

Insulin receptor (IR).

What role does the insulin receptor play in glucose homeostasis?

It plays a key role in the regulation of glucose homeostasis.

What is the function of carrier proteins?

To bind to a specific substance, change shape, and carry it to the other side of the membrane.

Do carrier proteins allow movement in both directions?

Yes, as concentration gradients change.

What is an example of carrier proteins?

Glucose transport proteins or 'GLUTS'.

What is the requirement for active transport across the plasma membrane?

Movement against its concentration gradient (from low to high).

What is primary active transport?

Moves ions/molecules against concentration gradient using ATP

What is the energy source for primary active transport?

ATP

What is the role of ATP in primary active transport?

Provides energy by shifting a phosphate group to the transport protein

What is the result of ATP hydrolysis in primary active transport?

Allows for energy to transport ions across the membrane

What is secondary active transport?

Moves ions/molecules against concentration gradient using electrochemical gradient

What is the energy source for secondary active transport?

Electrochemical gradient

What are the three types of carrier proteins involved in active transport?

Uniporters, symporters, antiporters

What do uniporters do?

Carry one molecule or ion

What do symporters do?

Carry two different molecules or ions in the same direction

What do antiporters do?

Carry two different molecules or ions in different directions

What is an example of primary active transport?

The Sodium-Potassium Pump

How does the Sodium-Potassium Pump work?

Moves 3 Na+ out and 2 K+ in using 1 ATP

What is the role of electrochemical gradients in secondary active transport?

Energy source for moving ions/molecules against concentration gradient

What are electrogenic pumps?

Transport proteins that generate voltage across a membrane

What is membrane potential?

Voltage difference across a membrane

Why are electrogenic pumps important?

Maintenance and functioning of the nervous system

What is bulk transport?

Transport of large molecules or particles across the membrane

What is the energy source for bulk transport?

Not specified in the notes

What are some examples of molecules that enter the cell through secondary active transport?

Amino acids and glucose

What is bulk transport?

Transport of large molecules/particles in/out of cell

What is exocytosis?

Transport vesicles fuse with plasma membrane, releasing contents outside

What is the main function of the endomembrane system?

Bulk transport of substances

What is endocytosis?

Formation of vesicles from cell membrane to bring molecules inside

What are the three main methods of endocytosis?

Phagocytosis, Pinocytosis, Receptor-mediated endocytosis

Phagocytosis

"Cell eating"; an endocytic pathway by which a cell engulfs particles such as microbes or cellular debris.

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Receptor-mediated endocytosis

The uptake of specific molecules based on a cell's receptor proteins (Cholesterol/Hormones).