GNUR 442: Exam 1

what is homeostasis?

regulation of the internal environment to maintain a stable, constant, balanced state

what does cellular dysfunction indicate?

disruption of homeostasis

how is most homeostatic regulation controlled?

by release of hormones into the bloodstream, although other processes such as simple diffusion also help maintain balance.

why does homeostasis require energy?

automatic regulation requires additional energy because the body is constantly working to maintain a stable internal environment

what is simple diffusion?

movement of molecules from an area of high concentration to an area of low concentration

what is the primary function of the mitochondria?

generating cellular energy

why are mitochondria called the “powerhouse or “motor” of the cell?

they generate the energy the cell needs to function

how do mitochondria generate ATP?

through oxidative phosphorylation, using oxygen to release energy stored in cellular nutrients, typically glucose, to generate ATP

why is mitochondrial failure serious?

enough cellular dysfunction can lead to organ dysfunction

what are ribosomes?

complexes of RNA and protein molecules where proteins are produced

what is the function of ribosomes?

they perform biological protein synthesis by linking amino acids together according to the codons of mRNA

where can ribosomes be located?

free-floating in the cell or bound to a membrane

what does the nucleus contain?

the cell’s chromosomes/DNA

what processes occur in the nucleus?

DNA replication and RNA synthesis (transcription)

what happens to DNA during transcription?

DNA is transcribed into mRNA

what happens to mRNA after it leaves the nucleus?

it is transported out of the nucleus and translated into a specific protein

what is the function of the nucleolus?

it is the region of the nucleus where ribosome subunits are assembled and RNA is synthesized

what is the overall function of the endoplasmic reticulum (ER)?

it serves as a transport network for molecules and helps produce proteins

what is the rough ER?

ER with ribosomes on its surface that secretes proteins into the cytoplasm

What is one important function of the smooth ER?

Calcium sequestration and release.

What is the Golgi apparatus?

A processing and packaging center for proteins and lipids made by the cell.

What happens to proteins in the Golgi apparatus?

They are further processed, sorted, and sent to their eventual destinations.

What are possible destinations for proteins processed by the Golgi?

Lysosomes, the plasma membrane, or secretion outside the cell.

What is the function of lysosomes?

They contain digestive enzymes and are involved in phagocytosis.

What is the function of the centrosome?

Produces microtubules that create the cytoskeleton/framework of the cell.

What is the function of vacuoles?

Store food, waste, and extra water and move them to the cell surface for release as needed.

What is a major function of the cellular membrane?

It acts as a permeability barrier that maintains the composition of the cytoplasm and separates it from extracellular fluid.

How does the cellular membrane help maintain homeostasis?

It regulates what enters and leaves the cell in an organized manner.

What percentage of body weight is water?

Approximately 50–70%.

How is total body water divided?

Approximately ⅔ is intracellular fluid (ICF) and ⅓ is extracellular fluid (ECF).

What are the two major compartments of extracellular fluid?

Plasma and interstitial fluid.

What is interstitial fluid?

An ultrafiltrate of plasma that surrounds or bathes the cells.

What is the cellular membrane made of?q

A phospholipid bilayer.

What are the two parts of a phospholipid?

A hydrophilic head and hydrophobic tail.

Where are the hydrophobic tails located?

On the inside of the phospholipid bilayer.

Where are the hydrophilic heads located?

Oriented toward the outside/water-containing environments.

What substances can readily penetrate the lipid bilayer?

Lipid-soluble substances such as CO₂, O₂, and alcohol.

What substances have difficulty crossing the lipid bilayer?

Water-soluble substances such as ions, glucose, and amino acids.

What does the fluid mosaic model describe?

The structure and function of cell membranes, with proteins embedded within a lipid bilayer.

What does the phospholipid bilayer provide to the membrane?

Fluidity and elasticity.

What are intrinsic membrane proteins?

Transmembrane proteins embedded in the lipid bilayer that extend from one side to the other.

What are extrinsic membrane proteins?

Proteins located outside the membrane and weakly bound to it.

What is the function of cholesterol in the cellular membrane?

It strengthens/stiffens and fortifies the membrane.

What is the function of carbohydrates in the cellular membrane?

They serve as receptors and antigens and allow proteins to be loaded onto them.

What are the functions of membrane proteins?

They serve as enzymes, transporters, and receptors.

What is diffusion?

Passive movement of molecules down a concentration/electrical gradient.

Does diffusion require energy?

No.

What is active transport?

Movement of molecules against their concentration gradient using energy.

Does active transport require energy?

Yes, usually ATP.

What is the easiest way to remember diffusion vs. active transport?

Diffusion = “downhill,” no energy. Active transport = “uphill,” requires energy.

What does Fick’s law describe?

The relationship between the rate of diffusion and factors affecting diffusion.

According to Fick’s law, what increases diffusion?

Greater surface area and greater concentration difference.

What decreases the rate of diffusion?

Greater membrane thickness.

What is osmosis?

Diffusion of water through a cell membrane.

Does water undergo active transport across the membrane?

No. Water does not move actively against its concentration gradient.

In osmosis, where does water move?

From low solute concentration toward high solute concentration.

What is osmotic pressure?

The pressure on one side that is just sufficient to keep pure water from entering.

What happens to a cell in a hypotonic solution?

Water moves into the cell, causing it to swell and potentially burst.

Give an example of a hypotonic solution.

0.45% NaCl (½ NS).

What happens to a cell in an isotonic solution?

Water concentration is equal inside and outside the cell, maintaining cellular equilibrium.

Give an example of an isotonic solution.

0.9% NaCl (normal saline/NS).

What happens to a cell in a hypertonic solution?

Water leaves the cell, causing the cell to shrink/dehydrate.

Give an example of a hypertonic solution.

3% NaCl.

Hypotonic

cell takes on water

Isotonic

stays balanced

Hypertonic

cell loses water

What is facilitated diffusion?

Movement of molecules down their concentration gradient with assistance from membrane proteins.

Does facilitated diffusion require ATP?

No

What types of gated channels are involved in facilitated diffusion?

Ligand-gated, mechanically-gated, and voltage-gated channels.

What is a ligand-gated channel?

A channel that opens when a signaling molecule (ligand) binds to the channel protein.

What is a mechanically-gated channel?

A channel that opens in response to a physical/technical force.

What is an example of mechanically-gated channels?

Sound waves bending cilia in inner-ear hair cells, opening ion channels and generating nerve impulses.

What is a voltage-gated channel?

A channel that opens or closes in response to changes in voltage across the membrane.

Where are voltage-gated channels especially important?

Nerve cells during propagation of action potentials.

What is primary active transport?

Transport against a concentration gradient using energy directly from ATP.

What is secondary active transport?

Transport that uses the downhill movement of one ion to drive another molecule/ion against its gradient.

What is the usual driving ion in secondary active transport?

Sodium (Na⁺).

What is symport?

Two molecules move in the same direction.

What is antiport?

Two molecules move in opposite directions.

Give an example of symport.

Sodium-glucose pump.

Give an example of antiport.

Sodium-magnesium pump.

What does the sodium-potassium pump transport?

3 Na⁺ out of the cell and 2 K⁺ into the cell for each ATP used.

What type of transport is the sodium-potassium pump?

Primary active transport.

Why is the sodium-potassium pump important?

It helps maintain the resting electrical charge/membrane potential.

What does the hydrogen-potassium pump do?

Parietal cells use it to secrete acid in the stomach.

What does Ca²⁺-ATPase do in skeletal muscle?

Returns Ca²⁺ to the sarcoplasmic reticulum after contraction.

What is endocytosis?

The cell captures substances from outside by engulfing them with the cell membrane and bringing them into the cell.

What are two forms of endocytosis?

Phagocytosis and pinocytosis.

What is an example of endocytosis?

Engulfing bacteria by phagocytes.

What is exocytosis?

Vesicles fuse with the plasma membrane and release their contents outside the cell.

What is an example of exocytosis?

Release of hormones from a cell.

What is the resting membrane potential?

The electrical potential/voltage difference across a cell membrane when the cell is at rest.

How is the cytoplasm electrically charged compared with extracellular fluid?

The cytoplasm is usually electrically negative relative to extracellular fluid.

Which ions are important in membrane potentials?

Na⁺, K⁺, Ca²⁺, Cl⁻, and Mg²⁺.

How does the sodium-potassium pump affect resting membrane potential?

It moves 3 Na⁺ out and 2 K⁺ in using ATP, helping maintain the resting potential.

What determines an ion's movement across the membrane?

Its concentration difference and electrical potential difference.

What is equilibrium potential?

The point at which two opposing forces are equal and opposite, resulting in no net movement of an ion.

What does the Nernst equation calculate?

The electrical potential difference required to balance the concentration force for a specific ion.

What is the Nernst potential?

The membrane potential at which a specific ion is in equilibrium and has no net movement across the membrane.

What are causes of hypokalemia?

• Insufficient intake

• excessive fluid loss

• vomiting

• diarrhea

• excess perspiration

• surgical losses

• medications

• DKA

• hypomagnesemia

• high aldosterone levels.