Cell Biology: Organelles, Membranes, Transport & Osmosis

What are the characteristics of life?

Organization and complexity, response to the environment, growth and metabolism, reproduction/heredity, evolution, and composed of one or more cells.

What does homeostasis refer to in living organisms?

The maintenance of a stable internal environment within ideal ranges/set points.

What distinguishes prokaryotic cells from eukaryotic cells?

Prokaryotic cells lack a nucleus and internal membrane systems, while eukaryotic cells have both.

What is the significance of cell size in biology?

As cell size increases, volume (demand) increases faster than surface area (supply), making it important for cells to remain small for efficient function.

What are the two domains of prokaryotic cells?

Bacteria (eubacteria) and Archaea (extremophiles).

What is the microbiome?

A community of microorganisms that can be found in one habitat.

What are the main differences between prokaryotic and eukaryotic cells?

Prokaryotic cells have no nucleus, no internal membrane system, and a cell wall made of peptidoglycans; eukaryotic cells have a nucleus and membrane-bound organelles.

What is the function of ribosomes?

To synthesize proteins.

What is the structure of the nucleus?

A double lipid bilayer membrane (nuclear envelope) with nuclear pores, containing chromatin and a nucleolus.

What is the role of the nucleolus?

To assemble ribosomes and produce ribosomal subunits.

What are the components of the endomembrane system?

Includes the endoplasmic reticulum (smooth and rough), Golgi apparatus, and nuclear envelope.

What is the function of the smooth endoplasmic reticulum (SER)?

Site of lipid synthesis, fatty acid desaturation, and cholesterol synthesis.

What is the function of the rough endoplasmic reticulum (RER)?

Site for the synthesis of proteins that are bound for export from the cell or for use in the endomembrane system.

What is the Golgi apparatus responsible for?

Sorting and packaging proteins and lipids.

What is the structure of the Golgi apparatus?

A series of flattened tubes (sacs) with walls made of a lipid bilayer, not connected to other structures.

What is chromatin?

Chromosomal DNA bound to DNA binding proteins, found in the nucleus.

What is the significance of the number of prokaryotic cells in soil?

The number of prokaryotic cells in a handful of soil is roughly equal to the number of people that have ever lived (~100 billion).

How many prokaryotic cells live on/in a human body?

Approximately 40 trillion, which is greater than the number of eukaryotic cells (~30 trillion).

What is the primary component of a prokaryotic cell wall?

Peptidoglycans (protein sugars).

What are pili used for in prokaryotic cells?

To physically attach to other prokaryotes.

What is the function of the flagellum in prokaryotic cells?

To provide mobility by whipping around.

What is the outer plasma membrane of all cells composed of?

A phospholipid bilayer.

What is the cytoplasm?

A semi-solid substance that contains the cell's internal components.

What is the function of the Cis face of the Golgi apparatus?

Receives transport vesicles from the endoplasmic reticulum (ER).

What occurs at the Trans face of the Golgi apparatus?

Transport vesicles exit from the Golgi.

What are the main functions of the Golgi apparatus?

Modifies proteins and other molecules, sorts them by destination, and releases them in vesicles.

What is the role of vesicles in cellular transport?

Transport and secretion of materials into and out of the cell.

Describe the process of exocytosis.

The process by which material is exported out of the cell, such as the production and export of insulin.

What is endocytosis?

The process of taking material into the cell by surrounding it with the plasma membrane, forming an endocytic vesicle.

What are lysosomes?

Membrane-bound vesicles with a low internal pH that contain digestive enzymes.

What is the function of lysosomes?

To digest materials from inside or outside the cell, including worn-out organelles.

What happens when a primary lysosome fuses with an endocytic vesicle?

A secondary lysosome is formed.

How does the tuberculosis bacterium evade destruction within cells?

It prevents the fusion of the endocytic vesicle and primary lysosome.

What is the structure of mitochondria?

A double lipid bilayer membrane with an outer membrane, an extensively infolded inner membrane (cristae), and a liquid center (matrix).

What is the endosymbiotic theory?

The theory that mitochondria reproduce themselves and have their own DNA.

What is the structure of chloroplasts?

A double lipid bilayer membrane with an internal membrane organized into stacks of disks called thylakoids.

What is the function of chloroplasts?

The site of photosynthesis in plant cells, converting light energy into usable chemical energy.

What is the extracellular matrix?

A network of multiple types of proteins outside of cells that provides structural support and facilitates cell-cell communication.

What is the plasma membrane?

A barrier that defines the inside and outside of a cell and regulates the transport of materials.

What did Gorter's experiment in the 1920s demonstrate about cell membranes?

That cell membranes are phospholipid bilayers.

What are peripheral proteins?

Proteins attached to the surface of the plasma membrane, either inner or outer.

What are transmembrane proteins?

Proteins that span the entire width of the plasma membrane.

What is the fluid mosaic model?

A model describing plasma membranes as fluid structures where molecules float in a 'lake' of phospholipids.

What evidence supports the fluidity of cell membranes?

Cell fusion experiments showed that membrane proteins from different cells mixed over time.

What is the significance of cristae in mitochondria?

They increase the surface area for chemical reactions involved in energy production.

What is the role of thylakoids in chloroplasts?

They are the sites where light energy is converted into chemical energy during photosynthesis.

What is the role of the stroma in chloroplasts?

The liquid substance surrounding the grana where the Calvin cycle occurs.

What is the significance of membrane fluidity?

Membrane fluidity is crucial for maintaining the integrity of the cell membrane; it allows transmembrane proteins to flex and perform their functions.

What happens if a membrane becomes too fluid?

If a membrane becomes too fluid, it cannot serve as a barrier and may fall apart, losing the cell's contents.

What happens if a membrane becomes too solid?

If a membrane becomes too solid, transmembrane proteins cannot flex, impairing their ability to function.

How can cells regulate membrane fluidity?

Cells can regulate membrane fluidity by altering the fatty acid chains of phospholipids, either by changing the saturation or length of the chains.

What is the effect of unsaturated fatty acids on membrane fluidity?

Unsaturated fatty acids pack less tightly, increasing membrane fluidity.

What is the effect of saturated fatty acids on membrane fluidity?

Saturated fatty acids pack more tightly, decreasing membrane fluidity.

How does temperature affect membrane fluidity?

Lower temperatures can make membranes too solid, prompting cells to create shorter, more unsaturated fatty acid chains. Higher temperatures can make membranes too fluid, leading to the production of longer, more saturated fatty acid chains.

What role does cholesterol play in membrane fluidity?

Cholesterol helps maintain membrane integrity by preventing phospholipid fatty acid chains from packing too tightly and by partially immobilizing them.

What is the primary barrier for molecules crossing a plasma membrane?

The hydrophobic interior of the plasma membrane is the major barrier for molecule passage.

What type of molecules can easily cross the plasma membrane?

Nonpolar molecules can easily cross the plasma membrane.

What is passive transport?

Passive transport is the movement of molecules across the membrane from high concentration to low concentration without the use of energy (ATP).

What is active transport?

Active transport is the movement of molecules across the membrane from low concentration to high concentration, requiring energy (ATP).

What is simple diffusion?

Simple diffusion occurs when a membrane is permeable to a molecule, allowing it to move from an area of high concentration to low concentration without ATP or transport proteins.

What is facilitated diffusion?

Facilitated diffusion involves transport proteins that help molecules that cannot cross the membrane on their own to diffuse down their concentration gradient without using ATP.

What are channel proteins?

Channel proteins are transmembrane proteins that form tunnels for molecules to pass through the membrane; they do not bind to the molecules they transport.

What are carrier proteins?

Carrier proteins bind to the molecules they transport and change shape to facilitate their movement across the membrane.

What are uniporters?

Uniporters are carrier proteins that transport only one type of molecule at a time.

What are symporters?

Symporters are carrier proteins that transport two types of molecules in the same direction simultaneously.

What are antiporters?

Antiporters are carrier proteins that transport two types of molecules in opposite directions.

What is osmosis?

Osmosis is the diffusion of water molecules across a selective (semi-permeable) barrier from an area of high water concentration to an area of low water concentration.

What determines the concentration of water in a solution?

The concentration of water is determined by the concentration of solutes dissolved in it.

What is an isotonic solution?

An isotonic solution has equal solute potential and water concentration inside and outside the cell.

What happens in a hypotonic solution?

In a hypotonic solution, the solute potential is higher outside the cell, causing water to diffuse into the cell, potentially leading to swelling or lysis.

What happens in a hypertonic solution?

In a hypertonic solution, the solute potential is higher inside the cell, causing water to diffuse out of the cell, leading to cell shrinkage.

What is the clinical significance of the blood-brain barrier?

The blood-brain barrier restricts most medicines from entering the brain, posing challenges for medical treatments.

How can a solute be used to breach the blood-brain barrier?

Injecting a solute into the blood can lower the water concentration in blood compared to the capillary wall cells, causing water to diffuse out and creating space for medicine to pass through.