Cell Structure and Membrane Transport

Flashcards testing knowledge on cell structure, membrane lipids, membrane proteins, and passive and active transport mechanisms.

What is a generalized cell?

A model showing the basic structures and functions that cells have in common.

What are the three basic parts of human cells?

1. Plasma membrane (flexible outer boundary)
2. Cytoplasm (intracellular fluid containing organelles)
3. Nucleus (DNA-containing control center)

What is the function of the plasma membrane?

It acts as the flexible outer boundary of the cell, separating the inside of the cell from the outside and controlling anything entering or leaving the cell.

How is the plasma membrane structured according to the fluid mosaic model?

It is described as a flexible structure composed of a phospholipid bilayer with proteins embedded within it and small amounts of cholesterol.

How do the phosphate heads and fatty acid tails of phospholipids differ in terms of polarity and water affinity?

Phosphate heads are charged, polar, and hydrophilic (water-loving), facing toward watery fluid. Fatty acid tails have no charge, are nonpolar, and are hydrophobic (water-hating), pointing away from watery fluid.

What role does cholesterol play in the plasma membrane, and what percentage of membrane lipids does it comprise?

Cholesterol makes up about $20\%$ of membrane lipids, sitting between phospholipid tails to increase membrane stiffness and help support the membrane.

What proportion of the plasma membrane's mass is made up of membrane proteins, and what are the two main types?

Proteins make up half the mass of the membrane. The two main types are integral proteins and peripheral proteins.

What is the difference between integral proteins and peripheral proteins?

Integral proteins are inserted into the membrane (most are transmembrane), functioning as transport proteins, enzymes, or receptors. Peripheral proteins are loosely attached to integral proteins or the membrane, functioning as enzymes, motor proteins, and cell-to-cell connections.

What are six major functions performed by membrane proteins?

1. Transport (channels or carriers)
2. Receptors for signal transduction
3. Enzymatic activity
4. Cell-to-cell recognition (e.g., glycoproteins acting as ID tags)
5. Cell-to-cell joining
6. Attachment to the cytoskeleton inside and extracellular matrix (ECM) outside

What is ATP, and why is it important for membrane transport?

ATP stands for adenosine triphosphate, which provides energy for the cell to do work; active transport requires $ATP$, while passive transport does not.

What is selective permeability?

The ability of the plasma membrane to allow certain substances to cross while blocking others, keeping valuable proteins inside, allowing nutrients in, and letting waste leave.

What are the three types of passive membrane transport?

1. Simple diffusion
2. Facilitated diffusion
3. Osmosis

What is simple diffusion, and what are two examples of molecules that use it?

The slow, direct movement of small molecules from high to low concentration straight through the membrane without requiring $ATP$ or transport proteins. Examples include oxygen ($O_2$) and carbon dioxide ($CO_2$).

What is facilitated diffusion?

The passive movement of molecules from high to low concentration across the membrane with the assistance of a transport protein and without using $ATP$.

How does carrier-mediated facilitated diffusion operate, and what types of molecules does it transport?

A specific molecule binds to a carrier protein, causing the protein to change shape and release the molecule on the other side. It transports larger polar molecules like sugars and amino acids.

What is the distinction between leakage channels and gated channels in channel-mediated facilitated diffusion?

Leakage channels are always open, whereas gated channels open and close in response to chemical or electrical signals.

What is osmosis, and what specialized membrane channels facilitate it?

Osmosis is the movement of water across a selectively permeable membrane from an area of different solute concentration to balance the difference. Water moves directly through the membrane or through specialized water channels called aquaporins.