BIO 111 - Membrane Structure and Function

Flashcards covering key concepts from lecture notes on membrane structure, phospholipids, cholesterol, membrane proteins and their functions (transport, enzymes, receptors, adhesion, cytoskeleton attachment), and passive transport mechanisms.

How is the membrane structure described?

It is not rigid, but rather described by the fluid mosaic model.

What are the components of a phospholipid?

A phosphate head (hydrophilic and charged) and two fatty acid tails (hydrophobic and nonpolar).

What holds the fluid mosaic model of the membrane together?

Hydrophobicity, where the hydrocarbon fatty acid tails cluster together.

How do the fatty acid tails of phospholipids influence membrane fluidity?

If both tails are straight (saturated), they stack tighter and the membrane is less fluid. If both are unsaturated and bent, the membrane is more fluid. A balance of saturated and unsaturated tails is important for fluidity.

What is a glycolipid?

A phospholipid that has sugars linked to it.

What are specialized phospholipids often associated with?

Specialized responses like inflammation.

What is the primary role of cholesterol in a membrane?

It can increase the rigidity of the membrane; more cholesterol makes it more rigid, less cholesterol makes it less rigid.

Where are lipid rafts found and what is their function?

Lipid rafts are areas in the membrane with more cholesterol that provide platforms for specific functions.

In which organisms is cholesterol found?

Cholesterol is found only in animal cells, not in plant cells or prokaryotes.

What is a significant health concern related to high cholesterol levels?

Cholesterol, being nonpolar, doesn't break down easily and can accumulate in blood vessels as plaque, decreasing blood flow and potentially leading to heart attacks or strokes.

Why do animals need cholesterol?

Cholesterol is an important precursor molecule for making different types of hormones, such as sex hormones (testosterone, estrogen) and stress hormones (cortisol).

What is one function of membrane proteins related to transportation?

They act as transporters to move polar substances, like glucose, across the hydrophobic membrane barrier.

What is the function of an enzyme?

Enzymes speed up specific chemical reactions without being used up in the process.

In terms of nomenclature, how can one often identify an enzyme?

Enzyme names usually end in '-ASE' (e.g., sucrase).

What is the function of cell surface receptors in membranes?

They are proteins on the cell surface that bind to specific signals, initiating a response within the cell (cell communication).

What is the role of cell surface identity markers?

These markers (e.g., sugars, glycolipids) allow an organism's body to distinguish its own cells from foreign cells, as seen in transplant matching.

How do cells in a tissue or organ remain together?

Through cell-to-cell adhesion proteins and structures like tight junctions.

What is the function of membrane proteins that attach to the cytoskeleton?

They link to cytoskeletal components (like actin or intermediate filaments) to anchor things on the cell's periphery or span the membrane.

What are tight junctions and what is their significance?

Tight junctions are structures involving intermediate filaments that hold cells together very tightly, preventing liquid from passing between them, as exemplified by the stomach lining resisting strong acid.

How can transmembrane proteins allow polar substances to cross the hydrophobic membrane?

They can form structures like alpha helices or beta sheets that create a hydrophilic central core or channel through the membrane.

What are the characteristics of passive transport?

It does not require energy and involves substances moving across the membrane based on a concentration gradient, from an area of high concentration to an area of low concentration.

Which small molecules can easily pass through the cell membrane via diffusion?

Water (due to its small size, despite being polar) and oxygen (due to its small size and nonpolar nature).

What types of molecules generally cannot easily pass through the cell membrane?

Polar molecules that are larger than water, and especially charged molecules (ions), even small ones like hydrogen ions.

How do large, charged viruses enter cells, given the membrane barrier?

Viruses bind to specific cell surface receptors, which triggers the cell to engulf the virus through phagocytosis.

What is a 'seven-pass transmembrane protein' also commonly called?

A serpentine protein, due to its shape, and it is a very common type of transmembrane protein.

How is cholesterol transported into cells, despite its high hydrophobicity?

It is transported by binding to specific proteins called lipoproteins, such as high-density lipoproteins (HDL) and low-density lipoproteins (LDL).