Chapter 5-6 Lipids, Cell Membranes, and Carbohydrates

Vocabulary practice flashcards covering lipid structure, plasma membrane permeability, transport mechanisms, and carbohydrate classification.

Lipids

A diverse group of biological molecules that do not mix with water due to their nonpolar structure.

Steroids

Lipids characterized by a carbon skeleton consisting of four fused rings with various chemical groups attached.

Cholesterol

A crucial steroid component of cell membranes that serves as the precursor for synthesizing other steroids, such as sex hormones.

Low-Density Lipoprotein (LDL)

A lipid-protein complex that carries cholesterol in the blood and can deposit plaque in arteries when levels are elevated.

High-Density Lipoprotein (HDL)

A lipid-protein complex that removes LDL cholesterol from the bloodstream, leading to increased cholesterol excretion.

Fat (Triacylglycerol)

A non-polymer lipid synthesized from two smaller component molecules: one glycerol molecule and three fatty acids.

Saturated Fatty Acid

A fatty acid with a hydrocarbon chain containing no double bonds, saturated with as many hydrogen atoms as possible.

Unsaturated Fatty Acid

A fatty acid with a hydrocarbon chain containing one or more double bonds, resulting in fewer hydrogen atoms and a bend or kink in the structure.

Trans Fat

An unsaturated fat modified, usually through man-made processing, by adding hydrogen atoms to alter its double bond configuration.

Phospholipid

An amphipathic lipid molecule consisting of a glycerol molecule attached to a hydrophilic head (choline and phosphate) and two hydrophobic fatty acid tails.

Amphipathic

Having both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region on the same molecule.

Fluid Mosaic Model

A model describing cell membranes as a fluid structure containing a mosaic of diverse embedded or attached proteins.

Integral Proteins

Membrane proteins (transmembrane proteins) that span the lipid bilayer, extending segments into both the interior and exterior of the cell.

Peripheral Proteins

Membrane proteins loosely attached to the surface of the lipid bilayer, often interacting with exposed parts of integral proteins.

CCR5

A cell membrane co-receptor protein that HIV requires alongside CD4 to infect cells; individuals lacking CCR5 are resistant to HIV infection.

Selective Permeability

The characteristic of biological membranes that allows small nonpolar molecules to cross easily while impeding ions and polar molecules.

Passive Transport

The diffusion of a substance across a membrane down its concentration gradient without requiring cellular energy.

Diffusion

The thermal movement of particles down their individual concentration gradient from a region of high concentration to low concentration.

Osmosis

The diffusion of water molecules across a semipermeable membrane from a region of lower solute concentration to higher solute concentration.

Isotonic Solution

A surrounding solution with a solute concentration equal to that inside the cell, resulting in no net water movement.

Hypertonic Solution

A surrounding solution with a higher solute concentration than inside the cell, causing water to exit the cell and the cell to shrivel.

Hypotonic Solution

A surrounding solution with a lower solute concentration than inside the cell, causing water to enter the cell and making it swell or burst.

Facilitated Diffusion

Passive transport of ions or polar molecules across a membrane down their concentration gradient using specific transmembrane transport proteins.

Aquaporins

Channel proteins that specifically facilitate the rapid passive movement of water molecules across cell membranes.

Active Transport

The movement of a solute across a cell membrane against its concentration gradient, requiring energy expenditure (usually ATP).

Sodium-Potassium Pump ($\text{Na}^+ / \text{K}^+\text{-ATPase}$)

An active transport transmembrane protein that uses ATP breakdown to pump three sodium ions ($\text{Na}^+$) out of the cell and two potassium ions ($\text{K}^+$) into the cell.

Secondary Active Transport (Cotransport)

A mechanism that couples the downhill diffusion of a solute (down a concentration gradient generated by an active transport pump) to the uphill transport of a second substance against its concentration gradient.

Monosaccharide

A simple sugar molecule, such as glucose, that is water-soluble and sweet, typically having a chemical formula that is a multiple of $\text{CH}_2\text{O}$.

Disaccharide

A carbohydrate formed by joining two monosaccharides together through a covalent glycosidic linkage.

Glycosidic Linkage

A covalent bond formed between two monosaccharide units through a dehydration reaction.

Polysaccharide

A macromolecule composed of hundreds to thousands of monosaccharides joined by glycosidic linkages, functioning in energy storage or structural support.

Starch

A plant storage polysaccharide consisting entirely of $\alpha$-glucose monomers linked primarily by $1-4$ glycosidic bonds (e.g., amylose and amylopectin).

Glycogen

A highly branched animal storage polysaccharide composed of $\alpha$-glucose monomers, stored primarily in the liver and skeletal muscle tissues.

Cellulose

An unbranched structural polysaccharide found in plant cell walls composed of $\beta$-glucose monomers connected by $1-4$ glycosidic linkages.

Chitin

A structural polysaccharide composed of modified glucose monomers ($\text{NAG}$) that forms the cell wall of fungi and the exoskeleton of arthropods.

Peptidoglycan

A structural polymer containing sugars and amino acids that constitutes the cell wall of bacteria.

Starch vs Cellulose Linkages

The structural distinction where $\alpha$-glucose in starch forms helical storage chains ($1-4$ linkages), whereas $\beta$-glucose in cellulose forms straight, unbranched structural microfibrils.

Cell-Cell Recognition

The ability of a cell to distinguish host self-cells from foreign invaders or other cell types based on cell-surface carbohydrates like glycolipids, glycoproteins, and erythrocyte antigens.

Lipids

A group of biological molecules that do not mix with water due to their nonpolar structure, including steroids, fats, and phospholipids.

Steroids

Lipids characterized by a carbon skeleton composed of four fused rings, distinguished by different attached chemical groups.

Cholesterol

An important steroid component of cell membranes that serves as the precursor from which other steroids, such as estrogen and testosterone, are synthesized.

HDL vs. LDL

Low-Density Lipoprotein (LDL) carries cholesterol that can clog arteries with plaque, whereas High-Density Lipoprotein (HDL) removes LDL from the bloodstream for excretion.

Triacylglycerol (Fat)

A lipid molecule composed of one glycerol molecule linked to three fatty acids via ester linkages.

Saturated Fatty Acid

A fatty acid hydrocarbon chain containing no double bonds between carbon atoms, saturated with the maximum number of hydrogen atoms.

Unsaturated Fatty Acid

A fatty acid hydrocarbon chain containing one or more double bonds, resulting in fewer hydrogen atoms and a bend caused by cis double bonds.

Trans Fat

An unsaturated fat containing trans double bonds, typically created artificially by adding hydrogen atoms to unsaturated oils.

Phospholipid

An amphipathic lipid consisting of a glycerol bound to two hydrophobic fatty acid tails and a hydrophilic head containing choline and phosphate.

Amphipathic

Describing a molecule that contains both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Fluid Mosaic Model

A structural depiction of the plasma membrane as a fluid lipid bilayer embedded with a diverse mosaic of proteins.

Integral Protein

A transmembrane protein that spans the hydrophobic interior of the cell membrane, extending segments into both the cytoplasm and extracellular space.

Peripheral Protein

A membrane protein loosely attached to the inner or outer surface of the cell membrane, often interacting with exposed integral proteins.

CCR5 Co-receptor

A plasma membrane co-receptor required alongside CD4 for HIV entry into cells; individuals lacking CCR5 are resistant to HIV infection.

Selective Permeability

The property of cell membranes that allows small nonpolar molecules like $\text{CO}_2$ and $\text{O}_2$ to cross easily while impeding ions and polar molecules.

Diffusion

The passive transport of molecules down their individual concentration gradients from an area of higher concentration to lower concentration without energy expenditure.

Osmosis

The passive diffusion of water molecules across a selectively permeable membrane.

Isotonic Solution

A surrounding solution with a solute concentration equal to that of the cell, resulting in no net movement of water across the membrane.

Hypertonic Solution

A surrounding solution with a higher solute concentration than inside the cell, causing water to exit the cell and leading to cell shriveling or plasmolysis.

Hypotonic Solution

A surrounding solution with a lower solute concentration than inside the cell, causing water to enter the cell and leading to cell swelling or lysis.

Facilitated Diffusion

The passive transport of ions and polar molecules across a cell membrane down their concentration gradient assisted by channel or carrier proteins.

Aquaporin

A specialized channel protein that facilitates the rapid passive diffusion of water molecules across cell membranes.

Carrier Protein

A transport protein that binds a specific molecule and undergoes conformational shape changes to shuttle it across the membrane.

Active Transport

The movement of solute molecules across a membrane against their concentration gradient, requiring cellular energy expenditure through ATP.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+\text{-ATPase}$)

An active transport mechanism driven by ATP breakdown that undergoes conformational changes to pump three $\text{Na}^+$ out of the cell and two $\text{K}^+$ into the cell.

Cotransport (Secondary Active Transport)

A transport mechanism where the downhill diffusion of one solute (such as $\text{H}^+$) drives the active transport of another solute (such as sucrose) against its concentration gradient.

Monosaccharides

Water-soluble, simple sugar monomers usually having chemical formulas that are multiples of $\text{CH}_2\text{O}$, such as glucose ($\text{C}_6\text{H}_{12}\text{O}_6$).

Glycosidic Linkage

A covalent bond formed between two monosaccharide molecules via a dehydration synthesis reaction.

Disaccharides

Sugars composed of two monosaccharides joined together by a covalent glycosidic linkage, such as sucrose, lactose, and maltose.

Sucrose

A disaccharide synthesized by a dehydration reaction linking glucose and fructose through a $1\rightarrow 2$ glycosidic linkage.

Starch

A plant storage polysaccharide consisting of $\text{α}$-glucose monomers joined primarily by $1\rightarrow 4$ linkages, existing in unbranched (amylose) or branched (amylopectin) forms.

Glycogen

A highly branched storage polysaccharide made of $\text{α}$-glucose monomers stored mainly in animal liver and muscle tissues.

Cellulose

An unbranched structural polysaccharide composed of $\text{β}$-glucose monomers connected by $1\rightarrow 4$ glycosidic linkages that forms plant cell walls.

Chitin

A structural polysaccharide made of modified glucose monomers ($N$-acetylglucosamine / NAG) found in fungal cell walls and arthropod exoskeletons.

Peptidoglycan

A structural polysaccharide in bacterial cell walls containing alternating NAG and NAM monomers cross-linked by amino acid chains.