Biochemistry Overview: Membranes and Transport

A fatty acid is a linear chain of carbons with hydrogens and a carboxylic acid group at one end.

Saturated fatty acids have only single bonds, while unsaturated fatty acids have at least one double bond between carbon atoms.

Plasma membranes are made up of lipids and proteins.

The hydrophobic core of the membrane prevents most water-soluble molecules from passing through.

Eukaryotic cells have internal compartments, each surrounded by membranes.

Membranes control what enters and exits the cell or specific compartments within.

Fatty acids with one or more double carbon bonds; usually cis configuration.

Fatty acids in which the carbons are bonded to the maximum number of hydrogens; no double bonds.

Essential fatty acids are needed by the body but cannot be produced. Must be consumed.

A fat molecule that stores energy, consisting of glycerol with three fatty acids attached.

Phospholipids have a glycerol backbone, two fatty acid tails, and a polar head group.

Fatty acids with a double bond at a particular position counting from the omega end (the methyl end).

A way to name fatty acids based on the number of carbons and double bonds, and the position of the double bonds.

A protein embedded within the cell membrane, often with hydrophobic regions interacting with the lipid bilayer.

A helical region in a membrane protein that has both hydrophilic and hydrophobic sections, allowing it to interact with both the membrane and aqueous environments.

A lipid anchor that attaches some proteins to the membrane, composed of a phospholipid, oligosaccharide, and phosphoethanolamide.

Movement of molecules across a membrane from a high concentration to a low concentration, without requiring energy.

Transport of molecules across a membrane with the help of a membrane protein, down their concentration gradient, without requiring energy.

Membrane proteins that act like doors, opening or closing to allow specific molecules to pass through the membrane, often regulated by signals.

Membrane proteins that use energy to move molecules across the membrane against their concentration gradient.

Movement of molecules across the membrane without requiring energy, driven by concentration gradients.

The ability of an ion channel to allow passage of specific ions while blocking others, based on size and charge. This is achieved by a selectivity filter, which dehydrates the ion and requires strong interactions with channel proteins.

A potassium (K+) channel is designed to specifically transport K+ ions, preventing the passage of smaller sodium (Na+) ions. This is due to the selectivity filter that allows strong interactions with K+ but not with Na+, leading to dehydration of K+ within the channel.

The KcsA potassium channel is a tetrameric structure, meaning it consists of four subunits. The selectivity filter, composed of the TVGYG amino acid sequence, lies in the middle of the channel. This filter interacts with K+ ions through oxygen atoms, allowing their passage while excluding Na+ ions.

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride (Cl-) channel activated by both a ligand and phosphorylation. It requires phosphorylation of its regulatory domain by protein kinase A (PKA) and subsequent ATP binding. This leads to channel opening and Cl- diffusion out of the cell.

The difference in concentration of a substance across a membrane. Molecules naturally move from a region of high concentration to a region of low concentration, driven by the concentration gradient.

The combined effect of both concentration gradient and membrane potential on the movement of ions across a membrane. The electrical potential difference also influences the movement of charged ions.

A type of active transport where the energy required to move molecules against their gradient is directly obtained from ATP hydrolysis.

Uses the energy stored in the concentration gradient of one molecule to move another molecule across the membrane.

A primary active transporter that pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell.

A membrane protein that transports two different molecules in opposite directions.

A membrane protein that transports two different molecules in the same direction.

A secondary active transporter that uses the Na+ gradient to move glucose into the cell.

Bacteria or cancer cells can develop resistance to drugs by producing pumps that actively remove the drugs from the cell.

A specific multi-drug resistance protein found in Staphylococcus aureus. It functions as an ABC transporter, using energy from ATP to pump out a variety of drugs.

A type of membrane protein that uses energy from ATP to transport molecules across cell membranes. They are commonly involved in drug resistance.

The difference in concentration of ions (like Na+ and K+) across a cell membrane. Cells actively maintain these gradients to function properly.

Substances that make cell membranes permeable to ions. Some antibiotics act as ionophores, disrupting the ion balance and killing bacteria.

An ionophore that transports K+ ions out of the cell. It has a higher affinity for K+ compared to Na+, making it selective for potassium.

Antibiotics produced by bacteria, acting as ionophores. They consist of peptides with a unique amino acid composition.

A rare type of amino acid found in some peptides and antibiotics. These amino acids are mirror images of standard L-amino acids.

A thin outer layer of a cell that acts as a barrier between the cell's interior and its environment. It controls the movement of molecules in and out of the cell.

The middle region of the plasma membrane composed of fatty acid tails, which repel water and prevent most water-soluble molecules from passing through.

A long chain of carbon atoms linked together, with hydrogen atoms attached, and a carboxylic acid group at one end.

Lipids with a sugar molecule attached to their polar head group, like inositol or galactose.

A type of phospholipid that has an amino-alcohol core instead of glycerol and a choline head group.

A type of glycosphingolipid that has both an amino-alcohol core (like sphingomyelin) and a sugar head group.

Cholesterol has a rigid, hydrophobic sterol core made of 4 rings and a short tail. It has a small, hydrophilic OH group.

Cholesterol fills gaps in the membrane caused by unsaturated fatty acids, regulating membrane fluidity.

A spherical structure formed by hydrophobic tails of lipids pointing inward and hydrophilic heads facing outward in a watery environment.

A spherical vesicle formed by a phospholipid bilayer, with the hydrophobic tails facing each other and polar heads facing the aqueous environment.

The ability of a membrane to move and deform easily, due to the dynamic arrangement of its components.

Think of a protein tethered to the membrane by a fatty chain like a boat anchored to the seafloor.

Lipids rarely switch from one layer of the membrane to the other.

Enzymes that help lipids change layers. Flippases are specific and require energy, while Scramblases are random.

The two layers of the membrane have different compositions due to flippases, creating a functional difference.

The membrane is a fluid of lipids with proteins scattered like tiles in a mosaic, able to diffuse freely.

Thicker, more organized areas in the membrane, enriched in cholesterol and certain proteins, that act as platforms for specific interactions.

Lipid rafts influence cell signaling, membrane trafficking, and protein sorting by concentrating specific molecules.

Lipid rafts form due to favorable interactions between specific lipids, like cholesterol and long chain fatty acids.

A membrane protein that pumps sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, against their concentration gradients, using energy from ATP hydrolysis.

Secondary active transport is a common mechanism used by cells to transport nutrients, ions, and other essential molecules across their membranes.

A symporter moves two compounds in the same direction across the membrane, while an antiporter moves them in opposite directions.

A growing problem where bacteria have evolved mechanisms to resist the effects of antibiotics, making infections harder to treat.

A potassium (K+) channel is specifically designed to transport K+ ions, preventing the passage of smaller sodium (Na+) ions. This is because the selectivity filter interacts strongly with K+ ions, allowing them to dehydrate and pass through.

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride (Cl-) channel activated by a ligand and phosphorylation. It requires phosphorylation by protein kinase A (PKA) and subsequent ATP binding to open.

Movement of molecules from a region of high concentration to a region of low concentration, driven by the concentration gradient. This can be simple or facilitated by a transport protein.