Unit 2 Flash Cards

Amphipathic

A molecule that has both hydrophilic (water-loving) and hydrophobic (water-fearing) parts.

Phospholipid

A type of lipid molecule that is a major component of cell membranes, consisting of a hydrophilic 'head' and two hydrophobic 'tails'.

Fluid mosaic model

A model describing the structure of cell membranes as a mosaic of various proteins that float in or on the fluid lipid bilayer.

Membrane fluidity

The viscosity of the lipid bilayer of a cell membrane; affects the movement of substances across the membrane.

Selective permeability

The property of biological membranes that allows some substances to pass through while excluding others.

Diffusion

The process by which molecules spread from areas of high concentration to areas of low concentration.

Osmosis

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

Endocytosis

The process by which cells internalize substances from their external environment by engulfing them in a vesicle.

Exocytosis

The process by which cells expel materials in vesicles that fuse with the plasma membrane.

Carrier proteins

Transmembrane proteins that bind to specific molecules and transport them across the membrane.

Channel proteins

Integral proteins that form pores in the membrane, allowing specific ions or molecules to pass through by facilitated diffusion.

Na+/K+ pump

An antiporter that moves sodium ions out of the cell and potassium ions into the cell, maintaining the cell's membrane potential.

Receptor-mediated endocytosis

A form of endocytosis in which specific molecules are internalized after binding to receptors on the membrane.

Homeostasis

The maintenance of a stable internal environment within an organism despite changes in external conditions.

Tonicity

The ability of a solution to affect the fluid volume and pressure in a cell by altering the water content.

Integral membrane proteins

• Proteins that are embedded in the phospholipid bilayer, with regions that are hydrophilic (interacting with the fatty acids) as well as hydrophobic (amino acids). Sticks out on both sides of the membrane, playing key roles in transport, signalling, and cell recognition.

Peripheral membrane proteins

Proteins that are not embedded within the lipid bilayer but are noncovalently attached to either membrane surface. They can associate with the membrane indirectly.

Glycolipids

Lipids that are covalently bonded to a carbohydrate, consisting of one or more short carbohydrate chains covalently bonded to a protein (oligosaccharides). They contribute to cell recognition.

Cytoskeleton

A network of protein filaments and tubules that provide structural support for the cell and help in cell movement and transport.

Describe the structure of a phospholipid

They contain fatty acids bound to glycerol by ester linkages. The first or third fatty acid can be replaced by a phosphate group (contain negative electric charge), forming a hydrophilic head and hydrophobic tails.

Phosphate functional group

A chemical group consisting of a phosphorus atom bonded to four oxygen atoms, typically involved in energy transfer and forming hydrophilic heads in phospholipids. Its negative charge attracts polar water molecules.

Fatty acid chains

A hydrophobic, long hydrocarbon chains that are components of lipids, with a carboxylic acid group at one end.

Differences in Membranes

• Some have more protein than lipids

• Some are lipid-rich

• Some have significant amounts of cholesterol or other sterols

• Some are rich in carbohydrates

How does temperature influence fluidity?

Temperature affects membrane fluidity by altering the movement of lipid molecules; higher temperatures increase energy, movement and thus fluidity, while lower temperatures decrease it, potentially leading to phase transitions.

How does chain length affect fluidity?

Shorter chains result in increased fluidity due to less van der Waals interactions, while longer chains decrease fluidity by enhancing these interactions.

How does saturation affect fluidity?

Saturated (no double bonds) fatty acids pack tightly together, resulting in decreased fluidity, while unsaturated fatty acids, with their kinks, create more space, weaker interactions and increase fluidity.

How does cholesterol affect fluidity?

Anchored membrane protein

A type of membrane protein that is covalently attached to lipids or carbohydrates that are inserted into the membrane, which helps maintain its position within the membrane and influences membrane fluidity.

Transmembrane proteins

Membrane proteins

Asymmetrically distributed proteins on the inner and outer surfaces of membranes that move around in the membrane.

What membrane carbohydrate are there?

Membrane carbohydrates are glycoproteins and glycolipids that are located on the outer surface of the cell membrane.

Glycolipid

A type of membrane carbohydrate that consists of a carbohydrate covalently bonded to a lipid; being a recognition signal for interactions between cells.

Glycoprotein

A type of membrane carbohydrate that consists of one or more short carbohydrate chains covalently bonded to a protein. These are called oligosaccharides. Glycoproteins play essential roles in cell recognition and adhesion.

Proteoglycan

A type of membrane carbohydrate that is a more heavily glycosylated; having more carbohydrates attached to it with longer carbohydrate chains than glycoproteins.

What are the types of cell junctions?

Cell junctions include tight junctions, gap junctions, and desmosomes, each serving distinct roles in cell adhesion and communication.

Tight junction

A type of cell junction that prevents the passage of molecules and ions through the space between cells, maintaining the integrity of tissues.

Desmosomes

A type of cell junction (connected to intermediary filaments) that provides strong adhesion between adjacent cells, allowing them to withstand mechanical stress. Materials can still move around in the extracellular matrix.

Gap junctions

Specialized intercellular connections that allow direct communication between adjacent cells by permitting the passage of substances (ions and small molecules).

Cell adhesion

The process by which cells interact and attach to neighboring cells through specialized structures, playing a crucial role in tissue formation and maintenance.

Intergrin

A transmembrane protein that facilitates cell adhesion by connecting the extracellular matrix to the epithelial cells/cytoskeleton. They bind to a protein in the extracellular matrix (outside the cell) and to microfilaments (inside the cell).