Ch. 7 Bio

Vocabulary flashcards covering key concepts from Chapter 7 on cell membranes and transport, including membrane structure, fluidity, passive and active transport mechanisms, and bulk transport.

Membranes

Composed of phospholipids and proteins, they form spontaneously due to hydrophobic interactions and are self-assembled structures that define cell boundaries.

Phospholipid bilayer

A long sheet that forms circular spherical vesicles, with hydrophilic heads facing water and hydrophobic tails forming the interior of the membrane.

Semi-permeable membrane

A characteristic of phospholipid bilayers that allows some substances to pass through easily while restricting others.

Fluid Mosaic Model

A model proposed by Singer and Nicholson describes how proteins are inserted into membranes, predicting proteins can move/float anywhere however some don’t move at all

• main idea: proteins can MOVE

Realistic model of proteins

Proteins move much less than expected and are connected to things inside and outside of the cell, and proteins can be anchored to other proteins 

• main idea: proteins are STABLE

Membrane Carbohydrates

Molecules on the cell surface, often bound to lipids (glycolipids) or proteins (glycoproteins), used by cells for recognition.

Glycolipids

Membrane carbohydrates covalently bound to lipids, playing a role in cell-cell recognition.

Glycoproteins

Membrane carbohydrates covalently bound to proteins, crucial for cell-cell recognition.

Human ABO blood types

An example of how specific carbohydrates on membrane proteins vary among individuals and cell types, influencing cell-cell recognition.

Permeability of the Lipid Bilayer

Describes that hydrophobic (nonpolar) molecules can pass through the membrane, but polar or charged molecules cannot easily.

hydrophobic

non-polar, water repelling, able to cross the lipid bilayer easily

hydrophilic

polar, water-attracting, unable to cross the lipid bilayer easily

Passive transport

The diffusion of substances across a membrane down their concentration gradient, from high to low concentration, WITHOUT the cell expending energy (no ATP used)

• happens with hydrophobic molecules unless a protein is involved

• important in drug design

  • has to be slightly hydrophobic and hydrophilic

    • lipids can pass membrane but aren’t soluble within blood stream

Osmosis

• diffusion of water across a selectively permeable membrane

• a region of lower solute concentration (higher water concentration) to a higher solute concentration (lower water concentration) until solute concentrations are equal.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water.

Isotonic solution

A solution where the solute concentration is the same as that inside the cell, resulting in no net water movement and the cell being in its 'happy place'.

Hypertonic solution

A solution where the solute concentration is greater than that inside the cell, causing the cell to lose water and shrivel.

Hypotonic solution

A solution where the solute concentration is less than that inside the cell, causing the cell to gain water and potentially burst (animal cell) or become turgid (plant cell).

• plant cells like being hypotonic

Osmoregulation

The cellular control of internal solute concentrations and water balance to prevent excessive water uptake or loss

• trying to get things back to isotonic

Concentration gradient

The difference in the concentration of a substance between two regions, which drives diffusion

• high to low concentration

Diffusion

The movement of substances from an area of higher concentration to an area of lower concentration, happening spontaneously.

Membrane fluidity

The measure of how easily membrane components (lipids and proteins) can move laterally within the membrane, essential for proper function.

Flip-flopping vs. lateral diffusion

• Flip-flopping: movement of phospholipids between the inner and outer layers of the membrane,

  • rarely happens because it would require taking the head group through the hydrophobic region and getting it out the other side 

• lateral diffusion: the movement of lipids and proteins within the same layer

  • occurs more frequently 10^7 times per second as phospholipids can move around in one leaflet of the bi-layer easily 

Temperature (membrane fluidity)

higher temperature = higher fluidity

Saturated fatty acids (membrane fluidity)

• LESS fluid membranes at higher temperatures

  • hydrocarbon tails pack together more tightly

  • higher viscosity

Unsaturated fatty acids (membrane fluidity)

• MORE fluid membranes at lower temperatures

  • due to cis double bonds creating kinks in their hydrocarbon tails, preventing tight packing

  • trans double bonds don’t occur naturally 

Cholesterol (membrane fluidity)

A steroid in animal cell membranes that acts as a 'fluidity buffer'; at higher temperatures, it reduces fluidity, and at lower temperatures, it maintains fluidity by hindering tight packing.

Why would you want to change the fluidity of membranes?

• respond to the temperature of climate

  • warm → produce more saturated fatty acids

  • cold → produce more unsaturated fatty acids

Transport Proteins

• Membrane proteins

  • proteins are how charged molecules get across the membrane

• allow hydrophilic substances & charged molecules to pass across the membrane, essential for molecules that cannot pass through the lipid bilayer directly 

• high to low concentration gradient

Facilitated diffusion

The passive transport of molecules across the plasma membrane aided by transport proteins, speeding up movement down a concentration gradient without ATP expenditure.

Channel proteins

• A type of transport protein

• provides hydrophilic tunnels acting as an open pore allowing specific molecules or ions to cross the membrane rapidly 

• MANY pass at once as pore opens and closes 

Aquaporins

Specific channel proteins that facilitate the rapid passage of water across the membrane.

Carrier proteins

• A type of transport protein

• shuttles molecules across the membrane

• changes shape to a molecule to open and close

• allows less through than channel proteins and typically moves fewer molecules at a time

Membrane proteins

proteins determine the membrane function by facilitating transport, acting as receptors, and providing structural support.

Peripheral proteins

• Membrane proteins

• bound to the surface of the membrane

• attached to ONE SURFACE

  • not embedded within the bilayer.

Integral proteins

Membrane proteins

• that penetrate the hydrophobic core of the lipid bilayer

• goes through the membrane

• can be partially embedded or span the entire membrane (transmembrane proteins)

Transmembrane proteins

Integral proteins that span the entire membrane

• regions exposed on both the extracellular and cytoplasmic sides.

6 major functional types of proteins

Transport, enzyme activity, signaling transductor, cell recognition, intercellular joining, and attachment to the cytoskeleton and ECM

Signal transduction (membrane protein function)

• receptor proteins on the membrane receive signal molecules from outside and transmit information to the inside of the cell. 

• could be peripheral 

Cell-cell recognition (membrane protein function)

• membrane proteins with attached carbohydrates allow cells to recognize each other by binding to specific surface molecules

• occurs through carbohydrates

• Ex: ABO blood types

  • certain carbohydrates in proteins A blood will reject B blood due to the different types of carbohydrates

Intercellular joining (membrane protein function)

• membrane proteins of adjacent cells hook together in various kinds of junctions (like desmosomes or tight junctions).

Attachment to the cytoskeleton and ECM (membrane protein function)

• membrane proteins (integrins) help anchor a cell in a position within the extracellular matrix and attach to the cytoskeleton.

Active transport

The movement of substances against their concentration gradients (from low to high concentration), requiring energy (ATP) and performed by specific membrane proteins like ion pumps.

Ion pumps

use ATP energy for transport

• form of active transport

• goes against the concentration gradient

• create membrane potentials that allow ions to be transported across a membrane

  • named after a specific ion/element 

Membrane potential

The voltage difference across a membrane, created by differences in the distribution of positive and negative ions; this voltage represents stored energy.

voltage 

created by differences in distribution of positive & negative ions across a membrane 

Proton pump

• active transport protein (ion pump) that moves H+ ions out of the cell, generating an electrochemical gradient and membrane potential

• become an energy source for other processes

  • due to increased concentration

• protons then come back down through the concentration gradient through the “sucrose H+ cotransporter & the energy gained from flowing down the concentration gradient becomes stored energy

• stored energy is being used to pull sucrose back into the cell (no ATP involved)

Cotransport

• active transport of one solute indirectly drives the transports of other solutes 

  • utilizing the stored energy from an ion gradient created by an active pump.

Bulk transport

The transport of large molecules, macromolecules, and particulate matter across the plasma membrane, requiring energy, via processes like exocytosis and endocytosis.

Exocytosis

• process of bulk transport

• Transport vesicles fuse with the plasma membrane and RELEASE their contents to the outside of the cell

  • transport contents OUT of cell

Endocytosis

• process of bulk transport

• cell TAKES in macromolecules by forming vesicles from the plasma membrane

• transporting contents INTO the cell.

3 types of endocytosis

phagocytosis, pinocytosis, and receptor-mediated endocytosis (reactions can technically go both ways)

Phagocytosis

• endocytosis

• the engulfment of food particles or large substances by forming a vacuole 

  • aka “cellular eating”

Pinocytosis

• endocytosis

• the gulping of extracellular fluid containing various solutes by forming small vesicles

  • aka “cellular drinking”

Receptor-mediated endocytosis

• highly specific type of endocytosis

• let’s cell acquire bulk quantities of specific substances (ligands) by binding them to receptors on the plasma membrane before forming a coated vesicle.

• apart of cell transduction or cell signaling and receptors are being brought in and out

Ligand

Any molecule that specifically binds to a receptor site, often in receptor-mediated endocytosis.

Coated vesicle

Vesicle in receptor-mediated endocytosis, covered in coat proteins; aids formation and cargo selection.