Midterm 2 (TOPIC 5)

fluid-mosaic model

describes the cell membrane & says that membranes are fluid structures in which some proteins can be found with hydrophobic parts in the middle and their hydrophilic parts outside

peripheral

Peripheral membrane proteins are only temporarily associated with the outside of membranes.

They can be easily removed

Integral membrane proteins

Proteins with portions that go through membranes. They’re permanently embedded within the lipid bilayer of a cell membrane

Trans-membrane proteins

A type of integral membrane protein that span the entire lipid bilayer of cell membranes, extending from one side to the other (pass completely through membranes).

They act as crucial gateways, facilitating the transport of substances & relaying signals

Glycoprotein

a protein molecule with one or more carbohydrate (sugar) chains covalently attached to it

Transport protein

specialized proteins that facilitate the movement of molecules across cell membranes

Channel protein

integral membrane proteins that span the entire phospholipid bilayer, forming hydrophilic tunnels or pores.

They allow specific molecules/ ions to move across the membrane by only passive transport (facilitated diffusion), so, substances move down their concentration gradient w/o the use of cellular energy (ATP)

Carrier protein

integral membrane proteins that facilitate the movement of specific molecules/ ions across cell membranes.

They bind to the molecule on one side of the membrane, undergo a conformational (shape) change, & release the molecule on the other side.

The transport can be Passive/ facilitated diffusion, or Active/ requiring energy. 

Selective permeability

the ability of the cell membrane to allow certain substances to pass through while restricting others.

Bc of the Hydrophobic interior of membranes, only nonpolar molecules (hydrocarbons, CO2, O2) can pass directly through cellular membranes

Passive transport

the process of diffusion across a membrane (substances move from area of higher concentration to area of lower concentration).

It doesn’t require an input of energy, it relies on the the energy in the system that causes natural KE of molecules (their random collisions)

• like a ball rolling downhill, requiring no extra effort

Active Transport

Cells move solutes against their concentration gradient, from area of low concentration to high concentration, by investing energy (usually ATP)

• Uses only carrier proteins

• Required for cells to keep certain solutes out, and others in

• essential for maintaining homeostasis

Diffusion

the passive movement of molecules from an area of high concentration to low concentration.

This movement occurs naturally due to the random motion of molecules (KE) & continues until the molecules are evenly distributed (Equilibrium)

• doesn't require energy input from the cell
  

Solute

Substances such as (ions, sugars, amino acids) that move across membranes — either by Passive or Aequilibriumctive transport

Equilibrium

a state where the concentration of molecules or ions is balanced on both sides of the membrane, resulting in no net movement of those molecules or ions

• the solute continues to move across the membrane in both directions (KE) but concentration stays the same

Concentration Gradient

Difference/Measurement in concentration of a substance between two areas.

It drives the movement of molecules, typically from an area of high concentration to a low concentration, (diffusion)

• The steeper the concentration difference, the stronger the gradient and the faster the diffusion rate
  

Facilitated Diffusion

a Passive transport where molecules move across a cell membrane with the help of membrane proteins (channel or carrier)

• substances move down their concentration gradient (high to low), w/o requiring the cell to expend energy (ATP)

Ion Channel

pore-forming Channel proteins that allow ions (Na⁺, K⁺, Ca²⁺, Cl⁻) to pass through the channel pore

• They’re gated & selective, open & close & only allow specific types of ions to pass through

Semi-permeable membrane

type of membrane that allows some molecules or ions to pass through it while restricting others Small, nonpolar molecules

• pass: (O₂, CO₂, N₂) (H₂O)

• no : (glucose, amino acid, protein) (Na⁺, K⁺, Cl⁻)

Osmosis

the movement of water across a semi-permeable membrane (permeable only to water).

There’ll be a net diffusion of water from the region of lower solute concentration to higher solute.

• requires no energy (passive process)
  

Osmotic pressure

Pressure required to stop water from diffusing through a membrane by osmosis

• increases as the diff. in solute concentration between the 2 sides of the membrane increases

• its a colligative property so its dependent only on concentration of solute, & not on what the solute itself is / size of particles

Isotonic

Concentrations of solutes are approx. equal, just as much water will flow in and out of cells

• so there’s no net osmo pressure on the cell’s outer membrane

• water moves equally in both directions maintaining the cell's shape and size
  

Hypotonic

Solution outside cell has a lower solute concentration

• Water moves into cells by osmosis (low to high) -

  it causing them to burst (lyse)

• makes plant cells (strong cell wall) become turgid, (normal condition)

Hypertonic

Solution outside cell has higher concentration than inside

• Water moves out of cells by osmosis (low to high)

• makes plant cells lose water, causing the cell membrane to shrink away from the cell wall (plasmolysis)

Na+/K+ pump ; Sodium-potassium pump

Active transport pump in which Cells keep :

higher conc. of Sodium ions (Na+) outside

higher conc. of Potassium ions (K+) inside

• For each cycle:

  • 3 Na⁺ ions pumped out

  • 2 K⁺ ions pumped into

  requires energy (ATP)
  

Proton Pump

intergral membrane protein that uses energy (ATP) to transport (H+/protons) across a cell membrane, creating a proton gradient

Electrochemical Gradient

Chem (Concentration) gradient & an Electrical gradient across a cell membrane, affecting the movement of ions

• determines the direction that ions will flow through an open ion channel

Cotransporter

proteins in cell membrane that move two or more molecules through the membrane in the same direction at once

• harnesses the energy of ions moving down their concentration gradient to actively transport another solute

Exocytosis

vesicles fuse w/ the outer membrane, causing the contents that were inside the vesicle to now be outside

• the way cells add new membrane for growth

• used by secretory cells,

  (ex: pancreatic islet cells), which release insulin into bloodstream

• the way Neurons release neurotransmitters

Endocytosis

vesicles bud off of the outer membrane to enclose substances outside the cell & bring them inside

• 3 types of endocytosis: Phagocytosis, Pinocytosis, Receptor-mediated endocytosis
  

Phagocytosis

“cellular eating"

cell internalizes /engulfs of large solids like bacteria

The engulfed material is enclosed in a membrane-bound vesicle called (phagosome)

Phagosome fuses w/ lysosomes for digestion. 

• used for intake of nutrients, & by immune system in destruction of pathogens

Pinocytosis

("cell drinking")

forms very small vesicles & is used to internalize (bring in) liquids & very small particles

It’s nonspecific ab the substances that are engulfed

Receptor-mediated endocytosis

cells can bring in specific substances as determined by the interaction of them w/ specific receptors on the surface of the plasma membrane

• Ligands bind the receptors, & a pit will form, coated on the cytoplasmic side w/ protein

A vesicle will form & bring the contents into the cell

Ligand

Substances that bind receptors / molecule on a cell's surface or inside the cell.

• sometimes, delivering a signal in the process

• ex ; hormones, protein, ions