Fluid Mosaic Model & Types of membrane Transport

What is the function of peripheral proteins?

• involved in cell signalling

• allows the transmission of molecular signals from the cell’s exterior to the interior to initiate a response

• transports molecules & may easily dissociate from the membrane

What is osmoregulation? Who uses it?

osmoregulation is the control of water balance
~ animals use this when they are exposed to hypertonic and hypotonic environments for survival

ex. freshwater fish that live in hypotonic environments use their kidneys and gills to prevent excess water buildup in the body

What happens if the cell membrane is not fluid enough?

the bilayer restricts the movement of molecules across

What is secondary active transport

• indirect use of ATP

• energy is derived secondarily from energy that has been stored in an electrochemical gradient
  ~ this energy is used to transport a solute by facilitated diffusion from high to low concentration

ex. hydrogen-sucrose pump

Whats a carrier protein

a protein that selectively interacts with specific molecules or ions so it can cross the membrane

ex. sodium and potassium pump

What is tonicity?

the capability of a solution to alter the water content of cells
~ there are 3 outcomes, depending on the solute content of the solution
~ water will diffuse across the membrane in response to establish equilibrium

What is bulk vesicle transport

• used to transport larger particles (which cannot fit through an integral protein) into, or out of the cell
  ~ ex. proteins and polysaccharides

• involves rearrangement of the cell membrane into vesicles to get molecules across

What is the effect of hypotonic and isotonic environments on plant cells?

• most plant cells thrive in a hypotonic environment

• in an isotonic environment, plants become wilted

A phospholipid Structure

hydrophilic head (polar) and hydrophobic tails (non-polar)

• the polar heads love water & dissolve

• the non-polar tails hide from water

How does temperature affect fluidity of the cell membrane?

• increasing temperature increases the fluidity of the membrane

• decreasing temperature causes the bilayer to solidify into a gel as the phospholipids pack closer together (solidification causes enzyme deactivation)

What happens if the cell membrane is too fluid?

the bilayer permits too many molecules to diffuse across

What is hypotonic?

• solution with a lower solute concentration and a higher water concentration

• net movement of water into the cell

• hypo = below

Animal = LYSING
Plant = TURGID

Why is fluidity so important?

to maintain the transport of molecules into and out of the cell

What is receptor-mediated endocytosis?

membrane proteins lock onto specific molecules and bring these into the cell
~ ex. insulin

How does the presence of cholesterol affect fluidity of the cell membrane?

• High temp—> cholesterol INCREASES intramolecular forces and holds it more tightly, which REDUCES/DECREASES fluidity

• Low temp—> cholesterol molecules PREVENT the close packing of phospholipids into a gel, which INCREASES fluidity

How does the cell membrane move?

• a membrane is held together by weak hydrophobic interactions between the carbon-hydrogen chains

Describe the structure of the phospholipid bilayer

phospholipids in the cell membrane are arranged in two layers forming the phospholipid bilayer
~ it has a bimolecular lipid layer that contains proteins

Whats a cell recognition protein

• also called glycoproteins

a protein that allows the cell to be recognized by the body’s immune system

What is isotonic?

• solutions of equal solute concentration on both sides of the membrane

• no net movement as an equilibrium is reached (ISOS = equal)

What is diffusion

movement of particles from an area of high to low concentration
~ they reach a dynamic equilibrium

channel protein

a protein that allows a substance to move across the membrane

ex. aquaporins allow water to easily diffuse across

What is a concentration gradient?

a difference between the concentration on the inside of the membrane and the concentration on the outside of the membrane

what are the two types of endocytosis? explain each

1) Pinocytosis (cell drinking): transport of liquids INTO the cell

2) Phagocytosis (cell eating): transport of large molecules/cells INTO the cell
~ ex. macrophages (white blood cells that fight infection by engulfing bacterial cells)

What are the different integral proteins?

Channel Protein
Carrier Protein
Cell Recognition Protein
Receptor Protein
Enzymatic Protein

What is exocytosis

used to export, or remove large molecules from the cell

what is active transport

transport from lower concentration to higher concentration which REQUIRES energy (ATP) to move molecules against a concentration gradient

What is a proton pump? How does it work?

• ATP is used to transport proteins AGAINST the concentration gradient

what is facilitated diffusion

when large or hydrophilic molecules are allowed to diffuse through the cell membrane by specialized transport proteins:
~ Channel proteins (hydrophilic)
~ Carrier proteins (specific to a certain solute such as glucose or amino acids; change shape to allow passage

passive transport

requires NO energy (ATP) to move substances across cell membranes

what is primary active transport

• direct use of ATP

• moves ions to establish a concentration gradient between the inside and outside of the cell membrane

• the difference in change results in a voltage (potential difference) across the membrane; this difference is called ELECTROCHEMICAL GRADIENT

Describe the structure of the cell membrane

• a fluid mosaic (combination of different parts) made up of lipids, proteins, and carbohydrates

• protein molecules are “bobbing” in a fluid bilayer of phospholipids

• carbohydrate marks are present on the surface to identify cell type

What are the two types of proteins present in cell membranes

1) Integral proteins: span through the bilayer
2) Peripheral proteins: attached to the outer surface

Both of these proteins act to transport molecules

How does the sodium-potassium pump work?

• the pump transports sodium ions out of the cell while transporting potassium ions into the cell

• when the 3 sodiums bind to the pump, a phosphate from ATP also binds which changes the shape of the protein and causes it to face the opposite side (towards the outside)

• after the sodiums are released outside the cell, 2 potassiums bind to the protein/pump, the phosphate that was binded before gets released, and the protein returns back to its original shape
  ~ the pump then releases both the potassiums into the cell

What’s the main idea of a Sodium/Potassium pump? (“products”)

3 sodiums are released outside; 2 potassiums are released inside

What is hypertonic?

• more dissolved solute outside the cell than inside the cell (hyper = above)

• net movement of water out of the cell

Animal = CRENATION
Plant = PLASMOLYSIS

What’s an enzymatic protein

a protein that catalyzes specific reactions (eg. ATP metabolism)

What’s a receptor protein

a protein that is specifically shaped to a specific molecule

eg. liver stores glucose after insulin binds to cell receptor

What is osmosis

The passive transport of water across a semi-permeable membrane
~ water moves from higher concentration to lower concentration of H20 OR from lower to higher concentration of dissolved solute (towards the solute because there’s less water there)

What is plasmolysis?

when a plant in a hypertonic environment goes through water loss, leading the plant to shrivel and its cell membrane to pull away from the cell wall

Whats the function of the cell membrane

• controls what enters and exits the cell to maintain a balance called homeostasis

• provides protection and support for the cell

• is selectively permeable (allows some molecules in and keeps others out)

What are some factors that affect fluidity?

Temperature
Chemistry of Fatty acid tails
Presence of cholesterol

What is cotransport

when active transport of one solute indirectly drives the transport of another

What is endocytosis?

used to move large molecules INTO the cell (endo - to enter)

~ material comes to the outside of the cell membrane, the membrane surrounds the material, and then pinches off inside the cell forming a vesicle; this vesicle travels to its final destination

Why are proteins the perfect molecules to build structures in the cell membrane?

• protein side chains act as anchors

• within membrane proteins there are:
  ~ nonpolar amino acids (hydrophobic; anchors proteins into membrane)

• on the outer surfaces of membrane:
  ~ polar amino acids (hydrophilic; extends into extracellular fluid & into cytosol)

How does the chemistry of fatty acid tails affect fluidity of the cell membrane?

• UNSATURATED hydrocarbon tails increase membrane fluidity

• cells may alter membrane lipid concentration in response to changes in temperature