🂱🧬 Bio 1.4 Chemistry basics

Cell membrane =

A security gate

• It controls:

  • What comes in

  • What goes out

  • The electrical charge of the cell

  • How much water is inside

How could something cross the cell membrane?

Passive transport or Active transport

What is Passive transport?

The movement of substances across the cell membrane without the use of energy

• It moves down / follows the concentration gradient

  • from an area of high concentration → to an area of low concentration

What is Active transport?

It is the movement of substances across the cell membrane with the use of energy

• It moves against the concentration gradient

  • from an area of low concentration → to an area of high concentration.

Solute =

Gets dissolved in a solvent to form a solution

• anything that disolves in water

Solvent =

Does the dissolving in a solution, typically liquid, that dissolves the solute

Concentration gradient =

The difference in concentration between two areas

• High → Low or Low → High

  • “if there are 20 molecules on one side and 5 on the other, there is a concentration gradient”

Selective permeability =

The membrane allows some substances to cross but prevents others from crossing

• think of how the cell membrane is the security guard ; some molecules are allowed through, and others arent

Passive transport =

The movement of substances across a cell membrane without the use of energy → NO ATP

This process occurs along the concentration gradient, through simple diffusion: Solutes move HIGH → LOW

What is simple diffusion?

The process for solutes to move (across a membrane) from areas of higher concentration to → areas of lower concentration ; without the help of energy

• Examples: Oxygen (O₂), Carbon dioxide (CO₂), Chloride, Urea

Simple = Just go!

Osmosis =

The movement of water

Water moves across a selectively permeable membrane

→ Water follows solute

→ Water moves toward the side with MORE solute

• water moves from (inside) higher water concentration → (outside) areas of lower water concentration, without the use of energy

  • because outside has more solute

Example: inside: 10% solute, outside: 20% solute

Tonicity =

The ability of a solution to affect the movement of water in and out of a cell by osmosis, determining whether a cell will swell, shrink, or remain the same size

• Tonicity is classified as isotonic, hypertonic, or hypotonic based on solute concentration relative to the cell

Hypertonic =

Hyper = High

→ High solute outside

→ Water leaves cell

→ Cell shrinks

Hyper = HIGH solute = water OUT → shrink

Isotonic =

Iso = Same

→ Same solute concentration inside and outside the cell

→ Water moves both in and out equally

→ Cell stays the same size

Hypotonic =

Hypo = Low

→ Low solute outside

→ Water enters cell

→ Cell swells and may burst

Hypo = LOW solute = water IN → swell

Filtration =

Fluid moves through a membrane because of pressure

Small molecules can fit through the openings vs large molecules cannot

• Filter = pressure pushes small things through

Facilitated Diffusion =

• No ATP

• High → Low

• Requires a protein helper

Facilitated = “helped” diffusion

Why would something (like facilitated diffusion) need a protein helper?

Because some molecules are too large or too polar / charged to cross the membrane by themselves, so they need a protein

Protein helpers:

• Channel protein = creates a tunnel

• Carrier protein = binds to the substance and changes shape to move it across

Active Transport =

Active = Requires energy (ATP)

• Requires ATP

• Moves substances LOW → HIGH

• Goes against the concentration gradient

Active vs Passive Transport =

Passive = HIGH → LOW

• NO ATP

Active = LOW → HIGH

• ATP required

Sodium Potassium Pump =

Pumps Na⁺ OUT of the cell & K⁺ IN the cell

• Sodium = out ; Potassium = in

• It requires ATP

What major ions are outside the cell?

Outside the cell there is more:

• Na⁺ (Sodium)

• Ca²⁺ (Calcium)

• Cl^- (Chloride)

What major ions are inside the cell?

Inside the cell there are more:

• K⁺ (Potassium)

• Mg²⁺ (Magnesium)

• Enzymes

• Glycogen

Secondary Active Transport =

The movement of ions or molecules across a membrane against their concentration gradient

• One substance helps another substance get across:

  • Na⁺ moves → helps glucose move

    • the sodium movement provides the energy needed to move glucose

Cotransport = Both substances move in same direction (co = together)

Countertransport = The substances move in opposite directions (counter = opposite)

Vesicles =

A small membrane-bound sacs / “bubble” that transports substances within or outside of a cell

• Large molecules are too big to simply pass through the membrane, so the cell uses vesicles

= delivery package

Exocytosis =

EXO = OUT / EXIT

The cell sends something OUT using vesicles that → moves to the membrane, fuses with the plasma membrane, then releases their contents into the (outside) extracellular space

• Requires energy

Endocytosis =

Endo = IN / ENTER

The process where the cell takes in substances by surrounding them with its membrane, forming vesicles that bring the materials into the cell

• Requires energy

What are the 3 types of Endocytosis?

1. Receptor Mediated Endocytosis:

   • A specific molecule binds to its receptor and gets brought into the cell

     • receptor = lock ; ligand = key

2. Phagocytosis:

   • Phago = food “Cell eating”

   • The cell surrounds a very large object

3. Pinocytosis:

   • Pino = “Cell drinking”

   • The cell takes in tiny droplets of fluid

Electrochemical Gradient =

Where concentration + electrical charge come together

• Determines how ions move across the membrane

Concentration Gradient =

Depends on how much of an ion is present

Electrical Gradient =

Depends on charge

• The difference in electrical charge across the membrane caused by ions

  • opposite charges attract

  • like charges repel
    
    

Membrane Potential =

The electrical difference across the cell membrane

• Cell membrane = tiny battery

The cell stores potential energy because ions are distributed differently on each side

Resting Membrane Potential =

The cells normal “resting” electrical state

• The inside of an animal is normally negative compared with the outside

  • approximately: -50 to -200mV

• Resting = Normal battery state

Depolarization / Charge Reversal =

Depolarization = The inside of the cell becomes less negative

• Example: -70mV →

Charge reversal = The inside can become positive instead of negative

• Negative → Positive = Charge reversal

Voltage Gated Channel =

Intracellular Signaling Cascade =