Cell Transport

Intro Video

What is the purpose for the cell membrane in all cells?

Is Selectively Permeable - Allows for the passage of some substances based on size

and the concentration of materials on either side of the membrane

- Made up of a double layer of phospholipids with proteins floating through it

What are the two main parts of the cell membrane?

• Phospholipids

• Proteins

• A phospholipid has a head and a tail region. The tails are made up of the fatty acid chain of a lipid

• Outer part of the membrane is made up of polar (charged), hydrophilic (water loving) heads.

• Inner part of membrane is made up of nonpolar (not charged), hydrophobic (water fearing) fatty acid tails

Phospholipid

Head

Tail

Head

TailsHead

• Due to the hydrophobic nature of the inside of the membrane:– Cells do not go into solution

with the environment. – Water can’t get past the

hydrophobic tails. Allows for the structure of the cell

• Materials like water, glucose, some amino acids, and ions (Na+, Cl-, K+), can’t pass through the membrane without going through the protein channels located throughout the membrane

• In the "fluid mosaic model" of membrane structure says that the molecules within the membrane move around.– Phospholipids regularly move sideways & flip– Proteins can not flip around but instead float like floats on waterRap

1. Hydrophobic means– Water fearing– Water molecules will be repelled

2. Hydrophilic means– Water loving– Water molecules will be attracted to it

3. Polar means– Has a positive end and a negative end to the

molecule

How does the cell membrane create a barrier that is also selectively permeable?

1. Inside of the membrane is made up of?– Hydrophobic fatty acid tails– Nonpolar– Repel polar molecules and ions

2. Outside of the membrane is made up of?– Hydrophilic heads– Attract polar molecules like water and ions

The Cell Membrane is Selectively Permeable• The membrane allows some materials to pass

and not others.• Maintains homeostasis with the cell• It can control what is coming in a going out of

the cell• It regulates permeably by:– The size of their pores– The size of the molecule (monomers can pass

through while polymers can’t)– The concentration of molecules on either side of the

membrane– Polarity of the molecules

What are the four factors that determine what can get through the cell membrane?

1. The size of their pores2. The size of the molecule (monomers

can pass through while polymers can’t)

3. The concentration of molecules on either side of the membrane

4. Polarity of the molecules

Label the parts of the Cell Membrane:Head, Fatty Acid tails and Proteins

Indicate which part of the cell membrane is hydrophilic and which part is hydrophobic, and

then nonpolar and polar

Passive Transport• The movement of molecules without requiring

an energy input to make it happen.– Like going down a hill. You don’t need energy

• Based strictly on the concentration gradient– The difference between the concentration of

molecules from one location to another– Air freshener

Diffusion• The movement of molecules from a region of

higher concentration to a region of lower concentration without the need for added energy.

• Depends on the kinetic energy of molecules• Goes down (or with) the concentration gradient

Potassium Permanganate is placed in the middle of a dish of water. What will happen?

• Crystals dropped in the middle of the water will start to diffuse to areas of lower concentration without the need of additional energy.

• Eventually, the molecules will be evenly distributed– Reach Equilibrium – the same

distance between molecules throughout

Why is diffusion considered a form of Passive Transport?

It is passive transport because molecules move from where they are highly concentrated (more solutes) to where they are in lower concentration (low solutes) (with the concentration gradient) without the need for energy.

Do you need energy to ski down a hill?

How does water get into plant cells?How does water get into or out of our skin?

Osmosis is the movement of water through a membrane from an area of high water concentration to an area of less water concentration– or from where there are less

solutes in solution to an area of where there are more solutes in solution

What happens when you eat salty foods and sugary drinks?

You will be really thirsty!!!!• This is because your food had a high solute

concentration of salt and sugar (hypertonic).• Your cells will be a lower solute concentration and

basically made up of water (hypotonic).• Water will move from where there are more water

molecules and less solutes (hypotonic) to where there are more solutes and less water (hypertonic)

• The cells will start to lose water and you will be thirsty! Glen’s Osmosis song

• The first diagram has very few solute molecules outside the cell and a lot inside the cell– Hypotonic solution – Water will flow into the cell and cell will enlarge

• The diagram on the right has a lot of solutes outside the cell and very few inside the cell– Hypertonic solution– Water will flow out of the cell and cell will shrivel

• The middle diagram has the same number of solutes on either side of the cell membrane– Isotonic solution– Water molecules will continue to flow into and out of the cell– The net movement of molecules is zero.

Osmosis lab with Osmosis Grape and onion cells

Predict what will happen in the U-Tube

Video

Sometimes, molecules need help getting through the membrane due to those hydrophobic, nonpolar tails

Facilitated Diffusion • Molecules that are polar cannot pass through the

nonpolar tails of the cell membrane. They need help to get through

• Glucose, Water, ions like Na+ and Cl-

• Will pass through protein channels which shield the polar molecules from the nonpolar tails. Like going through a tunnel

Why is facilitated diffusion necessary?• Since the inside of the cell membrane is made up

of fatty acid tails which are nonpolar and hydrophobic, molecules like water, glucose and ions such as Na+ and Cl- can’t pass through it.

• The protein channels protect them from the nonpolar tails.

Label the Carrier Proteins and the Channel Proteins. Draw an arrow to indicate the direction of flow of the solutes

Facilitated DiffusionDiffusion

Active Transport• Some molecules need to be

concentrated inside the cell or removed from the cell (such as wastes or products of the cell like glucose, lipids and proteins)

• These molecules will move from where they are in low concentration to where they are in higher concentration

• Energy will be needed to go against or up the concentration gradient– Like going up a hill. Energy will be

needed

Energy is needed

No energy is needed

Active Transport

Passive Transport

ATP is an energy transport molecule. • It transfers a phosphate group to another

molecule and transfers energy with it.• Powers all cellular activity

Sodium-Potassium PumpMoves Na+ out of the cell and K+ into the cell from low to high

concentration

Why is the Sodium – Potassium pump considered to be a form of Active Transport

Na+ is in higher concentration outside the cell than inside of it.

K+ is in higher concentration inside the cell than outside of it.

Both are moved through protein channels from where they are in low concentration to where they are in high concentration.

To go up the concentration gradient, ENERGY (ATP) is needed.

To walk back up the ski hill takes ENERGY!!

How many Sodium ions leave the cell?How many Potassium ions enter the cell?

What is needed to change the shape of the protein carrier and move the molecules against the concentration gradient?

Endocytosis and Exocytosis

• Energy will be needed (by ATP)to move large molecules like starch or proteins or small organisms like bacteria or paramecium into or out of a cell

EndocytosisEndocytosis– Is the process of taking in liquids or fairly large molecules into

a cell by engulfing them in a membrane– Cell membrane forms a pocket around the substance which

will become a vesicle inside the cell– Lysosomes fuse with the vesicles and puts digestive enzymes

into the vesicle

Phagocytosis (“cell eating”)

• Engulfing of bacteria, viruses or large molecules– How white blood cells and amoeba get their food.

Amoeba phagocytizing a Paramecium

A White Blood Cell (Macrophage) Phagocytizing bacteria

Exocytosis

• Opposite of Endocytosis• Release of substance through the cell membrane

What is the difference between Endocytosis and Exocytosis?

Endocytosis means coming into the cell process.This is the engulfing of molecules/organisms into a cell into vesicles

Exocytosis means leaving the cell processThe vesicles with macromolecules or wastes are sent out of the cell

Label the diagrams either exocytosis or endocytosis.