Introduction to Cell Transport and the Cell Membrane

Why do we need to move things in and out of cells (think of specific examples)?

1) We need to get necessary materials into cells• Cells need to get oxygen and glucose for cell

respiration• Cells need nutrients (proteins, lipids,

cholesterol) to help build/repair cell structures

Why do we need to move things in and out of cells (think of specific examples)?2) We need to get wastes out of cells.• Cells produce waste products like Carbon

dioxide and extra water that need to be removed from cells

What materials go “IN” to cells?

• Water• Glucose• Salt• Ions• Lipids

• Amino acids

What materials go “OUT” of cells?

• Carbon dioxide• Waste materials

• Ions• Water

Transport can be as simple as moving materials between a one celled organism and

its environment…O2 in

CO2 Out

• Does a one-celled organism have organ systems which aid in transport ?

NO

…or as complex as the transport systems in higher organisms such as humans.

Blood vessel

O2

CO2

wastes

Which organ systems aid higher animals in transporting materials throughout the

body?

• Circulatory• Respiratory • Digestive • Nervous

What is the boundary that controls what goes in and out of cells?

• Cell membrane

Let’s Review what we already know about cell membranes?

• They surround the entire cell• They are made of phospholipids• Phospholipids have a head and two fatty acid

tails

Polarity AGAIN?

• The head of a phospholipid is polar.• The tails of a phospholipid are non-polar.• Water is polar.• Which end do you think likes to mix it up with

water?

• That’s right, the polar head.

Hydrophylic or Hydrophobic

• Hydro = water• Phylic = loving • Phobic = hating

• Which part of the phospholipid is hydrophylic? Which part is hydrophobic?

• Head = hydrophylic, Tail = Hydrophobic

So why do cell membranes have two layers of phospholipids?

• HINT: Look at the arrangements of the phospholipids in the diagram below.

• HINT 2:Look at where the water is. Think. Is water polar or non polar? What would like to be next to the polar water….hydrophylic or hydrophobic?

All cells live at least PARTLY in touch with WATER (in AND out)

• When these lipids are mixed with water, their hydrophobic fatty acid tails cluster together while their hydrophilic heads are attracted to water.

• A lipid bilayer is the result

Fluid Mosaic Model

Fluid Mosaic Model

• ProteinProtein molecules are embedded and “float” among the lipids in the bilayer of most cell membranes.

• Many different kinds of molecules make up the cell membrane (carbohydrates, cell communication molecules)

• This is described the membrane as a fluid fluid mosaic. mosaic.

What are these different molecules doing?

PROTEINSPROTEINS

• Form channels/pumps to to help move material help move material across the cell across the cell membrane. membrane.

• Attach directly to the cytoskeleton, enabling cells to respond to their environment by using their membranes to help move/change shape

CARBOHYDRATESCARBOHYDRATES

• Many act like chemical identification cards, allowing individual cells to identify one another.

How can we describe what can get through the cell membrane?

Cell membranes are semi-permeable or Selectively Permeable

Membranes can be permeable to some things and impermeable to others.

Permeable…

• Permeable means that a substance is allowed to pass through

• If a cell membrane is permeable to a substance, diffusion proceeds normally.

X

X

X

X

O

O

O

O

Impermeable…

• Impermeable means a substance will not be allowed to pass through

• If the membrane is impermeable to a substance, diffusion will not occur

X

X

O

Semipermeable…

• Most cell membranes are selectively permeable. Only certain substances are allowed into or out of a cell

X

XX

X

O

What does this all add up to?

• Moving the right things in or out of a cell – in the right amounts – at the right time– For the right metabolic processes

• Helps cells maintain homeostasis

What are the methods for moving things in and out of cells?

• 1) Passive transport– Movement of things across the membrane from high

concentration to low concentration without the use of ATP

• Special Case 1: movement of water is called Osmosis

• Special Case 2: some necessary nutrient move with the gradients but are too big to slip through the phospholipids or have charges – so they use a a transport protein – called Facilitated Transport

What are the methods for moving things in and out of cells?

• 2) Active Transport – moving things AGAINST the gradient– Requires ATP– Requires Transport Proteins

What are the methods for moving things in and out of cells?

• 3) Endo/ Exocytosis – cell membrane folds around something to move it into or out of the cell.– Requires ATP– Is a form of Active Transport