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Lecture 1 Outline (Ch. 7). Plasma Membrane A. bilayer B. fluidity C. proteins II. Transport across membranes Simple diffusion Osmosis & Facilitated diffusion Active transport Bulk transport III. Preparation for next lecture. Membrane structure. Membrane structure.

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Lecture 1 Outline (Ch. 7)
  • Plasma Membrane
  • A. bilayer
  • B. fluidity
  • C. proteins
  • II. Transport across membranes
    • Simple diffusion
    • Osmosis & Facilitated diffusion
    • Active transport
    • Bulk transport
  • III. Preparation for next lecture
Membrane structure

Experiment to determine membrane fluidity:

• marked membrane proteins mixed in hybrid cell

Membrane structure

• cell can alter fatty acid tail saturation  affects fluidity

• cholesterol keeps membrane fluid at different temperatures

Membrane structure

1915, knew membrane made of lipids and proteins

Where to place proteins?

Lipid layer 1


Lipid layer 2

Membrane structure

• freeze fracture

• proteins intact, one layer or other

• two layers look different

Membrane structure

• cell membrane – amphipathic

- hydrophilic & hydrophobic




• membrane proteins that are inserted, also amphipathic

Membrane structure

“fluid mosaic model” – 1970s

• fluid – phospholipids move around





• mosaic – proteins embedded in membrane

Based on what we just discussed, of the following choices, which is true of cell membranes?
  • Membranes are hydrophobic inside the cell
  • Phospholipid tails are hydrophilic
  • Membrane proteins are amphipathic
  • Fluidity is static (not able to change)
  • Proteins are sandwiched between the two lipid layers
Membrane Proteins

Remember secondary and tertiary protein structure?!

Membrane Proteins

Hydrophobicity plot: determine hydrophobic/hydrophilic for each region of a protein

Membrane Proteins

What would a hydrophobicity plot look like for this protein?

Transport Across Membranes
  • Types of transport:
  • Passive transport
  • 1. simple diffusion
  • 2. osmosis & other facilitated diffusion
  • B. Active transport
  • C. Bulk transport

Keep track:

• Is Energy Required?

• Direction of Movement?

Selectively Permeable Membranes

• Small, non-polar molecules can move by simple diffusion

Selectively Permeable Membranes

• Large or charged molecules need help crossing membrane

Facilitated Diffusion

- Large, charged, polar (sugar, ions, water)

• NO ENERGY required

• DOWN concentration gradient

• Use transport proteins - channel or carrier proteins

Passive Transport - Osmosis

• osmosis – movement of water across cell membrane

• osmosis is a type of diffusion

• water moves via special channels called aquaporins

• water moves into/out of cell until soluteconcentration is balanced

animal cell

plant cell

Passive Transport - Osmosis

• tonicity – # solutes in solution in relation to cell

- hypotonic – fewer solutes in solution

- isotonic – equal solutes in solution

- hypertonic – more solutes in solution

Passive Transport - Osmosis

In each situation below, does water have net movement, and which direction:

fewer solutes in solution, than in cell

Isotonic? Hypertonic? Hypotonic?

equal solutes in solution as in cell

more solutes in solution, than in cell

Passive Transport - Osmosis

Paramecium example

• regulate water balance

• pond water hypotonic

• water into contractile vacuole

– water expelled

Passive Transport - Osmosis

Scenario: in movie theater, long movie.

You are: drinking water

What happens to your blood?

• becomes hypotonic to cells

• kidneys – remove water

• body excretes water

You are: eating popcorn

What happens to your blood?

• becomes hypertonic to cells

• kidneys – uptake water

• body retains water

Facilitated diffusion…..

A. Requires energy and is up the conc. gradient

B. Requires energy and is down the conc. gradient

C. Does not require energy and is up the conc. gradient

D. Does not require energy and is down the conc. gradient

Active Transport

• ENERGY IS required

- Usually ions or large molecules (Na+, K+, glucose)

• UP/AGAINST concentration gradient

• uses transport carrier proteins/pumps

Active Transport

- Usually ions or large molecules (H+, Na+, K+, glucose)

• ENERGY IS required

• UP/AGAINST concentration gradient

• Ex. proton (H+) pump

• Pump H+ across inner membrane!

• ATP used, pump H+ ions

• uses transport carrier proteins/pumps

*gradients – used by cell for energy potential

Bulk Transport

• Molecules moved IN  endocytosis

• phagocytosis – “food” in

• pinocytosis – water in

• Molecules moved OUT

- exocytosis

Things To Do After Lecture 1…
  • Reading and Preparation:
  • Make sure you are ready for lab 1 this week
  • Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms.
  • Read chapter 7, focus on material covered in lecture (terms, concepts, and figures!)
  • Ch. 7 Test Your Understanding: #1-4, 6 (correct answers in back of book)
  • Skim next lecture (ch. 8)
  • “HOMEWORK” (NOT COLLECTED – but things to think about for studying):
  • Draw and label a phospholipid bilayer including integral and peripheral proteins.
  • Name three molecules that easily cross membranes; name three molecules that are blocked by cell membranes.
  • Describe diffusion and osmosis – then, how is active transport different?