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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

Proteins

Lipid layer 2


Membrane structure

• freeze fracture

• proteins intact, one layer or other

• two layers look different


Membrane structure

• cell membrane – amphipathic

- hydrophilic & hydrophobic

hydrophilic

hydrophobic

hydrophilic

• membrane proteins that are inserted, also amphipathic


Membrane structure

“fluid mosaic model” – 1970s

• fluid – phospholipids move around

Glycoproteins

Integral

Glycolipids

Peripheral

• 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 which is true of cell membranes?


Membrane Proteins which is true of cell membranes?

Remember secondary and tertiary protein structure?!


Membrane Proteins which is true of cell membranes?

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


Membrane Proteins which is true of cell membranes?

What would a hydrophobicity plot look like for this protein?


Transport Across Membranes which is true of cell 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 which is true of cell membranes?

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


Selectively Permeable Membranes which is true of cell membranes?

• Large or charged molecules need help crossing membrane


Facilitated Diffusion which is true of cell membranes?

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

• NO ENERGY required

• DOWN concentration gradient

• Use transport proteins - channel or carrier proteins


Passive Transport - Osmosis which is true of cell membranes?

• 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 which is true of cell membranes?

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 which is true of cell membranes?

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 which is true of cell membranes?

Paramecium example

• regulate water balance

• pond water hypotonic

• water into contractile vacuole

– water expelled


Passive Transport - Osmosis which is true of cell membranes?

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….. which is true of cell membranes?

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 which is true of cell membranes?

• ENERGY IS required

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

• UP/AGAINST concentration gradient

• uses transport carrier proteins/pumps


Active Transport which is true of cell membranes?

- 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 – all types require energy! which is true of cell membranes?

Exocytosis


Bulk Transport which is true of cell membranes?

• Molecules moved IN  endocytosis

• phagocytosis – “food” in

• pinocytosis – water in

• Molecules moved OUT

- exocytosis


Self check
Self-Check which is true of cell membranes?


Things To Do After Lecture 1… which is true of cell membranes?

  • 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?


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