Bellwork Monday 11/7*Reminder: if you missed the test last Friday, take it during tutorial

1. What is one important thing you learned from the last unit on digestion, cellular respiration, and photosynthesis, and why is it important or useful2. What are all living things made of?

Agenda:

1. Notes

2. Whiteboard

3. Notes

HydrophillicWater loving, attracted to waterPolar (+ and – charges attract)Ex: sugar, salt

Hydrophobic-Water fearing, doesn’t mix with water-Nonpolar (no charges to attract water)Ex: oil, fat

X

CELL MEMBRANE NOTES

• Forms a barrier around all cells• Are made mostly from fats

– They don’t dissolve in water– Are special fats called Phospholipids

Cell Membrane

Polar Head

Non-Polar Tails

Phospholipids

Hydrophillic

(Attracted to water)

-Hydrophobic

(Water fearing)

- a macromolecule similar to fats

Reminder:• only draw answers to the questions• Clean off your board when you are

finished• Throw paper towels away• Return the markers

Whiteboards: how scientists made sense of the cell membrane

1925: in the Netherlands • Cell membrane made of phospholipids • Water inside and outside the cell• Twice as many phospholipids as it takes to

cover the entire cell• What is the structure of the cell membrane?

Whiteboards: how scientists made sense of the cell membrane

Outside cell

Inside cell

Cell Membrane

1. Cell membrane made of phospholipids 2. Water inside and outside the cell3. Twice as many phospholipids as it takes to

cover the entire cell4. What is the structure of the cell membrane?

Water

Phospholipids

1935: James Danielli and Hugh Davson in London

• Hydrophillic molecules like water can get across

• There are proteins in the cell membrane• There’s about as much protein as there

are phospholipids

1972: Jonathan Singer and Garth Nicholson in California

• The bilayer is up to 7-8nm (nanometers) thick

• The phospholipids are 5nm long• Proteins are 7-8nm long• If two different cell membrane combine,

the proteins can spread between them• How are the proteins moving through the

membrane?

Neuron cells in your brain

Cell Membrane is not rigid!

- Phospholipids in the cell membrane Form a Lipid Bilayer

- 2 layers back-to-back

• Lipid Bilayer is flexible (or fluid)• Cholesterol embedded in membrane

– Cholesterol adjusts fluidity– More cholesterol makes membrane stiffer– Less cholesterol makes membrane more liquidy

3 Most important things

1. Cell membrane is made of phospholipids2. Phospholipids arranged with hydrophobic

part on the inside3. Proteins cross the membrane