Regents Biology Cell Membranes & Movement Across Them

Regents Biology Cell (plasma) membrane  Cells need an inside & an outside…  separate cell from its environment  cell membrane is the boundary IN food sugars proteins fats salts O 2 H 2 O OUT waste ammonia salts CO 2 H 2 O products cell needs materials in & products or waste out

Regents Biology Building a membrane  How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn’t mix with water?  FATS   LIPIDS  oil & water don’t mix!!

Regents Biology Lipids of cell membrane  Membrane is made of phospholipids  phospholipid bilayer “attracted to water” “repelled by water” inside cell outside cell phosphate lipid

Regents Biology Semi-permeable membrane  Need to allow passage through the membrane  But need to control what gets in or out  membrane needs to be semi-permeable So how do you build a semi-permeable membrane? aa H2OH2O sugarlipidsalt NH 3 So what needs to get across the membrane?

Regents Biology Phospholipid bilayer  What molecules can get through directly? inside cell outside cell fats & other lipids can slip directly through the phospholipid cell membrane, but… what about other stuff? lipid salt aa H2OH2O sugar waste

Regents Biology Permeable cell membrane  Need to allow more material through  membrane needs to be permeable to…  all materials a cell needs to bring in  all waste a cell needs excrete out  all products a cell needs to export out inside cell outside cell lipidsugaraa H2OH2O salt “holes”, or channels, in cell membrane allow material in & out waste

Regents Biology outside cell Semi-permeable cell membrane  But the cell still needs control  membrane needs to be semi-permeable  specific channels allow specific material in & out inside cell sugaraa H2OH2O salt waste

Regents Biology How do you build a semi-permeable cell membrane?  channels are made of proteins  proteins both “like” water & “like” lipids bi-lipid membrane protein channels in bi-lipid membrane

Regents Biology Protein channels  Proteins act as doors in the membrane  channels to move specific molecules through cell membrane

Regents Biology Movement through the channel  Why do molecules move through membrane if you give them a channel? ? ?

Regents Biology Molecules move from high to low  Diffusion  move from HIGH to LOW concentration

Regents Biology Diffusion  Move from HIGH to LOW concentration  “passive transport”  no energy needed

Regents Biology Simple Diffusion  Move from HIGH to LOW inside cell outside cell Which way will fat move? low high  fat

Regents Biology Diffusion through a channel  Move from HIGH to LOW inside cell outside cell sugar Which way will sugar move? low high  sugar

Regents Biology Diffusion  Move from HIGH to LOW concentration  through membrane  simple diffusion  no energy needed  through a protein channel  facilitated diffusion (with help)  no energy needed high low

Regents Biology Active transport  Cells may need molecules to move against concentration difference  need to pump “uphill”  from LOW to HIGH using ATP  protein pump  requires energy  ATP ATP

Regents Biology Transport summary diffusion facilitated diffusion active transport ATP

Regents Biology Osmosis Movement of Water Across Cell Membrane

Regents Biology Osmosis  Water is very important, so we talk about water separately  Osmosis  diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane

Regents Biology Keeping water balance  Cell survival depends on balancing water uptake & water loss freshwaterbalancedsaltwater

Regents Biology  on-Cells-Plasmolysis on-Cells-Plasmolysis

Regents Biology Managing water balance  Balanced conditions  no difference between cell & environment  example: blood  problem: none  water flows across membrane equally, in both directions  volume of cell doesn’t change balanced

Regents Biology Managing water balance  Freshwater  a cell in fresh water  example: Paramecium  problem: gains water, swells & can burst  water continually enters Paramecium cell  solution: contractile vacuole  pumps water out of cell freshwater

Regents Biology Controlling water  Contractile vacuole in Paramecium

Regents Biology Managing water balance  Saltwater  a cell in salt water  example: shellfish  problem: lose water  plasmolysis in plants  shrinking cell  solution: take up water saltwater

Regents Biology

Active Transport

Regents Biology Exocytosis

Regents Biology Endocytosis

Regents Biology Hypercholesterolemia  Faulty LDL receptors in liver cells  Liver does not remove  Cholesterol builds up in blood vessels

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