1. Lecture 6: Membrane transport
Bio 93: DNA to Organisms
Lecture 6: Membrane transport
How can membrane transporters be used to treat diabetes?

2. Learning Objectives
6.1 – Compare and contrast diffusion, facilitated diffusion, osmosis, active transport, endocytosis, and exocytosis 6.2 – Predict how a molecule will cross a plasma membrane given a molecule’s properties 6.3 – Explain how tonicity affects cell function

3. Key terms Diffusion Active transport Concentration gradient
Sodium-potassium pump
Passive transport
Membrane potential
Osmosis
Electrochemical gradient
Tonicity
Electrogenic pump
Hypotonic
Protein pump
Isotonic
Cotransport
Hypertonic
Exocytosis
Facilitated diffusion
Endocytosis
Channel proteins
Phagocytosis
Ion channels
Pinocytosis
Gated channels
Receptor-mediated endocytosis
Carrier proteins

4. Lecture 6: Membrane transport
Diffusion, osmosis
Why do many molecules need transport across a membrane?
Passive transport
diffusion of a substance across a membrane with no energy investment (down gradient)
simple diffusion: movement directly through lipid membrane
facilitated diffusion: movement through membrane is aided by proteins (channels or carriers)
Active transport
Movement substance against its gradient (requires energy)
Forms of energy:
Pumps use ATP
Coupled transport powered by ion gradients
Bio 93 (Summer 2017), Copyright © 2017, Dr. Salme Taagepera. All rights reserved.

5. 2
Below is a photo of a beaker full of iodine in water. There is also a dialysis tubing bag which contains starch. The bag is permeable to iodine, but not starch. When starch and iodine mix, the solution turns blue. What will happen when this experiment reaches equilibrium?
A – the solution in the beaker turns blue B – the solution in the bag turns blue C – the solution in the bag and the beaker turns blue D – no color change occurs
6.1
6.2

6. 2
A student places gummy bears in three different containers as described below. What do you think will happen over time?
A – the yellow gummy bear will grow to be the largest B – the green gummy bear will grow to be the largest C – the red gummy bear will grow to be the largest D – all three bears will grow equally large E – no changes will occur
Water only
Water + NaCl
Water
+ glucose
6.1
6.3
1:29/4:17

7. 2 Osmosis has occurred! Which statement(s) is(are) TRUE?
A – The green gummy bear’s solution was more hypotonic than the red or yellow bear’s solutions B – More water flowed into the gummy bears than flowed out C – The red gummy bear’s solution was hypotonic to the bear D – None of the solutions were isotonic
6.1
6.3

8. 2
Put these molecules in order of how they cross the plasma membrane, from least to most difficult
Sodium ion C
Na+ A D
Sucrose
O=C=O B
Glycerol
Carbon dioxide
6.2

9. Due to its structure, a pure lipid bilayer is essentially impermeable to most water-soluble molecules and ions
THEREFORE, need membrane proteins to transport most molecules and all ions across biomembranes…

10. What kind of transport is used?1
6.1
6.2
Cholesterol (bound to LDLs)
Extracellular
Extracellular
Extracellular
ATP
Intracellular
Intracellular
Intracellular
Sodium ion (Na+)
Glucose

11. Membrane transporters are potential drug targets for diabetes
Diabetes is a disease characterized by high blood glucose levels (hyperglycemia)
Glucose is filtered by the kidneys and excreted in urine
Glucose is also reabsorbed by kidneys and put back into blood

12. 2 3 Kidney cell Blood Urine What could you do to treat diabetes?
What type of transport is being used in each case?
Where is ATP required?
Glucose transporter
Sodium glucose transporter
Kidney cell
Blood
Urine
Sodium potassium pump
ATP
6.1 2 3
6.2
What could you do to treat diabetes?

13. Summary: Membrane transport
channels
carriers
Pumps
GLUT2
SGLT
Na+ K+
pump
Passive transport
Driving force = Concentration gradient
Active transport
Primary active transport
Driving force = ATP
Secondary active transport (co-transport)
Driving force = Coupled transport powered by ion gradients
Bio 93 (Summer 2017), Copyright © 2017, Dr. Salme Taagepera. All rights reserved.