- Movement of water across a selectively permeable membrane - Water travels from an area of low solute concentration to an area of high solute concentration. Rate of osmosis is increased when water channel aquaporins are inserted into the membrane.

Secondary active transport of one substance up its concentration gradient, coupled to the movement of another substance down its concentration gradient - Direction of movement is the same for both molecules - Energy loss from downhill movement is captured to move alternate substance against its concentration gradient

Plasma membrane invaginates to form a vesicle that brings substances into the cell - Phagocytosis= cell eating - Pinocytosis= cell drinking - Fluid-phase endocytosis= uptake of materials dissolved in the ECF

Exam #1: Membrane Transport Flashcards by Jonathan Kallevang

Define osmosis.

Movement of water across a selectively permeable membrane
Water travels from an area of low solute concentration to an area of high solute concentration.

*Rate of osmosis is increased when water channel aquaporins are inserted into the membrane.

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Define simple diffusion.

Net movement of a substance from an area of high concentration of that substance, to an area of low concentration of that substance.

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Define facilitated diffusion. List the characteristics of facilitated diffusion.

Movement of a single molecule down a concentration gradient, utilizing a carrier or transporter.

Much faster than simple diffusion
Shows saturation kinetics/ vmax & has Km
Transport direction is reversible (if concentration grad. changes)
Transport is specific

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What factors control simple diffusion through a membrane? Write Fick’s Law of Diffusion & Membrane Permeability.

Increased membrane SA 
Increased concentration gradient 
Increased membrane permeability 
Increased lipid solubility 
Decreased molecular size 
Decreased membrane thickness

Temperature (increased= more diffusion)

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What factors control diffusion through pores or channels in the membrane?

Permeability= # of channels & % of channels open
Selectivity
Concentration gradient

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What factors control the rate of facilitated diffusion through uniporters?

Concentration gradient
Carrier number= Vmax
Km i.e. affinity

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What are the differences between carrier-mediated diffusion & active transport?

1) Active transport requires energy input

2) Active transport will transport uncharged & charged substances AGAINST their concentration gradients

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Define uniport.

Facilitated diffusion of a substance down its concentration gradient

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Define symport.

Secondary active transport of one substance up its concentration gradient, coupled to the movement of another substance down its concentration gradient

Direction of movement is the same for both molecules
Energy loss from downhill movement is captured to move alternate substance against its concentration gradient

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Examples of uniporters & symporters

Uniport= GLUT1
Symport= Na+/ Glucose Symporter (2 Na+ per glucose)

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What is an ABC protein?

ABC= ATP Binding Cassette

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What is the clinical importance of ABC proteins?

CFTR (cystic fibrosis)
MDR-proteins (multi-drug resistance proteins), which are often overexpressed in tumors & cause resistance to cancer drug therapy

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Define endocytosis.

Plasma membrane invaginates to form a vesicle that brings substances into the cell

Phagocytosis= cell eating
Pinocytosis= cell drinking
Fluid-phase endocytosis= uptake of materials dissolved in the ECF

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Define exocytosis.

Material inside the cell is packaged into vesicles & excreted into the extracellular medium

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What is fluid-phase endocytosis?

Uptake of materials dissolved in the ECF

- Note that this is a very INEFFICIENT process

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What is receptor-mediated endocytosis?

Uptake of material from ECF via receptors concentrated in the plasma membrane
- Much more efficient for the movement of specific substances

What is caveolae endocytosis?

Similar to clathrin mediated endocytosis, but uses caveolae & caveolin as coat protein.

What is clathrin? What shape does clathrin form?

A coat protein on the inner surface of the plasma membrane that mediates endocytosis
Triskelion shape that forms 3x interlocked spirals/ net

How does clathrin function in clathrin coated pits?

1) Receptor binding
2) Receptor/ adaptin interaction
3) Adaptin/ clathrin interaction
4) Clathrin coated pit formation

Compare & contrast passive, active, and vesicular transport.

Passive= no energy required

Diffusion through membrane
Diffusion through channels
Facilitated diffusion

Active= energy required but NO vesicles

Primary active
Secondary active

Vesicular= lipid fusion involved & energy required

Endocytosis
Exocytosis

What molecules can pass through a lipid membrane?

Gasses

- Small, uncharged, & polar molecules

What is Fick’s Law of Diffusion?

Rate of diffusion is proportional to surface area x concentration gradient x membrane permeability/ membrane thickness

What is Membrane Permeability?

Membrane permeability is proportional to lipid solubility/ molecular size

What are aquaporins?

Proteins that form water channels through the cell membrane.

What can a mutation of an aquaporin cause?

Nephrogenic Diabetes Insipidus (AQPS-2) - Patients produce large amount of dilute urine & complain of polydipsia - Unable to properly reabsorb water in renal collecting ducts

What is Km? How is Km related to affinity?

- Half the concentration of substrate at which transport is half maximal. - Lower Km= Higher affinity

Describe the function of the GLUT1 transporter.

- Found in plasma membrane & brings glucose into cell - Concentration gradient maintained by phosphorylating glucose upon entry - Insulin increases # of GLUT1 in skeletal muscle cells & adipocytes - Smaller Km= Higher affinity= Higher rate of transport

What is the relationship between Type-1 DM & GLUT1 transporters?

- DM-1= immune mediated destruction of beta cells in pancreas, resulting in vastly decreased insulin secretion - Insulin inserts GLUT1 into cell membranes to absorb glucose from blood - Thus, DM-1 results in hyperglycemia

Describe the function of the Na+/K+ Pump.

3x Na+ OUT & 2x K+ IN

How do mutations of the CFTR ABC transporter result in cystic fibrosis?

- CFTR is found in the epithelial cells of many organs including the lung. - Normally, the channel protein moves chloride out to the covering mucus, increasing the total electrolyte concentration in the mucus, resulting in the movement of water out of cell by osmosis. - CFTR mutations prevents Cl- ions movement out of the cell resulting in a buildup of thick mucus in the lungs

What is the clinical importance of receptor mediated endocytosis?

Familial hypercholestermia - Individuals lacking LDL receptors/ defective LDL receptors - High LDL in blood - Predisposition to atherosclerosis & heart disease