Blake_Biochem_18_Transport through membranes I

Question 1

Types of integral membrane proteins (4)

Answer 1

Monotopic

Bitopic type I (N term out)

Bitopic type II (C term out)

Polytopic

Question 2

Types of associated membrane proteins (3)

Answer 2

Protein associated

Acyl anchored

Phospholipid associated

Question 3

Transport proteins are usually what type of membrane proteins?

Answer 3

Polytopic, transmembrane, integral membrane proteins

Question 4

Transport properties of the plasma membrane: (4)

Answer 4

*Semi-permeable

*Permeable to : lipophilic

* Impermeable to : hydrophilic molecules

*require transport mechanisms to move large or polar molecules

Question 5

What determines the ionic composition of the cell?

Answer 5

activity and protein levels of specific transporters

Question 6

How do cells govern the biochemical/metabolic characteristics of their specific needs? Why is this significant?

Answer 6

Expression of specific transporters cells can only execute those reactions whose substrates can be taken up

Question 7

How can cells use transporters to regulate metabolism?

Answer 7

Alteration in expression levels of transport proteins

Question 8

Extra/Intracellular concentration of Na+ Fold-Difference

Answer 8

Extra 145 mM

Intra 12 mM

12

Question 9

Extra/Intracellular concentration of K+ Fold-Difference

Answer 9

Extra 4 mM

Intra 155 mM

0.026 fold difference

Question 10

Extra/Intracellular concentration of Ca2+ Fold-difference

Answer 10

Extra 1 mM

Intra 0.0001 mM

>10,000 fold difference

Question 11

Extra/Intracellular concentration of Cl- Fold-Difference

Answer 11

Extra 120 mM

Intra 4 mM

30 fold difference

Question 12

Energy independent movement of molecules down a gradient is called ___________ occurs in two ways:

Answer 12

Passive Transport

Simple diffusion, Facilitated diffusion

Question 13

What determines the rated of simple diffusion accross a membrane

Answer 13

The concentration gradient; Higher the difference, faster the diffusion.

Question 14

Unequal distribution of molecules is associated with ___________

How doe cells set up an ion gradient across the membrane?

Answer 14

• Free energy
• Energy is utilized by ATP driven membran proteins and then stored as free energy for the gradient.

Question 15

Gibbs free energy for an uncharged molecule:

Answer 15

DeltaG=2.303RTlog₁₀[C_o/C_i]

R = 8.3144598 J/mol*K

T = temp in Kelvin (273+ºC)

Question 16

Gibbs free engergy for a charged molecule

Answer 16

DeltaG=2.303RTlog10[Co/Ci] +ZFDeltaV

Z = Electrical Charge

F= Faraday’s Constant (9.648 70 x 10⁴)

Delta V= membrane potential

Question 17

How are concentration and membrane potential related to Free Energy?

Answer 17

both are directly proportional to free energy

Question 18

Two Types of ATP utilizing proteins:

Answer 18

P-type ATPases

ATP Binding Cassete Transporters

Question 19

4 kinds of P-Type ATPases:

Answer 19

• Na⁺, K⁺-ATPase
• Plasma Membrane Ca²⁺-ATPase (PMCA)
• Sarcoplasmic Reticulum Ca²⁺-ATPase (SERCA)
• H⁺, K⁺-ATPase

Question 20

Why are antioxidants important for brain health?

How are the colorful, anti-oxidants in fruits and vegitables broadly categorized?

Answer 20

• The rapid metabolic rate in the brain (20% of caloric intake), creates considerable amount of oxidative stress.
• Flavanoids*

*Flavonoids are a group of plant metabolites thought to provide health benefits through cell signalling pathways and antioxidant effects. These molecules are found in a variety of fruits and vegetables.Flavonoids are polyphenolic molecules containing 15 carbon atoms and are soluble in water.

Question 21

How were ATP binding cassette transporters discovered?

Answer 21

Studying multi-drug resistance in Tumor cells

Question 22

How does ATP change the conformation of P-type ATPases?

Answer 22

Phosphate is cleaved from ATP and covalently bonds with protein => energy is released => conformation is changed.

Question 23

How many types of P-type ATPases are present in the human genome?

Answer 23

70

Question 24

Which residue(s) does the cleaved phosphate from ATP covalently bond to on a P-type ATPase?

Answer 24

Aspartate (D)

Question 25

Steps in conformation of P-type ATPases:

Answer 25

1. **ATP breaks** into **ADP** and **phosphate** 2. Transporter forms a **covalent bond** with the phosphate to form an **enzyme-phosphate intermediate** 3. Phosphorylation occurs on a conserved **aspartate** residue 4. Transporter undergoes a drastic **convormational change** that facilitates the transport of ions accross the membrane

Question 26

What does it mean that P-type ATPases use a "fundimental mechanism of action?"

Answer 26

there is a single action that is only caused by ATP hydrolysis

Question 27

General facts about Sodium Pump (6) [purpose, ratio, outcomes(3), loccation]

Answer 27

1. Establishes Na+/K+ gradient 2. Stoichiometry: 3 Na+ out/2 K+ in for 1 ATP 3. Makes neurons and muscle cells electircally ecitable 4. controls cell volume 5. drives active transport of sugars and amino acids 6. 20-40% of brain ATP is used by Na+pump

Question 28

Inhibitors of Na+ pump (6)

Answer 28

1. Plant steroids 2. Inhibid DEphosphorylation of E2P 3. Eg: digitoxigenin and oubain 4. called cardiotonic steroids 5. digitalis contains mixture of cardiotonic steriods 6. used in treatment of congestive heart failure

Question 29

Two common Cardiac glycosides

Answer 29

Ouabain Digitoxigenin

Question 30

What is the effect of action for cardiac glycosides? (6)

Answer 30

1. Inhibit Na+/K+ ATPase activity 2. Increase levels of Na+ in cell 3. Reduce activity of Na+/Ca2+ antiporter 4. increase in Ca2+ in cell 5. Elevated Ca2+ increases the contractile force of cardiac muscle 6. Used in treatment of congestive heart failure

Question 31

Two kinds of Calcium Pumps

Answer 31

Plasma membrane (PMCA) Sarco-endoplasmic reticulum (SERCA)

Question 32

PMCA (3)

Answer 32

**Plasma Membrane Calcium ATPase** * **10 transmembrane domains** * size: 140 kDa * Stimulated by calcium binding protein **calmodulin (CaM)**

Question 33

Sites/Domains of PMCA (3)

Answer 33

* Phosphorylation domain * CaM Binding Domain * ATP Binding Site

Question 34

How does the CaM binding domain regulate PMCA?

Answer 34

* PMCA is autoinhibited by its own CaM binding domain * CaM binding domain blocks Phoshphorylation and ATP-binding sites until active CaM binds, at which point the CaM binding domain dissociates from the active site and "swings away". (like a "ball and " chain" plug but over active site).

Question 35

CaM and PMCA

Answer 35

Calmodulin stimulates PMCA into active state

Question 36

SERCA (4)

Answer 36

Sarco-endoplasmic Reticulum Caclium ATPase * 110kDa * Transoirts Calcium from cytosol to SR * 80% of SR membrane proteins * Relaxes contracted muscle

Question 37

* Where does phosphate bind to SERCA? * How does the conformation of SERCA change when phosphate binds to it? * How are the Calcium-Binding sites of SERCA affected by bound phosphate?

Answer 37

* Asp 351 * N and P domains close around the phosphoaspartate analog * Calcium-binding domains are disrupted

Question 38

ABC Transporters stands for \_\_\_\_\_

Answer 38

ATP Binding Cassette Transporters

Question 39

How many ABC transporter genes are on the human Genome?

Answer 39

150

Question 40

How were ABC transporters discovered? How do they generally work? how else are they identified? (2)

Answer 40

by studying drug resistance in tumor cells "put drug in and it pushes it back out" Multi-drug resistance protein/ P glycoprotein

Question 41

What are the 4 parts of MDR from N to C?

Answer 41

N-Membrane spaning domain-ATPbinding Cassette-Membrane spanning domain - ATPbinding Cassette-C

Question 42

Mechanism of Action of ABC Transporters

Answer 42

1. No substrate or ATP bound: channel faces in 2. Binding of substrate causes **conformational change in ATP binding cassettes** 3. Affinity for ATP increases SO **ATP Binds** 4. Binding of ATP causes conformation of ATP binding Cassettes to changse THEREFORE **membrane spaning domains are reoriented** 5. **Substrate is expelled** on extracellular side 6. **ATP Hydrolysis** resets transporter to Step 1

Question 43

Secondary Transporters

Answer 43

* Not **directly** driven by ATP * Thermodynamically **unfavorable flow of one species** against a gradient coupled to the **favorable flow of another species** down a gradient.

Question 44

Three types of Secondary Transporters

Answer 44

* Antiporters - oposite direction (eg: NCX) * Symporters - same direction (eg: lactose permease) * Uniporter - depends on concentration (eg: Mitochondrial Calcium Transporter)

Question 45

Lactose Permease

Answer 45

* a symporter * Uses the proton gradient generated by oxidation of fuel molecules to drive lactose and other sugars against the concentration gradient

Question 46

Mechanism of Action for Lactose Permease

Answer 46

H+ out; Lactose out H+ in; Lactose in