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Flashcards in Membranes & Transport Deck (68):
1

Membranes are composed of lipids, proteins, and carbs and are arranged in an ______ belayer

Asymmetric

2

Amphipathic

Hydrophilic head group facing the aqueous environment outside

Hydrophobic tail facing the interior

3

How are carbohydrate molecules attached to membrane lipids or proteins?

Covalently

4

Most abundant lipids found in biological membranes

Phospholipids (glycerophospholipids and sphingoolipids)

5

Glycerophospholipids are composed of:

Glycerol backbone + phosphate + 2 fatty acids

(Ex: phosphatidylcholine, phosphatidylserine, phosphatidylinositol)

6

Sphingolipids are composed of:

Sphingosine backbone + long chain fatty acid + phosphorylcholine

(Eg: sphingomyeline— most common SL in outer leaflet)

7

Sphingosine backbone with carbohydrate (oligosaccharide) residue(s)

Found in outer leaflet of lipid bilayer

Glycolipids

8

Embedded

Steroid nucleus + hydroxyl group + hydrocarbon side chain (interact with hydrophobic tails)

Cholesterol

9

Which 3 membrane lipids are located in the outer sheet?

Phosphatidylcholine
Sphingomyelin
Glycolipids

10

What 3 membrane lipids are located in the inner sheet?

Phosphatidylinositol
Phosphatidylserine
Phosphatidylethanolamine

11

What is a marker for apoptosis?

Describe how it works

Phosphatidylserine

During apoptosis, it is displayed on the outer leaflet, where it serves as a tag for phagocytes to recognize

12

What is the deficiency in Niemann-Pick disease? Describe what this normally does

Acid sphingomyelinase (A-SMase)

This is a lysosomal enzyme which breaks down sphingomyelin

13

What does the deficiency in Niemann-Pick disease cause?

SM accumulation in the lysosomes of the liver, spleen, CNS, and bone marrow

14

What are the symptoms of Niemann-Pick disease?

Enlargement of the liver and spleen, neurological damage

CHERRY RED SPOT in eye

15

Firmly embedded in the membrane

Stabilized by hydrophobic interactions with lipids

Integral membrane proteins

16

Integral membrane proteins

Span entire lipid bilayer
Weave in and out of membrane
Interact with internal and external environment

Include: transporters, ion channels, and receptors (regulate movement of molecules and transmit signals from external environment)

Polytopic transmembrane proteins

17

Loosely bound to membrane through electrostatic interactions with lipids or proteins

Peripheral proteins

18

Tethered to membranes via covalent attachment to a lipid

Lipid-anchored proteins

19

Carbohydrates are attached to lipids/proteins that face ______

Extracellularly

20

The glycocalyx is a carbohydrate shell. Discuss its 3 functions

Protection: mechanical injury or premature enzymatic degradation

Cell adhesion: tissue formation and fertilization

Cell identification: own healthy cells vs. diseased foreign cells; RBCs!!

21

RBCs have antigens on their surfaces. These can be either

H antigen (O blood type), A antigen, B antigen, or A+B antigen

22

Plasma produces antibodies. These can be eitherR:

Anti-A & Anti-B (for blood type O)

Anti-B for blood type A

Anti-A for blood type B

None for blood type AB

23

Universal donor

Type O (RBCs have no blood group antigen)

24

Universal acceptor

Type AB (plasma does not contain any antibodies)

25

Rh antigen is actually the ___ antigen and is inherited in an autosomal dominant fashion

D

26

Describe what occurs in erythroblastosis fetalis

There is incompatibility between the blood of mother and fetus

Mom is Rh- and the fetus is Rh+

More common in second pregnancy because the mom will have produced the antibodies already

27

Membranes switch from fluid to rigid state

Melting temp (Tm)

28

Temp >>> Tm = ?

Too fluid

29

Temp > Tm = ?

Optimal fluidity

30

Temp < Tm = ?

Rigid

31

What is the effect of saturated lipids on the membrane and why?

They decrease fluidity because they are more tightly packed

32

What is the effect of unsaturated lipids on the membrane and why?

They increase fluidity because of the kinks in the fatty acid chains

33

What happens if cholesterol is inserted into a membrane that is too rigid?

It increases fluidity by preventing close packing of the lipids

34

What happens if cholesterol is inserted into a membrane that is too fluid?

It decreases fluidity by fitting in thee gaps created by the kinks

35

Describe what occurs in spur cell anemia

Elevated levels of cholesterol in the RBC membrane lead to decreased fluidity —> RBCs lyse in the spleen

36

The membrane is permeable to what type of molecules?

Lipophilic

37

The membrane is impermeable to what type of molecules?

Hydrophilic/polar

38

Facilitate the transport of specific molecules across PM

Membrane proteins

39

Function as transporter proteins

Integral membrane proteins

40

What have a high concentration extracellularly?

Sodium, chloride, calcium

41

What has a high concentration intracellularly?

Potassium

42

What are the 2 types of passive transport?

Simple diffusion & facilitated diffusion

43

This type of diffusion occurs unaided

Transports molecules that are small, non-polar, and uncharged polar

Simple diffusion

44

This type of diffusion requires the assistance of transmembrane proteins

Large/charged molecules —> via proteins that act as ion channels or transporters

Ex: voltage-gated Na channel and glucose transporters

Facilitated diffusion

45

Allow charged/polar molecules (ions and water) to move across membranes down their concentration gradient

High throughput

Ion channels

46

Describe ligand-gated ion channels

Binding of ligand (neurotransmitter or hormone) causes conformational changes in protein —> opening of channel

Down concentration gradient

Ex: glutamate receptor

47

What is an antagonist of the glutamate receptor that is often used to treat Alzheimer’s disease?

Mimantine/Namenda

48

Describe what occurs with voltage-gated ion channels

Depolarization occurs due to an influx of positively charged ions —> open channels —> ions go down concentration gradient

Found in excitable cells such as neurons

Ex: sodium channel

49

Active transport is mediated by?

Integral membrane proteins

50

This type of active transport uses ATP directly

Primary

51

This type of active transport uses energy stored in a concentration gradient and is coupled to a primary transport system

Secondary

52

There are 2 types of primary active transport. Describe them:

1. P type ATPases: ATP is hydrolyzed, protein gets phosphorylated

2. ABC transporters: ATP is hydrolyzed but does not phosphorylated the transporter

53

In this type of primary active transport, the following occurs:

ATP breaks down into ADP an phosphate

Transporter forms a covalent bond with phosphate to form an intermediate

Phosphorylation on a conserved aspartame residue —> conformational changes

Ex: Na+/K+-ATPase and Ca2+-ATPase

P type ATPases

54

Type of primary active transport:

Pump wide range of small molecules out of cells against their gradient

Use ATP as energy source

Ex: P glycoproteins, multi-drug resistant proteins

ABC transporters

55

Thermodynamically unfavorable flow of one species of ion against a gradient coupled to a favorable flow of another species down a gradient

Eg: sodium-glucose transporter and sodium-calcium exchanger

Secondary active transport

56

Describe an antiporter and give an example:

Secondary transporter

Go in opposite directions

Sodium calcium exchanger (NCX)

57

Describe a symporter and give an example:

Secondary transporter

Go in same direction

Lactose permease

58

Describe a uniporter and give an example:

Secondary transporter

Can go either way depending on concentration

Mitochondrial calcium transporter

59

Present in epithelial cells that line the small intestine and renal tubules

Mediates unidirectional movement of Na+ and glucose

Movement of Na occurs down gradient; movement of glucose occurs against gradient

Sodium-glucose transporter 1

60

Antiporter that functions to maintain low levels of intracellular calcium

Imports 3 Na+ down gradient and exports 1 Ca2+ again gradient

NCX

61

Describe the transport mechanisms in the uptake of dietary monosaccharides:

D-glucose and D-galactose enter intestinal epithelial cells from lumen along with Na+: secondary active transport mediated by SGLT1 in apical surface

Transported across enterocyte into blood: facilitated diffusion using GLUT2

Fructose: facilitated diffusion using GLUT5 on apical side and GLUT2 on basal side

Na+: transported in by SGLT1; primary active transport mediated by Na+/K+-ATPase in basolateral membrane

62

What causes cystic fibrosis? What does it normally do?

Mutation in CFTR (cystic fibrosis transmembrane conductance regulator) gene —> misfolds and won’t leave ER

CFTR is a chloride channel that mediates active transport of Cl- from inside cells to the outside via airways and sweat ducts

63

What does the deficiency in cystic fibrosis cause?

Buildup of Cl- inside the airway epithelial cells —> increased Na+ —> water follows salt decreasing the water content of the mucous layer —> thicker mucous susceptible to bacterial infections

64

What is the defect in cystinuria?

Defect in transport responsible for uptake of diametric amino acid cystine and other dibasic amino acids

COAL: cystine, ornithine, arginine, lysine

65

What does the defect in cystinuria cause?

Cystine crystals or stones in the kidney

Positive nitroprusside test

Renal colic

66

What is the defect in Hartnup disease?

Defect in a transporter for non-polar or neutral amino acids (alanine, valine, threonine, leucine, tryptophan, etc)

This transporter is typically found in the kidneys and intestine

67

What does the deficiency in Hartnup disease cause?

Tryptophan is a precursor for serotonin, melatonin, and niacin (precursor for NAD+), so all of those are lacking

Cerebellum ataxia— lack of muscle coordination

Nystagmus

Photodermatitis and photosensitivity

68

Cardiac glycosides (cardiotonic) drugs do what?

They are contraction inducing

Ex: Ouabain and Digoxin

Inhibit the Na/K-ATPas on cardiac myocytes —> increase in intracellular Na+ —> increase in Ca2+ d/t slowing of NCX —> stronger contraction of heart muscle

Used for CHF and a fib