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Module 1 Biochem > Membrane Structure and Transport > Flashcards

Membrane Structure and Transport Flashcards

1
Q

describe lipid rafts, what the are rich in and what they facilitate

A
  • An area with unique proteins and lipid composition which separates them from other fluid membrane areas
  • Lipid rafts are rich in:
    • Cholesterol
    • Glycosphingolipids
    • Sphingomyelin
  • Lipid rafts can facilitate signal transduction and virus infection
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2
Q

describe the composition of the leaflets in the PM

A
  • The outer leaflet contains
    • mainly PC
    • sphingomyelin
    • some PE
    • glycosphingolipids
  • The inner leaflet contains
    • mainly PE
    • some PC
    • PS
    • PI
    • PIP2
  • Glycolipids and glycoproteins are only found in the outer layer and form a glycocalyx (2-10% of the weight)
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3
Q

what determines the fluidity of the PM

A

Fluidity of the PM is determined by the FA composition of phospholipids and also by the amount of free cholesterol

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4
Q

what role does cholesterol play in the PM and where is it in the PM

A
  • Cholesterol is present in both layers
  • Cholesterol decreases the fluidity of the PM close to the polar head groups and increases the fluidity inside of the bilayer
  • Cholesterol binds in the space that is generated by cis-double bonds of FA
  • Cholesterol prevents drastic changes in fluidity due to high or low temps
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5
Q

how does temp affect fluidity of PM

A
  • Low temp: the fatty acyl groups are stiffer and cholesterol increases the membrane fluidity by separating them and prevents close packing
  • High temp: the fatty acyl groups are more fluid and cholesterol decreases the membrane fluidity with its steroid ring system and slows down their movement
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6
Q

describe the composition of other biomembranes

A
  • Membranes inside the cell do not contain cholesterol. The fluidity is mainly regulated by the FA composition
  • The inner mitochondrial membrane contain cardiolipin which is not found in other membranes
  • Lipoprotein membranes are composed of a phospholipid monolayer which allows transport of nonpolar lipids (TAGs and cholesteryl ester) in the blood and lymph. Free cholesterol is found in monolayer
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7
Q

what determines membrane fluidity?

A

it is determined by the FA found int he polar lipids in the membrane

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8
Q

why is the FA composition especially important for intracellular membranes?

A

This is because intracellular membranes have little or no cholesterol is help regulate fluidity

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9
Q

what characteristics of phospholipids make the membrane more fluid? Name 2.

A

Shorter FA and unsaturated fatty acids make the membrane more fluid. Especially arachidonic acid (20:4; w-6) and DHA (22:6, w-3) increase fluidity

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10
Q

glycerophospholipids contain normally ____ fatty acid at position 1 and _____ fatty acid at position 2

A
  1. Saturated
  2. Unsaturated
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11
Q

transport of glucose into cells: name the sodium independent glut transporters, facilitated diffusion transport

A
  • GLUT 1: brain, RBC
  • GLUT 2: liver, kidney, B-cells of pancreas, intestine
  • GLUT-3: neurons
  • GLUT 4: muscle and fat
  • GLUT 5: intestine, seminal vesicles
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12
Q

transport of glucose into cells: name the sodium-dependent glucose transporters, secondary active transport

A

SGLT-1: intestine (epithelial cells at the luminal side)

SGLT-2: kidney (epithelial cell in renal tubules)

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13
Q

High affinity GLUT transporters are

A

GLUT1, GLUT3 and GLUT4

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14
Q

Low affinity GLUT transporters are

A

GLUT2 and GLUT5

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15
Q

describe the glucose uptake with GLUT1 and GLUT3

A

The uptake with GLUT1 and GLUT3 remains at a constant rate with normal and lower blood glucose concentrations

GLUT1 is abundant in RBC, and it is also found in the blood-brain barrier as well as in the kidneys

GLUT3 is dominant in neurons and brain

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16
Q

which GLUT transporter is insulin-dependent?

A
  • GLUT4 is insulin-dependent.
  • GLUT4 is abundant in fat cells, skeletal muscle and the heart
  • Insulin mobilizes the transport of GLUT4 from the endosome to the PM. Once the GLUT4 arrives at the PM, it allows the influx of blood glucose into the cell
  • Insulin injection can lead to hypogylcemia due to rapid uptake of blood glucose into skeletal muscle and fat cells via the mobilized GLUT4
17
Q

what mobilizes GLUT4?

A

Insulin and vigorous exercise of the skeletal muscles

18
Q

describe the efficiency and rate of glucose transport with GLUT2

A

GLUT2 (low-affinity transporter) is capable of transporting large amounts of glucose molecules at a high glucose concentration (1/2 maximal transport of glucose is reached at 10-15 mmol/L)

19
Q

where is GLUT2 found?

A
  • Intestinal mucosal cells and facilitates release of dietary sugars into portal vein
  • Hepatocytes: GLUT2 takes up glucose when there are high levels of dietary sugars. During fasting, glucose is released into the blood from hepatocytes with the concentration gradient
  • Renal tubular cells for the re-uptake of glucose
  • B-cells of pancreas: GLUT2 transports large amounts of glucose and is used to “measure” high blood glucose levels
20
Q

summarize the transport rates for GLUT3, GLUT4 and GLUT2 related to fasting blood glucose levels

A
21
Q

why is GLUT5 different?

A
  • GLUT5 prefers the transport of fructose over glucose
  • GLUT5 transports mainly dietary fructose. Dietary glucose only at very high level of glucose concentration
22
Q

where is GLUT5 found?

A
  • Found in the intestinal mucosal cells on the luminal side of the intestinal membrane
  • GLUT5 is also found in seminal vesicles which release fructose into semen. The seminal vesicles use blood glucose to form fructose to supply the energy metabolism of sperm cells
23
Q

describe problems that arise from GLUT1 deficiency and what it causes

A
  • Deficiency of GLUT1 leads to microcephaly and epilepsy-like seizures in the first few months of life
  • As individuals mature they develop the follwing:
    • Ataxia
    • Delayed psychomotor development
    • Movement disorders
    • Impaired speech
24
Q

how does the Na/K/ATPase pump work?

A

By cleaving ONE ATP, 3 Na+ are pumped out and 2 K+ ions are pumped into the cell.

25
Q

describe what SGLT1 is

A
  • It is a symporter that transports Na ions and glucose or galactose into the intestinal mucosal cell
  • The transport of glucose or galactose is performed against a gradient and the Na/K ATPase has to be active
26
Q

what are ABC transporters?

A
  • ATP Binding Cassette
  • In eukaryotes, ABC transporters allow the active transport of molecules from the cytosol to the extracellular space:
    • This process needs hydrolysis of ATP
    • The transported molecules are often lipids or lipid-related compounds
  • Example: liver releases bile salts, cholesterol and conjugated bilirubin into the bile ducts using ABC transporters
27
Q

what is the CFTR?

A
  • It is a gated channel with a pore for chloride ions. This pore can be opened or closed following a stimulus.
  • Although a few molecules of ATP are cleaved the transport is considered PASSIVE TRANSPORT which leads to many chloride ions flowing through the open channel
28
Q

describe the CFTR

A
  • Cystic fibrosis transmembrane conductance regulator is a special ABC transporter which is more a chloride ion channel than a transport protein
  • CFTR does NOT pump Cl ions–they flow with the gradient once channel is opened
29
Q

name the epithelial cells where CFTR is present

A
  • Reproductive ducts
  • Intestinal lumen
  • Pancreatic ducts
  • Airway ducts
  • Skin
30
Q

describe the structure of CFTR

A
  • CFTR consists of 2 transmembrane domains
    • 2 groups of 6 alpha helices
    • Each is connected to an ATP-binding site
    • One regulatory domain of the channel is intracellular
31
Q

what are symptoms of deficient CFTR?

A
  • In the newborn the early sign are salty skin
  • Later in life
    • Recurrent lung infections
    • Chronic pancreatitis
    • Steatorrhea (abnormal amount of fat in feces)
32
Q

describe the normal process of sweating

A
  • In a typical epithelia cell, Cl ions are first accumulated inside the cell which generates a higher Cl ion concentration than in the extracellular space
  • These negatively charged Cl ions are then released with the gradient into the extracellular lumen via CFTR, where sodium ions and water follow
  • In the sweat gland coil, large amounts of Na and Cl ions are released along with water
  • The sweat formed in the coiled section of the sweat gland has a higher concentration of NaCl than the sweat actually released
  • In the secretory duct, the Cl ions flow back into epithelial cells via CFTR.
  • This allows the salvage and re-uptake of Cl ions by the epithelial cells using passive transport (with graident)

Module 1 Biochem (12 decks)

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