Transport%20across%20cell%20membrane%20by%20Vani%20Gupta

1
Transport across cell membraneby Vani Gupta
2
Types of cell membrane
transport

• Factors affecting transport
• Cell membrane
• Chemical gradient
• Electrical gradient
• Rate of transport
• Passive transport
• Diffusion
• Osmosis
• Facilitated diffusion
• Active transport
• Pumps
• phagocytosis
• Endocytosis/exocytosis

3
Factors affecting transport cell membrane

• The cell needs to absorb and excrete various
  compounds throughout its life.
• These compounds need to pass through the membrane
  which is made from a phospholipid bilayer
• The phospholipid bilayer is formed by
  phospholipid molecules ?bipolar molecule the
  fatty acid side is hydrophobic, the phosphoric
  side is hydrophilic

4

• The membrane is impermeable to

• The membrane is permeable to

• Small, charged molecules
• large molecules such as amino acids, glucose
  and larger
• These compounds must go through channels present
  in the membrane in order to enter or exit the
  cell

• H2O
• Gases (O2, CO2, N2)
• Lipids
• Small, neutral molecules (such as urea)

5
Factors affecting transport Chemical gradient

• Compound moves from an area of high concentration
  to low concentration (or concentration gradient)
• All compounds permeable to the phospholipid
  bilayer will move this way

6
Factors affecting transport Electrical force

• Positive ions are attracted to negative ions and
  vice versa
• Ions are repelled by ions of the same charge (
  against and against -)

7
Movement across the cell
membrane

• Both chemical and electrical forces
  (electrochemical force) drive the movement of
  compounds across the cell membrane

8
Factors affecting the rate of transport

• The rate of transport will depend on
• The concentration gradient
• The compound permeability to the membrane
• The type and number of charges present on the
  compound

9
Crossing the cell membrane

• fats and oils can pass directly through

lipid
inside cell
sat
waste
sugar
aa
H2O
outside cell
10
Types of Transport Proteins

• Channel proteins are embedded in the cell
  membrane have a pore for materials to cross
• Carrier proteins can change shape to move
  material from one side of the membrane to the
  other

11
Cell membrane channels

• Need to make doors through membrane
• protein channels allow substances in out
• specific channels allow specific material in
  out
• H2O channel, salt channel, sugar channel, etc.

inside cell
outside cell
12
Protein channels

• Proteins act as doors in the membrane
• channels to move specific molecules through cell
  membrane
• 
  

HIGH
LOW
13
Passive transport

• Compounds will move from area of high
  concentration toward area of lower concentration
• No ATP is needed for this type of transport
• Passive transport mainly TWO types
• A-Osmosis
• B-Diffusion-diffusion again two types
• a-simple diffusion- no energy needed
• b- facilitated diffusion- no energy needed
• -help
  through a protein channel

14
Osmosis

• Each compound obeys the law of diffusion
• diffusion of water from HIGH concentration of
  water to LOW concentration of water
• across a semi-permeable membrane
• However, some compounds are unable to cross the
  cell membrane (glucose, electrolytes)
• Water can cross ? will enter or exit the cell
  depending its concentration gradient.

15

• where is osmosis important

16
Cells in Solutions
17

• PLASMOLYSIS

Isotonic Solution
Hypotonic Solution
Hypertonic Solution
NO NET MOVEMENT OF H2O (equal amounts entering
leaving)
CYTOLYSIS
PLASMOLYSIS
18
Diffusion

• Simple diffusion-
• no energy needed
• Movement across higher to lower concentration
  gradient.
• Facilitated diffusion-
• Some compounds are unable to diffuse through the
  membrane.
• They will be allow to cross if the membrane has
  proteins that can bind these compounds and enable
  to cross toward the area of lower concentration

19

• Simple and facilitated
  diffusion

simple diffusion
facilitated diffusion
lipid
H2O
protein channel
H2O
20

• Simple Diffusion
• Doesnt require energy
• Moves high to low concentration
• Example Oxygen or water diffusing into a cell
  and carbon dioxide diffusing out.

21
Simple Diffusion

• The rate of diffusion will be increased when
  there is
• Concentration the difference in between two
  areas (the gradient) causes diffusion. The
  greater the difference in concentration, the
  faster the diffusion.
• Molecular size smaller substances diffuse more
  quickly. Large molecules (such as starches and
  proteins) simply cannot diffuse through.
• Shape of Ion/Molecule a substances shape may
  prevent it from diffusing rapidly, where others
  may have a shape that aids their diffusion.
• Viscosity of the Medium the lower the
  viscosity, the more slowly molecules can move
  through it.

22

• Movement of the Medium currents will aid
  diffusion. Like the wind in air, cytoplasmic
  steaming (constant movement of the cytoplasm)
  will aid diffusion in the cell.
• Solubility lipid - soluble molecules will
  dissolve through the phospholipid bilayer easily,
  as will gases like CO2 and O2.
• Polarity water will diffuse, but because of
  its polarity, it will not pass through the
  non-polar phospholipids. Instead, water passes
  though specialized protein ion channels

23

• Facilitated diffusion
• Doesnt require energy
• Uses transport proteins to move high to low
  concentration
• Examples Glucose or amino acids moving from
  blood into a cell.

24

• where is facilitated transport
  important

25

26
Active Transport- Pumps - phagocytosis
- Endocytosis/exocytosis
27
Active transport

• ATP (energy) is needed ? pump
• Moves materials from LOW to HIGH concentration
• AGAINST concentration gradient

28
Example-1 ATPase
pumps

• The most common Na/K pumps ? reestablish
  membrane potential. Present in all cells.
• Two K ions are exchanged with 3 Na ions

29

• EXAMPLES OF ACTIVE TRANSPORT
• Example 2 the thyroid gland accumulates iodine
  as it is needed to manufacture the hormone
  thyroxin.
• The iodine concentration can be as much as 25
  times more concentrated in the thyroid than in
  blood.

30

• Example 3 In order to make ATP in the
  mitochondria, a proton pump (hydrogen ion) is
  required.

31

• where is active transport important

32
Endocytosis

• Endocytosis (Endo means in).
• Endocytosis is the taking in of molecules or
  particles by invagination of the cell membrane
  forming a vesicle. Integrity of plasma membrane
  is maintained.
• This requires energy.
• Endocytosis is fallowed by exocytosis on the
  other side. Transcytosis, vesicle trafficking,
  or cytopempsis.

33

• There are two types of
  endocytosis
• 1. pinocytosis (cell drinking) small molecules
  are ingested and a vesicle is immediately formed.
  This is seen in small intestine cells (villi)

2. phagocytosis (cell eating) large
particles, (visible with light microscope)
are invaginated into the cell (ie white blood
cells eat bacteria
34
(No Transcript)
35
Phagocytosis

• Used to engulf large particles such as food,
  bacteria, etc. into vesicles
• Called Cell Eating

36

• Capture of a Yeast Cell (yellow) by Membrane
  Extensions of an Immune System Cell (blue)

37

• Receptor-Mediated Endocytosis
• Some integral proteins have receptors on their
  surface to recognize take in hormones,
  cholesterol, etc.

38
Exocytosis

• Exocytosis (Exo means out.)
• Exocytosis is the reverse of endocytosis.
• This is where a cell releases the contents of a
  vesicle outside of the cell.
• These contents may be wastes, proteins, hormones,
  or some other product for secretion.
• This also requires energy.
• Example vesicles from the Golgi fuse with the
  plasma membrane and the proteins are released
  outside of the cell.

39
(No Transcript)
40

• Fusion of vesicle with plasma membrane is
  mediated by a number of accessory proteins-
  SNARE protein.
• Require stimulus and Ca.
• Exception- Renin from JG cells and PTH from
  parathyroid gland by decrease in intracellular
  Ca.
• Constitutive Secretion- Immunoglobulin from
  plasma Cells and collagen from fibroblast.
• Regulated- endocrine gland, pancreatic acinar
  cells

41
Membrane Transport Proteins

• 1. Water Channels or Aquaporins (AQPs)
• 12 types
• Amount of water is regulated by No.
  of AQPs
• They are known as gated channel
  although
• they are pores.
• Two types a) Aquaporins- only
  water.
• b)
  Aquaglyceroporins- also for
• small
  molecules.

42

• 2- Ion Channels-
• All cells specially on excitable cells Neurons
  and muscle cells
• Selective and non selective
• Gated voltage gated and extracellular agonist
  or antagonist gated ex acetylcholine gated
  cationic specific channel at motor end plate of
  skeletal muscle.
• Conductance- 1-2 picosimens and gt 100
  picosimens.
• Ex- Na, K, Ca, Cl, Anion , cation.

43
3.Solute Carriers-

• gt 40 types , gt 300 transporters.
• three gps-1. Uniporters- single molecule across
  the membrane (GLUT )
• 2. Symporters- Two or more
  molecules
• Ex- Na-k-cl
  Symporter (Kidney)
• Na -
  Glucose Cotransporter.
• 3. Antiporters- Two or
  more molecules in
• 
  opposite directions
• Ex Na- H
  antiporter ( PH regulation)
• 3Na- Ca
  , Cl- HCO3

44
4.ATP DEPENDENT TRANSPORTERS

• 1. ATPase Ion Transporters
• 1. P- Type- gate phosphorylted
  during
• transport. Na- K ATP
  ase.
• 2. V- Type- Vacuolar H- ATPase
  urine
• acidification on Vacules
  like endosomes
• and lysosomes.
• 2. ATP binding cassette (ABC) transporters 7
  subgroups transport diverse group of ions ex-
  Cl, Cholesterol, bile acids, drugs, iron and
  organic anions.
• EX- Cystic fibrosis transmembrane regulator.
• Multidrug Resistance Protein.
• organic Anions.
• .

45

• Molecular Motors
• Kinesin- over the microtubule
• Dynein- retrogate transport
• Myosin- over the microfilaments.- 18 types a

46

• Q-1 all membrane processes, such as pumping and
  channelling of molecules are carried out by.
• a-lipid
• b-carbohydrate
• c-nucleic acid
• d-protein

47

• Q-2 Which of the following statement about
  membrane transport protein is incorrect
• a-carrier proteins are similar to enzymes in that
  they show saturation
• b-carrier protein can facilitate both active and
  passive transport
• c-channel protein can facilitate both active and
  passive transport
• d-the Na /Glucose transport protein carries out
  secondary active transport.

48

• Q-3 Diffusion across the plasma membrane is
  more rapid if a substance is
• a-a protein
• b-hydrophilic
• c-high in its oil water partition coefficient
• d-larger and globular in shape

49

• Q-4 the difference between simple diffusion and
  facilitated transport is that facilitated
  transport.
• a-is concentration dependent
• b-occurs across plasma membrane
• c-require membrane protein
• d-utilize a substance moving with its
  concentration gradient

50

• Q-5 Erythrocyte glucose transporter
  specifically transports glucose down its
  concentration gradient and exhibit hyperbolic
  saturation kinetics .This is an example of
• a-active mediated transport
• b-passive mediated transport
• c-non- mediated transport
• d-group translocation

51

• Q-6 which one of the following is a correct
  statement for Na-K ATPase.
• a-it gives out 3 Na-ions and takes in 2 K-ions
• b- it gives out 2 Na-ions and takes in 3 K-ions
• c- it gives out 3 Ca-ions and takes in 2 K-ions
• d-it gives out 3 Na-ions and takes in 2 Ca-ions

52

• Q7-which of the following effects of the
  steroid digitalis is observed after treatment of
  congestive heart failure.
• a-decrease in cytosolic sodium levels
• b-inhibition of Na-K ATPase
• c-decrease in the force of heart muscle
  contraction
• d-stimulation of the plasma membrane ion pump.

53

• Q8-you wish to design a new drug which will
  act as an ionophore to deliver Ca2 across the
  nerve cell membrane .This drug would most likely
  be
• a-hydrophobic on the outside and hydrophilic on
  inside
• b-insoluble in lipid
• c-soluble in proteins
• d-smaller than 0.001 nm in diameter

54

• Q9- the process by which a cell secretes
  macro-molecule by fusing a vesicle to the plasma
  membrane is called
• a-endocytosis
• b-exocytosis
• c-pinocytosis
• d-phagocytosis

55

• Q10- free fatty acids enter cell by
• a-passive diffusion
• b-active diffusion
• c- through carrier protein
• d Active transport

56

• Q-11 Aquaporins transport-
• a. Water only
• b. water and small molecules.
• c. Water and Glucose
• d. Water and salt.

57

• Q-12 Which of the fallowing is responsible for PH
  
• Regulation-
• a. Antiporters.
• b. Symporters
• c. Uniporters.
• d. Co-porters.

58

• Q-13 V type transporters are
• a. ATPase dependent.
• b. Symporters.
• c. Carrier Proteins.
• d. Receptor Proteins.

59

• Q-14 .GLUT is an example of-
• a. Antiporters.
• b. Symporters
• c. Uniporters.
• d. Co-porters.

60

• Q-15 Presence of Ion channels are must on
• a. Excitable tissue.
• b. Non excitable tissue.
• c. Renal tissue
• d. Cardiac muscle.

61

• Q-16 Na- K ATPase transport Na-
• a. Towards Concentration gradient.
• b. Against Concentration gradient.
• c. Towards electro chemical gradient.
• d. Against electrochemical gradient.

62

• Q-17. Rennin secretion from JG cells is an
  example of-
• a.) Exocytosis
• b.) pincocytosis
• c.) Vacular movement.
• d.) Transcytosis.

63

• Q.- 18. PTH secretion fro parathyroid glands
  require-
• a.) low intracellular Ca.
• b.) high Intracellular Ca.
• c.) Low intracellular K.
• d.) high Intracellular K.

64

• Q-19. Transcytosis incudes-
• a. Endocytosis and phagocytosis.
• b. Endocytosis and pincocytosis.
• c. Endocytosis and exocytosis.
• d. Endocytosis only.

65

• Q-20. Transcytosis occurs at
• a). Epethelial Cells.
• b). Endocrine Cells.
• c). Nerve cells.
• d). None of the above.