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biology > Transport Across Cell Membranes > Flashcards

Transport Across Cell Membranes Flashcards

1
Q

What is a brush border?

A

A collection of microvilli on the surface of epithelial cells

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2
Q

How are the epithelial cells of the small intestine adapted for absorption of digested food?

A

Many microvilli
Increase SA= more carrier + channel proteins = more facilitated diffusion at once.

Many protein channels and carrier proteins = more facilitated diffusion at once.

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3
Q

Define diffusion

A

Net movement of molecules or ions from an area of high to an area of low concentration

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4
Q

What is the ileum and lumen?

A

The space inside the small intestine = lumen

Ileum = small intestine

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5
Q

How is the glucose concentration gradient maintained between the epithelial cells and the blood?

A

The blood is constantly circulated to remove glucose next to cells

Maintain conc. gradient

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6
Q

What role do K+/Na+ pumps play in glucose absorption?

A

Pumps remove Na+ from cell into blood.

Maintains low conc. of Na+ in cell so Na+ move into cell via facilitated diffusion (carrier proteins)

Glucose moves along with Na+

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7
Q

By what processes does glucose move from the ileum to the blood?

A

Co-transport with Na+

Facilitated diffusion

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8
Q

What would occur if active transport didn’t happen in the small intestine?

A

Glucose and amino acids would pass out unabsorbed

Only absorb 50% of digestive products (equilibrium reached with diffusion)

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9
Q

What two main substances are absorbed into the blood that require active transport?

A

Glucose and amino acids

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10
Q

What is co-transported with sodium ions into the epithelial cells from the ileum?

A

Glucose or amino acids

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11
Q

Describe how starch is digested and absorbed

A

Starch broken down by amylase and then Maltase into glucose

Sodium ions are actively transported out of epithelial cell via K+/Na+ pump to set up conc. gradient of Na+

Na+ enter epithelial cells with glucose via co-transport proteins.

High glucose concentration in cell, low in blood. Move via facilitated diffusion (carrier protein)

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12
Q

What is the function of the cell surface membrane?

A

separate cytoplasm from environment

Allow and control transport of molecules and ions

Allow small, lipid soluble, non-polar molecules to diffuse across

Cell recognition and signalling

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13
Q

What is the function of the phospholipids in the cell surface membrane ?

A

Allow membrane to be flexible and self sealing

Allow lipid soluble substance across

Form phospholipid bilayer

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14
Q

What is the function of extrinsic proteins in the cell surface membrane ?

A

Structural support

Help cells stick together

Bind with carbohydrates to form glycoproteins for cell recognition

Act as hormone receptors

Enzymes

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15
Q

What is the function of cholesterol in the cell surface membrane ?

A

Make membrane less flexible (stronger)

Prevent leakage of water and dissolved ions

Prevent membrane becoming too fluid at high temps

Prevent lateral movement

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16
Q

What are the function of intrinsic proteins in the cell surface membrane ?

A

Transport water soluble molecules and ions

Allow active transport

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17
Q

What is the function of the glycoproteins in the cell surface membrane ?

A

Allow cells to adhere

Recognition site (hormone and neurotransmitters)

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18
Q

What is the function of the glycolipids in the cell surface membrane ?

A

Maintain stability of cell membrane

Recognition site (cholera toxins)

Allow cells to adhere

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19
Q

What is the function of a membrane within a cell?

A

Seperate organelles (seperate conditions and metabolic reactions)

Allow transport of substances (ER

Separate harmful enzymes (hydrolytic) in lysosomes

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20
Q

Why might a substance be unable to enter a cell?

A

Too large to fit through channels or bilayer

Same charge as channels (repelled)

Water not lipid soluble

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21
Q

How is the cell membrane described and why?

A

Fluid mosaic

Fluid = able to move

Mosaic = proteins of different sizes and shapes like mosaic

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22
Q

Why are the phospholipids able to move?

A

Weak forces of attraction between them

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23
Q

What are channel proteins also called?

Why

A

Aquaporins

Filled with water and lined with hydrophillic amino acids

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24
Q

Define simple diffusion

A

Net movement of molecules or ions from an area of high concentration to an area of low concentration untill an equilibrium is reached

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25
Q

Why and how is simple diffusion passive?

A

No ATP required

Powered by kinetic energy of particles

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26
Q

Give an example of simple diffusion within cells

A 
CO2 
O2 
urea 
enzymes 
hormones
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27
Q

What factors affect the rate of simple diffusion?

A

Temperature

Surface area

Diffusion pathway

Concentration gradient

28
Q

How and why does SA affect simple diffusion?

A

Larger = more

More area for diffusion to occur at once

29
Q

What law links diffusion and the factors affecting it?

A

Ficks law

30
Q

What is ficks law?

A

Rate of diffusion is proportional to

SA X Conc. gradient
———————————
Length of diffusion pathway

31
Q

How can you tell facilitated diffusion is occurring rather than just simple diffusion?

A

Diffusion occurs faster than concentration gradient should allow

32
Q

Is facilitated diffusion active or passive ?

A

Passive

33
Q

What factors affects the rate of facilitated but not simple diffusion?

A

Intrinsic Proteins

34
Q

Describe how carrier proteins work

A

Have complementary shape to specific molecule or ion

Molecule binds to protein causing change in shape.

Causes molecules to be deposited on other side

35
Q

Describe how channel proteins work

A

Channel specific to certain ions or molecules

Opens in presence of specific substance allowing it to cross (large and water soluble)

36
Q

Define osmosis

A

Net movement of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane

37
Q

What is meant by a selectively permeable membrane?

A

Only allows H2O and small molecules through via simple diffusion

38
Q

What is water potential?

A

The force exerted by free water molecules on a membrane

39
Q

Why does water potential get more negative when more solute is added?

A

Water molecules adhere to solute molecules and so are no longer free

Less free water molecules to exert pressure

40
Q

What occurs to plant cells and body cells when the solution surrounding it has a higher water potential?

A

Water moves in vía osmosis down water concentration gradient

Plant cell goes turgid (protoplast pushes against cell wall)

Animal cell swells and bursts

41
Q

What is the protoplast?

A

The cell membrane and it’s contents

42
Q

What does isotonic mean?

A

Same water potential

43
Q

What occurs to plant cells and body cells when the solution surrounding it is isotonic ?

A

No net movement of water molecules

Plant= incipient plasmolysis

Animal = no change

44
Q

What occurs to plant cells and body cells when the solution surrounding it has a lower water potential?

A

Water moves out vía osmosis down water concentration gradient

Plant = plasmolysed

Animal= shrivelled (red blood cell will appear dark due to higher haemoglobin conc)

45
Q

Why do plant cells require cell walls in terms of swelling?

A

Plant cells surrounded by almost pure water

Can’t control water potential surrounding cells

Water constantly moves in via osmosis

Turgid = pressure on cell wall = no more water enters

46
Q

Define active transport

A

The movement of molecules or ions from an area of low concentration to an area of high concentration using energy released from hydrolysis of ATP and a carrier protein

47
Q

Explain how active transport works

A

Complementary molecule binds to carrier protein.
ATP and ATP hydrolase bind to protein.

Energy released from ATP hydrolysis changes shape of carrier protein depositing molecule on other side.

Pi is released cause protein to revert back to original shape

ADP +Pi =ATP in mitochondrion during aerobic respiration

48
Q

How many sodium ions and potassium ions are moved in the sodium/potassium pump?

A

3x sodium

2x potassium

49
Q

What is the sodium/potassium pump an example of?

A

Active transport

50
Q

What determines whether a molecule is transported by active transport or facilitated diffusion using a carrier protein?

A

Depends on the concentration gradient and where the molecule is moving to.

If moving out of cell but concentrations are higher out of cell then must move via active transport

51
Q

How is the sodium/potassium pump complementary to two molecules?

A

Originally complementary to sodium ions inside of cell

Change to tertiary structure causes sodium ions to be deposited on outside. Change causes new shape which is complementary to potassium

52
Q

What substances can move via facilitated diffusion and active transport?

A

Molecules or ions

53
Q

Define bulk transport

A

The movement of a large group of molecules or ions via a vesicle

54
Q

Describe exocytosis

A

When a vesicle membrane fuses with the cell membrane releasing contents to external environment

55
Q

Describe endocytosis

A

When a large molecule or group of molecules is engulfed.

The cell membrane forms pseudopods around the substance and pinches off around it to form a vesicle which is inside the cell

56
Q

How is the villi adapted for maximum absorption?

A

Good blood supply

Thin surface layer of cells

Large surface area

57
Q

What is a lacteal and where is it found?

A

Found in villi

Lymphatic capillary that absorbs dietary lipids

58
Q

What’s the difference between microvilli and villi?

A

Villi is a finger like projection made of many cells

Microvilli and small projections of cell membrane on epithelial cells

59
Q

How does a large surface area maximise nutrient uptake?

A

More space for carrier and channel proteins so more area which molecules or ions can cross

60
Q

How is active transport used in the uptake of glucose into epithelial cells?

A

Active transport moves sodium ions out of (and potassium ions in to) cell into blood.

Creates and maintains a lower conc. of Na in cell than ileum so Na moves into cell along with glucose

61
Q

What is co-transported from the ileum to epithelial cells?

A

Sodium and glucose or amino acids

62
Q

Describe how starch is digested and absorbed from the ileum

A

Starch is broken down by amylase into maltose then by maltase into glucose. (enzymes = extrinsic proteins in membrane)

Glucose uptake by facilitated diffusion untill equilibrium occurs

Sodium ions are transported out cell into blood via active transport by sodium/potassium pump

Sodium ion concentration gradient set up (lower in cell than ileum)

Sodium moves down concentration gradient via co-transport with glucose which moves against concentration gradient.

Glucose concentration higher in cell so moves via facilitated diffusion out into blood

63
Q

What is an osmometer?

A

A device used to experiment with Osmosis

Selectively permeable bag

64
Q

Name the method used to make solutions of different concentrations using a concentrated solution

A

Dilution series

65
Q

Why is more pigment released at higher temps?

A

Membrane more fluid and proteins denature

biology (28 decks)

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