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Transport Across Cell Membranes Flashcards

(65 cards)

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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
Why and how is simple diffusion passive?
No ATP required Powered by kinetic energy of particles
26
Give an example of simple diffusion within cells
``` CO2 O2 urea enzymes hormones ```
27
What factors affect the rate of simple diffusion?
Temperature Surface area Diffusion pathway Concentration gradient
28
How and why does SA affect simple diffusion?
Larger = more More area for diffusion to occur at once
29
What law links diffusion and the factors affecting it?
Ficks law
30
What is ficks law?
Rate of diffusion is proportional to SA X Conc. gradient ——————————— Length of diffusion pathway
31
How can you tell facilitated diffusion is occurring rather than just simple diffusion?
Diffusion occurs faster than concentration gradient should allow
32
Is facilitated diffusion active or passive ?
Passive
33
What factors affects the rate of facilitated but not simple diffusion?
Intrinsic Proteins
34
Describe how carrier proteins work
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
Describe how channel proteins work
Channel specific to certain ions or molecules Opens in presence of specific substance allowing it to cross (large and water soluble)
36
Define osmosis
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
What is meant by a selectively permeable membrane?
Only allows H2O and small molecules through via simple diffusion
38
What is water potential?
The force exerted by free water molecules on a membrane
39
Why does water potential get more negative when more solute is added?
Water molecules adhere to solute molecules and so are no longer free Less free water molecules to exert pressure
40
What occurs to plant cells and body cells when the solution surrounding it has a higher water potential?
Water moves in vía osmosis down water concentration gradient Plant cell goes turgid (protoplast pushes against cell wall) Animal cell swells and bursts
41
What is the protoplast?
The cell membrane and it’s contents
42
What does isotonic mean?
Same water potential
43
What occurs to plant cells and body cells when the solution surrounding it is isotonic ?
No net movement of water molecules Plant= incipient plasmolysis Animal = no change
44
What occurs to plant cells and body cells when the solution surrounding it has a lower water potential?
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
Why do plant cells require cell walls in terms of swelling?
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
Define active transport
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
Explain how active transport works
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
How many sodium ions and potassium ions are moved in the sodium/potassium pump?
3x sodium 2x potassium
49
What is the sodium/potassium pump an example of?
Active transport
50
What determines whether a molecule is transported by active transport or facilitated diffusion using a carrier protein?
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
How is the sodium/potassium pump complementary to two molecules?
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
What substances can move via facilitated diffusion and active transport?
Molecules or ions
53
Define bulk transport
The movement of a large group of molecules or ions via a vesicle
54
Describe exocytosis
When a vesicle membrane fuses with the cell membrane releasing contents to external environment
55
Describe endocytosis
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
How is the villi adapted for maximum absorption?
Good blood supply Thin surface layer of cells Large surface area
57
What is a lacteal and where is it found?
Found in villi Lymphatic capillary that absorbs dietary lipids
58
What’s the difference between microvilli and villi?
Villi is a finger like projection made of many cells Microvilli and small projections of cell membrane on epithelial cells
59
How does a large surface area maximise nutrient uptake?
More space for carrier and channel proteins so more area which molecules or ions can cross
60
How is active transport used in the uptake of glucose into epithelial cells?
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
What is co-transported from the ileum to epithelial cells?
Sodium and glucose or amino acids
62
Describe how starch is digested and absorbed from the ileum
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
What is an osmometer?
A device used to experiment with Osmosis Selectively permeable bag
64
Name the method used to make solutions of different concentrations using a concentrated solution
Dilution series
65
Why is more pigment released at higher temps?
Membrane more fluid and proteins denature

biology (28 decks)

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