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Biology AS > 2.3 Transport across cell membranes > Flashcards

2.3 Transport across cell membranes Flashcards

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1
Q

What is the function of the cell-surface membrane? (x3)

A

-Forms a boundary between the cell cytoplasm and the environment
-Different conditions can be established between the inside and outside of the cell
-Controls the movement in and out of the cell

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2
Q

What molecules make up the cell-surface membrane?

A

-Phospholipids
-Proteins
-Cholesterol
-Glycolipids
-Glycoproteins

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3
Q

What is the structure of Phospholipids?

A

-Similar to lipids except one fatty acid molecule is replaced with a phosphate molecule
-Made of 2 parts, a hydrophilic head and hydrophobic tail
-Hydrophilic heads point towards the outside of the cell-surface membrane
-Hydrophobic tails point to the inside of the cell-surface membrane
-Forms a phospholipid bilayer

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4
Q

What is the function of a Phospholipid?

A

-Allow lipid-soluble substances to enter and leave the cell
-Prevent water-soluble substances entering and leaving the cell
-Make the membrane flexible and self-sealing

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5
Q

What are the 2 types of transmembrane proteins?

A

-Protein channels
-Carrier proteins

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6
Q

What 2 main ways are proteins embedded in the phospholipid bilayer?

A

-Peripheral proteins
-Transmembrane proteins

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7
Q

What do peripheral proteins do?

A

-Provide structural support
-They are embedded in the surface of the membrane

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8
Q

What is the structure of a transmembrane proteins?

A

Completely span the phospholipid bilayer from one end to another

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9
Q

What do protein channels do?

A

Act as channels transporting water-soluble substances across the membrane

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10
Q

What do carrier proteins do?

A

Bind ions or molecules such as glucose and amino acids, then change shape to move these molecules through (Active transport)

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11
Q

Where does cholesterol occur?

A

Within the phospholipid bilayer

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12
Q

What are the functions of cholesterol?

A

Add strength to the membrane without making it too rigid:
-Reduces lateral movement of other molecules including phospholipids
-Makes membranes less fluid at high temperatures to make bilayer more stable
-Prevents leakage of water and dissolved ions from the cell

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13
Q

What are the properties of cholesterol molecules?

A

They are very hydrophobic so help to prevent loss of water and dissolved ions from the cell

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14
Q

What is the structure of a glycolipid?

A

-Made of a carbohydrate chain covalently bonded with a lipid
-Extends from the outside of the phospholipid bilayer

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15
Q

What are the functions of a glycolipid?

A

-Act as recognition sites (for hormones and neurotransmitters)
-Help maintain stability of the membrane
-Help cells to attach to one another to form tissues

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16
Q

What is the structure of a glycoprotein?

A

-Made of carbohydrate chains attached to proteins on the outer surface of the cell membrane

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17
Q

What are the functions of a glycoprotein?

A

-Act as recognition sites (for hormones and neurotransmitters)
-Allows cells to recognise one another
-Help cells to attach to one another to form tissues

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18
Q

What is the main function of a cell surface membrane?

A

-To control what comes in and out of the cell

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19
Q

Why do most molecules not freely diffuse across the cell-surface membrane?

A

-Not soluble in lipids
-Too large to pass through the channels
-Electrically charges (polar) so cannot pass through non-polar hydrophobic tails of phospholipids
-Have the same charge as the charge on the protein channel

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20
Q

What is the fluid of the fluid mosaic model?

A

Individual phospholipid molecules can move giving the membrane a flexible structure that is constantly changing shape

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21
Q

What is the mosaic of the fluid mosaic model?

A

Fluid: Proteins embedded in the phospholipid bilayer in which individual phospholipids can move = has a flexible shape - vary in shape, size and pattern so looks like a mosaic
Mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded

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22
Q

What is diffusion?

A

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed (equilibrium) moving down the concentration gradient

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23
Q

Is simple diffusion active or passive?

A

Passive transport

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24
Q

How do substances exchange?

A

By:
Active transport - Requires metabolic energy
Passive transport - Does not require metabolic energy

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25
Q

What is osmosis?

A

The diffusion of water molecules that are free to move from an area of high water potential to a low water potential through a partially permeable membrane

26
Q

What is water potential?

A

-Measured in Kilopascals (kPa)
-Pure - 0kPa
-Cell cytoplasm contains dissolved sugars, salts etc. so water potential is more negative
-A solution with a high water potential has a large number of water molecules that are free to move

27
Q

What does hypotonic mean?

A

-Higher water potential
-One of two solutions with MORE water and less solute

28
Q

What does hypertonic mean?

A

-Lower water potential
-One of two solutions with less water and MORE solute

29
Q

What does isotonic mean?

A

Solution that has the same amount of water and solute

30
Q

What happens to animal cells in a hypotonic solution?

A

Will eventually burst - HAEMOLYSED

31
Q

What happens to plant cells in a hypotonic solution?

A

Swelling cytoplasm and vacuole will push against the cell wall which will stop the cell getting any larger - TURGID

32
Q

What happens to animal cells in a hypertonic solution?

A

Cell contents shrink and membrane wrinkles - FLACCID

33
Q

What happens to plant cells in a hypertonic solution?

A

Cytoplasm and vacuole shrink and plant membrane pulls away from the cell wall - PLASMOLYSIS

34
Q

What are plasma membranes?

A

All membranes around and within all cells (including those around and within cell organelles) with the same basic structure

35
Q

Is facilitated diffusion active or passive?

A

Passive

36
Q

What is facilitated diffusion?

A

The transport of charged ions and polar molecules down the concentration gradient made easier (facilitated) by protein channels and carrier proteins with complementary binding sites.

37
Q

What 2 types of protein are involved in facilitated diffusion?

A

Protein channels and carrier proteins

38
Q

What can diffuse across easily in facilitated diffusion?

A

Only small, non-polar molecules can diffuse easily

39
Q

Where does facilitated diffusion happen?

A

Happens at only certain points in the membrane and it occurs down a concentration gradient

40
Q

How do protein channels work?

A

hydrophilic channels bind to specific ions = one side of the protein closes and the other opens

41
Q

How do carrier proteins work?

A

binds to complementary molecule = conformational change releases molecule on other side of membrane; in facilitated diffusion, passive process; in active transport, requires energy from ATP hydrolysis

42
Q

What is a solute?

A
  • Any substances that is dissolved in a solvent, for example, water.
  • The solute and solvent together form a solution.
43
Q

How can you find the water potential of cells or tissues?

A
  • Place them in a series of solutions of different water potentials.
  • Where there is no net gain or loss of water from the cells or tissues, the water potential inside the cells or tissues must be the same as that of the external solution.
44
Q

How is water potential affected?

A
  • The addition of a solute to pure water will lower its water potential.
  • The water potential of a solution (water + solute) must always be less than 0 (a negative value).
  • The more solute that is added (the more concentrated a solution), the lower (more negative) its water potential.
45
Q

What does selectively permeable mean?

A

a membrane allows the passage of some molecules or ions and inhibits the passage of others

46
Q

What is the function of extrinsic proteins in membranes?

A

• binding sites/receptors e.g. for hormones
• antigens
• bind cells together
• involved in cell signalling

47
Q

What is the function of intrinsic proteins in membranes?

A

• electron carriers ( respiration/photosynthesis)
• channel proteins (facilitated diffusion)
• carrier proteins (facilitated diffusion/active transport)

48
Q

What are the functions of membranes within cells?

A

• provide internal transport system
• selectively permeable to regulate passage of molecules into/out of organelles
• provide reaction surface
• isolate organelles from cytoplasm for specific metabolic reactions

49
Q

What are the functions of the cell-surface membrane?

A

• isolates cytoplasm from extracellular environment
• selectively permeable to regulate transport of substances
• involved in cell signalling/cell recognition

50
Q

Name and explain 3 factors that affect membrane permeability.

A

• Temperature - high temp denatures membrane proteins/phospholipid molecules have more kinetic energy and move further apart
•pH - changes tertiary structure of membrane proteins
• use of a solvent - may dissolve membrane

51
Q

How could colorimetry be used to investigate membrane permeability?

A
  1. use plant tissue with soluble pigment in vacuole. Tonoplast and cell-surface membrane disrupted. increased permeability = pigment diffuses into solution
  2. select colorimeter filter with complementary colour
  3. use distilled water to set colorimeter to 0. Measure absorbance/ % transmission value of solution
  4. high absorbance/low transmission = more pigment in solution
52
Q

How does osmosis affect plant and animal cells?

A

• osmosis INTO cell:
plant - protoplast swells = cell turgid
animal - lysis
• osmosis OUT of cell:
plant- protoplast shrinks = cell flaccid
animal: crenation

53
Q

What is simple diffusion?

A

• passive process requires no energy from ATP hydrolysis
• net movement of small, lipid soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration

54
Q

Name 5 factors that affect the rate of diffusion.

A

• temperature
• diffusion distance
• surface area
• size of molecule
• difference in concentration

55
Q

What is Fick’s law?

A

surface area x difference in concentration / diffusion distance

56
Q

How are cells adapted to maximise the rate of transport across their membranes?

A

• many carrier/channel proteins
• folded membrane increases surface area

57
Q

Explain the difference between the shape of a graph of concentration against rate for simple vs facilitated diffusion.

A

Simple diffusion - straight diagonal line; rate of diffusion increases proportionally as concentration increases
Facilitated diffusion - straight diagonal line later levels off when channel/carrier proteins are saturated

58
Q

What is active transport?

A

Active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.
Specific carrier protein transports molecules/ions from area of low concentration to area of higher concentration

59
Q

Compare and contrast active transport and facilitated diffusion.

A

• both may involve carrier proteins
• active transport requires energy from ATP hydrolysis; facilitated diffusion is a passive process
• facilitated diffusion may also involve channel proteins

60
Q

What is co transport?

A

• movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration/electrochemical gradient
• substances bind to complementary intrinsic protein:
symport - transports substances in same direction
antiport - transports substances in opposite direction e.g. sodium-potassium pump

61
Q

How is co-transport involved in the absorption of glucose/amino acids in the small intestine

A
  1. Na+ actively transported out of epithelial cells and into bloodstream
  2. Na+ concentration lower in epithelial cells than lumen of gut.
  3. Transport of glucose/amino acids from lumen to epithelial cells is coupled to facilitated diffusion of Na+ down electrochemical gradient

Biology AS (36 decks)

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