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Biology > Pack 3 - Transport across cell Membrane > Flashcards

Pack 3 - Transport across cell Membrane Flashcards

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1
Q

Name the 5 basic components of the cell membrane.

A
  • Phospholipids
  • Cholesterol
  • Proteins
  • Glycoproteins
  • Glycolipids
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2
Q

Describe the arrangement of phospholipids in the cell membranes and why it is like this.

A
  • Hydrophilic heads point to outside the cell - attracted by water inside and outside the cell.
  • Hydrophobic tails of both phospholipid layers point into the centre of the membrane - repelled by water.
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3
Q

What are the 3 functions of phospholipids in the cell

Membrane?

A
  • To allow lipid soluble substances to enter and leave the cell.
  • To prevent water soluble substances from entering and leaving the cell.
  • To make the membranes flexible and self-sealing
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4
Q

Name the two types of protein in the cell membrane and their 6 functions.

A

Intrinsic (channel/carrier)
• transport water soluble substances across the membrane through channel proteins.
• allow active transport though carrier proteins.

Extrinsic (surface) proteins.
 • structural support
 • receptors, e.g. hormones
 • cell-surface receptors for identifying cells
 • help cells adhere and together
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5
Q

Name the 3 functions of cholesterol in the cell membrane.

A
  • Reduce lateral movement of other molecules. (Strength)
  • Make the membrane less fluid at higher temperatures
  • Prevent leakage of water and dissolved ions from the cell (very hydrophobic).
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6
Q

Give 3 functions of glycolipids in the cell surface membrane.

A
  • Recognition sites
  • Help to maintain stability of the membrane
  • Help cells attach to one another
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7
Q

Give a specific example of how glycolipids function on the cell surface membrane.

A

ABO blood system operates due to glycolipids acting as cell-surface receptors for specific chemicals.

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8
Q

Give 4 functions of glycoproteins in the cell surface membrane.

A
  • Recognition sites
  • Help cells attach to one another, forming tissues
  • Allows cells to recognise one another (e.g. lymphocytes can recognise an organisms own cells)
  • Cell-surface receptors for hormones and neurotransmitters
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9
Q

Give 4 reasons most molecules do not freely diffuse across the phospholipid bilayer.

A
  • Not lipid soluble
  • Too large
  • Of the same charge as protein channels (repelled).
  • Polar (cannot pass through phospholipid bilayer)
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10
Q

Why is the cell surface membrane described using the ‘fluid-mosaic’ model?

A

Fluid - individual phospholipid molecules move relative to one another, it is flexible/constantly changing shape.

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11
Q

What is the main difference between active and passive transport?

A

Active requires metabolic energy from ATP.

Passive does not (still requires kinetic energy molecules possess).

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12
Q

Define diffusion.

A

The NET movement of molecules or ion from a region of HIGHER concentration to a region of LOWER concentration until DYNAMIC equilibrium is reached.

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13
Q

Is facilitated diffusion a passive or active process?

A

Passive

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14
Q

What is required for facilitated diffusion to take place in the cell membranes (three things)?

A
  • Carrier/channel proteins
  • Difference in concentration gradient
  • Kinetic energy of the molecules
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15
Q

Define facilitated diffusion.

A

Diffusion of specific molecules (down a concentration gradient) at specific points in the cell membrane (carrier/channel proteins).

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16
Q

Describe, using 4 points, how channel proteins work.

A
  • Water-filled hydrophilic channels.
  • Specific water-soluble ions.
  • Only open in the presence of a specific ion.
  • Ions bind causing it to change shape so that it remains closed on one side of the membrane but opens on the other.
17
Q

Describe, using 2 points, how carrier proteins work.

A
  • A molecule (e.g.glucose), specific the protein shape, binds to the protein.
  • This causes the protein to change shape, so that the molecule is released on the other side of the membrane.
18
Q

Define osmosis.

A

The passage of water from a region of HIGHER water potential (Ψ) to a region where it has a LOWER Ψ through a SELECTIVELY permeable membrane until dynamic equilibrium is established.

19
Q

What is the Ψ of pure water?

A

0 kPa

20
Q

If a red blood cell is placed in a solution with a HIGHER water potential than that of the cell, what will happen to the cell?

A
  • Water will enter the cell.

* The cell will swell and eventually burst.

21
Q

If a red blood cell is placed in a solution with a LOWER water potential than that of the cell, what will happen to the cell?

A
  • Water will leave the cell.

* The cell will shrink/shrivel.

22
Q

If a red blood cell is placed in an ISOTONIC solution, what will happen to the cell?

A

No change.

23
Q

If a plant is placed in a solution with a HIGHER water potential than that of the cell, what will happen to the cell? What word(s) describes the condition of the cell?

A
  • Water will enter the cell.
  • Protoplast will swell
  • The cell becomes TURGID
24
Q

If a plant is placed in a solution with a LOWER water potential than that of the cell, what will happen to the cell? What word(s) describes the condition of the cell?

A
  • Water will leave the cell.
  • The protoplast shrinks
  • This is called PLASMOLYSIS
25
Q

If a plant is placed in an ISOTONIC solution, what will happen to the cell? What word(s) describes the condition of the cell?

A
  • No change

* This is called INCIPIENT PLASMOLYSIS

26
Q

What is a protoplast.

A

All parts of a plant cell inside the cell wall.

27
Q

Define active transport

A

The movement of molecules or ions into or out of a cell from a region of LOWER concentration to a region of HIGHER concentration using ATP and carrier proteins.

28
Q

Describe, in 5 stages, direct active transport of a single molecule.

A
  • Carrier proteins bind to a specific molecule or ion on one side at their receptor site.
  • On the inside of the cell, ATP binds to the protein, splitting into a phosphate molecule and ADP.
  • As a result, the protein changes shape and opens on the opposite side of the membrane
  • The molecule or ion is released.
  • Phosphate molecule is released from the protein causing it to revert to its original shape.
29
Q

Describe how the sodium-potassium pump works (6 steps).

A
  • On the inside of the cell sodium binds to the receptor site of the molecule.
  • ATP binds to the protein, splitting into ADP and a phosphate molecule that remains bound to the protein.
  • This causes the protein to change shape releasing sodium ions outside the cell.
  • Two potassium ions the bind to the protein on the outside of the cell.
  • This releases the phosphate group back inside the cell.
  • The protein changes shape and potassium ions are released into the cell.
30
Q

Give two ways movement across the cell surface membrane from the ileum lumen to the epithelial cells.

A
  • Microvilli - increase surface area for insertion of carrier proteins in the cell surface membrane.
  • Increase the number of challenges/carrier proteins in the cell surface membrane.
31
Q

What is the role of active transport in the absorption of glucose and amino acids from the ileum?

A

• Passive transport will, at best, create equal concentration of glucose and amino acids either side of the cell surface membrane of epithelial cells. Therefore active transport helps to absorb molecules when the concentration is lower in the ileum, thus not wasting nutrients.

32
Q

Describe, in 4 stages, co-transportation of glucose.

A
  • Sodium ions are actively transported from the Epithelial cell, via the sodium-potassium pump, into the BLOOD. (requires ATP).
  • This maintains a much higher concentration of sodium ions in the lumen of the ileum than inside the epithelial cells.
  • Sodium ions diffuse (down the concentration gradient) into the epithelial cells form the ileum lumen, via a co-transport protein, carrying glucose or amino acids with them.
  • Glucose/amino acids pass into the blood by facilitated diffusion.
33
Q

Why is the co-transportation of glucose indirect active transport.

A
  • The glucose-sodium carrier protein does not require metabolic energy to move glucose against its concentration gradient, as it used the concentration gradient of sodium.
  • The concentration gradient of sodium is achieved by actively moving sodium out of the cell (which require ATP).
34
Q

What is starch converted to in the ileum lumen and using what enzyme?

A

Maltose (amylase).

Biology (18 decks)

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