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Biological membranes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is the function of cell membranes?

A

They control what enters/exits the cell and act as barriers.
Partially permeable.

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2
Q

What is the cell membrane made up of?

A

Phospholipid bilayer - barrier and keeps the membrane fluid but stable.

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3
Q

What is the fluid mosaic model?

A

Constituent compounds can move - fluidity
Components differ in size and shape.

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4
Q

What are different types of membrane proteins?

A

Intrinsic - embedded in membrane. Hydrophobic. Some can span both layers of the membrane = transmembrane proteins.

Extrinsic - only on 1 side sand not embedded in membrane. Loosely held in place by electrostatic forces.

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5
Q

Why is it important that cell membranes are permeable?

A

Some very small molecules diffuses through
Some dissolve in the lipid layer
Channel/carrier proteins allow specific molecules/ions through
Uptake and secretion of bigger molecules

Regulates transport of substances in/out cell.

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6
Q

What are the roles of membrane proteins?

A

Channel proteins have pores forming hydrophilic channels.
Carrier proteins transport specific molecules across by changing shape.

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7
Q

What are functions of intrinsic and extrinsic proteins?

A
  • Receptors for drugs and hormones
  • Recognition sites for the immune system
  • Cells can adhere to form tissues
  • Structural support for the membrane
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8
Q

What are glycoproteins?

A

Proteins with a carbohydrate chain attached.

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9
Q

What are glyoclipids?

A

Lipids with a carbohydrate chain attached.

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10
Q

What are the main roles of glycoproteins and glycolipids?

A
  • Recognition sites for the immune system
  • Cells can adhere to form tissues
  • Stability for membrane
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11
Q

What is cholesterol?

A

A lipid molecule with a hydrophilic and phobic end.

It regulates membrane fluidity by staying between phospholipid molecules and stopping the membrane becoming too stiff by spreading out phospholipids.
Stops it becoming too fluid by interacting with the fatty acid tails.

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12
Q

What happens when a membrane becomes too fluid?

A

Water and small, soluble molecules can easily pass through. It can break apart.

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13
Q

How do cell membranes act as barriers?

A

The cell surface membrane separates the cell from the environment to maintain conditions inside and outside.

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14
Q

Why is compartmentalisation important for cells?

A

Protection - eg. nucleus envelope protects DNA from chemical reactions in the cytoplasm.
Different conditions for different metabolic reactions.

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15
Q

How do cell membranes act as sites of chemical reactions?

A

They contain proteins that are involved eg. respiration needs electron carriers and ATP synthase. Epithelial cells in the small intestine contain digestive enzymes.

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16
Q

How are cell membranes involved in cell signalling?

A

Secretion of hormones and other signalling chemicals. Also contain cell receptors that hormones etc. can bind to.

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17
Q

How does temperature affect cell membranes?

A

At low temps, the phospholipids are compressed - membrane can stiffen or fracture.
At high temps, the phospholipids gain kinetic energy and move further away.
Disordered membrane and proteins can move position so they do not function correctly.

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18
Q

How can the effect of low temperatures be reduced?

A

Compression can be reduced by the proportion of unsaturated and saturated phospholipid tails = fatty acids. Unsaturated tails have kinks - push apart.

Also by cholesterol as it spaces phospholipids further apart.

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19
Q

How can the effect of high temperatures be reduced?

A

Cholesterol, as it pulls the phospholipids closer by interacting with their tails.

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20
Q

How is the structure of the bilayer maintained?

A

Behaviour of phospholipids in water (polar solvent).

Organic solvents disrupt the bilayer and dissolved the membrane. At low concentrations, the membrane is more permeable.
At high concentrations, cells are destroyed.

21
Q

What is simple diffusion?

A

The net movement of particles from an area of high concentration to an area of lower concentration.

22
Q

What drives simple diffusion?

A

Kinetic energy that all molecules have.

23
Q

How does simple diffusion occur across cell membranes?

A

Only specific molecules can do this - small and non polar. Lipid soluble molecules can also diffuse across even though they are bigger.

24
Q

What is facilitated diffusion?

A

The net movement of particles down their concentration gradient across a partially permeable membrane via carrier/channel proteins.

25
Q

Why is facilitated diffusion needed?

A

To transport big and polar or shared molecules across the membrane. It is a passive process.

26
Q

How do channel proteins work?

A

They can open/close if a specific ion is present.
Cells with a lot of water have aquaporins.

27
Q

What are examples of channel proteins?

A
  • Epithelial cells in airways have Cl- channels to regulate mucus composition
  • Synapses have calcium/chloride ion channels
28
Q

How do carrier proteins work?

A

The molecule binds with the protein and it changes shape to transport it to the inside of the cell. The molecule detaches and the protein returns to its original shape.

29
Q

Why are cell membranes selectively permeable?

A

Channel and carrier proteins are specific to 1 molecule. Can control what enters/exits the cell.

30
Q

What is the effect of temperature on diffusion distance?

A

Diffusion is due to random particle movement, so when temperature increases, kinetic energy increases - move faster.
Rate increases.

31
Q

What is the effect of concentration gradient on diffusion?

A

The steeper the gradient, the greater the difference in concentration. Bigger net movement in a time = faster rate.
If gradients not maintained, equilibrium is reached and diffusion stops.

32
Q

What is the effect of distance on diffusion?

A

If must move a longer distance, slower rate.
Thin specialised exchange surfaces increase the diffusion rate.
eg. alveoli in lungs have squamous cells.

33
Q

What is the effect of surface area on diffusion?

A

As it increases, rate increases as more particles can diffuse across the membrane.
Specialised exchange surfaces normally have cells with large SA.
eg. microvilli in small intestine.

34
Q

What is the effect of the number of transport proteins on facilitated diffusion?

A

Rate increases if there are more transport proteins as more particles can cross the membrane faster.

35
Q

What is the effect of the size of diffusing molecules?

A

Smaller molecules/ions diffuse faster.

36
Q

What is water potential?

A

A measure of the tendency of water molecules to move from one area to another. It describes the pressure created by water molecules. The more dilute a solution, the higher the water potential.

37
Q

Are water potential values negative or positive?

A

Negative - pure water is 0 kPa.

38
Q

What is osmosis?

A

The net movement of water from an area of higher water potential to an are of lower water potential across a partially permeable membrane.

39
Q

When does osmosis occur?

A

When a water potential gradient is present. Areas with a higher water potential have more water molecules free to move.

40
Q

What is the effect of osmosis on animal cells?

A

If water leaves, it becomes shrivelled.
If water enters, cell swells and can burst (cytolysis).

41
Q

What is the effect of osmosis on plant cells?

A

If water leaves the cell, the cytoplasm volume decreases and the cell membrane and wall separate. Cell shrinks and is plasmolysed and flaccid.
If water enters the cell, the cell volume increases and the membrane pushes against the wall. It is turgid.

42
Q

What is active transport?

A

The movement of particles from an area of low concentration to an area of high concentration across a cell membrane, using ATP and carrier proteins.

43
Q

How does active transport work?

A

The molecule binds to a specific site in the carrier protein. Inside the cell, ATP also binds.
ATP is hydrolysed to ADP and P - the protein changes shape.
The carrier protein releases the molecule inside the cell.
Phosphate ion is released, so the protein returns to its original shape.

44
Q

What is bulk transport?

A

Some substances entering/exiting the cell are too big for the membrane, so must use a process needing ATP.

45
Q

What are the 2 types of bulk transport?

A

Endocytosis - large molecules into a cell.
Exocytosis - large molecules out of a cell.

46
Q

What is ATP used for in bulk transport?

A
  • The fusion of cell membranes to create/destroy vesicles
  • Movement of vesicles using motor proteins along the cytoskeleton.
47
Q

What is endocytosis?

A

Phagocytosis - bulk transport of solid material into a cell.
Pinocytosis - bulk transport of liquids into a cell.

Invagination of the cell membrane around the material, which fuses, enclosing it in a vesicle. The vesicle pinches off the membrane towards the cell interior.

48
Q

How does exocytosis work?

A

When a secretory vesicle moves towards the cell membrane. The vesicle fuses with the membrane, releasing the material to the outside of the cell.

Biology (32 decks)

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