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Biological Membranes Flashcards

1
Q

What is a partially permeable membrane?

selectively permeable

A

A membrane where some substances pass freely in and out of the cell while others are controlled selectively.

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2
Q

What is compartmentalisation?

A

The formation of separate membrane-bound areas.

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3
Q

What are some of the roles of membranes? (9)

A

Isolate harmful enzymes in lysosomes.
Form vesicles to transport molecules around the cell.
Provide a large SA for enzymes to occupy.
Permit cell recognition by the immune system.
Allow cell signalling (hormones).
Form microvilli for absorption.
Help cells to attach forming tissues.
Protect cells from external environment.
Compartmentalise the cytoplasm of cells.
Allow formation of concentration gradients.

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4
Q

How is the phospholipid bilayer formed?

A

Phospholipids have polar hydrophilic heads and 2 non-polar hydrophobic tails. This causes them to form membrane structures as a bilayer with the hydrophobic tails facing inwards.

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5
Q

What is the fluid mosaic model?

A

Membranes can be described as a fluid mosaic of different molecules that perform different functions and are constantly moving.

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6
Q

What are the roles of phospholipids in the membrane?

A

Allow lipid-soluble substances to enter/leave cell.
Prevent water-soluble substances passing through.
Give the membrane fluidity.

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7
Q

What is the role of cholesterol in the membrane?

A

Reduces lateral movement of phospholipids, making the membrane less fluid at high temperatures. This helps prevent the leakage of water and dissolved ions from the cell.
(Maintains fluidity).

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8
Q

What are the roles of proteins in the membrane?

A

Provide structural support.
Intrinsic proteins can be carrier or channel proteins, transporting water-soluble substances and large molecules.
Function as enzymes.
Form ion channels.

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9
Q

What is the role of glycolipids in the membrane?

A

(Antigens)

Act as recognition sites allowing self-recognition.

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10
Q

What is the role of glycoproteins in the membrane?

A

Act as recognition sites for hormones and neurotransmitters.
Act as binding sites for drugs.
Help cells attach to one another, forming tissues.

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11
Q

How can a membrane be interrupted?

A

A solvent or heat causing the phospholipid bilayer to lose its structure.

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12
Q

How can a solvent cause interruption of a membrane?

A

Phospholipids are soluble in solvents less polar than water (organic solvents) such as alcohol or detergent. This disrupts the structure of the bilayer, affecting permeability.

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13
Q

How can temperature cause a membrane to be interrupted?

A

Molecules have greater kinetic energy, so the membrane becomes more fluid. At high temperatures, the bilayer loses its structure becoming more permeable. Also, intrinsic proteins denature, disrupting the membrane.

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14
Q

What are factors that increase the rate of diffusion through a membrane? (7)

A 
Steeper concentration gradient.
Shorter diffusion pathway.
More pores (channel/carrier proteins).
Smaller molecules diffuse faster.
Fat soluble (non-polar molecules) diffuse faster.
Higher temperatures.
Greater surface area.
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15
Q

Which molecules cannot pass through a phospholipid bilayer via diffusion?

A

Large/Hydrophillic molecules.

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16
Q

Which molecules can pass through a phospholipid bilayer via diffusion?

A

Small/Hydrophobic molecules.

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17
Q

What are the 6 different methods of membrane transport?

A 
Diffusion
Facilitated diffusion
Active transport
Endocytosis
Exocytosis
Osmosis
18
Q

Which membrane transport methods are passive?

A

Diffusion, Facilitated diffusion and osmosis.

19
Q

What is diffusion?

A

Net movement of non-polar (hydrophobic) molecules down a concentration gradient.

20
Q

What is facilitated diffusion?

A

Net movement of polar molecules/ions down a concentration gradient through channel proteins or via carrier proteins that change shape as the molecules binds.

21
Q

What is active transport?

A

Movement of molecules/ions across a membrane up a concentration gradient.

22
Q

How is the metabolic energy required for active transport produced and used?

A

ATP binds to a carrier protein.
ATP is hydrolysed to ADP + Pi this provides the energy for the carrier protein to change shape, transporting the molecule.

23
Q

What is endocytosis/exocytosis?

A

The bulk transport of materials into/out of cells.

24
Q

How does endocytosis work?

A

Cell surface membrane invaginates to accept the material, forming a vesicle inside the cell containing the material. The vesicle then pinches off from the cell surface membrane and moves into the cytoplasm.

25
Q

How does exocytosis work?

A

Fusion of a vesicle with the cell surface membrane, discharging the material.

26
Q

Why is endocytosis/exocytosis not a passive process?

A

Energy is required to transport vesicles/membrane along the cytoskeleton.

27
Q

What is the difference between pinocytosis and phagocytosis?

A

Pinocytosis is for liquid and phagocytosis is for solid.

28
Q

What is osmosis?

A

The passive, net movement of water from a region of high water potential to a region of lower water potential through a partially permeable membrane.

29
Q

What is water potential?

A

The tendency of water molecules to move from one place to another.
Water always moves from high to lower water potential.
Water potential always has a negative or zero value.

30
Q

What is hydrostatic pressure in a cell?

A

The build up of pressure due to an increase in the volume of water in a cell.

31
Q

What does it mean if a cell is in a hypertonic solution?

A

The solution has lower water potential than the cell, water leaves the cell.

32
Q

What does it mean if a cell is in a hypotonic solution?

A

The solution has higher water potential than the cell, water enters the cell.

33
Q

What does it mean if a cell is in an isotonic solution?

A

Equal water potential inside and outside cell, no net movement of water.

34
Q

What is the effect of a hypertonic solution on a plant cell?

A

Plasmolysis.
-membrane shrinks away from cell wall
(flaccid)

35
Q

What is the effect of a hypotonic solution on a plant cell?

A

Cell becomes turgid.

36
Q

What is the effect of an isotonic solution on a plant cell?

A

Incipient plasmolysis.

37
Q

What is the effect of a hypertonic solution on an erythrocyte?

A

RBC becomes crenated.

Haemoglobin more concentrated, so cell appears darker.

38
Q

What is the effect of a hypotonic solution on an erythrocyte.

A

Cytolysis (cell bursts).

39
Q

What is water potential measured in?

A

Pascals

as type of pressure

40
Q

What is an example of where exocytosis is used in the body?

A

The release of neurotransmitters/hormones.

41
Q

What is an example of where endocytosis is used in the body?

A

Phagocyte engulfing a pathogen.

bio (33 decks)

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