Plasma Membranes Flashcards Preview

OCR Biology AS H020 > Plasma Membranes > Flashcards

Flashcards in Plasma Membranes Deck (59):
1

Define compartmentalisation...

The formation of separate membrane bound areas in a cell.

2

What is the importance of compartmentalisation?

Metabolism includes different and incompatible reactions hence different conditions for different reactions can be maintained eg. chemical gradients.

3

The cell surface membrane is also know as...

The plasma membrane.

4

What are membranes formed from?

A phospholipid bilayer.

5

Describe the structure of a phospholipid bilayer...

The hydrophilic phosphate heads form the inner and outer surfaces sandwiching the hydrophobic fatty acid tails which comprise the core.

6

The inside of cells and organelles are usually aq environments, why does this make phospholipid bilayer said perfectly suited as membranes?

The outer surfaces of the hydrophilic phosphate heads can interact with water.

7

Who proposed the fluid mosaic model?

Singer and Nicholson 1972

8

What are the two types of membrane proteins?

Intrinsic and extrinsic proteins.

9

What is the fluid mosaic model?

Proteins occupy various positions within a membrane, phospholipids are free to move in the layer relative to one another.

10

Name the different types of intrinsic proteins...

Carrier proteins, channel proteins, glycoproteins and glycolipids.

11

What is an alternative name for intrinsic proteins?

Integral proteins.

12

What is an intrinsic protein?

A transmembrane protein that is embedded through both layers of the phospholipid bilayer.

13

What keeps intrinsic proteins in place?

Hydrophobic outer R groups which interact with the tails.

14

What is a channel protein?

A hydrophilic channel allowing the passive movement of polar molecules/ions down a concentration gradient.

15

Which particles travel through channel proteins?

Polar molecules and ions.

16

Which process occurs through channel proteins?

Passive diffusion down a concentration gradient.

17

What is a carrier protein?

A protein that allows the passive movement of molecules AND active transport which involves the protein changing shape.

18

What is attached to a glycoprotein?

A carbohydrate (sugar) chain.

19

What are the 2 roles of glycoproteins?

Cell adhesion and as receptors for chemical signals (cell signalling).

20

What is cell signalling?

When a chemical binds to a receptor (glycoprotein) a response is elicited from the cell, either direct or a cascade of events.

21

What is an example of cell signalling?

Receptors for peptide hormones (insulin and glucagon) which effect the uptake and storage of glucose.

22

What are glycolipids?

Lipids with attached carbohydrate chains.

23

What is the function of a glycolipid?

Cell markers/antigens recognised by the immune system as self or non-self.

24

What is an extrinsic protein?

A protein present in one side of the bilayer.

25

How do extrinsic proteins stay in place?

Hydrophobic R groups interact with the polar heads of phospholipids of with intrinsic proteins.

26

What is cholesterol?

A lipid/sterol with a hydrophobic end and a hydrophilic end.

27

What is the function of cholesterol in a membrane?

It regulates the fluidity of membranes by preventing phospholipids packing too closely, adding stability to the membrane.

28

How does temperate affect the membrane structure?

An increase in temperature means the phospholipids will have more kinetic energy and move around more making the membrane more fluid so it looses it's structure increasing the permeability of the membrane, proteins will denature causing the permeability to further increase.

29

How do solvents affect the permeability of a membrane?

Organic solvents (alcohols and benzene) that are less polar than water will dissolve membranes as they disrupt the membrane/phospholipid structure increasing the fluidity and permeability.

30

Define diffusion...

The net movement of particles from a region of high concentration to low concentration down a concentration gradient, it is a passive process.

31

What effect he the rate of diffusion?

Temperature, concentration difference, surface area and diffusion distance/membrane thickness.

32

Why are membranes described as partially permeable?

Non polar molecules can pass through but charged molecules cannot. Small polar molecules can but at a slow rate eg. H2O. Channel/carrier proteins are usually specific to one molecule.

33

What is simple diffusion?

Diffusion in the absence of a barrier.

34

What is facilitated diffusion?

The diffusion of ions/polar molecules through channel proteins. It is a passive process.

35

Name an additional factor affecting the rate of facilitated diffusion...

The number of proteins present.

36

What is active transport?

The movement of particles from an area of low concentration to high concentration against a concentration gradient requiring energy and carrier proteins. Metabolic energy is supplied by ATP.

37

Describe the process of active transport...

The transport molecule binds to receptors in the carrier protein. ATP binds to the carrier protein and is hydrolysed to ADP and a phosphate group. The carrier protein changes shape opening up the inside of the cell. The molecule is released. The phosphate is released and recombines with ADP to form ATP. The carrier protein returns to its original shape.

38

What is bulk transport?

Active transport for large molecules.

39

What is the name for bulk transport into cells?

Endocytosis

40

What is the name for bulk transport out of cells?

Exocytosis

41

What is bulk transport for solids?

Phagocytosis

42

What is bulk transport for liquids?

Pinocytosis.

43

What does invaginate mean?

Bending inwards.

44

Describe the process of bulk transport...

The cell surface membrane invaginates when it comes into contact with the material. The membrane enfolds the material forming a vesicles. The vesicle pinches off and enters the cytoplasm.

45

What is osmosis?

The passive diffusion of water across a partially permeable membrane.

46

What is a solute?

A substance dissolved in a solvent.

47

Define water potential...

The pressure exerted by water molecules as they collide with a membrane, it is measured in pascals.

48

What is the water potential of pure water at RTP?

0

49

Water potential is always...

Negative

50

The diffusion of water into a solution leads to an increase in volume, in a closed system this is known as...

Hydrostatic pressure.

51

What is a solution with equal water potential called?

Isotonic

52

What is a solution with a high water potential called?

Hypotonic.

53

What is a solution with a low water potential called?

Hypertonic.

54

In animal cells in an external hypotonic solution what happens?

Water moves in increasing the hydrostatic pressure leading to the cell swelling and bursting, called cytolysis.

55

In animal cells in an external hypertonic solution what happens?

Water leaves the cell shrinking it leading to crenation.

56

In plant cells in an external hypotonic solution what happens?

Water enters the cell, it sells and becomes turgid, creating turgor against the cell wall (hydrostatic pressure).

57

What does turgor prevent?

Further entry of water.

58

In plants cells in an external hypertonic solution what happens?

Water leaves the cell so the cell shrinks, the cell membrane is pulled away from the cell wall called plasmolysis.

59

What do membranes separate?

The contents of cells from their environment and organelles rom each other and the cytosol.