5.1 Structure of Cell Membranes Flashcards Preview

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Flashcards in 5.1 Structure of Cell Membranes Deck (43)
1

Not only do membranes physically separate cells from their external environment, they also:

define spaces within many cells that allow them to carry out their diverse functions

2

what are the main component of cell membranes?

lipids because they have properties that allow them to form a barrier in an aqueous environment
also has proteins and carbohydrates embedded or associated

3

what is the major type of lipid found in cell membranes?

phospholipids (made up of a glycerol backbone attached to a phosphate-hydrophilic group and two fatty acids-hydrophobic)

4

amphipathic

having both hydrophilic and hydrophobic regions

5

how do amphipathic molecules arrange themselves in aqueous environment? (in water)

they arrange themselves so hydrophilic side faces outwards to interact with water and non polar groups face away from water

6

polar molecules like water tend to....

exclude nonpolar molecules or nonpolar groups of molecules (useful for healing cell membranes)

7

what is the shape of the structure determined by?

the bulkiness of the head group relative to the hydrophobic tails

8

micelle

a spherical structure in which lipids with bulky heads and a single hydrophobic tail are packed

9

bilayer (formed by lipids with less bulky head gouts and two hydrophobic tails)

a two-layered structure of the cell membrane with hydrophilic "heads" pointing outward toward the aqueous environment and hydrophobic "tails" oriented inward, away from water

10

the bilayer structure forms spontaneously and without the action of an enzyme as long as:

the concentration of free phospholipids is high enough and the pH of the solution is similar to that of a cell

11

the pH of the environment is important for cell membranes/phospholipids because :

it ensure that the head groups are in their ionized (charged) form and thus hydrophilic

12

liposome

an enclosed spherical bilayer structure spontaneously formed by phospholipids in environments with neutral pH, like water

13

lipids freely associate with one another because of:

extensive van der Waals forces between their fatty acid tails (very weak forces, can easily be broken and re-formed)

14

fluid

describes lipids that are able to move in the plane of the cell membrane

15

the degree of membrane fluidity depends on:

which types of lipid make up the membrane

16

in a single layer of the lipid bilayer, the strength of van der Waals interactions between the lipids' tails depends on:

the length of the fatty acid tails and the presence of double bonds between neighbouring carbon atoms

17

the longer the fatty acid tails, the more surface is available for van der Waals interactions resulting in:

tighter packing and reduced mobility

18

saturated fatty acid tails have no double bonds which has what result on mobility?

reduced mobility because of tighter packing

19

unsaturated fatty acid tails have double bonds and kinks resulting in:

enhanced lipid mobility due to reduced tightness of packing

20

cholesterol

an amphipathic lipid that is a major component of animal cell membranes

21

the amphipathic structure of cholesterol allows it to:

pack tightly with phospholipids: hydrophilic hydroxyl group interacts with polar head of phospholipids, ring structure participates in van der Waals interactions with the fatty acid chains

22

cholesterol increases or decreases membrane fluidity depending on:

temperature

23

at temperatures typically found in a cell, cholesterol:

decreases membrane fluidity because of interactions between rings of cholesterol and phospholipid fatty acid tail (van der Waals forces)

24

at low temperatures, cholesterol:

increases membrane fluidity because it prevents phospholipids from packing tightly with other phospholipids

25

cholesterol helps maintain a consistent state of membrane fluidity by:

preventing dramatic transitions from a fluid to solid state.

26

lipid raft

lipids assembled in a defined patch of the cell membrane

27

membranes are not always a uniform fluid bilayer, but instead can contain regions with:

discrete components

28

what is a lipid flip-flop?

the spontaneous transfer of a lipid between layers of the bilayer (VERY RARE)

29

there is little exchange of components between the two layers of the membrane which results in:

the two layers to differ in composition; different types of lipids are present primarily in one layer or the other

30

transporters

Membrane proteins that move ions or other molecules across the cell membrane.

31

receptor

A molecule on cell membranes that detects critical features of the environment. Receptors detecting signals that easily cross the cell membrane are sometimes found in the cytoplasm.

32

enzyme

A protein that functions as a catalyst to accelerate the rate of a chemical reaction; enzymes are critical in determining which chemical reactions take place in a cell.

33

anchor

A membrane protein that attaches to other proteins and helps to maintain cell structure and shape.

34

membrane proteins can be classified into two groups depending on:

how they associate with the membrane

35

what are the two groups of proteins?

integral membrane proteins and peripheral membrane proteins

36

integral membrane protein

A protein that is permanently associated with the cell membrane and cannot be separated from the membrane experimentally without destroying the membrane itself.

37

peripheral membrane protein

A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions. easily separated from the lipid membrane

38

transmembrane proteins

Proteins that span the entire lipid bilayer; most integral membrane proteins are transmembrane proteins

39

transmembrane proteins are composed of three regions:

two hydrophilic regions, one protruding from each face of the membrane, and a connecting hydrophobic region that spans the membrane.

40

structure of transmembrane proteins allows for:

separate functions and capabilities of each end of the protein

41

Peripheral membrane proteins may be associated with either the internal or external side of the membrane, they interact with either:

the polar heads of lipids or with integral membrane proteins by weak noncovalent interactions such as hydrogen bonds.

42

how can one prove protein mobility experimentally

fluorescence recovery after photobleaching, or FRAP

43

fluid mosaic model

A model that proposes that the lipid bilayer is a fluid structure that allows molecules to move laterally within the membrane and is a mosaic of two types of molecules, lipids and proteins.