(Dr. McLachlin) (Unit B) Topic Note 6

Question 1

What are the main functions of biological membranes?

Answer 1

1. Separate contents of a cell or organelle from the surrounding environment
2. Control import and export of molecules into and out of the cell or organelle, using proteins that span the membrane
3. Contain sensors or receptors that allow the cell to respond to external stimuli including communications from other cells
4. They are involved in cell movement

Question 2

What are lipids?

Answer 2

Biological molecules that have little or no solubility in water
* Soluble in organic solvents

Question 3

Functions of lipids

Answer 3

• Structural components
• Energy storage molecules
• Enzyme cofactors
• Signalling molecules
• Pigments

Question 4

Fatty acids

Answer 4

Hydrocarbon chains ending in a carboxylic acid group

Question 5

What are general characteristics of fatty acid groups?

Answer 5

• Contain even number of carbon atoms
• Length from 4-24 carbons

Question 6

What are saturated and unsaturated fatty acids?

Answer 6

• Saturated: No double bonds
• Monounsaturated: 1 double bond
• Polyunsaturated: More than 1 double bond

Question 7

What conformation are double bonds in fatty acid chains?

Answer 7

Always cis

Question 8

How are carbon atoms counted in a fatty acid chain?

Answer 8

• Chemists count from carboxyl end
• Nutrition literature counts from methyl end

Question 9

What would an omega-6 fatty acid be like?

Answer 9

Double bond 6 carbons from the omega carbon (including the omega carbon)

Question 10

What is the end terminal carbon known as? (Nutrition Literature)

Answer 10

Omega Carbon

Question 11

Glycerol

Answer 11

3-carbon molecule with hydroxyl groups at each carbon

Question 12

Triacylglycerols

Answer 12

Also known as triglycerides

Fatty acid chain attached to each hydroxyl of glycerol via an ester linkage

Question 13

Do triacylgycerols contain different or same fatty acids?

Answer 13

Usually contain two or there different types of fatty acids

Question 14

What are triacylglycerols used for?

Answer 14

Store fatty acids as energy reservoirs in adipocytes (fat cells)

Question 15

Glycerophospholipids

Answer 15

Similar to triacylglycerols
* Fatty acid on one end of glycerol is replaced with a charged phosphate group

Question 16

What usually happens to the charged phosphate group in glycerophospholipids?

Answer 16

Often conjugated to a polar alcohol like:
* Serine (makes phophatidylserine)
* Choline (makes phosphatidylcholine)

Question 17

Sphingolipids

Answer 17

Based on molecule sphingosine
* Long hydrocarbon chain
* Second chain added by joining a fatty acid to sphingosine’s amin group to form a ceramide

Question 18

What are modified ceramides called?

Answer 18

Sphingomyelins
* Modify the terminal hydroxyl group
* With phosphoethanolamine or phosphocholine

Question 19

Where are sphingomyelins found?

Answer 19

Myelin sheath of nerve cells

Question 20

Besides sphingomyelins, how else can ceramide be modified?

Answer 20

With one or more monosaccharide groups to make glycosphingolipids

Question 21

Steroids

Answer 21

Based on a system of four fused rings
* Three with six carbons
* One with five carbons

Question 22

Sterols

Answer 22

Steroids with a hydroxyl group at C3

Question 23

Which lipids are amphipathic?

Answer 23

• Fatty acids
• Glycerophospholipids
• Sphingolipids

Question 24

Amphipathic

Answer 24

One part of the molecule is hydrophobic and the other is hydrophilic

Question 25

Micelle

Answer 25

Formed when hydrophilic groups have a larger diameter than the hydrophobic groups * Lipid is triangular or wedge-shaped * Water is excluded from the centre

Question 26

Are micelles found in living systems?

Answer 26

Not common, often seen in soaps and detergents

Question 27

Lipid bilayer

Answer 27

Formed when hydrophilic and hydrophobic groups of amphipathic lipids have approximately equal diameters * Hydrophilic heads form two surfaces that contact water and protect the hydrophobic groups

Question 28

Are lipid bilayers flexible?

Answer 28

Yes

Question 29

Why are lipid bilayers flexible?

Answer 29

Prevents their hydrophobic edges from making contact with water by spontaneously closing to form spherical vesciles or liposomes that enclose an aqueous interior

Question 30

What does it mean the lipid bilayers are "fluid"?

Answer 30

Individual lipid molecules can move and diffuse within the plane of the bilayer

Question 31

What factors determine the fluidity of a lipid bilayer?

Answer 31

1. Temperature 2. Proportion of unsaturate fatty acyl chains whithin the phospholipids and glycolipids 3. Length of fatty acyl chains present in the phospholipids anf glycolipids 4. Amount of cholesterol in the bilayer

Question 32

How does temperature affect fluidity of lipid bilayer?

Answer 32

Fluidity increases at high temperatures Decreases as temperatures decrease

Question 33

What happens to the lipid bilayer when the temperature gets below a certain phase transition temperature?

Answer 33

Lipid bilayer will exist in a gel state * Lipid movement is reduced

Question 34

How does unsaturated fatty acyl chains affect bilayer fluidity?

Answer 34

Cis double bonds impede tight packing, increasing fluidity

Question 35

Are shorter or longer chains more mobile and flexible?

Answer 35

Shorter chains

Question 36

How does cholesterol affect the lipid bilayer fluidity?

Answer 36

* Reduces fluidity at higher temperatures * Increases fluidity at lower temperatures

Question 37

Are biological lipid bilayers symmetrical?

Answer 37

No

Question 38

What is the fluid mosaic model?

Answer 38

Describes that proteins are free to diffuse laterally wthin the bilayer, unless their movement is restricted by cellular components

Question 39

Integral membrane proteins

Answer 39

Portion of the polypeptide chain contacts the hydrophobic interior of the membrane

Question 40

Transmembrane proteins

Answer 40

Integral membrane proteins that completely crosses the membrane at least once

Question 41

What secondary structure are transmembrane sections of proteins usually? Why?

Answer 41

Alpha helices * Maximize hydrogen bonding

Question 42

How do beta-sheets form transmembrane sections?

Answer 42

Form barrels

Question 43

Peripheral membrane proteins

Answer 43

Not anchored to the lipid bilayer, associated with integral membrane proteins or with the hydrophilic head groups of membrane lipids

Question 44

Lipid-linked proteins

Answer 44

One or more lipid molecules are covalently attached to the end of the protein or to particular side chains, usually cysteine

Question 45

Where are lipids in a lipid-linked protein usually located?

Answer 45

Lipids are embedded in the membrane

Question 46

What proteins cannot be removed from the membrane without disrupting the lipid bilayer?

Answer 46

* Integral membrane proteins * Lipid-linked proteins

Question 47

The use of detergents in purification may alter what protein structures?

Answer 47

Secondary, Tertiary, and Quaternary structure of proteins

Question 48

What are membrane proteins often modified by?

Answer 48

Carbohydrates * On asparagine, serine, or threonine side chains * These proteins are called glycoproteins

Question 49

Where do sugars never attach on proteins?

Answer 49

Cytosolic surface

Question 50

What are the 4 main functions of membrane proteins?

Answer 50

1. Transporters and channels 2. Receptors 3. Enzymes 4. Anchors

Question 51

What process do transport proteins and channels do?

Answer 51

Facilitated transport

Question 52

Transporters vs Channels

Answer 52

Transporters undergo conformation changes to move ions or molecules across the membrane Channels (when open) form continuous pores through the bilayer

Question 53

Uniporters vs. Symporters vs. Antiporters

Answer 53

* **Uniporters**: Transporters that move a **single** species across the membrane * **Symporters**: Transport **two** species across the membrane in the **same** direction * **Antiporters**: Transport **two** species across the membrane in **opposite** directions

Question 54

What forms across the membrane when the concentration of a given ion/molecule is larger on one side of the membrane than the other?

Answer 54

Electrochemical gradient

Question 55

Passive transport

Answer 55

Pathway is provided via a transporter or channel, ions and molecules will spontaneously move across the membrane down their electrochemical gradient

Question 56

Active transport

Answer 56

A source of energy is used to move ions of small molecules across the membrane

Question 57

Receptor proteins

Answer 57

Sense chemical signals on the outside of the cell and carry the message to the inside of the cell, so the cell can react to its environment

Question 58

Enzyme proteins

Answer 58

Catalyze chemical reactions; can be associated with membranes

Question 59

Anchor proteins

Answer 59

Structural proteins that provide stability to the membrane and help control the shape of the cell and its position relative to other cells * Binds to other macromolecules on one or both sides of the membrane

Question 60

Give examples: 1. Transporters/Channels 2. Receptors 3. Enzymes 4. Anchors

Answer 60

1. Potassium channels 2. Insulin receptors 3. Insulin receptors (adds phosphates) 4. Integrins