Lecture 5: Cell Membranes

Question 1

Lipids are the one class of biomolecules that do not form ________.

Answer 1

Polymers

Question 2

The unifying feature of lipids is that they have ___________________________ (_________), this is because they consist mostly of _______ which are ________.

Answer 2

Little or no affinity for water (hydrophobic); hydrocarbons; nonpolar

Question 3

What are 4 functions of lipids?

Answer 3

1. Long-term energy stores (very rich)
2. Provide insulation from the environment for plants and animals
3. Serve as building blocks for some hormones
4. Important component of cellular membranes

Question 4

What are the biologically important classes of lipids?

Answer 4

1. Fats
2. Waxes
3. Steroids
4. Phospholipids

Question 5

Fats (also known as ______ or ______) are constructed from ______ and _______________.

Answer 5

Triacylglycerol; triglyceride; glycerol; 3 fatty acids

Question 6

_______ is a 3-carbon alcohol with a hydroxyl attached to each carbon

Answer 6

Glycerol

Question 7

What is glycerol?

Answer 7

A 3-carbon alcohol with a hydroxyl attached to each carbon

Question 8

________ consist of a carboxyl group linked to a long hydrocarbon chain.

Answer 8

Fatty acids

Question 9

What is a fatty acid?

Answer 9

A carboxyl group linked to a long hydrocarbon chain.

Question 10

Fatty acids vary in:

Answer 10

Length
Number of double bonds
Location of double bonds

Question 11

_______ do not have double bonds, and is solid at room temp.

Answer 11

Saturated fatty acids

Question 12

______ have one or more double bonds, and may be liquid at room temp.

Answer 12

Unsaturated fatty acids

Question 13

What is an unsaturated fatty acid?

Answer 13

have one or more double bonds, and may be liquid at room temp.

Question 14

What is a saturated fatty acid?

Answer 14

do not have double bonds, and is solid at room temp.

Question 15

What is a wax?

Answer 15

Waxes are long fatty acid chains esterified to long chain alcohols. They are hydrophobic and prevent water from sticking to its surface.

Question 16

Where can waxes be found?

Answer 16

On feathers of some aquatic birds and on the surface of leaves from certain plants.

Question 17

What type of lipids are found on some aquatic birds and on the surface of leaves from certain plants?

Answer 17

Waxes

Question 18

______ are long fatty acid chains esterified to long chain alcohols. They are ________ and prevent water from sticking to its surface.

Answer 18

Waxes; hydrophobic

Question 19

What are steroids?

Answer 19

Steroids are lipids with a carbon skeleton consisting of four fused rings.

Question 20

______ are lipids with a carbon skeleton consisting of four fused rings.

Answer 20

Steroids

Question 21

What is cholesterol?

Answer 21

A component in animal cell membranes and a precursor for many types of steroid hormones.

Question 22

_______ a component in animal cell membranes and a precursor for many types of steroid hormones.

Answer 22

Cholesterol

Question 23

A ________ (also known as _______) has 2 fatty acids and a phosphate group are attached to glycerol. The 2 fatty acid tails are hydrophobic. The phosphate head group is hydrophilic. The phosphate may be modified by the addition of charged or polar chemical groups.

Answer 23

Phospholipid; diacylglycerol

Question 24

Regions of the plasma membrane called “lipid” rafts have high concentrations of cholesterol and sphingomyelin. Consequently, the proteins in lipid rafts:
A. Diffuse more freely
B. Tend to stay clustered together
C. Are able to flip across the lipid balayer from inside to outside and vice versa
D. Cannot function as receptors

Answer 24

B

Question 25

A phospholipid (also known as diacylglycerol) has _________ and _______ are attached to _____. The 2 ______ tails are _______. The _________ head group is ________ which may be modified by the addition of _______ groups.

Answer 25

2 fatty acids; a phosphate group; glycerol; fatty acid; hydrophobic; phosphate; hydrophilic; charged or polar chemical

Question 26

Phospholipids are major constituents of the plasma membrane because when added to water, they __________________, due to ________. Phospholipids contribute to the _____ nature of the plasma membrane.

Answer 26

Spontaneously self-assemble into a bilayer; their structure (hydrophilic face fluid environments/ hydrophobic face billard centre region); dynamic

Question 27

Does the relative proportion of membrane components remain the same from cell to cell?

Answer 27

No

Question 28

Which of the following explains what is happening when sodium chloride dissolves in water? A. More hydrogen bonds are forming between water molecules. B. Na & Cl atoms are separating from one another C. Hydration shells are forming around the Na and Cl ions D. Covalent bonds are breaking and reforming

Answer 28

C

Question 29

Ceviche is prepared by marinating fresh raw fish in citrus juice for several hours, until the flesh becomes opaque and firm, as if cooked. How does citrus juice render the seafood safe to eat? A. Acidic pH denatures (unfolds and inactivates) proteins by disrupting their hydrogen bonds B. Acidic pH denatures proteins by disrupting their ionic bonds C. Acidic pH contains enzymes that hydrolyse peptide bonds to break apart proteins D. Acidic pH dissolves cell membranes by disrupting hydrophobic interactions

Answer 29

A

Question 30

Will membranes be more fluid at high temperatures with or without cholesterol?

Answer 30

Without

Question 31

The plasma membrane of human red blood cells is __% lipid. The mitochondrial inner membrane contains __% protein and __% lipid. Myelin contains __% protein and __% lipid.

Answer 31

30 76; 24 28; 76

Question 32

The plasma membrane of _______ is 30% lipid. The _________ contains 76% protein and 24% lipid. ______ contains 18% protein and 76% lipid.

Answer 32

human red blood cells; mitochondrial inner membrane; Myelin

Question 33

What is a myelin?

Answer 33

An outgrowth of specialized cells’ membrane that insulates neuronal axons.

Question 34

_______ is an outgrowth of specialized cells’ membrane that insulates neuronal axons.

Answer 34

Myelin

Question 35

Are plasma membranes static? ___, since _____&_____ in the plasma membrane can move within the _______. Most move _______, rarely do they _______.

Answer 35

No; phospholipids; proteins; bilayer; laterally; switch bilayers

Question 36

Which membrane will be more fluid at room temperature? The one with: A. 20% saturated and 80% unsaturated fatty acids 342 B. 80% saturated and 20% unsaturated fatty acids 18 C. 50% saturated and 50% unsaturated fatty acids

Answer 36

A

Question 37

The temperature at which a membrane solidifies depends on its ____________.

Answer 37

lipid composition

Question 38

Why are unsaturated hydrocarbon tails more fluid than saturated hydrocarbons?

Answer 38

Because unsaturated hydrocarbon tails have double bonds that cause them to have a bend in their tail which prevents tight packing of hydrocarbons allowing more space thus causing them to be more fluid. Whilst saturated hydrocarbons are single bonded tails that are straight and can thus pack closely together, creating a more timely packed structure limiting fluidity.

Question 39

Describe the effects of the steroid lipid cholesterol on membrane fluidity at different temps.

Answer 39

At warm temp: cholesterol restrains movement of phospholipids = membrane is less fluid At cold temps: cholesterol prevents tight packing = membrane maintains fluidity

Question 40

Variations in the lipid composition of cell membranes of many species are likely due to ____.

Answer 40

adaptations to specific environmental conditions

Question 41

The ability of ____ has evolved by organism that live in temperature that vary from season to season.

Answer 41

To change membrane lipid composition

Question 42

Plasma membranes are ____, the inner surface ____ the outer surface.

Answer 42

Asymmetrical; differs from

Question 43

What are some organelles that are found on the inner surface or the outer surface of the plasma membrane?

Answer 43

OUTER: exterior proteins, glycoproteins, glycolipids, INNER: interior proteins

Question 44

When is the asymmetrical distribution of plasma membrane components determined?

Answer 44

When the membrane is synthesized and is assembled by the ER and Golgi

Question 45

An oligosaccharide covalently linked to a lipid in the lumen of the rough ER may end up on the

Answer 45

Extracellular face of the plasma membrane

Question 46

What is the difference in phospholipid composition in the outer vs inner plasma membrane?

Answer 46

Outer: has more phosphatidylcholine and sphingomyelin Inner: has more phosphatidylethanolamine, phosphatidylserine, and inositol