cellb u10: memb structure

Question 1

What are key properties of membranes?

Answer 1

They grow with the cell, can bend without breaking, and are self-healing

Question 2

How do bacterial and eukaryotic membranes differ?

Answer 2

Bacteria: only have a plasma membrane.

Eukaryotes: have plasma + internal membranes (ER, Golgi, etc.).

Question 3

What are the three main types of lipids in membranes?

Answer 3

Phospholipids, glycolipids, and steroids (like cholesterol).

Question 4

What is the structure of a phospholipid?

Answer 4

A hydrophilic phosphate head and two hydrophobic fatty acid tails

Question 5

What are glycolipids?

Answer 5

Lipids with a sugar group instead of phosphate; found only in eukaryotes.

Question 6

How does the lipid bilayer form?

Answer 6

Lipids spontaneously arrange into a bilayer so hydrophobic tails avoid water and hydrophilic heads face it.

Question 7

What types of movement can lipids perform in the membrane?

Answer 7

Lateral movement, rotation, and rarely flip-flop between layers

Question 8

What determines membrane fluidity?

Answer 8

he length and saturation of fatty acids and the amount of cholesterol.

High temp: longer, more saturated tails prevent melting.

Low temp: shorter, more unsaturated tails prevent freezing.

Question 9

What is cholesterol’s role in membranes?

Answer 9

Fills gaps between lipids and acts as a fluidity buffer, keeping the membrane from being too rigid or too fluid.

Question 10

Where are new membrane lipids made?

Answer 10

In the endoplasmic reticulum (ER) by enzymes on the cytosolic side.

Question 11

What enzyme randomly flips new lipids in the ER to even out both sides?

What enzyme in the Golgi selectively moves specific lipids using ATP?

Answer 11

Scramblase.
flippase

Question 12

What maintains membrane asymmetry?

Answer 12

vesicle budding and fusion preserve the orientation of lipids and proteins

Question 13

On which side of the plasma membrane are glycolipids found?

Answer 13

The non-cytosolic (outer) side.

Question 14

How much of the membrane mass do proteins make up?

Answer 14

50% of plasma memb mass

Question 15

What are the main types of membrane proteins?

Answer 15

Integral (transmembrane)

Peripheral (lipid-linked or protein-attached

Question 16

What are the four ways proteins associate with membranes?

Answer 16

Transmembrane (span bilayer)

Cytosolic (anchored by an α-helix)

Lipid-linked (covalently attached to lipid)

Protein-attached (bound to other proteins

Question 17

What structures allow proteins to cross membranes?

Answer 17

α-helices: form hydrophobic spans (single or multi-pass).

β-barrels: rolled β-sheets forming pores (porins).

Question 18

What are porins and where are they found?

Answer 18

β-barrel proteins forming large water-filled pores in mitochondria and bacteria.

Question 19

How do scientists study membrane proteins?

Answer 19

Using detergents that dissolve membranes and isolate protein–detergent complexes.

Question 20

How do animal cells reinforce their membranes without a cell wall?

Answer 20

Using the cell cortex — a meshwork of proteins under the membrane (e.g., spectrin in red blood cells).

Question 21

What are tight junctions?

Answer 21

Barriers between cell regions that restrict protein movement, creating distinct membrane domains.

Question 22

What is the glycocalyx?

Answer 22

The sugar coating on the outer surface made of glycolipids, glycoproteins, and proteoglycans.

Question 23

What are the functions of the glycocalyx?

Answer 23

Protects against mechanical stress, retains water for lubrication, and helps with cell recognition.

Question 24

What are glycoproteins and proteoglycans?

Answer 24

glycoproteins: proteins with short sugar chains.

Proteoglycans: proteins with long sugar chains

Question 25

What are lectins and what do they do?

Answer 25

Membrane proteins that bind specific sugar chains on other cells; used for cell recognition and adhesion.

Question 26

Give an example of lectin function in the human body.

Answer 26

Neutrophils use lectins to recognize sugars on infected cells and move toward infection sites.

Question 27

How do carbohydrates contribute to membrane diversity?

Answer 27

They can form linear or branched chains linked in many ways, creating diverse surface patterns.