Lecture 5 - Membrane structure, function, composition (proteins)

Question 1

what kind of errors can happen during protein synthesis?

Answer 1

misfolding, damage, short-lived proteins

Question 2

what is a protease

Answer 2

an enzyme that breaks down protein by hydrolyzing their peptide bonds

Question 3

What proteins need for proteasome to degrade them?

Answer 3

Ubiquitin chain

Question 4

what is proteasome?

Answer 4

cylinder protein machine that degrades other proteins in the eukaryotic cell located in the nucleus and cytosol

Question 5

The concentration of a protein in a cell depends on the rates at which the mRNA and protein are _______ and _____.

Answer 5

synthesized and degraded

Question 6

Protein degradation in the cytosol and nucleus occurs inside large protein complexes called ______.

Answer 6

proteasome

Question 7

Proteins that enter to proteasome have been marked by ______, a small protein
tag, which is ______ bond

Answer 7

ubiquitin and covalently bonded

Question 8

what is Proteolysis

Answer 8

the breakdown of proteins by proteasomes

Question 9

how do you see specific protein?

Answer 9

western blot and you have to know the protein you are looking for

Question 10

most abundant lipid in cell membrane

Answer 10

phospholipids, which has hydrophilic head and hydrophobic tail

Question 11

what is amphipathic?

Answer 11

having both hydrophobic and hydrophilic regions in a molecule

Question 12

what other lipids are amphipathic?

Answer 12

sterol and glycolipid

Question 13

hydrophobic molecules tend to do what in water?

Answer 13

come together to form a fat droplet

Question 14

why do hydrophobic molecules avoid water?

Answer 14

primarily because it is uncharged and unpolarized

Question 15

describe the function of the cell membrane

Answer 15

• Serve as boundary and permeability barriers for molecules to specific compartments
• Regulate transport of molecules and ions.
• Provide platforms/surface area (e.g., ER, thylakoid membranes)
• Serves as sites of signaling for cellular communication (e.g., detect and transmit electrical and chemical signals)
• Enable capacity for cell movement and expansion

Question 16

why do bilayers form the ball?

Answer 16

as a sheet it is energetically unfavored because of the exposed hydrophobic tails, when it is enclosed then it is energetically favored

Question 17

does an unsaturated hydrocarbon tail have a kink?

Answer 17

yes

Question 18

what happens to free edges in the cell membrane?

Answer 18

it is quickly resolved

Question 19

the ____ the hydrocarbon tail, the more movement is allowed

Answer 19

shorter because there is less Van der Waal forces

Question 20

what kind of movement happens to the lipid bilayer?

Answer 20

flexion, rotation, and lateral diffusion

Question 21

the _____ unsaturated the hydrocarbon tail, the more movement is allowed

Answer 21

more

Question 22

cholesterol are classified as?

Answer 22

sterol

Question 23

phospholipids form bilayers only in _____ solvents 1

Answer 23

polar

Question 24

where are new phospholipids formed?

Answer 24

in the cytosolic surface of the ER to the cytosolic half of the bilayer

Question 25

how does the inner layer of the bilayer have new phospholipids?

Answer 25

outer lipids are transferred by scramblase to the inner layer, a transporter protein

Question 26

what is scramblase?

Answer 26

a phospholipid translocator that flips phospholipids for symmetrical growth of the bilayer

Question 27

most cell membranes are asymmetric, why?

Answer 27

occurs in the golgi, where specific phospholipd translocators (flippase) selectively remove phospholipids from the non-cytosolic side to cytosolic side. | flippase is an enzyme ## Footnote ATP dependent and new membrane is still from the ER

Question 28

what is flippase?

Answer 28

An enzyme that catalyzes the transfer of extracellular phospholipids to the cytosolic monolayer of the bilayer, needs ATP

Question 29

How does cholesterol affect the membrane?

Answer 29

can stiffen bilayer, make it less flexible, and less permeable

Question 30

what is the cytosol

Answer 30

The gel-like fluid that is mostly water

Question 31

All membranes have distinct surfaces with varying composition of .....

Answer 31

phospholipids, glycolipids and proteins.

Question 32

what is it called when the membrane of the golgi breaks of?

Answer 32

A tranport vesicle | the cytosolic face always faces the cytosol, even when fusing with the p

Question 33

where are the glycolipids found?

Answer 33

Mainly in the plasma membrane and are on the noncytosolic side | no flippase happens ## Footnote sugar groups (from golgi) face extracellular space and is trapped in this monolayer

Question 34

what are the three main membrane lipid molecules?

Answer 34

phospholipids, sterols, and glycolipids

Question 35

the two monolayers of a cell membrane have diff. lipid compositions. (T/F)

Answer 35

True | this provides different functions of the two faces of the membrane

Question 36

does choloeterol have a fatty acid tail?

Answer 36

No | it has a hydrocarbon tail but isnt fatty acid

Question 37

New membrane phospholipids are synthesized by enzymes bound to the ----- side of the ----- membrane.

Answer 37

cystolic and the ER

Question 38

polypeptide chains often cross the bilayer as ......

Answer 38

an alpha helix

Question 39

what are different ways proteins associate with the membrane?

Answer 39

1. transmembrane (embedded within) 2. monolayer association (embedded on 1 side by alpha helix) 3. lipid-linked (covalently attached lipid molecule) 4. protein attached (noncovalent attached with other proteins)

Question 40

what do plasma membrane proteins do?

Answer 40

1. transport molecules and ions 2. act as anchors 3. detect signals for cell comm. 4. act as enzymes

Question 41

what is a peripheral membrane protein?

Answer 41

indirectly attached to the membrane | "protein attached"

Question 42

how is the alpha helix oriented in the membrane?

Answer 42

hydrophobic section of the amino acid is embedded to the hydrophobic section of the membrane, although backbone is hydrophilic | formed by hydrogen bonding the backbones and the hydrophobic side chains

Question 43

what is a beta barrel?

Answer 43

made from beta sheet rolled into cylinder. outside of barrel is hydrophobic and inside barrel is hydrophilic ## Footnote example would be Porin Proteins in mitochondrial and bacterial outer membranes

Question 44

how is a hydrophilic pore made?

Answer 44

From alpha helices(many) so its like cylinders that sit circular and form an aqueous pore for transport

Question 45

what do you use to destroy the lipid bilayer?

Answer 45

use detergent, which disrupts hydrophobic associations

Question 46

glycoprotein = ?

Answer 46

glycosylated protein

Question 47

Explain the carbohydrate layer of the plasma membrane

Answer 47

sugars attached on the outside of the embedded proteins of the membrane form slippery surface | protects against mechanical forces and lubricate ## Footnote covalently attached

Question 48

how can proteins move in the membrane?

Answer 48

membrane is fluid so they can move by lateral diffusion

Question 49

how can lateral mobility be restriced?

Answer 49

1. tethered by protein-protein intertaction (inside) 2. tethered to ECM molcules (outside) 3. tethered to another cell cortex inside cell 4. diffusion barriers

Question 50

define glycocalyx

Answer 50

the carbohydrate layer of the membrane