Membranes

Question 1

What are membranes

Answer 1

Thin films composed of mixtures of lipids and proteins

Question 2

What do lipids do

Answer 2

Act as barrier to the movement of H2O and h20 soluble molecules

Question 3

What is the function of proteins

Answer 3

Includes the transportation of molecules across the membrane

Question 4

What is the purpose of the plasma membrane

Answer 4

Maintains movement between intracellular and extracellular environments

Question 5

What are amphipathic molecules

Answer 5

Molecules that have hydrophobic (non-polar) end and hydrophilic (polar) end and form spontaneously from bilayers

Question 6

What is a common fatty acid

Answer 6

Palmitate (palmitic acid) with 2 distinct chemical regions

Question 7

What are phospholipids composed of

Answer 7

Have polar head group and two hydrophobic hydrocarbon tails (tails usually fatty acids)

Question 8

What impact does the length and saturation of the tail have on membrane fluidity

Answer 8

Affects ability of phospholipid molecules to pack together and effects membrane fluidity

Question 9

How to identify a kink in lipid structure

Answer 9

Cis double bond means unsaturated fatty acid which forms kink

Question 10

Characteristics of saturated fatty acids

Answer 10

-Common in dairy and meat products
-solid at room temp

Question 11

Characteristics of unsaturated fatty acids

Answer 11

-common in plants
-liquid at room temp

Question 12

How do phospholipids aggregate to form bilayers

Answer 12

In aqueous environment hydrophobic tails pack together to exclude H2O => forms lipid bilayer

Question 13

Are the fatty acid tails soluble or insoluble to H2O and why

Answer 13

Insoluble in H2O as all atoms are uncharged, non-polar and the tails are hydrophobic

Question 14

Are the heads of the phospholipid bilayer insoluble or soluble in H2O and why

Answer 14

Soluble in water due to charger polar groups and forms favourable electrostatic interactions or H bonds with H2O molecules
-heads hydrophilic (polar)

Question 15

How is membrane fluidity controlled

Answer 15

By fatty acid composition and cholesterol content

Question 16

What are the two states lipid bilayers can exist in

Answer 16

-ordered rigid state
-relatively disordered, fluid state

Question 17

What is a key regulator of membrane fluidity in eukaryotes

Answer 17

Cholesterol

Question 18

What are transmembranes formed by

Answer 18

Multiple alpha helices and a cylinder forming a beta barrel

Question 19

What is the function of transporters

Answer 19

Transports metabolites e.g ions across lipid bilayer

Question 20

What is the function of anchors

Answer 20

Anchor membrane to macromolecules on either side

Question 21

What is the function of receptors

Answer 21

Detect chemical signals in the cells environment and relay them into the cell interior

Question 22

What is the function of enzymes

Answer 22

To catalyse specific reactions at membrane

Question 23

What are the membrane-bound intracellular organelles in eukaryotic cells

Answer 23

-endoplasmic reticulum
-Golgi apparatus
-mitochondria

Question 24

What functional group is at one end of the hydrophobic tails on fatty acid

Answer 24

-COOH (Carboxylic acid)

Question 25

When does phase transition between two states occur

Answer 25

Tm (melting temperature)

Question 26

How can fluidity of lipid bilayers be studied

Answer 26

Using synthetic lipid bilayers

Question 27

How are synthetic lipid bilayers produced

Answer 27

By spontaneous aggregation of amphipathic lipid molecules in water

Question 28

What is the permeability of gasses and small, uncharged polar molecules

Answer 28

Freely permeable through the synthetic lipid bilayer

Question 29

What is the permeability of larger uncharged polar molecules

Answer 29

Cannot permeate through synthetic lipid bilayer

Question 30

What is the permeability of charged ions through synthetic lipid bilayer

Answer 30

Impermeable due to charged ions

Question 31

What are the two main classes of transport proteins

Answer 31

Carrier protein and channel protein

Question 32

Function of carrier proteins

Answer 32

Bind to molecule to be transported and move through the membrane by a series of conformational changes

Question 33

What is the function of channel proteins

Answer 33

Form hydrophilic pores through membrane to allow charged ion solutes to pass through -faster than carrier proteins

Question 34

What do protein channels discriminate on

Answer 34

On basis of size and charge

Question 35

what is passive transport

Answer 35

Aka as facilitated diffusion where molecules move down conc. gradient (For all channels and most carriers)

Question 36

What is active transport

Answer 36

Movement of molecules against electrochemical gradient “uphill” - requires energy

Question 37

What is the apical glucose transporter in intestinal epithelial cells

Answer 37

Glucose/Na+ symport allows the uptake of glucose even when concentration in cell is already high

Question 38

What is the basal glucose transporter in the intestinal epithelial cells

Answer 38

passive glucose transporters and glucose is released as required

Question 39

What is the uniport in carrier mediated transport

Answer 39

transport of soluble molecules from one side of membrane to the other e.g glucose transporters

Question 40

What is the symport in carrier mediated transport

Answer 40

Coupled transport of two types of solute

Question 41

What is the antiport of carrier mediated transport

Answer 41

Transport of one solute in one direction coupled to transport another in the opposite direction

Question 42

What is phagocytosis

Answer 42

Process of large particles (e.g bacteria) are internalised (engulfed) by eukaryotic cells

Question 43

Characteristics of cholesterol

Answer 43

Very insoluble in lipids and is carried in blood in low density lipoprotein (LDL) particles

Question 44

What is the result of defective LDL receptors

Answer 44

LDL (low density lipoprotein) uptake decrease => high circulating cholesterol levels causing hypercholesterolaemia and leads to atherosclerotic plaque formation

Question 45

How do cell surface receptors work

Answer 45

Large hydrophilic signalling molecules unable to bind directly to plasma membrane => bind to cell surface receptors => generate 1 or more intracellular signalling molecules in target cell

Question 46

How do intracellular receptors work

Answer 46

Small hydrophobic signalling molecules pass through cell plasma membrane => activate intracellular enzymes in cytosol or nuclease => regulates gene transcriptions

Question 47

Are steroid hormones e.g cortisol, oestrogen and testosterone hydrophobic or hydrophilic

Answer 47

Hydrophobic => can pass through plasma membrane

Question 48

What is the function of lysosomes

Answer 48

Small sacs of digestive enzymes

Question 49

What is the mitochondria

Answer 49

Site of ATP synthesis

Question 50

What are the functions of the Golgi apparatus

Answer 50

Site of post translational modification of proteins and modification of oligosaccharides added in the ER

Question 51

What climate is to have more unsaturated fatty acids

Answer 51

Colder climates

Question 52

What climate is to have more saturated fatty acids

Answer 52

Hotter climates