Biological Membranes

Question 1

Fluid Mosaic Model

Answer 1

Accounts for the presence of lipids, protein, and carbohydrates in a
dynamic, semisolid plasma membrane that surrounds cells

Question 2

Phospholipid

Bilayer:

Answer 2

Each phospholipid has a hydrophilic head and hydrophobic
tail. They are arranged so the heads are facing outward
and the tails make up the inside of the membrane.
Proteins are embedded in the bilayer

Question 3

Lipid Rafts

Answer 3

Lipids move freely in the plane of the membrane and can

assemble into lipid rafts

Question 4

Flippases:

Answer 4

Specific membrane proteins that maintain the bidirectional
transport of lipids between the layers of the phospholipid
bilayer in cells

Question 5

How do proteins and carbohydrates move within the membrane?

Answer 5

May also move within the membrane, but are slowed by

their relatively large size

Question 6

True/False: Triacylglycerols are found in low levels in the membrane.

Answer 6

True

Question 7

How does temperature effect cholesterol membrane fluidity

Answer 7

Low temperature = increased fluidity

High temperature = decreased fluidity

Question 8

How does temperature effect lipid fluidity in the membrane?

Answer 8

Higher temperature causes and increase in fluidity

Lower temperature causes a decrease in fluidity

Question 9

Transmembrane

Proteins:

Answer 9

A type of integral protein that spans the entire

membrane. They are often glycoproteins.

Question 10

Embedded Proteins

Answer 10

Are most likely part of a catalytic complex or

involved in cellular communication

Question 11

Membrane-Associated

Proteins:

Answer 11

May act as recognition molecules or enzymes

Question 12

Ligands

Answer 12

: Extracellular ligands can bind to membrane
receptors, which function as channels or as
enzymes in second messenger pathways

Question 13

Gap Junctions

Answer 13

Allow for rapid exchange of ions and other small

molecules between adjacent cells

Question 14

Tight Junctions

Answer 14

Prevent solutes from leaking into the space
between cells via a paracellular route, but do not
provide intercellular transport

Question 15

Desmosomes:

Answer 15

Desmosomes bind adjacent cells by anchoring to

their cytoskeletons

Question 16

Hemidesmosomes

Answer 16

are similar,
but their main function is to attach epithelial cells
to underlying structures

Question 17

What does glycogenesis do?

Answer 17

Produces glycogen

Question 18

What two main enzymes are used in glycognesis?

Answer 18

Branching enzyme and glycogen synthase

Question 19

Where does glycogenesis occur?

Answer 19

Liver and muscle cells

Question 20

Where is glycogen stored?

Answer 20

Liver

Question 21

What type of bonds does glycogen synthase create?

Answer 21

Creates alpha-1,4 glycosidic bonds between glucose.

Question 22

What type of bonds do branching enzymes make?

Answer 22

Creates branches with alpha 1-6 glycosidic bonds

Question 23

What is the function of Glycogenolysis?

Answer 23

Breakdown of glycogen

Question 24

What are the two main enzymes involved in glycogenolysis?

Answer 24

Glycogen phosphorylase and debranching enzyme

Question 25

How does glycogen phosphorylase work?

Answer 25

Removes single glucose 1-phosphate molecules by | breaking a-1,4 glycosidic bonds

Question 26

Where is glycogen phosphorylase activated? Why is it activated?

Answer 26

In the liver, it is activated by glucagon to prevent low blood sugar. In exercising skeletal muscle, it is activated by epinephrine and AMP to provide glucose for the muscle itself.

Question 27

What does the debranching enzyme do?

Answer 27

Moves a block of oligoglucose from the branch and connects it to the chain using an a-1,4 glycosidic bond. It also removes the branchpoint, which is connected via an a-1,6 glycosidic bond, releasing a free glucose molecule

Question 28

Where does gluconeogenesis occur?

Answer 28

Occurs in both the cytoplasm and mitochondria, predominantly in the liver with a small contribution from the kidneys.

Question 29

What does gluconeogenesis do?

Answer 29

Most gluconeogenesis is simply the reverse of glycolysis, using the same enzymes. The 3 irreversible steps of glycolysis must be bypassed by different enzymes

Question 30

What does pyruvate carboxylase do and in which biochemical pathway is it found?

Answer 30

Occurs in gluconeogenesis and it converts pyruvate to oxaloacetate which is converted to PEP by PEPCK. Together these two enzymes bypass pyruvate kinase.

Question 31

What activates pyruvate carboxylase?

Answer 31

Acetyl-coA

Question 32

What activates phosphoenolpyruvate carboxykinase? (PEPCK)

Answer 32

Glycogen and cortisol

Question 33

Fructose-1,6 bisphosphatase converts _____ to ____

Answer 33

Fructose 1,6 - Bisphosphate to fructose-6-phosphate, bypassing PFK-1

Question 34

What is the rate limiting step of gluconeogenesis?

Answer 34

Fructose-1,6- bisphosphatase

Question 35

What inhibits Fructose-1,6-bisphosphatase?

Answer 35

AMP and insulin

Question 36

Where is GLUT-2 found? What are its effects on Km?

Answer 36

Found in liver (for glucose storage) and pancreatic b-islet | cells (as part of the glucose sensor). Has ­Km

Question 37

Where is GLUT-4 found? What stimulates GLUT-4? What does it do to the km?

Answer 37

Found in adipose tissue and muscle. Stimulated by insulin. Decreases Km

Question 38

Formula glycolysis

Answer 38

Glucose + 2NAD+ + 2ADP + 2P --> 2Pyruvate + 2ATP + 2NADH + 2H+

Question 39

List the three irreversible enzymes used in Glycolysis

Answer 39

Glucokinase/hexokinase PFK-1 Pyruvate Kinase

Question 40

Glucokinase:

Answer 40

Converts glucose to glucose 6-phosphate in the pancreatic b-islet cells as part of the glucose sensor.

Question 41

Hexokinase

Answer 41

Converts glucose to glucose 6-phosphate in in | peripheral tissues. Inhibited by its product G 6-P

Question 42

Phosphofructokinase-1

Answer 42

PFK-1. Phosphorylates fructose 6-phospate to fructose 1,6-bisphosphate in the rate-limiting step. Activated by AMP and fructose 2,6- bisphosphate. Inhibited by ATP and citrate

Question 43

What activates PFK1

Answer 43

AMP and Fructose 2,6-bisphosphate

Question 44

What inhibits PFK-1

Answer 44

ATP and citrate

Question 45

Phosphofructokinase-2

Answer 45

PFK-2. Produces fructose 2,6-bisphosphate that activates PFK-1. It is activated by insulin; inhibited by glucagon.

Question 46

Glyceraldehyde-3-phosphate | dehydrogenase:

Answer 46

Produces NADH, which can feed into the electron transport chain.

Question 47

Pyruvate Kinase:

Answer 47

Perform substrate-level phosphorylation, placing | an inorganic phosphate onto ADP to form ATP

Question 48

What happens to the NADH produced in glycolysis when O2 is present?

Answer 48

Perform substrate-level phosphorylation, placing | an inorganic phosphate onto ADP to form ATP

Question 49

What happens to the NADH produced in glycolysis if O2 or mitochondrial are absent?

Answer 49

If O2 or mitochondria are absent, the NADH produced in glycolysis is oxidized by cytoplasmic lactate dehydrogenase.

Question 50

What does pyruvate dehydrogenase do?

Answer 50

A complex of enzymes that convert pyruvate to Acetyl-CoA right before the citric acid cycle.

Question 51

What stimulates pyruvate dehydrogenase?

Answer 51

Insulin

Question 52

What inhibits pyruvate dehydrogenase?

Answer 52

Acetyl-coA

Question 53

Where does the pentose phosphate pathway occur?

Answer 53

Also known as the hexose monophosphate (HMP) shunt, it occurs in the cytoplasm of most cells.

Question 54

What are the reactants and products of the pentose phosphate pathway?

Answer 54

Reactant: Glucose-6-phosphate Product: NADPH, sugars for biosynthesis, and glycolysis intermediates

Question 55

What is the rate limiting step enzyme for the pentose phosphate pathway? What activates it and inhibits it?

Answer 55

Glucose-6-phosphate dehydrogenase (G6PD), which is activated by NADP+ and insulin and inhibited by NADPH

Question 56

Galactose

Answer 56

Comes from lactose in milk. Trapped in the cell by galactokinase, and converted to 1-phosphate via galactose-1-phosphate uridyltransferase and an epimerase

Question 57

Fructose

Answer 57

Comes from honey, fruit, and sucrose. Trapped in the cell by fructokinase, then cleaved by aldolase B to form glyceraldehyde and DHAP.