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MCAT Bio/Biochem > Biological Membranes > Flashcards

Biological Membranes Flashcards

1
Q

Fluid Mosaic Model

A

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

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2
Q

Phospholipid

Bilayer:

A

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

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3
Q

Lipid Rafts

A

Lipids move freely in the plane of the membrane and can

assemble into lipid rafts

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4
Q

Flippases:

A

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

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5
Q

How do proteins and carbohydrates move within the membrane?

A

May also move within the membrane, but are slowed by

their relatively large size

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6
Q

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

A

True

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7
Q

How does temperature effect cholesterol membrane fluidity

A

Low temperature = increased fluidity

High temperature = decreased fluidity

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8
Q

How does temperature effect lipid fluidity in the membrane?

A

Higher temperature causes and increase in fluidity

Lower temperature causes a decrease in fluidity

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9
Q

Transmembrane

Proteins:

A

A type of integral protein that spans the entire

membrane. They are often glycoproteins.

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10
Q

Embedded Proteins

A

Are most likely part of a catalytic complex or

involved in cellular communication

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11
Q

Membrane-Associated

Proteins:

A

May act as recognition molecules or enzymes

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12
Q

Ligands

A

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

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13
Q

Gap Junctions

A

Allow for rapid exchange of ions and other small

molecules between adjacent cells

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14
Q

Tight Junctions

A

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

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15
Q

Desmosomes:

A

Desmosomes bind adjacent cells by anchoring to

their cytoskeletons

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16
Q

Hemidesmosomes

A

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

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17
Q

What does glycogenesis do?

A

Produces glycogen

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18
Q

What two main enzymes are used in glycognesis?

A

Branching enzyme and glycogen synthase

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19
Q

Where does glycogenesis occur?

A

Liver and muscle cells

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20
Q

Where is glycogen stored?

A

Liver

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21
Q

What type of bonds does glycogen synthase create?

A

Creates alpha-1,4 glycosidic bonds between glucose.

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22
Q

What type of bonds do branching enzymes make?

A

Creates branches with alpha 1-6 glycosidic bonds

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23
Q

What is the function of Glycogenolysis?

A

Breakdown of glycogen

24
Q

What are the two main enzymes involved in glycogenolysis?

A

Glycogen phosphorylase and debranching enzyme

25
Q

How does glycogen phosphorylase work?

A

Removes single glucose 1-phosphate molecules by

breaking a-1,4 glycosidic bonds

26
Q

Where is glycogen phosphorylase activated? Why is it activated?

A

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.

27
Q

What does the debranching enzyme do?

A

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

28
Q

Where does gluconeogenesis occur?

A

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

29
Q

What does gluconeogenesis do?

A

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

30
Q

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

A

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

31
Q

What activates pyruvate carboxylase?

A

Acetyl-coA

32
Q

What activates phosphoenolpyruvate carboxykinase? (PEPCK)

A

Glycogen and cortisol

33
Q

Fructose-1,6 bisphosphatase converts _____ to ____

A

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

34
Q

What is the rate limiting step of gluconeogenesis?

A

Fructose-1,6- bisphosphatase

35
Q

What inhibits Fructose-1,6-bisphosphatase?

A

AMP and insulin

36
Q

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

A

Found in liver (for glucose storage) and pancreatic b-islet

cells (as part of the glucose sensor). Has ­Km

37
Q

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

A

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

38
Q

Formula glycolysis

A

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

39
Q

List the three irreversible enzymes used in Glycolysis

A

Glucokinase/hexokinase

PFK-1

Pyruvate Kinase

40
Q

Glucokinase:

A

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

41
Q

Hexokinase

A

Converts glucose to glucose 6-phosphate in in

peripheral tissues. Inhibited by its product G 6-P

42
Q

Phosphofructokinase-1

A

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

43
Q

What activates PFK1

A

AMP and Fructose 2,6-bisphosphate

44
Q

What inhibits PFK-1

A

ATP and citrate

45
Q

Phosphofructokinase-2

A

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

46
Q

Glyceraldehyde-3-phosphate

dehydrogenase:

A

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

47
Q

Pyruvate Kinase:

A

Perform substrate-level phosphorylation, placing

an inorganic phosphate onto ADP to form ATP

48
Q

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

A

Perform substrate-level phosphorylation, placing

an inorganic phosphate onto ADP to form ATP

49
Q

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

A

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

50
Q

What does pyruvate dehydrogenase do?

A

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

51
Q

What stimulates pyruvate dehydrogenase?

A

Insulin

52
Q

What inhibits pyruvate dehydrogenase?

A

Acetyl-coA

53
Q

Where does the pentose phosphate pathway occur?

A

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

54
Q

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

A

Reactant: Glucose-6-phosphate

Product: NADPH, sugars for biosynthesis, and glycolysis intermediates

55
Q

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

A

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

56
Q

Galactose

A

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

57
Q

Fructose

A

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

MCAT Bio/Biochem (30 decks)

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