Biochemistry

Question 1

Fluid mosaic model

Answer 1

Describes biological membranes.

Phospholipid bilayer containing embedded proteins.

Fluid because lipids and protein molecules move laterally.

Question 2

Lipid rafts

Answer 2

“Microdomains” in the plasma membrane that contain:

1. sphingolipids/sphingomyelin
2. cholesterol
3. glycosphingolipids

Signal transduction
Membrane fluidity 
Membrane protein trafficking
Facilitate virus infection
Regulating neurotransmission and receptor trafficking

Question 3

Where is free cholesterol found in the plasma membrane?

Answer 3

Free cholesterol found in both inner and outer leaflet.

Question 4

Where is glycocalyx (glycolipids/glycoproteins) found?

Answer 4

Found in the outer leaflet.

Question 5

Lipids found in outer leaflet

Answer 5

Phosphatidycholine
Sphingomyelin
Phosphatidylethanolamine
Glycosphingolipids

Question 6

Lipids found in inner leaflet

Answer 6

Phosphatidylethanolamine
Some phosphatidylcholine
*Phosphatidylserine
Phosphatidylinositol
PIP2

Question 7

What determines the fluidity of the plasma membrane?

Answer 7

Determined by:

1. fatty acid composition of phospholipid
2. By free cholesterol

Question 8

Role of cholesterol in fluidity
and
Where is cholesterol found

Answer 8

Decreases fluidity by polar heads.
Increases fluidity inside bilayer.
Cholesterol prevents extreme changes in fluidity due to temperatures.

Cholesterol is found in the cis-bond regions of fatty acids (kink).

Question 9

Fluidity of intracellular membranes

Answer 9

NO cholesterol.
Shorter fatty acids & unsaturated fatty acids=membrane more fluid.

ie arachidonic acid (20:4, Ω 6)
ie docosahexaenic acid (2:6, Ω 3)

Question 10

Passive transport: transporter facilitates diffusion

Answer 10

A compound flows with the [] gradient from a high [] to a low [].

Process is SPECIFIC and SATURABLE.

NO energy required in process.

Question 11

Glucose Transporters

Sodium independent

Answer 11

*Facilitated diffusion transport system

High affinity transporters—
GLUT-1: Brain, RBC
GLUT-3: Neurons
GLUT-4: Skeletal muscle, heart & fat cells (insulin dependent)

Low affinity transporters—
GLUT-2: LIVER, KIDNEY, beta-cell, intestine
GLUT-5: Intestine, seminal vesicles

*Glucose uptake from the blood

Question 12

Glucose Transports

Sodium dependent

Answer 12

*Secondary active transport system

SGLT-1: INTESTINE (epithelial cells at the lumen side)
SGLT-2: KIDNEY (epithelial cell in renal tubules)

Question 13

GLUT-1

Answer 13

Abundent in RBC

Also found in BBB and kidneys

Question 14

GLUT-3

Answer 14

Dominant in neurons and brain

Question 15

GLUT-4

Answer 15

*Insulin dependent

Abundant in fat cells, skeletal muscles, and heart.
GLUT-4 stored in cells and can be mobilized by insulin or vigorous exercise of skeletal muscles.

Question 16

GLUT-2

Answer 16

*Low affinity transporter

Capable of transporting large amts of glucose molecules at high []s.

Found in:
Intestinal mucosal cells
Hepatocyptes
Renal tubular cells
Beta-cells of pancreas

Question 17

GLUT-5

Answer 17

Found in:
Intestinal mucosal cells on the luminal side of the intestinal membrane
Seminal vesicle

Mainly transports dietary fructose. (Glucose ONLY if in high [])

Question 18

Hereditary GLUT-1 deficiency

Answer 18

Deficiency of GLUT-1 leads to microcephaly and epilepsy-like seizures

Individuals develop:
Ataxia
Delayed psychomotor development
Movement disorder
Impaired speech

Question 19

Primary active transport

and

Secondary active transport

Answer 19

Primary active transport is performed by Na+/K+-ATPase

Active pumping=3 Na+ out, 2 K+ in

One ATP needs to be cleaved
Against [] gradient
———
Secondary active transport is coupled to Na+/K+-ATPase

Transports both Na+ and a specific molecule into the cell. Molecules may be taken up against a [] gradient.

Question 20

Secondary active transport

Answer 20

SGLT-1=symporter

Transports Na+ and glucose/galactose against [] gradient.

Question 21

ABC Transporters

and

CFTR

Answer 21

ATP Binding Cassette

Allow the active transport of molecules from cytosol to extracellular space.

Needs hydrolysis of ATP.
Mostly transporting lipids.
——-
CFTR (cystic fibrosis transmembrane conductance regulator)
Chloride ion channel. No pump, but cleaves ATP (passive). Flows with gradient.
*Gated channel with pore for chlorine ion.

Found in:
airway ducts
pancreatic ducts
reproductive ducts
intestinal lumen and skin

Question 22

Cystic fibrosis cause and diagnosis

Answer 22

CFTR is impaired in the sweat glan, leading to a lack of re-uptake of chloride ions which leads to salty skin.

Characterized by lung congestion/infection and malabsorption of nutrients by the pancreas.

Diagnosis- Sweat test. [] of NaCl is measured.