Fat Synthesis

Question 1

What are the two transport mechanisms for glucose in a cell?

Answer 1

Sodium independent facilitated transport system and Sodium-monosaccharide co-transport system (SGLT)

Question 2

This glucose transport mechanism utilizes GLUT and moves glucose down a concentration gradient.

Answer 2

Sodium independent facilitated transport system

Question 3

This glucose transport mechanism is ATP dependent, transports glucose against a concentration gradient and is found in the epithelial cells of intestines, renal tubules, and choroid plexus.

Answer 3

Sodium-monosaccharide co-transport system (SGLT)

Question 4

This glucose transporter transports glucose, galactose, and fructose into the liver, kidney, and pancreas beta-cells and is insulin independent

Answer 4

GLUT 2

Question 5

This glucose transporter transports glucose into muscle and adipose tissue, is stimulated by insulin and low energy charges (AMPkinase), and deals with facilitated diffusion

Answer 5

GLUT4

Question 6

As long as the concentration of glucose is lower in muscle (and transporters are available) where will glucose go?

Answer 6

Glucose will move from the blood to the muscle

Question 7

By adding a ____ to glucose, the glucose concentration in muscle remains low and glucose keeps coming in.

Answer 7

Phosphate

Question 8

When muscle ____ is low, glucose 6 phosphate runs through glycolysis, prep step and Krebs to make more ATP.

Answer 8

Energy charge

Question 9

When muscle glycogen is low, _____ is converted into glycogen.

Answer 9

Glucose 6 phosphate

Question 10

About 90% of insulin-stimulated glucose uptake occurs where?

Answer 10

Skeletal muscle

Question 11

Exercise increases the number of what glucose transporter in skeletal muscle?

Answer 11

GLUT4

Question 12

When glucose is consumed and transported to muscle, if the muscle is full of glycogen what happens?

Answer 12

The glucose goes to the liver

Question 13

When glucose is consumed and transported to muscle, if the muscle is not full of glycogen what happens?

Answer 13

Glucose is stored as glycogen

Question 14

How do muscles say “no” to incoming glucose?

Answer 14

• High energy charge will inhibit PFK
• Glucose 6 phosphate accumulates
• Hexokinase is inhibited
• Inhibition of glucose 6 phosphate causes glucose to accumulate, which stops the flow of glucose from blood to muscle

Question 15

This enzyme has a lower affinity for glucose, is not inhibited by its product, stimulated by insulin, and is stimulated by fructose.

Answer 15

Glucokinase

Question 16

What primary tissues are involved with the synthesis of fatty acids?

Answer 16

• Liver
• To a lesser extend adipose tissue and kidneys
• Mammary glands during lactation

Question 17

Where does the synthesis of fatty acids occur?

Answer 17

Cytosol

Question 18

What are the “ingredients” for the synthesis of fatty acids?

Answer 18

• Two carbon pieces (acetyl)
• Electrons (NADPH)
• Energy (ATP)

Question 19

What are the steps of fatty acid synthesis?

Answer 19

-Sugar runs through glycolysis
-Prep step to make acetyl CoA
-Kreb’s cycle
-Citrate is made
-Too much ATP causes Kreb’s cycle to slow
Citrate is kicked out of the mitochondria
-Two carbon acetyl CoA is given back to start fat synthesis
-Acetyl CoA is converted to malonyl CoA
-Malonyl CoA is given to fatty acid synthase (FAS), which adds them to a growing fatty acid

Question 20

What enzyme in the Kreb’s cycle is inhibited by ATP, resulting in citrate accumulating?

Answer 20

Isocitrate dehydrogenase

Question 21

What enzyme converts acetyl CoA to malonyl CoA?

Answer 21

Acetyl CoA carboxylase

Coenzyme: Biotin

Question 22

What is the rate limiting step of fatty acid synthesis?

Answer 22

Acetyl CoA carboxylase

Question 23

What is acetyl CoA carboxylase activated by? Deactivated by?

Answer 23

Citrate; Long chain fatty acyl CoA

Question 24

Short term regulation of acyl CoA carboxylase involves what type of process? What are some examples?

Answer 24

Reversible phosphorylation

• AMPK phosphorylates and inactivates acyl CoA carboxylase (ACC)
• Epinephrine and glucagon increase cAMP, which phosphorylates and inactivates ACC
• Insulin dephophorylates and activates ACC

Question 25

What are some ways acyl CoA carbocylase (ACC) is regulated over the long term?

Answer 25

- High calorie/high carb diet increases ACC synthesis which increases fatty acid synthesis. Low calorie/low carb diet does the opposite - Upregulated by insulin: increased response/increased receptors (sterol regulatory element-binding protein (SREBP-1))

Question 26

What stimulates acetyl CoA carboxylase?

Answer 26

Citrate and Insulin

Question 27

What inhibits acetyl CoA carboxylase?

Answer 27

- Malonyl CoA - Palmitoyl CoA - Epinephrine - Glucagon

Question 28

This substance is involved in type II diabetes and inhibits ACC leading to activation of AMPK, a decrease of SREBP-1, and a lowering of blood glucose.

Answer 28

Metformin

Question 29

This multienzyme complex contains an acyl carrier protein, is similar to coenzyme A, and has a terminal thiol group at the end of an "arm".

Answer 29

Fatty acid synthase

Question 30

What are the first three reactions that set the stage for fatty acid synthesis?

Answer 30

1) Acetyl group (2C) is transferred to the thiol group on ACP by acetyl CoA-ACP acetyl transacylase 2) Acetyl group moved to a temporary holding site on a cysteine residue on the enzyme 3) Malonyl group (3C) transferred to the thiol group on ACP by malonyl-CoA-ACP transacylase

Question 31

What are the last four reactions of fatty acid synthsis?

Answer 31

- Condensation: Acetyl ACP and Malonyl ACP are converted to Acetoacetyl-ACP by beta-ketoacyl-ACP synthase - Reduction: Acetoacetyl-ACP is converted to D-3-hydroxybutyryl-ACP by beta-ketoacyl-ACP reductase - Dehydration: D-3-hydroxybutyryl-ACP is converted to crotonyl-ACP by beta-hydroxyacyl-ACP dehydratase - Reduction: crotonyl-ACP is converted to butyryl-ACP by enoyl-ACP reductase

Question 32

After the last four reactions of fatty acid synthesis (condensation, reduction, dehydration, reduction) we have a four carbon molecule (butyryl). What happens to this molecule?

Answer 32

It is transferred to a holding site (cysteine), another malonyl is added, and the steps are repeated until it is 16 carbons long (Palmitate, 16:0)

Question 33

Release of the fatty acid is the last step in fatty acid synthesis. How is this accomplished?

Answer 33

The thioester bond of palmitoyl-S-ACP is cleaved by palmitoyl thioesterase releasing the saturated palmitate.

Question 34

Where does the NADPH needed for fatty acid synthesis come from?

Answer 34

- Pentose phosphate pathway | - Malate-->pyruvate in the cytosol

Question 35

How is palmitate elongated?

Answer 35

Elongases. NADPH is required

Question 36

How is palmitate desaturated?

Answer 36

Desaturases (adds double bonds)

Question 37

Can humans create double bonds beyond the 9th-10th carbon?

Answer 37

No

Question 38

What is the primary site for fructose disposal?

Answer 38

Liver

Question 39

What enzymes are essential for fructose metabolism and are highly expressed in the liver?

Answer 39

Fructokinase and triokinase