Module 8 - Cell-Cell Interactions Pt2

Question 1

Where do we get fat from

Answer 1

from consuming too many calories from sugar, fat or protein

Question 2

WHat are sources of acetyCoA

Answer 2

Pyruvate breakdown, breakdown of fats (beta oxidation), ketone bodies and some amino acids

Question 3

What is structure of triglycerides, what do they do in our body

Answer 3

●Fats are stored in the body as triacylglycerols (aka triglycerides)
●Triglycerides made of 3 fatty acids that have been esterified with glycerol
Usually made of 2 or more types of fatty acids

Question 4

Where is fat stored

Answer 4

found in adipose tissue in specialized cells called adipocytes
- some muscle also as small amounts of fat

Question 5

Where are triglycerides broken down

Answer 5

In adipocytes

Question 6

How are triglycerides broken fown

Answer 6

● Lipase is enzyme which releases the free fatty acids from the glycerol moiety by hydrolyzing the ester bonds

Question 7

What causes lipase to be stimulated

Answer 7

●When glucose levels are low, hormone glucagon is released and stimulates the lipase to breakdown fats to provide energy
●Beta oxidation allows free fatty acids will be broken down and oxidized to generate reducing equivalents NADH, FADH2 and acetylCoA, which feeds into the citric acid cycle to make energy in the form of GTP and even more reducing equivalents

Question 8

Where do fatty acids go when theyre NOT beta oxidized

Answer 8

● Fatty acids from lipase leave the adipose tissue and enter the bloodstream to be delivered to other tissues
● Fatty acids are carried through the bloodstream bound to protein albumin, which keeps fatty acids soluble

Question 9

What happens to fatty acids that get takedup into tissue

Answer 9

● Fatty acids taken up into tissues are broken down to acetylCoA via beta oxidation pathway

Question 10

What happens to the glycerol from triacylglycerol

Answer 10

● The glycerol moiety is also unstable energy and leaves the adipose tissue to be taken up by liver which is where gluconeogenesis takes place (converted into glucose)
● Glycerol is a substrate for gluconeogenesis entering the gluconeogenic pathway at midpoint

Question 11

Where in body are fatty acids used

Answer 11

preferred fuel for muscles at rest

Liver uses fat for energy

Question 12

What must happen before fatty acid enters beta oxidation pathway

Answer 12

Must be activated

Question 13

How are fatty acids activated and what does this allow

Answer 13

• Attaching attaching a long chain hydrocarbon of fatty acid to coenzymeA
• similar to pyruvate becoming acetyl CoA
• Now acyl CoA is ready to be transported into mitochondrial matrix to be oxidized

Question 14

Where are enzymes of beta oxidation located and where does it occur

Answer 14

● Enzymes of beta oxidation are all located in the matrix

Question 15

What happens during Beta Oxidation of Fatty acids

Answer 15

● One round of beta oxidation involves sequential removal of two carbons at a time from the acyl group
- Cleaving bond involves series of four reactions that occur in single round beta oxidation
●you make 1NADH and 1 FADH and acetylCo
●Beta oxidation since it cleaves the carbon-carbon bond adjacent to beta carbon
●Then shortened acylCoA starts the process again entering a subsequent round of beta oxidation and cleaves two more carbons
●The process reapers until all of the acyl group is cut into two carbon acetylCoAs (for even-numbered fatty acids)

Question 16

What is an alternate fate for AcetylCoA then the citric acid cycle

Answer 16

under starvation → ketogenesis
●Convert fatty acids to ketone bodies in the liver and during fasting or starvation with low glucose since bodies glycogen stores are depleted, can use ketone bodies for energy in brain

Question 17

What happens to Ketone bodies during fasting

Answer 17

during faster enter bloodstream and cross blood-brain barrier and be taken up by brain and broken back down into acetylCoA which can enter citric acid cycle and produce energy

Question 18

Does anabolic fat synthesis share any of the same enzymes

Answer 18

No unlike glycolysis and gluconeogenesis

Question 19

What happens conceptually during fat synthesis

Answer 19

the process is reverse of beta oxidation

● Two carbons originating from acetylCoA are added one at a time to elongating fatty acyl chain

Question 20

When do bodies synthesize fat

Answer 20

1. Bodies are in mode of synthesizing fat when we have excess intake of carbohydrates (replenish stores then excess broken down via glycolysis and pyruvate dehydrogenase rxn to make acetylCoA) → where acetyl CoA originates from

Question 21

What does the anabolic process of fat synthesis involve/need

Answer 21

2. Anabolic process = reductive → we have to inject or donate e= into newly synthesized compound (in this case fatty acid)

Question 22

Where must acetyl CoA be for fat synthesis to take place and how does it get there

Answer 22

3. Tricarboxylate transport system must remove acetylCoA via citrate intermediate out of mitochondrial matrix into cytosol (that’s where fat synthesis takes place)

Question 23

What does fatty acid synthetase do

Answer 23

catalyzes synthesis of fatty acids

Question 24

What do enzymes elongases and desaturases do

Answer 24

Elongase - can make longer chain fatty acids

desaturases - create double bonds in unsaturated fatty acids

Question 25

What happens once fatty acids are synthesized

Answer 25

they are esterified with glycerol to form triacylglycerols used to make membrane lipids

Question 26

What happens to fatty acid metabolism after a meal

Answer 26

●Insulin activates fat synthesis in the liver and simultaneously inhibits fat breakdown in adipose tissue
●Futile cycling: we want to avoid breaking down fats when glucose is plentiful and body is in mode of synthesizing fats

Question 27

What happens to fatty acid metabolism during periods of low glucose

Answer 27

● Glucagon released during low glucose which is insulins counter hormone
● It stimulates fat breakdown by stimulating lipase in adipose tissue
● Then fats broken down to acetylCoA used for energy or acetylCoA diverted to ketone body synthesis (although not ideal)

Question 28

What else is AcetylCoA a precursor for

Answer 28

for cholesterol synthesis and synthesis of some amino acids

Question 29

What does HMG-CoA reductase do

Answer 29

help lower cholesterol levels in those afflicted with high levels of “bad cholesterol”, LDL

Question 30

Can amino acids made AcetylCoA or pyruvate

Answer 30

Yes certain amino acids can become acetyl CoA while others can become Pyruvate by either entering the citric cycle or directly becoming pyruvate or acetyl CoA

Question 31

what does Aconitase do

Answer 31

• an enzyme called aconitase converts citrate into isocitrate
• Aconitase contains an iron-sulfur center which acts both in the binding of the substrate at the active site and in the catalytic addition or removal of H2O.