Lipids: Biosynthesis of Fatty Acids

Question 1

HCl

Answer 1

secreted by parietal cells to help digest protein in stomach.

Question 2

Chief cells

Answer 2

secrete pepsinogen, which is activated by HCl to pepsin. Breaks down protein to peptides

Question 3

Trypsinogen

Answer 3

in the intestines, converts to trypsin which is the active form by enteropeptidase.

Question 4

trypsin

Answer 4

activates trypsinogen, chymotrypsinogen, proelastase, and procarboxypeptidase A and B. Peptides break down into tri and di and amino acids

Question 5

Intestinal lumen

Answer 5

absorbs di and tri peptides and amino acids through Na+ dependent secondary active transport

Question 6

a-amylase

Answer 6

secreted by salivary when starch, lactose, or sucrose enter the mouth

Question 7

HCl from cheif cells

Answer 7

stop the salivry amylase

Question 8

Pancreas

Answer 8

secretes a-amylase to help break down the carbs that go into the intestines and tri and oligosaccharides, maltose and isomaltose

Question 9

Carbs absorbed

Answer 9

ONLY monosaccharides, these are transported from the cell to the blood by facilitated diffusion

Question 10

Glucose, fructose and galactose

Answer 10

used by cell for energy
stored as glycogen
enter portal circulation and go to the liver to be converted to fat.

Question 11

Duodenum

Answer 11

where most fat digestion occurs.

Question 12

Fat globule

Answer 12

bound by bile salts from the liver and a phospholipid which causes emulsification. This increases the surface area of the hydrophobic lipid.

Question 13

Jejunum

Answer 13

free fatty acids, cholesterol, and 2-monoacylglycerol are primary products of dietary lipid degradation here. They mix with bile salts to form micelles.

Question 14

Micelles

Answer 14

disk shaped clusters of amphipathic lipids. Mixed micelles are soluble in aqueous solution of the intestinal lumen. Their hydrophilic suface helps facilitate transport of hydrophic lipids

Question 15

Enterocytes

Answer 15

primary site of particle absorption at the brush border membrane

Question 16

Which FA are directly absorbed into bloodstream?

Answer 16

short and medium chain. Do not require mixed micelles. This makes them an effective way to give people energy

Question 17

mono and diacylglycerolacyltransferase

Answer 17

converts 2-monoacylglycerols to triacylglycerols. occurs within the cell

Question 18

Chylomicrons

Answer 18

Triacylglycerols and cholesteryl esters and incorporated into them. released by exocytosis from enterocytes into the lacteals. They travel through lymph, enter blood. Go to peripherals.

Question 19

Lacteals

Answer 19

lymphatic vessels. Basically the immune system and waste disposal

Question 20

Fatty Acids

Answer 20

low levels are in all tissues. Found in fatty acyl esters in more complex molecules. 90% contained in lipoprotein particles. HDL and LDL. 
Large amounts in plasma during fasting 
Transported in blood by albumin
Precursors to hormones
Stored in adipose 
Major energy reserve

Question 21

Structure of FA

Answer 21

Hydrophobic hydrocarbon chain
terminal carboxyl group - high water affinity, amphipathic (hydrophobic compound with a hydrophilic end)
Long chain FA hydrophobic portions predominate

Question 22

Saturated FA

Answer 22

No double bonds
longer FA, higher meling point
solid at room temp
butter

Question 23

Unsaturated FA

Answer 23

Double bonds - create a kink 
Lower melting point
Cis config - Trans is synthetic
Liquid at room temp
Oil
They produce less energy, are less highly reduce, and less products are produced

Question 24

Cis config

Answer 24

loose pliable membranes,

Question 25

Trans config

Answer 25

still membranes –> CV disease

hydrogen gas is pushed through an unsaturated FA. Converts to saturated. Some double bonds reform, but it is different

Question 26

Linoleic acid (w-6)

Answer 26

can metabolize into arachidonic acid
Key part in Dihomogamma linolenic acid
potentially produces PGE1 prostaglandins non-inflamatory
anti-spasmotic
can potentially product PGE2 - inflammatory prostaglandins

Question 27

Linolenic acid (w-3)

Answer 27

Metabolized into PGE3 - non inflammatory
inhibits AA production
deficiency results in decreased vision and altered behavior.

Question 28

VLDL

Answer 28

assembled in liver from cholesterol and apolipoproteins.
Convertd to LDL in bloodstream
Transport endogenous products (chylomicrons exogenous)
associated with small dense LDL and TG - marker of metabolic syndrome, particularily atherogenic

Question 29

De Novo Synthesis of FA

Answer 29

supplied by diet as carbs, proteins and other molecules in excess
Stored as triacylglycerols
Synthesis occurs primarily in the liver and lactating mammary glands - some in adipose
uses Acetyl CoA from glycolysis and kreb cycle

Question 30

Fatty Acid Synthase

Answer 30

mnomer is multicatalystic polypeptide with seven different enzymatic activities plus domain
Domain covalently binds to 4’phosphopanteheine - is a derivative of pantothenic acid and an enzyme component of vitamin A

Question 31

Storage

Answer 31

mono, di, and tri cylglycerols consist of one, two, or three molecules of faty acid esterified to a molecule of glycerol.

Question 32

Triacylglycerol structure

Answer 32

3 FA esterified to a glycerol molecule. Not typically same
C1 FA saturated
C2 FA unsaturated - decrease melting temp
C3 FA either

Question 33

Glycerol Phosphate

Answer 33

initial acceptor of FA during TAG synthesis
made in liver and adipose. Adipocytes can take up glucose only in presence of insulin. Low plasma glucose and insulin limit capacity to synthesize glycerol phosphate.
2 pathways - 1st from glucose using reactions from glycolysis produced by dihyroxyacetone phosphate
Reduced by glycerol phosphate dehydrogenase
2nd only in lvier uses glycerol kinase

Question 34

FA to active form

Answer 34

must be converted to active form (have a CoA attached) before it can TAG synthesis

Question 35

Fates of TAG

Answer 35

Adipose - stored in cytosol of cells. anyhydrous
“Depot Fat” - available to mobilize when fuels needed
Liver - very little
exported, packaged with cholesteryl esters, cholesterol, phospholipid and protein to form lipoprotein particles VLDL
VLDL secreted into blood
Mature and function to deliver endogenously derived lipids to peripheral tissues

Question 36

Release FA from TAG

Answer 36

mobilization requires hydrolytic release of FA and glycerol
Initiated by hormone sensitive lipase - which removes FA from C1 and or C3
Additional lipases specific for di and mono acylglycerols remove the remaining FA

Question 37

Glycerol

Answer 37

released during TAG degradation.
Cannot be metabolized by adipocytes
lacks glycerol kinase
Transported to liver - phosphorylated - used to form TAG in liver or converted to DHAP

Question 38

Hormone-Sensitive Lipase

Answer 38

activated by phosphorylated by 3’ 5’ cyclic AMP dependent protein kinase. Produced in adipocyte. Binds to receptors on the cell membrane. Activated adenylate cyclase.