L9 Adipose CT and Energy Storage

Question 1

What are components of unilocular adipose CT

Answer 1

▪️Contain one large lipid droplet that must occupy cytoplasm
▪️Well developed smooth ER and golgi
▪️Plasma membrane contains receptors for several subtances including insulin, growth hormone,norepinephrine and glucocorticoids that facilitate uptake and release of fatty acids and glycerol
▪️reticular fibers support cells
▪️limited amount of ground substance and highly vascular tissue

Question 2

What are the sites of unilocular cells

Answer 2

Deep layer of the skin(subcutaneous)
Variable between females and males
Around vital organs such as heart and kidney

Question 3

What are components of multilocular adipose CT

Answer 3

▪️store multiple fat droplets
▪️tissue may appear tan to reddish due to extensive vascularity and the cytochromes present in its abundant mitochondria
▪️un myelinated nerve fibers enter the tissue with the axons ending in the blood vessels as well as on fat cells

Question 4

What are the functions of mulitocular cells

Answer 4

▪️production of body heat due to large number of mitochondria
Can oxidize fatty acids up to 20 times that of white fat inc body heat
▪️sensory receptors in skin send signals to temp regulating center of the brain resulting in the relaying sympathetic nerve impulses directly to brown fat cells
Neurotransmitter norepinephrine activates the enzyme that cleaves triglycerides in to fatty acids and glycerol initiating heat production

Question 5

What are the sites of multilocular cells

Answer 5

Only type in new born located in neck and inter scapular region
Brown turns to white with age

Question 6

Why could oxidation energy produced be lost as heat instead of fat synthesis

Answer 6

Due to presence of uncoupler protein in brown adipose tissue

Question 7

What are the 2 ways in which obesity can develop and compare them

Answer 7

Hypertrophic: results from accumulation and storage of fat in unilocular
Hyper cellular: results from overabundance of adipocytes
Usually severe
Appears to be genetic
Mutations in gene responsible for coding for leptin and produces inactive form of that hormone

Question 8

How are fatty acids mobilized from adipose tissue and what does it require

Answer 8

By lipolysis in conditions where dietary supply of carbohydrates is limited
Requires release of FFA and glycerol from their TAG form

Question 9

How does lipolysis occur

Answer 9

Initiated by adipose triglyceride lipase which generates a diacylglycerol that is the preferred substrate for hormone sensitive lipase
The monoacylglycerol product of HSL is acted upon by MAG lipase
Reaction results in 3 free fatty acids and glycerol

Question 10

What happens to the free fatty acids

Answer 10

Move through plasma membranes of adipose cells and endothelial cells of blood capilares by simple diffusion and bind to albumin in blood plasma which are transported to peripheral tissues where it might undergo oxidation to produce energy

Question 11

What happens to the glycerol

Answer 11

Taken up by the liver and phosorylated and oxidized to dihydroxyacetone phosphate which is isomrised to glyceraldhydes 3 phosphate and intermediate of both glycolysis and gluconeogenesis
So either converted in to glucose
Or pyruvate

Question 12

How is lipolysis regulated

Answer 12

In fed state:insulin inhibits lipolysis by converting HSL to its inactive dephosorylated form
In fasting state: primarily epinephrine and to a little extent glucagon hormones activate lipolysis by converting HSL to its active phosphorylated form

Question 13

Where does de novo fatty acid synthesis occur

Answer 13

Primarily in the liver and lactating mammary glands and to a lesser extent adipose tissue

Question 14

What is de novo fatty acid synthesis

Answer 14

Cytosolic process that takes place by action of a single multifunctional enzyme complex called fatty acid synthase that contains 7 enzyme activities
It adds 2 carbons by 2 to the elongating chain
Function stops upon formation of palmitate(16C)

Question 15

Where do the carbons come from

Answer 15

From acetyl Co A and atp is used and NADPH(source of hydrogen)

Question 16

Where is the acetyl co a produced and how does it reach the cytoplasm

Answer 16

In mitochondria by pdh

By citrate shuttle

Question 17

What must happen to acetyl co a in order to be used as an elongating unit during FA synthesis and how

Answer 17

Converted to malonyl co A
Occurs by CO2 fixation catalyzed by enzyme acetyl co a carboxylase
Committed step for FA synthesis
Biotin needed and ATP

Question 18

How can palmitate be freed

Answer 18

Must be activated to palmitoyl COA before it can proceed through any metabolic pathway
Usual fate is esterification to form TAG

Question 19

How can elongation occur

Answer 19

Requires a system of separate enzymes rather than a multifunctional enzyme
Malonyl Coa is a 2 carbon donor and NADPH supplies electrons
Brain has additional elongating capabilities allowing it to produce the very ling fatty acid chain(over 22 carbons)

Question 20

How is fatty acid synthesis regulated in hormonal pathway

Answer 20

Through regulation of acetyl carboxylase

Insulin in fed state:
Activates acetyl carboxylase by dephosphorylation
Induces synthesis 
Glucagon in fasting state:
Inhibits by phosphorylation 
Represses synergy

Question 21

How is fatty acid synthesis regulated by allosteric regulation

Answer 21

Acyl co a(palmitoyl co a):allosteric inhibitor of acetyl co a carboxylase
Also inhibits the transport of citrate from mitochondria to cytosol
Citrate is an allosteric activator of the enzyme