BIOC Lecture 4: Fat Flashcards
What are adipocytes?
specialized cells primarily found in adipose tissue, commonly known as fat cells
Can fats cross cell membranes?
TAG cannot but fatty acids can
How do TAG’s move from one cell to another?
TAG’s need to be broken down into free fatty acids where the backbone is disconnected
What breaks down TAG?
Lipoprotein lipase (LPL)
What are free fatty acids transported in circulation in?
Bound to serum albumin
What is TAG breakdown modulated by?
Hormones (hormone sensitive LPL)
What will inhibit the conversion of TAG’s into fatty acids?
Insulin
What encourages the conversion of TAG’s into fatty acids?
Glucagon
How many carbons are typical fatty acids?
Long chain molecules - typically 14-maybe 20 carbons
We can’t make glucose from fatty acids, but we can make what?
Glycerol, which can be used to make glucose
How is TAG broken down?
Lipolysis - Sequential removal of fatty acids by related lipases
What is TAG breakdown catalyzed by?
Enzymes called lipases
After how long fasting are ketone bodies produced?
> 1-2 days
What are the two major forms of ketone bodies?
Acetoacetate and hydroxybutyrate
What gives rise to the characteristic odour of breath from ketosis?
Acetone produced from acetoacetate
How can almost all fuels be converted to AcCoA and to fatty acids?
- Glucose through glycolysis
- AA’s to oxo acids and AcCoA
- Fats are already fats
Where are the enzymes involved in synthesising fat located?
In the cytosol
Where are the enzymes involved in breaking down fat located?
Inside the mitochondria
Where is AcCoA produced?
In mitochondria
Where does fatty acid synthesis occur?
In cytosol
How are fatty acids synthesised?
- Citrate shuttle moves AcCoA into cytosol
- Oxaloacetate shuttles back
- Net transfer of two C from within mitochondria
Is fatty acid synthesis a cyclic process?
Yes
What reducing equivalent does fatty acid synthesis involve?
NADPH
What number chain length are almost always produced by animals?
Even-numbered
What does fatty acid synthesis start with?
Acetyl-CoA molecule
What happens during one cycle of fatty acid synthesis?
Join AcCoA to a malonyl-CoA and lose a CO2 - this means we go from 2C to 4C - then we go around again and again
What primarily happens to surplus fatty acids?
Involved in TAG synthesis
Other than TAG synthesis, what are surplus fatty acids used for?
- Other fatty Acyl-CoA
- Phospholipids
- Specialised lipids
- Modifications to proteins
What does short term fasting (8-12) hours result in?
Mostly just CHO differences
What does long term fasting (several days) result in?
- No liver glycogen stores
- Body breaks down proteins to make glucose
- Ketone bodies are synthesised for the brain
- Fatty acid usage increased
What effect does insulin have in the muscle?
Increases glucose uptake and glycogen synthesis
What effect does insulin have in adipose tissue?
Increases glucose uptake and lipogenesis, decreases lipolysis
What effect does insulin have on the liver?
Increases glycogen synthesis and lipogenesis, decreases gluconeogenesis
What effect does glucagon have on adipose tissue?
increased lipolysis
What effect does glucagon have on the liver?
decreased glycogen synthesis, increased glycogenolysis
What effect does epinephrine have on muscle?
increased glycogenolysis
What effect does epinephrine have on adipose tissue?
increased lipolysis
What effect does epinephrine have on the liver?
Decrease glycogen synthesis. increased glycogenolysis and gluconeogenesis
What is glycogenolysis?
Glycogen is broken down
