Introduction to lipids Flashcards
what are the functions of lipid molecules
Phospholipids and cholesterol: cell membranes
Triglyceride is a key energy store
Steroids and fatty acids play regulatory roles as hormones, vitamins and bile acids
how is energy stored in cells (short term)
ATP (and other phosphate bonds)
Redox agents (NADH, FADH2)
Ionic transmembrane gradients (H+ across mitochondria membrane, Na+ across plasma membrane)
All are labile
how is energy stored in cells long term
There is a limit to how much ATP can be stored (some energy is stored intracellularly as creatine phosphate)
Energy stored as large, stable energy efficient precursors eg carbs and fats
Acetyl-CoA as energy mediator
what is acetyl-CoA
Made from glucose, used to form citric acid + ATP and fatty acids (stored energy) (can be reversed)
Also converted to cholesterol – blocked by statins
how can carbs be stored as energy
Starch digested into sugars (glucose) in the gut
Sugars absorbed from gut into bloodstream
Sugars absorbed by liver and stored as glycogen (via hepatic portal vein)
Also sugars stored throughout body as glycogen
what is glycogen used for
Glycogen can be broken down when body needs energy
No glycogen in brain, needs glucose or ketone bodies from plasma constantly
what is the citric acid cycle
Citric Acid (6C) > +O2 > rel CO2+ATP > Oxalo-acetic acid (OAA - 4C) + Acetyl-CoA (2C)
What is fatty acid synthesis
synthesis leads to fatty acids with even number of carbons, consumes ATP
what is beta oxidation
fat mobilisation by shortening fatty acids by 2 carbons at a time to produce ATP and acetyl CoA
what are fatty acids
Simple straight carbon chains + COOH
In humans mostly 16-20 carbons long
50% have double bonds
Esp FA at position 2 (middle) of glycerol
what is the difference between mono and poly unsaturated
one DB monounsaturated, two DB polyunsaturated
how are double bonds made in mammals
Mammals have limited ability to make double bonds (some types of fatty acids must be in the diet – essential fatty acids)
how are fatty acids stored
as triglycerides (a glycerol and 3 fatty acids)
what is cholesterol
Essential components of cell membranes
Precursor of bile acids, steroid hormones and vit D
Ring system so very rigid
where is cholesterol found
Sources: from diet or made in liver
A major emphasis on recycling
Bile salts
Endogenous pathways
what are cholesterol esters used for
A large portion of plasma cholesterol is esterified (75%)
Broken down by lipases to free cholesterol and fatty acids
Cholesterol is amphipathic as free alcohol but hydrophobic when esterified
what are the steroids (4)
Cholesterol
Vit D (produced by skin by action of light on a cholesterol derivative)
Cortisol (hormone secreted by adrenal cortex)
Testosterone (male sex hormone)
what does acetyl-coenzyme A do
Energy production - oxidises fatty acids
Acetyl-CoA can’t be transported in plasma so is converted to acetate
what are ketone bodies
3 soluble chemicals, not bodies
Made from acetyl coA during fasting, by liver, only lasts for 5 hours
what do ketone bodies do
During fasting they’re major energy source (esp heart and brain)
Form Acetoacetic acid and beta hydroxybutic acid
Acetone = waste product
Made spontaneously by decarboxylation and eliminated by kidney
how do unsaturated fatty acids compare to saturated
have a lower MP (more liquid at body temp so increase fluidity of cell membranes)
how are unsaturated fatty acids found
Most naturally occurring fatty acids are cis (even no of carbons, 14-22)
why are saturated fats popular
popular with manufacturers of processed foods as they’re less vulnerable to rancidity and are more solid at room temp
how can unsaturated fatty acids be classified
2 classifications terminologies
Named from alpha carbon at carboxyl end
Omega (opposite end) counting of double bonds
