Lecture 4 Flashcards
what are steroids
one subclass of a broad range of lipids which includes cholesterol known as isprenoids or terpenes
What is cholesterol
- is a major human sterol
- present in the diet and synthesized, especially in the liver
- membrane component
- precursor to bile acids and steroid hormones
- Vitamin D precursor
true or false; cholesterol reduces the fluidity in the membrane stabilizing the extended chain of conformations of hydrocarbon tails of fatty acids due to hydrophobic interactions
true
where is cholesterol present
animal tissues in the diet; as free cholesterol and cholesterol esters
true or false; diets high in animal fats can result into dangerously high levels of blood cholesterol
true
what exacerbates high cholesterol levels in the blood
due to the presence of fatty acids in the diet eg. from butter
true or false; unsaturated fatty acids eg olive oil, help lower blood cholesterol
true
where is cholesterol synthesized in the human body
the liver and contributes to its concentration in the blood
What is a circulatory form of cholesterol
LDLs
true or false; high levels of cholesterol inhibits the synthesis of LDL receptor proteins
true
Why is bad that high levels of cholesterol inhibit the synthesis of LDL receptor proteins
means that LDL levels in the blood tend to increase, in turn enhancing atherosclerosis
true or false; there is a strong correlation between high blood cholesterol and the incidence of atherosclerosis
true
what happens during atherosclerosis
deposition of cholesterol, esters and other materials lead to the narrowing of the arteries and subsequent damage to arterial walls
what is a heart attach or myocardial infection due to
the blocking of coronary artery which part of the heart muscle is damaged by lack of oxygen
Where is cholesterol assembled from
acetyl CoA units
what are the key units to the biosynthesis of steroids and terpenes
isoprene
Stage 1 of isoprenoid synthesis
- ) condensation of 2 acetyl CoA
- ) condensation with another acetyl CoA
- ) formation of mevalonate is completed by the reduction of the thioester that gives primary alcohol
Stage 2 of isoprenoid syntehsis
- ) pyrophosphorylation of mevalonate (2 mol of ATP)
- ) ATP driven decarboxylation and B-elimination of phosphate ion gives IPP
- ) enzyme catalyzed isomeration —> DMAPP
- ) DMAPP coupled to 2X IPP —> H+ loss to give FPP
- ) joining together of two FPP by a two electron oxidation gives SQUALENE
Stage 3 of isoprenoid sythesis
key enzyme oxidosqualene cyclase; forms the multiple ring structure squalene 2,3 epoxide
What is the major regulatory enzyme in cholesterol biosynthesis
HMG-CoA reductase
true or false; HMG-CoA reductase is hormonally controlled by insulin and glucagon
true
true or false; the transcription and translation of the enzyme can be suppressed by the presence of cholesterol in cells
true
true or false; HMG-CoA reductase is also a target for drugs such as statins that are taken to lower blood cholesterol by inhibiting endogenous synthesis
true
true or false; cholesterol is the precursors for a number of steroid hormones including sex steroids and coricosteroids
true
what are androgens
male sex hormones
- synthesized in the testes
- responsible for the development of male secondary sex characteristics
what are estrogens
female sex hormones
- synthesized in the ovaries
- responsible for the development of the female secondary sex characteristics and control of the menstrual cycle
true or false; cholesterol undergoes minor modifications to make bile acids which condense with the amino acids glycine and taurine to form bile salts
true
What are the amino acids that cholesterol condenses with to form bile salts
glycine and taurine
What are isprenoids
come from mevalonate structure
Purpose of vit A
serves as the site of the primary photochemical reaction in vision
purpose of vit D
regulates Ca and Phosphorous metabolism
purpose of Vit E
serves an an antioxidant; necessary for reproduction in rats and may be necessary for the reproduction in humans
purpose of Vit K
has regulatory function in blood clotting
true or false Vit A only occurs in the animal world
true
Describe Vit A structure
- exclusively unsaturated hydrocarbon (B-carotene)
- found in the plant world in the form of a provitamin in a group of pigments called carotene
- enzyme catalyzed cleavage of B-carotene followed by reduction gives two molecules of vit A
What is Vit D
involved in the regulation of Ca and P metabolism
- most abundant in the circulatory system
true or false; if vit D is exposed to UV undergoes ring opening to create vit D3
true
What is the “English Disease” and what can cure it
- soft bones primarily in young children
- very common in the industrial revolution in England
- cured by sunlight or a good diet of cod liver oil
What causes Rickets
Vit D deficiency
- impaired mineralization , a lack of Calcium phosphate
Osteoporosis
lack of Vit D in the elderly
What is cholecalciferol
Vit D3
What is Vit D2
ergosterol
- derived from plant sterols and is present in milk
- inactive
What does active Vit D stimulate
the synthesis of calcium binding protein, increases the absorption of dietary calcium and phosphate from the gut and also assists with deposition of these ions in the bone as calcium phosphate
recommended does of Vit D
10 micorgrams, 250 micrograms is safe
what is hypervitaminosis
higher levels of vit D
- causes high plasma calcium
- over calcification
- hypertension
- kidney stones
What is Vit E
an antioxidant; traps HOO and ROO radicals formed as a result of oxidation of O2 of unsaturated chains in membrane phospholipids
What is the most acitive form of vit E
a-tocopherol
What is vitamin K
important role in blood clotting
- long hydrocarbon chain consists of repeating isoprene units
true or false; the biosynthesis of cholesterol proceeds by condensation of 5C isoprenoid unit
true
where are ispoprenoid units derived from
the reaction of 3 acetyl CoA units
