Lipids + hormones Flashcards
Describe the solubility of lipids
insoluble in water
soluble in organic solvents (eg. alcohol)
What are the classes of lipids?
fatty acids triacylglycerols (fats + oils) glycerophospholipids (membrane lipids) sphingolipids (membrane lipids) cholesterol
Describe the structure of fatty acids
long chain carboxylic acids
saturated + unsaturated
most unsaturated = cis-configuration
majority = unbranched
as number of carbon atoms increases, melting point increases
as number of double bonds increases, melting point decreases
What is an essential fatty acid?
fatty acids humans cannot synthesise and therefore must be ingested
What are fatty acids precursors for?
prostaglandins, thromboxanes and leukotrienes
Describe the structure of triacylglycerols
fatty acid triester of glycerols (AKA triglycerides)
transported by lipoproteins and stored in adipocytes
if body needs energy, hormone-sensitive lipase splits triacylglycerols into glycerol and fatty acids
fatty acids can then be released into the blood and transported in the form of fatty acid-albumin complex
Describe VLDLs
very low density lipoproteins lipids = triglycerides (endogenous) source = liver function = transport to fat tissue
Describe LDLs
low density lipoproteins lipids = cholesterol source = liver function = transport to peripheral tissue
Describe HDLs
high density lipoproteins lipids = cholesterol, phospholipids source = liver function = transport from peripheral tissue to liver
Describe the structure of glycerophospholipids
main components of cell membranes
amphiphilic (have both hydrophilic and hydrophobic parts)
hydrophobic fatty acid chain + polar head group (phosphate + alcohol)
2 fatty acids bonded to a glycerol which is bonded to a phosphate which is bonded to an alcohol
cleaved by phospholipases in the pancreas after being emulsified with bile
Describe the structure of sphingolipids
components of cell membranes
amphiphilic (have both hydrophilic and hydrophobic parts)
sphingomyelin = fatty acid - sphingosine - phosphate - choline
glycolipid = fatty acid - sphingosine - sugar
Describe the structure of cholesterol
weakly amphiphilic
condensed 4 ring system = steroid ring system
almost all molecule = hydrophobic
polar -OH group = hydrophilic
sources = dietary intake, endogenous synthesis (sites = all cells, major sites = liver + intestine)
precursor for synthesis of steroid hormones + other molecules
What is a hormone?
a substance that controls and regulates biological functions
chemical messenger
How do hormones act?
binding to a specific receptor on cell surface or within a target cell
interaction with receptor triggers and coordinates biological effect
Describe autocine signalling
local cell-cell diffusion
act on neighbouring cells of same type
eg. prostaglandins
Describe paracrine signalling
local cell-tissue diffusion
act on different cells in same tissue
eg. histamine
Describe endocrine signalling
distributed by blood
act on distant target cells
eg. insulin
Describe the different hormone types
peptide hormones = encoded by genes
amino acid-derived hormones = not directly encoded by genes, indirectly by genes of enzymes that synthesise hormones
steroid + sterol hormones = synthesised from cholesterol
lipid hormones = synthesised from fatty acids by specific enzymes
gaseous hormone = nitric oxide
What are the 4 membrane-bound receptors?
receptor that is also an ion channel
G protein-coupled receptor
receptor bound to guanylyl cyclase
receptor that is also a kinase
Describe what happens at a receptor that is also an ion channel
hormone binds to receptor
receptor opens ion channel
ions move into cell and leads to membrane depolarisation
membrane depolarisation = biological effect triggered by hormone
eg. serotonin, GABA
Describe what happens at a G protein-coupled receptor (adrenaline)
hormone binds to receptor
receptor changes conformation, switching GDP for GTP in alpha subunit of protein
exchange leads to dissociation of alpha subunit which binds to another effector protein (calcium channel)
calcium channel opens and calcium ions move into cell
increase in intracellular mediators
alpha subunit hydrolyses attached GTP —> GDP which leads to dissociation of alpha subunit from calcium channel
calcium channel closes, no more calcium ions enter
alpha subunit reassociates with beta and gamma subunits and a new activation cycle can begin
alpha subunit can also bind to PLC (phospholipase C)
PLC = enzyme that catalyses conversion of PIP2 into IP3 (inositol-triphosphate) + DAG (diacylglycerol)
IP3 + DAG regulate enzyme activity
Describe what happens at a G protein-coupled receptor (glucagon)
hormone binds to receptor
receptor changes conformation, switching GDP for GTP in alpha subunit of protein
exchange leads to dissociation of alpha subunit which binds to another effector protein (adenylyl cyclase (AC))
AC = enzyme that catalyses cyclisation of ATP into CAMP (Cyclic AMP)
CAMP = 2nd messenger which activates protein kinases which will phosphorylate proteins and activate them
Describe what happens at a receptor bound to guanylyl cyclase
hormone binds to receptor
GTP is converted to CGMP (cyclic GMP)
CGMP then causes activation of protein kinases
eg. atrial-natriuretic hormone
Describe what happens at a receptor that is also a kinase
hormone binds to receptor
conformational change triggers intrinsic kinase activity of receptor
receptor phosphorylates specific proteins using ATP
phosphorylation leads to activation or inhibition of protein
eg. insulin
