Exam 1 SG Flashcards
How do the classes of biomolecule compare in terms of % w/i the human body
- protein: 16%
- lipids: 15%
- carbohydrates: 1%
- nucleic acids: 1%
Lipids
- monomer: fatty acids
- water insoluble molecules
- amphipathic
Importance of lipids
- form barriers
- serve as stored fuel source
- involved in signal transduction
Proteins
- monomer: amino acids
- can be soluble/insoluble depending on AA 3D structure
- participate in essentially all cellular processes (workhorses)
Importance of proteins
- serve as catalysts, enhancing rate of chemical reactions
- serve as signaling molecules and receptors
- maintain cell shape/structural support
Carbohydrates
- monomer: monosaccharides
- water soluble rich in hydroxyl groups
- can be attached to proteins OR lipids
Importance of carbohydrates
- primary fuel source for living creatures
- serve as sites for cell-cell interaction
- maintain shape/structure
Nucleic Acids
- monomer: nucleotides
- RNA and DNA
- primarily found in phosphorylated form
Importance of nucleic acids
- store and transfer genetic information
Major Elements
CHNOPS
Why is Carbon so versatile?
- bond formation
- affinity for oxygen
- bond dissociation
- electronegativity
Covalent vs Noncovalent
- covalent: share electrons b/w pairs (strong)
- noncovalent: vary in electromagnetic interactions w/i or between molecules (weak)
Covalent vs noncovalent in H2O structure
- covalent: bonds b/w hydrogen and oxygen
- noncovalent: b/w one water molecule and another
Why are lipids not considered true polymers?
- they do not contain multiple polymers and they are not interlinked
Saturated FA
- composed of carbon-carbon single bonds
Unsaturated FA
- one or more c-c double or triple bonds
Omega-3 FA and Omega-6 FA
- the location of the first c-c double bonds counting from the methyl group
What is X:X
total carbons: c-c double bonds
Why must humans obtain. most of their cis-polyunsaturated fatty acids from their diet?
- our bodies do not make them because we cannot synthesize them
Four Classes of lipids
- Triacylglycerols
- Phospholipids
- Glycolipids
- Steroids
Classes that contain FA
- triacylglycerols, phospholipids, glycolipids
Classes that are found in the membrane
- phospholipids, glycolipids, steroids
Why is the plasma membrane important?
- surrounds the outside of every prokaryotic and eukaryotic cells
- composed of two layers and contains proteins and carbs
- impermeable to MOST molecules
Attributes membranes share
- contain amphipathic phospholipids
- are asymmetric, non covalent assemblies
- are electrically polarized and fluid structures
- have specific proteins, which mediate distinct functions
Why are membranes electrically polarized?
- because of the electrical differences across the membrane
What affects the rigidity of the membrane?
- temperature. the lower the temperature, the more rigid, due to the degree of brownian motion and non-covalent interactions
What type of proteins are transporters?
- integral proteins
Voltage-gated vs Ligand-gated channels
- voltage-gated: open in response to changes in membrane potential
- ligand-gated: open in response to signal molecule binding
What powers a primary active pump?
- hydrolyzed ATP
What powers a secondary active pump?
- electrochemical gradient
How do signal transduction pathways operate?
- A stimulus triggers release of a primary messenger
- PM is recognized by a receptor
- info is relayed to cells interior by SM
- SM activate/inhibit effector molecule
- signal cascade is terminated
Why are lipid messengers synthesized on demand?
- diffuse through membranes as lipophilic; cannot be stored in vesicles
Where are lipid receptors?
- ligand lipids bind to extracellular and intracellular receptors
- seven-transmembrane-helix receptors
- nuclear hormone receptors
Why are seven-transmembrane-helix receptors also known as G protein coupled receptors?
- they are associated with guanyl nucleotide proteins
In the insulin transduction pathway, what does active protein kinase B (Akt) do?
- phosphorylates enzymes in cell
- leads to phosphorylation of GLUT4
- increase glucose intake
- glycogen synthesis
How is the insulin transduction pathway shut down?
- dephosphorylation
How are dietary triacylglycerols digested in the human body?
- TAGs are mobilized from adipose tissue
- FAs are activated and transported to mitochondria
- FAs are oxidized into acetyl CoA
Does cholesterol cross the intestinal plasma membrane considering it is lipophilic?
- cholesterol is moved to the intestinal cells by a transporter, NPC1L1, after it has been cleaved by enzymes
What do chylomicrons transport? where does it go?
- they are released into the lymph system and then into the blood carrying fat absorbed from the diet as well as fat-soluble vitamins
How is dietary cholesterol moved into intestinal cells?
- cholesterol esterase cleaves ester linkages in cholesterol esters
- NPC1L1 transports from there to intestinal cells
What is shared among metabolic pathways?
- intermediates
What is the rate limiting step in metabolism of TAGs
- transportation of FAs where they have to be attached to carnitine to cross the inner mitochondrial membrane
How are fatty acids synthesized in the human body?
- acetyl CoA is transported to cytoplasm
- acetyl CoA is activated and transferred
- FAs are synthesized
What is the committed step of FA synthesis?
- activation of acetyl CoA
How is acetyl CoA transported out of the mitochondria?
- acetyl CoA is converted to citrate by oxaloacetate and then cleaved into the cytoplasm as citrate
- two can be transported at a time for a given FA
What are the four repeating steps in FA synthesis?
- condensation
- reduction of the carbonyl group
- dehydration
- reduction of the double bonds
(synthesize saturated FA 2 at a time)
What molecule is used to synthesize even fatty acid chains?
Propionyl CoA (3-carbon molecule)
What molecule is used to synthesize odd fatty acid chains?
Propionyl CoA (3-carbon molecule)
What FA chain length can mitochondria synthesize?
- shorter chains
What FA chain length can ER synthesize
- longer chains
What two pathways can be used to synthesize TAGs in the intestine?
- monoacylglycerol (80%)
- glycerol phosphate pathway
What starting material is used to synthesize TAGs in the liver?
- phosphatidate–precursor has two hydrocarbon chains and glycerol
Which lipids are synthesized from ceramide?
- sphingolipid (ceramide reacted with phosphatidylcholine; generates sphingomyelin)
Which lipids are synthesized from acetyl CoA
- steroids
How do statins reduce cholesterol?
- statins are an inhibitor
- mimic enzymes substrates and steal the binding site
LDL
- transport cholesterol from liver to body
HDL
- transport cholesterol from body to liver
Regulation of lipid synthesis
- phosphatidic acid phosphatase plays a key role (PAP)
- upregulated: by phosphatidylinositol and cardiolipin
- serine palmitoyltransferase and ceramide play roles in sphingolipid and glycolipid synthesis
- activity regulated by small ER proteins
Regulation of cholesterol synthesis
- controlled my HMG CoA reductase
- has several levels:
1. HMG CoA reductase gene expression
2. Hormones (insulin and glucagon)
3. oxygenated-cholesterol derivatives
4. covalent modification of enzyme
