GI System Biochem 1 Flashcards
What 2 monosaccharides make up lactose?
Galactose and glucose
What 2 monosaccharides make up sucrose?
Glucose and fructose
Which polysaccharide is composed of glucose units linked by alpha-1,4 linkages?
Amylose
What polysaccharide has glucose linked by alpha-1,4 and alpha-1,6 linkages?
Glycogen
What polysaccharide has long chains of alpha-1,4 linkages and every 25 molecules has an alpha-1,6 branch?
Amylopectin
What polysaccharide has glucose molecules bound at beta 1,4 linkages?
Cellulose
Which disaccharide has 2 glucose units?
Maltose
Salivary and pancreatic amylase breaks down what type of linkages?
Alpha-1,4
Maltase cleaves which linkage?
Alpha-1,4
Isomaltase cleaves which linkage?
Alpha-1,6
The enzymes maltase, sucrase, dextrinase and lactase are found where?
In the brush borders of the mucosal cells
What is the rate limiting enzyme in the reaction of fructose to glucose?
Fructokinase
What is the rate limiting enzyme in the reaction of galactose to glucose?
Galactokinase
Dextrin is only released from the hydrolysis of which polysaccharide?
Amylopectin
What hormone is released when glucose levels are high?
Insulin
Which organ keeps a constant level of glucose in the blood by storing and producing it as needed?
The liver. These processes are called gluconeogenesis or glycogenesis.
Which tissues do not require insulin to take up glucose?
The liver, brain, RBC. Only skeletal muscle and adipose require insulin to uptake glucose. Brain and RBCs require a constant supply of sufficient oxygen and thus can’t afford to rely on a fluctuating insulin status. Liver is involved with the constant homeostasis of glucose and also thus should not be dependent on insulin status.
Which hormones are released when glucose levels are down?
Glucagon, epinephrine, cortisol. These hormones all mitigate hypoglycemia by influencing insulin.
Which of the catecholamines stimulates gluconeogenesis?
Epinephrine
Glucokinase is only found in which organ?
The liver.
In what part of the cell does glycolysis occur?
Cytosol of the cytoplasm.
What enzyme allows the liver to trap glucose in the form of glucose-6-phosphate?
Glucokinase
What are the 3 rate-limiting enzymes of glycolysis?
Hexokinase/glucokinase
Phosphofructokinase
Pyruvate kinase
How many molecules of pyruvate do we get from one molecule of glucose?
Two
What mineral is required for the phosphorylation reactions of glucokinase and phosphofructokinase?
Magnesium
What is the net harvest from aerobic glycolysis?
8 atp (2 atp, +6 atp from 2 nadh, +4 atp)
Which Krebs cycle intermediate inhibits action of phosphofructokinase and therefore inhibits glycolysis?
Citrate
What is the net harvest of anaerobic glycolysis?
2 atp (nadh still gets produced but under anaerobic conditions does not get oxidized)
What is the aerobic fate of pyruvate?
Acetyl-CoA
Under anaerobic conditions pyruvate is reduced to what?
Lactate
What enzyme complex converts pyruvate into Acetyl-CoA?
Pyruvate dehydrogenase complex. This enzyme requires Mg.
What vitamins are needed for the pyruvate dehydrogenase complex?
Vitamin B1 or thiamin
Vitamin B2 in the form of fad
Vitamin B3 in the form of nad
Vitamin B5 in the form of CoA
What mineral is required for the pyruvate dehydrogenase complex?
Magnesium
Pyruvate carboxylase converts pyruvate into what?
Oxaloacetate. Pyruvate carboxylase requires biotin.
What cofactor is important in the carboxylation reaction of pyruvate to oxaloacetate?
Biotin
Why is the production of oxaloacetate from pyruvate important?
In order for the Krebs cycle to run
What acts to promote pyruvate dehydrogenase and the subsequent formation of Acetyl-CoA?
The presence of pyruvate
What inhibits pyruvate dehydrogenase and promotes pyruvate carboxylase thus shuttling pyruvate into oxaloacetate?
The presence of Acetyl-CoA
Where does the Krebs cycle take place?
In the mitochondria
In which cells does the Krebs cycle not take place?
Rbc, as they lack mitochondria
Which metabolite of the Krebs cycle is used for fatty acid synthesis?
Citrate
Which 2 Krebs cycle metabolites are important for amino acid synthesis?
Oxaloacetate and alpha ketoglutarate
Which Krebs cycle metabolite is used in porphyrin/heme metabolism?
Succinyl-CoA
Acetyl-CoA joins with what substance to form citrate?
Oxaloacetate
What regulates the Krebs cycle?
The ratio of adp to atp
What does high levels of atp do to the Krebs cycle?
It slows it down
What coenzymes are needed in the Krebs cycle?
B3 as nad
B2 as fad
B5 to make Succinyl-CoA
Name four uses for Acetyl-CoA.
- atp production
- Fatty acid synthesis
- Ketone synthesis
- Cholesterol formation
Which enzyme regulates the levels of Acetyl-CoA?
Pyruvate dehydrogenase complex
What are the 2 reducing equivalents?
Nad and fad
What metabolite of the Krebs cycle is an important indicator of energy status of the cell?
Citrate
How is oxaloacetate transported out of the mitochondrion?
Via conversion to malate
In what organs does gluconeogenesis occur?
Mostly liver but also kidney
Which hormone by its involvement with glucagon inhibits glycolysis and promotes gluconeogenesis?
Epinephrine. Glucagon is a hormone (made by the pancreas) that influences the liver to break down glycogen into glucose.
What steroid hormone promotes the gluconeogenic pathway?
Cortisol
Name 3 substrates for gluconeogenesis.
- Alanine (and other amino acids)
- Glycerol
- Lactate
What are the 2 key products of the hexose monophosphate shunt?
Nadph
Ribose (used in nucleotide synthesis)
What is the harvest from the Krebs cycle?
3 nadh
1 fadh
1 gtp
What is the key rate-limiting enzyme in glycogen synthesis?
Glycogen synthase
What hormone activates glycogen synthase?
Insulin
What hormones inhibit glycogen synthesis?
Cortisol, glucagon
What substance in low quantities inhibits glycogen synthase?
cAMP
Which tissues have high amounts of glycogen?
Liver and skeletal muscle
Which metabolite in glycolysis is tranformed into glycogen?
Glucose-6-phosphate
What substance carries glucose molecules to the growing glycogen chain?
Udp
What is the rate-limiting enzyme in glycogenolysis?
Phosphorylase
How is nadph used by the body?
It maintains iron as Fe2+ in RBCs
How many atp do you get from nadh?
Three
How many atp from fadh?
Two
Where does fadh enter the electron transport chain?
At ubiquinone
What mineral is important in the electron transport chain?
Iron
What is the overall harvest of energy from 1 molecule of glucose?
8 atp from glycolysis
2 nadh from pyruvate to acetyl SCoA
–> 6 atp
6 nadh –> 18 atp
2 fadh –> 4 atp
2 gtp –> 2 atp
Total of 38 atp
What is the final electron acceptor in the electron transport chain?
Oxygen
The process of forming atp from electrons is called what?
Transduction
How many carbons in a short chain FA?
2-6
How many carbons in a medium chain FA?
8-10
How many carbons in a long chain FA?
16-22
Animal fat is a good source of what type of FA?
Saturated
Oleic, linoleic and alpha linolenic acids are examples of what type of FA?
Unsaturated
Hydrogenation of fatty acids produces what?
Cis and Trans fatty acids
What are the 2 essential fatty acids?
Linoleic acid
Alpha linolenic acid
Essential fatty acids mean the human body can’t make it and thus must ingest it.
What is a good source of linoleic acid?
Vegetables, nuts and seeds
What is a good source for alpha-linolenic acid?
Flaxseeds
What is the name of the enzyme that converts linoleic and alpha-linolenic acids into their metabolites?
Delta-6-desaturase
Which efa is omega-3?
Alpha-linolenic acid
What efa is omega-6?
Linoleic acid
Which FA is the precursor for pro-inflammatory, series 2 eicosanoids?
Arachidonic acid. Series 2 eicosanoids produce prostaglandins. Arachidonic acid is also a precursor for series 4 eicosanoids which produce leukotrienes.
Which efa is precursor for series 1 eicosanoids?
Linoleic acid. Series 1 is correlated with inflammation.
Which efa is precursor for series 3 eicosanoids?
Alpha-linolenic acid. Series 3 is correlated with anti-inflammation.
Linoleic acid is converted by delta-6-desaturase into what fatty acid?
Gamma-linolenic acid
What are some good sources of gamma-linolenic acid?
Evening primrose oil, borage oil, blackcurrant oil
What important fatty acid, also known as 20:5(n-3) can alpha-linolenic acid be converted into?
Eicosapentaenoic acid
What is a good source of eicosapentaenoic acid?
Cold water fish oils
What is the name of the enzyme that releases arachidonic acid from cell membranes?
Phospholipase A2. Corticosteroids inhibit Phospholipase A2. Angiotensin II and epinephrine activate this enzyme.
What is the name of the enzyme that converts arachidonic acid into prostaglandins?
Cyclooxygenase aka COX. NSAIDs inhibit this event.
What is the name of the enzyme that forms leukotrienes from arachidonic acid?
Lipoxygenase
What products inhibit phospholipase A2?
Corticosteroid anti-inflammatories
What product inhibits activity of cyclooxygenase?
NSAIDs
What hormone promotes the conversion of carbohydrates into triglycerides?
Insulin
What enzyme causes the release of fatty acids from triglycerides?
Hormone sensitive lipase
What are free fatty acids usually bound to in the blood?
Albumin
What hormone inhibits action of hormone sensitive lipase?
Insulin
What promotes hormone sensitive lipase?
Growth hormone, glucagon and Epi
Esterification is used in the forming of triglycerides from what 2 substances?
Acetyl-CoA and glycerol-6-phosphate
Free fatty acids are mobilized from what cell?
Adipose
What is the action of lipase?
It breaks down ester bonds
What is the optimal pH for gastric lipases?
4.5 to 6.0
Where does lipolysis of dietary triglycerides occur?
20-30% in the stomach, 80-70% in the small intestines
What constitutes a triglyceride?
3 Fatty acids attached to a glycerol backbone
Lecithin or phosphatidylcholine is found in what substance?
Phospholipids
What mineral is important in cell membranes?
Phosphorus. Lecithin (which contains phosphorus) is an integral component for cell membrane production.
What does saturated refer to?
All carbons of a fatty acid are saturated with hydrogens so no double bonds. Versus unsaturated means it contains at least 1 double or triple bond.
Double bonds are seen in what kind of FA?
Unsaturated
How are lipids transported in the blood?
Via lipoproteins. Versus TAG travels in general circulation via chylomicrons.
What are 2 effects of trans-fatty acids on the body?
- Interfere with essential fatty acid metabolism
- Atherogenesis
What substance emulsifies FAs?
Bile. Bile salts are amphipathic and thus can turn larger fat globules into smaller ones. This allows more surface area for lipase to impact on.
How do triglycerides cross the intestinal membrane?
They drop 2 fatty acids leaving one at the number 2 site on glycerol, cross membrane and get reformed on the other side
How do triglycerides travel in general circulation?
Via chylomicrons in the lymphatics and blood stream. Versus lipids are transported in the blood by lipoproteins.
Where does beta oxidation take place?
In the mitochondrion of all cells. Versus fatty acid synthesis occurs in the cytosol.
What is the activated form of FA?
Acetyl-CoA
How is Acetyl-CoA transported into the mitochondrion?
Via carnitine
What co-enzyme is needed in the activation of FA into Acetyl-CoA?
Vitamin B5
What co-enzymes are needed in the beta-oxidation pathway?
Vitamin B2 as fad
Vitamin B3 as nad
Where does FA synthesis take place?
In cytosol of all cells
What is the rate-limiting enzyme of FA synthesis?
Acetyl-CoA carboxylase
What is the immediate substrate for FA synthesis?
Acetyl-CoA
Acetyl-CoA carboxylase acts on Acetyl-CoA to produce what?
Malonyl-CoA
What co-enzyme is important for the production of Malonyl-CoA from Acetyl-CoA?
Biotin
What reducing agent is used in FA synthesis?
Nadph
How does Acetyl-CoA get out into the cytoplasm for FA synthesis?
Citrate leaves the mitochondrion and the action of citrate lyase forms Acetyl-CoA and oxaloacetate
What hormone activates Acetyl-CoA carboxylase?
Insulin
What is the end product of de novo FA synthesis?
Palmitate. De novo means to make new.
What substance is the activated end product of lipogenesis and will cause feedback inhibition on Acetyl-CoA carboxylase?
Palmitoyl-CoA
What 3 tissues undergo lipogenesis?
Liver, skeletal muscle, and cardiac muscle
Where does chain elongation take place?
In the mitochondrion and smooth ER
Which tissues undergo de novo synthesis?
Liver and adipose cells
Where does de novo synthesis take place?
In the cytoplasm
What are the 3 Ketone Bodies?
Acetoacetate, acetone and beta hydroxybutyrate
Ketone production takes place when which substance is low?
Oxaloacetate
In what tissue does ketone synthesis take place?
Liver
Where in the cell does ketone synthesis take place?
In the mitochondrial matrix
What is the fate of acetone?
It is usually exhaled
What is the fate of 3 hydroxybutyrate?
It gets oxidized to acetoacetate
What 2 tissues can use acetoacetate?
Brain and skeletal muscle
What apoprotein marks hdl for hepatic uptake?
Apoprotein E
How is dietary fat carried into the body?
In chylomicrons via the lacteals
Which tissues synthesize chylomicrons?
Mucosal cells of small intestine
Apoprotein A is found on what lipoprotein?
hdl
Which lipoprotein functions to carry triglycerides from the liver to extrahepatic tissue?
vldl
Which lipoprotein functions to carry cholesterol from liver to extrahepatic tissue?
ldl
Which apoprotein allows for uptake of cholesterol by cells?
Apoprotein B
Chylomicron remnants are formed from the action of which enzyme?
Apoprotein lipase
What enzyme facilitates cholesterol transfer to hdl from tissues?
Lecithin-cholesterol acyltransferase
What apoprotein activates Lecithin-cholesterol acyltransferase?
Apoprotein A on hdl
