Carbohydrates Flashcards
Functions of carbohydrates
- Act as energy reserves in plant/animals
- Metabolism of carbs provides energy
- source of intermediates needed for various pathways
- Provide structural framework (DNA, RNA, cell walls, etc)
Monosaccarides
-simplest sugar (can’t be hydrolyzed smaller)
C(n)H(2n)O(n)
Fisher projection
- used for monosaccharides, shows open-chain formula, can exist in 2 isomeric form D and L.
Haworth formula
4,5,6 carbon monosaccharides spend most of their time in cyclic form
Hemiacetal
= Aldehyde + Alcohol
Hemiketal
= Ketone + Alcohol
Pyranose
6 membered ring
- formed by aldoses containing 6 carbons
- Alpha = OH down
Furanose
5 membered ring
- formed by ketoses containing 6 carbons
- Alpha = OH down
Sugar carbon names
3, 4, 5, 6
3 carbons = triose
4 C = tetrose
5 C = pentose
6 C = hexose
Biochemical/medical importance of Glucose
- aka dextrose (5% dextrose solution is a source of water and calories)
- aka blood sugar
Biochemical/medical importance of Fructose
-found in fruits, honey, and in high fructose corn syrup (HFCS - derived from cornstarch)
Biochemical/medical importance of Galactose
- “brain sugar” - abundant in nervous and brain tissue
- not commonly free in nature
- found as a component in: oligosaccharides and polysaccarides in plants, glycoproteins, ceramide molecules of glycosphingolipids, lactose
Biochemical/medical importance of Ribose and Deoxyribose
Pentose sugars part of nucleic acids RNA and DNA
Disaccharides
- two monosaccharides in haworth configuration held together by glycosidic bonds
- one hemiacetal/ketal anomeric carbon = reducing sugar
Maltose
Found in digestion of starch. germinating seeds, sweetner, culture media, related to malt.
- alpha glucose + a/B glucose
- bond at alpha 1,4
- reducing sugar
- digestible by maltase
Cellobiose
Intermediate formed during hydrolysis of cellulose.
- beta glucose + a/B glucose
- bond at beta 1,4
- reducing sugar
- not digestible by humans (lack cellobiase)
Lactose
“milk sugar” = major carb in milk
- beta galactose + a/B glucose
- bond at beta 1,4
- reducing sugar
- digestible by lactase
Sucrose
In cane sugar, brown sugar, powdered sugar.
- glucose + fructose
- bond at 1,2
- non-reducing sugar
- digestible by sucrose-isomaltase
Trehalose
Found in young mushrooms, seafood, honey, bread, bear blood of insects. Used as sweetener, thickener, cryopreservation.
- glucose + glucose
- bond at 1,1
- non-reducing sugar
- digestible by trehalase
Oligosaccharides
- btwn 2-100 monosaccharides bonded together
- Ex: oligofructose and insulin
Reduction of Monosaccharides
-produces sugar alcohols (lack carbonyl group and exist only in open chain form)
- Reduce aldose = primary sugar alcohol
- Reduce ketose = secondary sugar alcohol
Mannitol
Example of sugar alcohols; Found in IV fluids and medications. BUT can be limitation in blood tests.
Reducing sugars
carbohydrates that undergo oxidation and reduce other species. Able to mutarotate.
Mutarotation
ability for a carbohydrate to equilibriate between alpha and beta forms; Requires hemiacetal/ketal at anomeric carbon.
Oxidation
Oxidation of aldehyde = carboxylic acid
-when in open-chain form
O-glycosides
-hemiacetal/ketal + alcohol
-reaction site at hydroxyl group
-permently in closed-ring form if glycoside can’t mutarotate
-seen as intermediates of reactions
Examples: Steviol (aglycone) and rebaudoside, Digoxin (cardiac glycoside that helps pump heart)
Aglycone
non-carbohydrate portion of glycoside
N-glycoside
AKA glycosylamine
-hemiacetal/ketal + amine group
-reaction site at hydroxyl group
Ex: Hemoglocin A1C
The Amadori reaction
-Glycosylation of hemoglobin
glucose + hemoglobin -> schiff base -> Hemaglobin A1C
Polysaccharides
- Most abundant carb found in nature
- More than 100 monosaccharides bonded together
- Includes: Starches, glycogen, cellulose
Amylose
- Type of starch (10-20%) = Storage form in plants
- unbranched (linear)
- > 1000 glucose molecules
- alpha 1,4 glycosidic bond
Amylopectin
- Type of starch (80-90%) = Storage form in plants
- branched (every 20-25 glucose)
- 300 - 6,000 glucose molecules
- alpha 1,4 and alpha 1,6 glycosidic bond
Glycogen
- storage form in animals (stored in liver and muscle tissue to act as reserve of glucose between meals and during muscular activity).
- highly branched (every 8-12 glucose)
- 6,000 glucose molecules
- alpha 1,4 and alpha 1,6 glycosidic bond
Cellulose
- provides support in plant cell walls
- unbranched
- 300-15000 glucose molecules
- beta 1,4 glycosidic bonds
- Dependent on normal flora to digest it
- provides bulk of fiber in diet
Fiber
Bulk of it is cellulose Functions: 1. Increases satiety 2. lowers serum cholesterol 3. alleviates diverticular diseases and constipation
alpha amylase
An important enzyme found in the saliva and pancreas that digests carbohydrates by hydrolyzing the glycosidic bonds in starch and glycogen.
What are the major monosaccharides derived from the breakdown of carbohydrates?
glucose, galactose, and fructose
Transporter proteins
Help transport carbohydrates in/out of cells to aid in carbohydrate absorption
- SGLUT1 = (sodium-glucose transporter) intestinal cell uptake of glucose and galactose
- GLUT 5 = mediates absorption of fructose
- GLUT 2 = hexose diffuse from cell to extracellular fluid/blood
Glucose transport proteins
GLUT 1 = transports glucose into cells
GLUT 2 = Gets glucose to liver for storage and tells pancreas to release insulin
GLUT 3 = transports glucose into brain tissue cells
GLUT 4 = insuline-dependent - transports glucose into heart, muclse, and adipose tissue/cells
Fed State of carbohydrate metabolism
- in liver
- in brain
- in adipose tissue
- in muscle tissue
- in RBCs
Glucose in the liver can:
- pass through to reach other organs
- convert into glycogen (glycogenesis)
- convert into pyruvate (glycolysis)
- produce fatty acids (PPP)
in brain = ATP generation
in adipose tissue = triglyceride synthesis
in muscle tissue = convert into glycogen or pyruvate (and pyruvate into TCA (O2) or lactic acid (no O2)
-in RBC = convert into lactate (glycolysis) or enter the PPP (when under oxidative stress)
Glycogenesis
Glucose -> -> -> Glycogen
-the synthesis of glycogen form glucose (for storage)
What does branching do for glycogenesis?
- increases solubility
- increases surface area = increases rate of glycogen synthesis
Glycolysis
Glucose -> -> -> Pyruvate + 2 ATP
Fate of Pyruvate
Depends on: organism, metabolic circumstances, tissue
Anaerobic: convert it to lactate
Yeast (anaerobic): covert it to ethanol
Aerobic: enter glycoloysis = acetyl CoA
Citric acid cycle
AKA the TCA or Krebs cycle
- makes 2 ATP per glucose (2 Acetyl CoA)
- acetyl CoA is oxidized to carbon dioxide and water
- yields a lot of NADH and FADH2 to generate ATP at the ETC
Electron transport chain
- create the proton gradient that drives ATP sysnthesis via the passing down of electrons to oxygen.
1. Oxidizing agents (NAD+ & FAD) restored
2. ATP produced (36 per glucose - 32 from ETC)
Pentose Phosphate Pathway
- Produces ribose-5-phosphate, needed for DNA/RNA synthesis
- requires G6PD to produce NADPH required for fatty acid and cholesterol biosynthesis; Also prevents oxidative stress by turning oxidized glutathione into reduced glutathione (which neutralized H2O2).
- pathways occurs in RBC during oxidatinve stress, liver, overies, testes, and adrenal glands
Glucose-6-phosphate dehydrogenase deficiency
- G6PD is the first enzyme in pentose phosphate pathway
- oxidative stress without G6PD results in hemolytic anemia
- This deficiency is adventagous in areas where malaria is endemic because it makes it difficult for the parasite to invade RBCs.
Glycolysis vs. PPP
Glycolysis
- Glucose -> pyruvate
- oxidative pathway
- yields NADH and ATP
PPP
- no ATP generated
- yields NADPH
- oxidative and non-oxidative phases
Glycogenolysis
-breakdown of glycogen (during early fasting state)
In the liver, kidney, and intestines: Glycogen -> glucose (to supply free glucose to bloodstream)
In brain/muscle tissue: glycogen enters early glycolytic pathway to generate ATP via TCA and ETC
-NOT the reverse of glycolysis
Hormone regulators of glycogenesis and glycogenolysis
Insulin - dephosphorylates - turns glycogenesis on and glycogenolysis off
Glucagon/epinephrin - phosphorylates - turns glycogenesis off and glycogenolysis on
(De)Phosphorylation of Glycogen Synthase and Glycogen Phosphorylase
Gluconeogenesis (GNG)
- synthesis of glucose from non-carbohydrate substances such as alpha-keto acids (muscle protein), glycerol (TG of adipose tissue), and lactic acid (muscle tissue).
- occurs when glucose derived from glycogenolysis starts to decline
- 90% takes place in liver (rest in kidneys)
- reverse of glycolysis
Cori Cycle
The interrelationship btwn glycolysis and gluconeogenesis.
Glycolysis: in muscle - Glucose -> 2 pyruvate -> lactate + 2 ATP
Gluconeogenesis: in liver - Lactate + 4 ATP -> 2 pyruvate -> glucose
Diabetes
group of disorders characterized by elevated blood glucose (hyperglycemia) and disordered insulin metabolism
3 major categories: T1DM, T2DM, gestational diabetes
Type 1 Diabetes Mellitus (T1DM)
2 types:
- Immune mediated = autoimmune destruction of beta cells in pancreas (responsible for production, storage, and release of insulin)
- Idiopathic = unknown cause but have no evidence of autoimmunity
Signs/Symptoms of T1DM
- Deficiency of insulin due to beta cells
- Hyperglycemia
- Excess glucose lost in frequenct urination (polyuria)
- Polydipsia (excessive thirst)
- Polyphagia (excessive hunger)
- Counter-regulatory hormones promote gluconeogensis
- Increase lipolysis in adipose tissue creates ketone bodies
- pH falls from ketone body production
- = Diabetc ketoacidosis
Type 2 Diabetes Mellitus (T2DM)
- 90-95% of diagnosed cases of diabetes at T2DM
- Used to be known as “adult onset” but now common in children
- the body isn’t able to use insulin the right way = insulin resistance.
Risk factors of T2DM
- Ethnicity (Native america/alaskans > black > hispanic)
- Family history
3 Obesity and body fat distribution (central body adiposity) - Insulin resistance
Insulin Resistance
- the inability to respond to insulin leading to hyperglycemia
- Fasting Hyperglycemia - increased glucose productions due to increase gluconeogenesis
- Post-prandial hyperglycemia - defect in GLUT 4 transport (important in transporting glucose to muscle cells) leading to hyperglycemia
- Inflammation and oxidative stress markers correlate with impaired insulin action
HFCS - high fuctose corn syrup
-nutritionists believe that is plays a major role in the obesity epidemic.
Galactose Metabolism
*Galactosemia
-Normally Lactose if digested into glucose and galactose in the intestines. Galactose is then converted into glucose metabolites
- Galactosemia - increase of galactose in blood and urine due to a defieciency in galactokinase (mild) or galactose-1-phosphate uridyl transferase (severe).
- Screening for these enzymes in infants is rountinely required.
Lactose Metabolism
*lactose intolerance
Lactose broken down into glucose and galactose by lactase. After age 2, the body produces less lactase to wean the young. Levels of lactase vary with age and race.
- Lactose intolerance - undigested lactose enters colon and is fermented by bacteria creating short chain fatty acids and gases. Large amoutns causes abdominal distension, gas, cramping, and diarrhea.
- Hydrogen (H2) breath test helps to diagnose lactose intolerance.
- measuring glucose and plasma galactose of blood or 13CO2 in breath are other ways of diagnosing lactose intolerance.
Sucrose Metabolism
*Congenital Sucrase-Isomaltase Deficiency
-Sucrase-isomaltase breaks down sucrose into glucose and fructose.
- CSID - a mutation in sucrase-isomaltase complex, causes diarrhea and failure to grow in infants.
- Sucrose tolerance test by meausring hydrogen in breath to diagnose this condition (typically diagnosed btwn 1-18 mo).
