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Biochemistry > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

Functions of carbohydrates

A
  1. Act as energy reserves in plant/animals
  2. Metabolism of carbs provides energy
  3. source of intermediates needed for various pathways
  4. Provide structural framework (DNA, RNA, cell walls, etc)
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2
Q

Monosaccarides

A

-simplest sugar (can’t be hydrolyzed smaller)

C(n)H(2n)O(n)

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3
Q

Fisher projection

A
  • used for monosaccharides, shows open-chain formula, can exist in 2 isomeric form D and L.
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4
Q

Haworth formula

A

4,5,6 carbon monosaccharides spend most of their time in cyclic form

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5
Q

Hemiacetal

A

= Aldehyde + Alcohol

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6
Q

Hemiketal

A

= Ketone + Alcohol

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7
Q

Pyranose

A

6 membered ring

  • formed by aldoses containing 6 carbons
  • Alpha = OH down
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8
Q

Furanose

A

5 membered ring

  • formed by ketoses containing 6 carbons
  • Alpha = OH down
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9
Q

Sugar carbon names

3, 4, 5, 6

A

3 carbons = triose
4 C = tetrose
5 C = pentose
6 C = hexose

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10
Q

Biochemical/medical importance of Glucose

A
  • aka dextrose (5% dextrose solution is a source of water and calories)
  • aka blood sugar
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11
Q

Biochemical/medical importance of Fructose

A

-found in fruits, honey, and in high fructose corn syrup (HFCS - derived from cornstarch)

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12
Q

Biochemical/medical importance of Galactose

A
  • “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
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13
Q

Biochemical/medical importance of Ribose and Deoxyribose

A

Pentose sugars part of nucleic acids RNA and DNA

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14
Q

Disaccharides

A
  • two monosaccharides in haworth configuration held together by glycosidic bonds
  • one hemiacetal/ketal anomeric carbon = reducing sugar
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15
Q

Maltose

A

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
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16
Q

Cellobiose

A

Intermediate formed during hydrolysis of cellulose.

  • beta glucose + a/B glucose
  • bond at beta 1,4
  • reducing sugar
  • not digestible by humans (lack cellobiase)
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17
Q

Lactose

A

“milk sugar” = major carb in milk

  • beta galactose + a/B glucose
  • bond at beta 1,4
  • reducing sugar
  • digestible by lactase
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18
Q

Sucrose

A

In cane sugar, brown sugar, powdered sugar.

  • glucose + fructose
  • bond at 1,2
  • non-reducing sugar
  • digestible by sucrose-isomaltase
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19
Q

Trehalose

A

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
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20
Q

Oligosaccharides

A
  • btwn 2-100 monosaccharides bonded together

- Ex: oligofructose and insulin

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21
Q

Reduction of Monosaccharides

A

-produces sugar alcohols (lack carbonyl group and exist only in open chain form)

  • Reduce aldose = primary sugar alcohol
  • Reduce ketose = secondary sugar alcohol
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22
Q

Mannitol

A

Example of sugar alcohols; Found in IV fluids and medications. BUT can be limitation in blood tests.

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23
Q

Reducing sugars

A

carbohydrates that undergo oxidation and reduce other species. Able to mutarotate.

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24
Q

Mutarotation

A

ability for a carbohydrate to equilibriate between alpha and beta forms; Requires hemiacetal/ketal at anomeric carbon.

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25
Q

Oxidation

A

Oxidation of aldehyde = carboxylic acid

-when in open-chain form

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26
Q

O-glycosides

A

-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)

27
Q

Aglycone

A

non-carbohydrate portion of glycoside

28
Q

N-glycoside

A

AKA glycosylamine
-hemiacetal/ketal + amine group
-reaction site at hydroxyl group
Ex: Hemoglocin A1C

29
Q

The Amadori reaction

A

-Glycosylation of hemoglobin

glucose + hemoglobin -> schiff base -> Hemaglobin A1C

30
Q

Polysaccharides

A
  • Most abundant carb found in nature
  • More than 100 monosaccharides bonded together
  • Includes: Starches, glycogen, cellulose
31
Q

Amylose

A
  • Type of starch (10-20%) = Storage form in plants
  • unbranched (linear)
  • > 1000 glucose molecules
  • alpha 1,4 glycosidic bond
32
Q

Amylopectin

A
  • 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
33
Q

Glycogen

A
  • 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
34
Q

Cellulose

A
  • 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
35
Q

Fiber

A 
Bulk of it is cellulose
Functions:
1. Increases satiety
2. lowers serum cholesterol 
3. alleviates diverticular diseases and constipation
36
Q

alpha amylase

A

An important enzyme found in the saliva and pancreas that digests carbohydrates by hydrolyzing the glycosidic bonds in starch and glycogen.

37
Q

What are the major monosaccharides derived from the breakdown of carbohydrates?

A

glucose, galactose, and fructose

38
Q

Transporter proteins

A

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
39
Q

Glucose transport proteins

A

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

40
Q

Fed State of carbohydrate metabolism

  • in liver
  • in brain
  • in adipose tissue
  • in muscle tissue
  • in RBCs
A

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)

41
Q

Glycogenesis

A

Glucose -> -> -> Glycogen

-the synthesis of glycogen form glucose (for storage)

42
Q

What does branching do for glycogenesis?

A
  • increases solubility

- increases surface area = increases rate of glycogen synthesis

43
Q

Glycolysis

A

Glucose -> -> -> Pyruvate + 2 ATP

44
Q

Fate of Pyruvate

A

Depends on: organism, metabolic circumstances, tissue
Anaerobic: convert it to lactate
Yeast (anaerobic): covert it to ethanol
Aerobic: enter glycoloysis = acetyl CoA

45
Q

Citric acid cycle

A

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
46
Q

Electron transport chain

A
  • 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)
47
Q

Pentose Phosphate Pathway

A
  1. Produces ribose-5-phosphate, needed for DNA/RNA synthesis
  2. 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
48
Q

Glucose-6-phosphate dehydrogenase deficiency

A
  • 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.
49
Q

Glycolysis vs. PPP

A

Glycolysis

  • Glucose -> pyruvate
  • oxidative pathway
  • yields NADH and ATP

PPP

  • no ATP generated
  • yields NADPH
  • oxidative and non-oxidative phases
50
Q

Glycogenolysis

A

-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

51
Q

Hormone regulators of glycogenesis and glycogenolysis

A

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

52
Q

Gluconeogenesis (GNG)

A
  • 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
53
Q

Cori Cycle

A

The interrelationship btwn glycolysis and gluconeogenesis.
Glycolysis: in muscle - Glucose -> 2 pyruvate -> lactate + 2 ATP
Gluconeogenesis: in liver - Lactate + 4 ATP -> 2 pyruvate -> glucose

54
Q

Diabetes

A

group of disorders characterized by elevated blood glucose (hyperglycemia) and disordered insulin metabolism
3 major categories: T1DM, T2DM, gestational diabetes

55
Q

Type 1 Diabetes Mellitus (T1DM)

A

2 types:

  1. Immune mediated = autoimmune destruction of beta cells in pancreas (responsible for production, storage, and release of insulin)
  2. Idiopathic = unknown cause but have no evidence of autoimmunity
56
Q

Signs/Symptoms of T1DM

A
  1. Deficiency of insulin due to beta cells
  2. Hyperglycemia
  3. Excess glucose lost in frequenct urination (polyuria)
  4. Polydipsia (excessive thirst)
  5. Polyphagia (excessive hunger)
  6. Counter-regulatory hormones promote gluconeogensis
  7. Increase lipolysis in adipose tissue creates ketone bodies
  8. pH falls from ketone body production
  9. = Diabetc ketoacidosis
57
Q

Type 2 Diabetes Mellitus (T2DM)

A
  • 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.
58
Q

Risk factors of T2DM

A
  1. Ethnicity (Native america/alaskans > black > hispanic)
  2. Family history
    3 Obesity and body fat distribution (central body adiposity)
  3. Insulin resistance
59
Q

Insulin Resistance

A
  • 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
60
Q

HFCS - high fuctose corn syrup

A

-nutritionists believe that is plays a major role in the obesity epidemic.

61
Q

Galactose Metabolism

*Galactosemia

A

-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.
62
Q

Lactose Metabolism

*lactose intolerance

A

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.
63
Q

Sucrose Metabolism

*Congenital Sucrase-Isomaltase Deficiency

A

-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).

Biochemistry (14 decks)

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