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fdsc 406 > 7. Carbohydrates > Flashcards

7. Carbohydrates Flashcards

1
Q

Major Monosaccharides in diet (4)

A

glucose
fructose
ribose
galactose

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2
Q

Major Disaccharides in diet (3)

A

sucrose
maltose
lactose

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3
Q

Major Polysaccharides in diet (2)

A

starch + glycogen (amylose, amylopectin)

fiber + resistant starch (cellulose, pectin, hemicellulose)

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4
Q

What is the dominant natural isomer of monosaccharides in the diet?

A 
D isomer (D-glucose)
(L-glucose is synthesized)
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5
Q

What are raffinose, stachyose, and verbascose? How are they digested?

A

They are oligosaccharides that are fermented by bacteria in the colon (gives you gas)

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6
Q

Amylose

A
  • straight chain glucose polymer
  • alpha 1-4 linkages
  • forms helical coils
  • STARCH
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7
Q

Amylopectin

A
  • branched chain glucose polymer
  • alpha 1-4 linkages and 1-6 branch linkages
  • branches (doesn’t coil)
  • forms colloidal suspensions in water
  • branches every 24-30 residues
  • STARCH
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8
Q

Glycogen

A
  • large, branched glucose polymer
  • alpha 1-4 linkages and 1-6 branched linkages
  • branches every 8-12 residues
  • found in the liver and muscle tissues
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9
Q

Dietary Fiber

A
  • plant material
  • both polysaccharide and lignin
  • RESISTANT TO HUMAN DIGESTIVE ENZYMES
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10
Q

Why is dietary fiber indigestible?

A

Humans don’t produce the enzymes required to break beta 1-4 linkages

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11
Q

Lignin

A
  • made of aromatic polymers and composed of coumaryl, coniferyl, and sinapyl
  • gives plants a “woody” characteristic
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12
Q

Cellulose

A
  • straight chain polysaccharide with repeating glucose subunits
  • INSOLUBLE (has BETA 1-4 linkages; body can’t break these down
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13
Q

Pectin

A
  • Homopolysaccharide with methylgalactosyluronic acid subunits
  • has jelly-like consistency
  • found in fruits and vegetables
  • SOLUBLE (fermentable)
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14
Q

Hemicellulose

A
  • made of pentoses and hexoses covalently bonded
  • contains side chains
  • some units include xylose, mannose, and galactose
  • found in plant cell walls
  • INSOLUBLE
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15
Q

What are the proposed health beneficial effects of fiber? How do they occur?

A
  • fiber binds to cholesterol in the small intestine and carries it out with waste
  • it binds to metals, increasing fecal bulk and alters the viscosity of intestinal contents
  • reduces the risk of diabetes by slowing sugar absorption as well as normalizing blood lipid levels
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16
Q

What are the major enzymes involved in carbohydrate digestion, and where are they located?

A
  • Salivary amylase (in saliva; first enzyme to break down carbs)
  • Alpha amylase (located in small intestine; secreted by pancreas)
  • Maltase, Sucrase, Lactase, and Alpha-dextrinase (break down disaccharides into their monomers; found in microvilli in small intestine)
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17
Q

What kinds of carbohydrates are absorbable?

A

Carbs must be broken down into mono and disaccharides before they’re absorbable

18
Q

What is Resistant Starch?

A
  • not completely hydrolyzed by amylases in upper digestive tract
  • considered a type of fiber in small intestine (aren’t broken down)
  • metabolized by bacteria in large intestine
19
Q

How are monosaccharides absorbed? What is the major energy source?

A
  • Fructose binds to a protein carrier for absorption
  • Absorptive cells in the small intestine use sodium gradient, ATP, and SGLT1 as energy sources to absorb glucose and galactose
20
Q

Glycemic response

A

degree and duration to which blood glucose level is elevated after consuming a portion of food that would provide 50 grams of digestible carbs and measured for 2 hours

21
Q

Glycemic index

A

comparison of glycemic response to a food standard, based on studies of healthy people

22
Q

Glycemic load

A

glycemic index normalized to actual serving standards

23
Q

6 major glucose transporters

A
  • GLUT1 (insures uptake during hypoglycemia)
  • GLUT2 (found in pancreas, intestine, and liver cells)
  • GLUT3 (main transporter in neurons)
  • GLUT4 (insulin regulated to help regulate hyperglycemia)
  • GLUT5 (the FRUCTOSE transporter)
  • GLUT7 (transports glucose out of endoplasmic reticulum after gluconeogenesis is complete)
24
Q

What does Km of GLUT transporters tell you about its function?

A
  • Km tells you when the transporter is most active
  • High Km (low affinity) - most active when high concentrations of glucose are present
  • Low Km (high affinity) - protein is active during hypoglycemia (low glucose concentrations)
25
Q

Describe how blood glucose causes insulin production

A
  • high amount of blood glucose causes glucose uptake via GLUT2
  • ATP formation through glucose utilizes inactivated potassium channels
  • Beta cell membrane becomes depolarized due to accumulation of potassium ions
  • calcium channels open and calcium diffuses into the cell
  • calcium promotes fusing of insulin secretory vesicles with plasma membrane
  • insulin is then released
26
Q

Describe how insulin causes glucose uptake

A
  • insulin causes an increase of the number of glucose transporters at the plasma membrane face in adipose and muscle tissues
  • increased glucose entry occurs by increasing the activity of glucokinase
  • once glucose enters, it is phosphorylated by glucokinase (maintains entry of glucose into cell)
27
Q

major hormones and stress signals (4) involved in glucose metabolism

A
  • Insulin (increases uptake of glucose into adipose and muscle tissues; LOWERS BLOOD SUGAR)
  • Glucagon (increases glycogen breakdown in liver; RAISES BLOOD SUGAR)
  • Epinephrine (increases glycogen breakdown in liver and skeletal muscles; aids in glucose uptake)
  • Cortisol (increases blood sugar through gluconeogenesis; antagonize insulin)
28
Q

Inputs of glycolysis

A

glucose
2 ATP
2 NAD+
2 ADP+P

29
Q

Outputs of glycolysis

A

2 Pyruvic Acid
NADH+H
4 ATP (2 net gain)

30
Q

How is glycogen synthesized (starting material and how its activated)?

A
  • glycogen synthesis starts with UDP-glucose and is formed from Glycogen Synthase
  • When chain reaches 11 or more glucose monomers, branching enzymes form a branch from an oligomer of about 6-8 monomers
31
Q

Glycogenolysis

A
  • the breakdown of glycogen into glucose-1-phosphate and glucose via glycogen phosphorylase
  • important role in fight-or-flight response and regulation of glucose levels in blood
32
Q

What is the input into the Pentose Phosphate Pathway and what are the outputs?

A

The PPP generates NADPH and pentose via two distinct phases (oxidative and non-oxidative phases)

33
Q

Gluconeogensis

A
  • the formation of glucose from carbon substrates (ex: pyruvate, lactate, glycerol, gluconeogenic amino acids, and odd-chain fatty acids)
  • glucose is formed when the body is low on blood glucose levels and requires energy
34
Q

Which organ is dependent on glucose?

A

the liver (synthesizes into glycogen for storage)

35
Q

What is the current recommendation for fiber intake? Whole grains?

A
  • fiber intake: 25-40 g per day

- whole grain: 3-5 16 g servings per day

36
Q

Whole Grain vs. Fiber

A

Whole grain - contains fiber but is made up of bran, germ, and endosperm (so it contains more nutrients than just fiber)
Fiber - indigestible part of whole grain (mostly contained in bran)

37
Q

Multigrain vs. Whole Grain

A

Multigrain - made of refined grains (not as healthy as whole grains)
Whole grains - use entire grain (versus just the endosperm)

38
Q

Metabolism of Fructose vs. Glucose

A

Fructose

  • no insulin response
  • doesn’t suppress hunger hormone
  • goes through unregulated metabolism in liver
39
Q

Consuming too much dietary fructose

A

increases liver fat

increases circulating triglycerides

40
Q

HFCS (high fructose corn syrup) vs. sucrose

A

they are pretty similar

41
Q

How has carbohydrate intake changed over the past 100 years in the US?

A

Cholesterol, Salt, and Sugar consumption has all increased

fdsc 406 (10 decks)

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