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NUT 111AV > 2. Carbohydrates > Flashcards

2. Carbohydrates Flashcards

1
Q

What % of the energy in the typical American diet do carbs provide?

A

55-60%

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2
Q

Function of carbs.

A
  • Involved in cell signaling
  • Form coenzymes like ATP, FAD, NAD (energy currencies of body)
  • Form backbone of RNA and DNA
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3
Q

If carbs aren’t used for immediate energy in our cells, where and in what form are they stored?

A
  • Stored in muscles and liver in the form of glycogen
  • Excess carbs converted to fatty acid precursors stored as triglycerides in our adipose
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4
Q

Define fiber.

A

Indigestible carbs

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5
Q

Why is fiber indigestible?

A

Humans don’t have the proper enzymes to break down the bonds b/t sugar molecules to release the individual sugars

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6
Q

What type of carb is in a slice of bread? Approx amount?

A
  • 15 g
  • Fiber and sugar
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7
Q

What type of carb is in a glass of milk? Approx amount?

A
  • 12 g
  • Sugars
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8
Q

What type of carb is in a potato? Approx amount?

A
  • 37 g
  • Fiber and sugar
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9
Q

What type of carb is in an egg? Approx amount?

A

LOOKUP

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10
Q

What type of carb is in pasta? Approx amount?

A

LOOKUP

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11
Q

What type of carb is in steak? Approx amount?

A

LOOKUP

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12
Q

What type of carb is in a carrot? Approx amount?

A

LOOKUP

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13
Q

What type of carb is in coffee? Approx amount?

A

LOOKUP

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14
Q

What type of carb is in soda? Approx amount?

A

LOOKUP

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15
Q

What type of carb is in an apple? Approx amount?

A

LOOKUP

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16
Q

What are the 2 designations of carbs?

A
  • Simple: monosaccharides, disaccharides
  • Complex: oligosaccharides, polysaccharides
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17
Q

Define monosaccharide.

A

Simple carb composed of 1 sugar unit

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18
Q

Define disaccharide.

A

Simple carb composed of 2 sugar units

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19
Q

Define oligosaccharide.

A

Complex carb composed of 3-10 sugar units

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20
Q

Define polysaccharide.

A

Complex carb composed of >10 sugars

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21
Q

List the monosaccharides?

A
  • Glucose
  • Fructose
  • Galactose
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22
Q

What is glucose?

A

Sugar our cells use for energy

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23
Q

List the disaccharides.

A
  • Lactose
  • Sucrose
  • Maltose
  • Trehalose
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24
Q

What is lactose broken down into?

A

Glucose and galactose

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25
Q

What is sucrose broken down into?

A

Glucose and fructose

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26
Q

What is maltose broken down into?

A

2 glucose units

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27
Q

What is trehalose broken down into?

A

2 glucose units

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28
Q

List the oligosaccharides that can be fermented by bacteria in our gut.

A
  • Raffinose
  • Stachyose
  • Verbacose
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29
Q

What monosaccharides make up oligosaccharides?

A
  • Glucose
  • Galactose
  • Fructose
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30
Q

List the polysaccharide categories.

A
  • Starch
  • Glycogen
  • Dietary fiber
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31
Q

What is starch?

A
  • Long-chain carb that we consume in foods
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32
Q

Where does glycogen come from? Where doesn’t it come from?

A
  • Don’t consume in foods
  • Have in our body
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33
Q

What monosaccharide is starch made of?

A

Glucose

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34
Q

What monosaccharide is glycogen made of?

A

Glucose

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35
Q

What characterizes a monosaccharide?

A
  • 3-7 carbon atoms
  • Ketone or aldehyde functional group
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36
Q

What do you call a monosaccharide w/ 3 carbon atoms? 4-7?

A
  • 3 = trios
  • 4 = tetrose
  • 5 = pentose
  • 6 = hexose
  • 7 = heptose
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37
Q

What do you call a sugar w/ an aldehyde group?

A

Aldose

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38
Q

What do you call a sugar w/ a ketone group?

A

Ketose

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39
Q

What do you call a 7C sugar w/ an ketone group?

A

Ketoheptose

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40
Q

What would you call a glucose w/ an aldehyde group?

A

Aldohexose

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41
Q

General formula of a monosaccharide

A

(CH2O)n

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42
Q

Define stereoisomer.

A

Have the same molecular formula and sequence of bonded atoms, but differe in 3D orientation of their atoms in space

  • D or L configuration
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43
Q

What constitutes an L-sugar?

A

Asymmetrical carbon has OH group on L side

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44
Q

What constitudes a D-sugar?

A

Asymmetrical carbon has OH group on R side

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45
Q

Where is the asymmetric carbon?

A

Second carbon from bottom

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46
Q

Which form of sugar is nutritionally important for humans? Why?

A

Glucose configuration (D form) can be phosphorylated by enzyme hexokinase during glycolysis

47
Q

What is the anomeric carbon? Which carbon is it on an aldehyde? Ketone?

A

Carbon around which rotation occurs

  • Aldehyde = C1
  • Ketone = C2
48
Q

Alpha vs. Beta anomers

A
  • Alpha: OH of the anomeric carbon pointing down
  • Beta: OH of the anomeric carbon pointing up
49
Q

What is a glycosidic bond?

A

Covalent linkage b/t 2 sugars

50
Q

What happens through condensation?

A

Monosaccharides combine to form disaccharides

51
Q

What is condensation?

A

2 molecules join together and realease an H2O molecule

52
Q

Where do glycosidic bonds occur in a disaccharide?

A

Bonds b/t the anomeric carbon on the 1st monosaccharide and the 4th or 6th carbon on the second monosaccharide

53
Q

Where is an alpha bond formed?

A

OH group on the bottom of the anomeric carbon of the 1st sugar

54
Q

Where is a beta bond formed?

A

OH group on the top of the anomeric carbon of the 1st sugar

55
Q

What is cellulose?

A
  • A structural polymer made up of hundreds to thousands of beta 1,4 linked glucose molecules
  • Indigestible to humans
56
Q

What is a homopolysaccharide? Examples?

A

A polysaccharide consisting of all the same type of sugar units

  • Starch
  • Glycogen
57
Q

What is a heteropolysaccharide?

A

A polysaccharide consisting of 2 or more diff types of sugar units

58
Q

What sugar chains is starch composed of? What % does each make up?

A
  • Amylose comprises ~15-20% of starch
  • Amylopectin comprises ~80-85% of starch
59
Q

What is amylose?

A

Linear chain of glucose molecules bonded together by alpha 1,4 glycosidic bonds

60
Q

What is amylopectin?

A

Branching form of starch that consists of glucose molecules bonded together

  • Has both alpha 1,4 and alpha 1,6 glycosidic bonds
61
Q

What kind of animals can digest cellulose?

A

Ruminant animals like cows and sheep

62
Q

What type of glycosidic bonds does glycogen have?

A

Alpha 1,4 and 1,6 bonds

63
Q

Why do humans need more easily accessible sugars than plants?

A

Humans have muscles that need energy to move while plants do not

64
Q

What is alpha amylase? Function? Where is it released from?

A
  • Enzyme released from salivary glands and pancreas
  • Hydrolyzes alpha 1,4 glycosidic bonds in amylose and amylopectin
65
Q

What are dextrins?

A

Smaller chains of sugars

66
Q

Where are amylose and amylopectin digested? Where are they not digested?

A
  • Digested in mouth
  • Not digested in stomach b/c pH is too low
67
Q

What cells in the pancreas secrete alpha amylase?

A

Acinar cells

68
Q

What is alpha dextrinase? Location? Funtion?

A
  • Enzyme in the brush border region
  • Breaks alpha 1,6 bonds in limit dextrins, leaving monosaccharides and some disaccharides
69
Q

What is maltose? What breaks it down? What is it broken down into?

A

A disaccharide that is broken down by maltase to 2 glucose units

70
Q

What enzyme is sucrose broken down by?

A

Sucrase

71
Q

What enzyme is lactose broken down by?

A

Lactase

72
Q

What are the 3 ways monosaccharide absorption can take place?

A
73
Q

What factors dictate the mechanism of monosaccharide absorption?

A
  • Type of monosaccharide
  • Concentration of monosaccharide in lumen
74
Q

Through what mechanisms are glucose and galactose absorbed? At what concentration? Receptor used?

A
  • Na+ dependent active transport vis SGLT1 receptor
    • Low conc of those sugars in the gut
      • b/c active transport is taking substances from low to high conc
  • Facilitated diffusion via GLUT 2 receptor
    • High conc of those sugars in the gut
75
Q

Is glucose typically higher in concentration inside the cells or out in the gut?

A

Inside the cells

76
Q

Explain how glucose is actively transported into the cell via the SGLT1 receptor.

A
  • Binding sites of SGLT1 are open to lumen of gut –> high Na+ conc make Na+ very likely to bind –> glucose binds more efficiently
    • Na+ and glucose can both bind to the pump, but the binding of Na+ makes the binding of glucose more effective
  • Both Na+ and glucose bound to SGLT1 –> changes conformation of SGLT1
  • Both solutes released into cell together
77
Q

Why can’t glucose just be exported back into the lumen of the gut via the SGLT1 receptor?

A

Low conc of Na+ in the cytosol –> binding of both Na+ and glucose occurs very rarely

78
Q

What do GLUT2 receptors do?

A
  • Brings glucose into enterocyte cells
  • How sugars get out of basal lateral membrane of enterocytes and into circulation
79
Q

When do GLUT2 receptors get recruited to the surface of cells? What is it dependent on?

A

Conc dependent receptor –> recruited when there’s a high conc of glucose or galactose in gut

80
Q

What is the function of beta cells in the pancreas?

A

Constnatly monitor blood glucose levels and release insulin in response to high blood glucose levels

81
Q

Describe the basic metabolic pathway and breakdown of carbs in the GI tract.

A

Carbs enter GI tract –> broken down into their monosaccharide components & absorbed –> monosaccharides get into the bloodstream and are taken to liver

  • Some glucose doesn’t have to go to the liver –> escapes out of bloodstream into cells to be used for energy
  • Most glucose and all fructose and galactose have to go to the liver –> get converted to glucose
82
Q

What monosaccharide doesn’t cause the secretion of insulin?

A

Fructose

83
Q

When is the liver considered to be in a low energy state? What happens to glucose when the liver is in a low energy state?

A
  • When there isn’t enough ATP present in liver cells
  • Glucose is used in the liver for energy
  • Extra glucose is stored as glycogen in liver until glycogen stores are full
84
Q

When is the liver considered to be in a high energy state? What happens to glucose when the liver is in a high energy state?

A
  • Enough ATP present in liver cells; glycogen stores are full
  • Excess glucose can be converted and stores as fatty acids
85
Q

Define gluconeogenesis. When does it occur?

A

The process by which the liver creates glucose from non-sugar/CHO precursors when blood glucose is low

86
Q

Define glycogenolysis. When does it occur?

A
  • Process by which liver releases glucose from the breakdown of glycogen stores
  • Occurs when blood glucose is low
87
Q

What processes in the liver occur to maintain glucose homeostasis?

A
  • Gluconeogenesis
  • Glycogenolysis
88
Q

What is the normal blood glucose level range?

A

90-110 mg/dL

89
Q

How does the body respond to high blood glucose levels?

A

Signal sent to pancreas –> beta cells secrete insulin –> lowers blood sugar

  • Insulin sends signal to liver to shut off glucose production and begin converting glucose to glycogen for storage
  • Insulin sends signals to muscles and fat cells to uptake glucose from blood via GLUT4 to use for energy
90
Q

What are the main glucose regulating hormones?

A

Insulin and glucagon

91
Q

What is insulin?

A

An anabolic hormone released by the pancreas to lower blood glucose

92
Q

What is glucagon?

A

A hormone secreted from alpha cells in the pancreas that can raise blood glucose levels

93
Q

How does the body respond to low blood glucose levels?

A

Glucagon secreted by pancreas –> glucagon causes liver to convert glycogen into glucose for release into the blood –> increases blood glucose levels

94
Q

What is GLUT2? What substrates does it transport? What are its major sites of expression?

A
  • Concentration dependent glucose transporter
  • Substrates: glucose, galactose, fructose, mannose, glucosamine
  • Sites: Liver, beta cells of pancreas, kidney, small intestine
95
Q

What is GLUT5? What substrate does it transport? What are its major sites of expression?

A
  • Fructose (not glucose)absorption into cell through facilitated diffusion
  • Sites: intestine, kidney, brain, skeletal muscle, adipose tissue
96
Q

What is GLUT4? What substrates does it transport? What are its major sites of expression?

A
  • Insulin dependent transporters that allow glucose to get into muscle and fat cells
  • Substrates: glucose, glucosamine, dehydroascorbic acid
  • Sites: muscle, heart, adipocytes (fat cells)
97
Q

What is the glycemic index?

A

Measure of the rate at which glucose levels increase during the 2 hr period after consumption of a certain amount (50g) of CHO compared w/ equal CHO from reference food

98
Q

What are the 2 standards used for the glycemic index?

A
  • Glucose
  • White bread
99
Q

Why is white bread not the best reference standard for the glycemic index?

A
  • Foods like potatoes release their sugars into the bloodstream quicker than white bread –> end up w/ glycemic index above 100
  • White bread contains starch, which needs to be broken down to glucose, and some fat and proteins which will slow the release of sugars into the bloodstream
100
Q

What do high glycemic foods tend to be made of?

A

Simple sugars and high starch foods, w/o much fiber, fat or protein in them

101
Q

What are low glycemic foods composed of? Significance?

A

Complex carbohydrates, fiber, and protein which cause them to be broken down more slowly to release their glucose

102
Q

What are the limitations of the glycemic index?

A
  • Doesn’t take into account the amount of carbs actually consumed
    • Just measures amount of glucose released into blood
  • Measures one food at a time
    • Some foods can slow down the rate of glucose entering bloodstream of other foods
103
Q

What sets aprat glycemic load from glycemic index?

A
  • Considers quality and quantity of CHO in a food
  • GI x g of CHO in one serving of food
104
Q

What is a limitation of both the glycemic index and glycemic load?

A
  • Both defined by the CHO content of food
  • Foods w/ no carb content can still trigger an insulin response due to high protein intake, so GI and GI provide little info
105
Q

What is the difference in insulin usage b/t normal vs. obese people? Significance?

A
  • Obese peeps take much more insulin to control same amount of blood glucose levels b/c they are more insulin resistant
  • Use more insulin –> beta cells work harder –> can lead to glucose intolerance
106
Q

What is glucose intolerance? When does it occur?

A

Occurs when insulin can no longer be produced in high enough levels by the beta cells of the pancreas to maintain blood glucose w/in the healthy range

107
Q

What is insulin resistance? When does it occur?

A
  • Begins when insulin receptors on the muscle and adipose cells are no longer functioning properly and fail to recruit GLUT 4 to their surface to let glucose into the cells
  • More likely to occur when a person has excess fat stored in their body
108
Q

What is type 2 diabetes? Cause?

A
  • Usually results from a combo of failing beta cells in the pancreas and also muscle cells that are resistant to insulin and therefore not appropriately able to recruit GLUT4 to the cell surface in order to get sugar in properly
  • Have higher than normal blood glucose levels all the time
109
Q

What is the pentose phosphate pathway?

A
  • Pathway parallel to glycolysis
  • Converts glucose (a 6C monosaccharide) to several important pentoses
  • Production of NADPH
110
Q

What is the Krebs Cycle? Where does it occur?

A
  • In mitochondrial matrix
  • Oxidation of acetyl-COa to CO2 and H2O
  • Electrons captures & sent to ETC to be used for ATP
111
Q

What is the purpose of cellular respiration?

A

Take foods we eat and capture the energy from those foods and convert it to ATP to fuel our cells

112
Q

Where does glycolysis occur?

A

Cytosol of a cell

113
Q

What happens during glycolysis?

A
  • One 6C glucose molecule is broken down into two 3C pyruvate molecules
  • Net of 2 ATPs and 2 NADHs are produced
114
Q

How much energy per gram do carbs supply?

A

4 cal/gram

NUT 111AV (5 decks)

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