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Foundations of Nutrition > Glucose & Carbohydrates > Flashcards

Glucose & Carbohydrates Flashcards

1
Q

What is the usual fasting range of glucose?

A

4-6 mmol/l

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2
Q

How long after eating does it take for glucose levels to normalise?

A

2-3 hours

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3
Q

Name 3 glucose dependant cell types

A

Neurons, Erythrocytes, Mammary Glands, Testis

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4
Q

Why is glucose homeostasis important?

A

Allows for a supply of energy to the cells dependant on glucose as their only form of energy source -> i.e. hypoglycaemia could cause N&V, seizure, coma or death due to the brain not being able to synthesise energy/ATP as glucose is not available.

Also important in preventing hyperglycaemia which also has negative effects -> CVD risks, DM complications, Inflammation

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5
Q

What are the 4 main pools of glucose in the body?

A

Blood
ECF
Liver Glycogen (70-120g)
Skeletal Muscle Glycogen (200-1000g)

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6
Q

Give an example of a glucose transporter that is dependant on insulin? Also where are these commonly found?

A

GLUT4 - these are commonly found in muscle and adipose tissues

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7
Q

Give an example of a glucose transporter that is independant of insulin? Also give an example of where this is found in the body

A

GLUT 1,2,3 or 8 - these are found in the glucose dependant cells so neurons and erythrocytes but also found in the liver

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8
Q

Give the 3 ways of how to get glucose levels to increase?

A

Digestion & Absorption of dietary carbs
Glycogenolysis
Gluconeogenesis

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9
Q

Give the 3 ways to reduce glucose levels

A

Glycolysis
Glycogenesis
Conversion of glucose into fat acids and amino acids

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10
Q

What does an item with a high glycaemic index mean?

A

Contains a greater proportion of digestible carbohydrates than non-digestible

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11
Q

What transporter is involved in monosaccharide absorption?

A

SGLT-1 = glucose and galactose

GLUT 5 = fructose

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12
Q

What is the difference between SGLT1 & GLUT5?

A

SGLT-1 is active transport

GLUT5 is facilitated transport

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13
Q

Where does absorbed monosaccharides go from the enterocyte?

A

Portal vein via GLUT2

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14
Q

Where does monosaccharides go once in the portal vein?

A

Goes to the liver where some glucose is taken up by the liver (approx. 30%) and then rest remains in circulation

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15
Q

How many steps are there to glycolysis?

A

10

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16
Q

What is the start and end of glycolysis

A

1 glucose -> pyruvate

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17
Q

What are the 3 key enzymes in glycolysis and why are they important / pointed out in the lectures?

A

The following 3 enzymes are involved in 3 of the 10 steps in glycolysis and make them non-reversible and are rate limiting

Hexokinase, Phosphofructokinase, Pyruvate Kinase

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18
Q

What are the end products of glycolysis if in anaerobic and aerobic conditions and where do they go?

A

Anaerobic -> lactic acid -> Cori Cycle

Aerobic - acetyl CoA -> citric acid cycle

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19
Q

What two options does acetyl CoA have following glycolysis?

A

Enters CAC to allow for oxaloacetate to become citric acid and enter the aerobic respiration pathway

Or the acetyl CoA can be utilised in fatty acid synthesis

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20
Q

How does fructose and galactose metabolism differ from glucose?

A

Fructose enters the glycolysis pathway at a different stage - it becomes monophosphorylated to F1P (fructose monophosphate) and then enters glycolysis later on in the pathway

Galactose is converted to G1P then G6P which enters the Leloir Pathways

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21
Q

What is unique / special about fructose in reference to its entry to glycolysis pathway?

A

It misses on of the rate limiting enzymatic steps, therefore there is less regulation as to how much fructose enters the pathway

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22
Q

Other than glycolysis what other pathway is glucose commonly used in?

A

Pentose Phosphate Pathways

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23
Q

What is the function of the Pentose phosphate pathway?

A

Two functions:

1st function is to produce NADPH to help alleviate the cells from oxidative stress (i.e. during the formation of the compound it mops up free radicals)

2nd function is to produce ribose sugars used in DNA synthesis

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24
Q

What is the main chemical reaction that outlines the function of the pentose phosphate pathway

A

Glucose 6 Phosphate + NADP -> Ribose-5-Phosphate + NADPH

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25
Q

How does glucose enter the PPP?

A

Glucose is converted to G6P in the first step of glycolysis and then this is 2 routes -> either enter the glycolysis or PPP pathway

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26
Q

Give a cell that depends on the PPP in practise?

A

Erythrocytes -> these undergo lots of reductive reactions producing lots of free radicals and oxidative stressors like H2O2

This is why it is linked to congenital anaemias
I.e. in glucose-6-phosphate dehydrogenase (G6PD) deficiency the enzyme that is required to convert G6P to the ribose-5-phosphate is missing, impaired / not functioning so therefore unable to produce NADPH and the cells undergo excessive oxidative stress resulting in haemolytic anaemia / favism

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27
Q

What is gluconeogenesis?

A

Formation of glucose from non-carbohydrate sources

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28
Q

What are the main sources of substrates used in gluconeogenesis?

A

Lactate -> cori cycle
Alanine / Amino acids
Glycerol from fatty acids

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29
Q

How does lactate become glucose in gluconeogenesis?

A

Cori Cycle -> lactate can be converted back to pyruvate and move up the glycolysis pathway

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30
Q

How does amino acids become glucose in gluconeogenesis?

A

Alanine is the main amino acids and this like lactate can be converted to pyruvate and move u[ the glycolytic pathway

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31
Q

How does fatty acids convert to glucose in gluconeogenesis?

A

The glycerol from FAs can be converted to acetyl CoA and then converted to pyruvate and move up the glycolytic pathway

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32
Q

Where does gluconeogenesis take place in the body?

A

Liver and Kidneys

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33
Q

What does the “reverse of glycolysis” mean in reference to gluconeogenesis

A

The reverse of glycolysis is how non-carbohydrate compounds are converted to glucose once they become pyruvate

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34
Q

How is gluconeogenesis regulated?

A

3 types of mechanisms:

Allosteric
Genetic Expression Mechanisms
Covalent Phosphorylation

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35
Q

What do the regulating mechanisms do to allow or gluconeogenesis to take place?

A

Forms key enzymes / allows for access of key enzymes that can reverse the 3 steps that are ‘non-reversible’ oin the normal glycolysis pathway

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36
Q

Name 2 key enzymes in gluconeogenesis

A

Glucose-6-phosphatase
Fructose-1,6-biphosphatase
PEP carboxykinase
Pyruvate Carboxylase

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37
Q

What is glycogenesis

A

Synthesis of glycogen

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38
Q

Where does glycogenesis take place?

A

Liver & Skeletal Muscle

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39
Q

What is glycogen?

A

A branched polysaccharide / polymer of glucose

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40
Q

What is the structure of glycogen

A

Straight chains of alpha-1,4- glycosidic bonds with alpha 1-6 glycosidic bond branching every 9-10 units

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41
Q

What are the two key enzymes in glycogen synthesis and degradation?

A

Glycogen Synthase

Glycogen Phosphorylase

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42
Q

What is the detailed explanation of glycogen synthesis?

A

Glycogenin acts as an enzymatic primer for the first few glucose monomers to attach to.

This enzyme then undergoes autoglycosylation to form proglycogen

Glycogen synthase then takes over to form macroglycogen (55,000 glucose subunits)

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43
Q

What is important to remember about glycogen and glycogen synthesis?

A

High energy costs

High water binding capacity

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44
Q

Where is glycogen stored?

A

Cytosol of cells

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45
Q

What is the main stimulator for glycogenesis?

A

Insulin

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46
Q

What is glycogenolysis

A

Glycogen degradation to produce glucose

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47
Q

WHat enzyme mediates glycogenolysis

A

Glycogen phosphorylase

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48
Q

How is glucose produced from glycogen?

A

Glycogen Phosphorylase cleave the glycosidic bonds and attaches a phosphate to each glucose unit to form glucose monophosphate (G1P).
This is then isomerised to G6P
G6P is then able to convert back to glucose via glucose-6-phosphatase or go down the glycolysis pathway

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49
Q

Name 2 things that down regulates glycogenolysis

A

Glucose, G6P, F1P, ATP, ADP,

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50
Q

What is the difference between liver and skeletal muscle glycogenolysis?

A

Liver is more responsive to external stimuli such as hormones and blood glucose concentration

Skeletal muscle is more responsive to allosteric stimuli such as AMP (the break down product of ATP), G6P.

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51
Q

What situations upregulates glycogenolysis?

A

Stress -> exercise, hypoglycaemia, hypoxia

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52
Q

How does catelcholamines upregulate glycogenolysis?

A

Catecholamines are able to phosphorylate glycogen phosphorylase to its active form via activation of PKA - protein kinase A

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53
Q

What is the endocrine proportion of the pancreas collectively called?

A

Islet of Langerhans

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54
Q

What do alpha, beta and delta cells produce in the pancreas?

A 
Alpha = Glucagon
Beta = Insulin
Delta = Somatostatin
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55
Q

What is the structure of the insulin hormone?

A

51 amino acids in two polypeptide chains

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56
Q

What is the half life of insulin

A

5mins

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57
Q

How is insulin secreted into the blood?

A

Beta Cells have GLUT2 transporters to allow plasma glucose enter the cells by facilitated transport

Increased glucose entry means more can undergo glycolysis so therefore increased ATP production

High ATP concentration closes voltage gated K channels to build up K conc. inside cell resulting in membrane depolarisation opening Ca2+ channels, causing Ca2+ influx.

This results in insulin granule exocytosis

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58
Q

How is insulin secretion stopped?

A

Low glucose in the plasma, results in less entering the pancreatic beta cells via GLUT2 facilitated transport. This lowers ATP production within these cells

This allows for K channels to remain open, keeping the membrane potential of the cell hyperpolarised so no conformational changes can happen to the Ca2+ channels meaning no influx and therefore no exocytosis of insulin granules

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59
Q

What pattern can be used to describe insulin secretion?

Explain the theory behind it

A

Biphasic
Phase 1 : transient wave in first 5-8 mins
Phase 2 : gradual rise over a longer period

Theory is that the first wave = membrane bound vesicle release and phase 2 = central vesicle release

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60
Q

How else does glucose and carbs help regulate insulin secretion?

A

Theory is that glucose and carbs can directly impact insulin gene expression & increase synthesis

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61
Q

How does fatty acids and amino acids affect insulin secretion?

A 
FAs = short term increases, long term inhibits 
AAs = increases secretion
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62
Q

What are the functions of the incretin hormones?

A

GLP-1 & GIP indirectly stimulate insulin secretion via g-protein coupled receptors when glucose levels are high

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63
Q

What is GLP-1 and GIP?

A

Glucagon-Like-Peptide-1

Gastric inhibitory peptide

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64
Q

Give 3 sites of action for insulin

A

Liver, Skeletal Muscle, Adipose Tissue

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65
Q

What is insulins activity in skeletal muscle? (2)

A

Increases glucose uptake via GLUT4 (insulin dependant transporter) and promotes glycogenesis.

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66
Q

What is insulins activity in liver? (3)

A

Promotes glycogenesis, glycolysis
Promotes lipogenesis, TAG & Cholesterol synthesis

Suppresses gluconeogenesis, beta-oxidation. ketogenesis

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67
Q

What is insulins activity in adipose tissue? (3)

A

Aids TAG removal from plasma
Aids TAG synthesis
Prevents fat mobilisation

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68
Q

What is the structure of the glucagon hormone?

A

29 AA single polypeptide chain

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69
Q

What is the intermediate compound called that is actually secreted from the pancreatic cells?

A

Proglucagon

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70
Q

How does glucagon act on cells (generically)

A

Via transmembrane G protein coupled receptors

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71
Q

What stimulates glucagon release?

A

Low glucose and amino acids

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72
Q

Name 3 actions of glucagon

A

Glycogenolysis
Gluconeogenesis
Ketogenesis

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73
Q

What is the key determininent in the glucagon : insulin ratio and why?

A

Insulin because glucagon secretion is normally stable where as insulin is much more variable, therefore having more of an effect on overall ratio

74
Q

Name 5 hormones, other than insulin and glucagon, that may impact glucose homeostasis

A

Somatostatin (decreases D&A & G&I secretion)
Catecholamines (increases glucose & mobilises FAs)
Cortisol (catabolic actions including gluconeogenesis)
Growth Hormone (increase glucose production via IGFs)
Thyroid Hormones (alters insulin sensitivity & increases gluconeogensis)

75
Q

What main organs uptake glucose and which ones requires insulin?

A

> 80% taken up by skeletal muscle
2-5% by adipose tissue
Both are insulin dependant

Most of the rest of glucose is taken up by the liver which is not insulin dependant. (However remember that the liver requires insulin to tell it what to do with the insulin)

76
Q

What role does the kidney have in glucose homeostasis?

A

Gluconeogenesis, Glucose Uptake, Glucose Reabsorption, Excretion of glucose excess

77
Q

What are the 5 outcomes of being in a fasted state in relation to the hormone ratio balance

A

Insulin secretion will be low so the ratio between insulin and glucagon will be lower

Low insulin levels means reduced glucose uptake, reduced protein synthesis & release of NEFA from adipose tissues

Low ratio of I:G results in glycogenolysis and gluconeogenesis

78
Q

In the fed state what two key points results in the many outcomes of glucose homeostasis?

A

Increase glucose concentration in the plasma

Increased I:G ratio

79
Q

How does the increase in glucose concentration in plasma result in changes in glucose homeostasis

A

Stimulates insulin release and more glucose can be uptaken by insulin independant organs (i.e. liver)

80
Q

What changes occur when the ratio of I:G increases?

A

Suppression of FA mobilisation
FA synthesis in adipose tissues
Increased AA uptake & protein synthesis
Increased lactate production

81
Q

What is the glucose/lactate paradox in fed states?

A

Increased peripheral glucose uptake results in increased glycolysis which can result in increased lactate levels. The paradox is that the lactate can go to the liver to be converted and used to form glycogen.

This indirect glycogenesis pathway is the Cori Cycle

82
Q

What is the link between excess carbohydrate and fat metabolism?

A

Excess glucose (and AAs that can convert to acetyl-CoA) can be converted to TAGs & FAs in adipose tissue and the liver

83
Q

What role does insulin have in fat metabolism?

A

Insulin reduces fat mobilisation & promotes FA synthesis from citrate via activating acetyl-CoA carboxylase

84
Q

What is the key enzyme insulin works on in converting carbohydrates to FA’s

A

Acetyl CoA carboxylase

85
Q

How does the glucose-fatty acid cycle link to post-absorptive and fasted states?

A

In fed state glucose is high so can use that for energy so fat mobilisaition (release of NEFAs) is turned off and rely of glucose oxidation

In fasted state glucose is low and need to keep it a high as possible for the brain so there is a switch to fatty acid oxidation via NEFA release into plasma and glucose oxidation is turned off

86
Q

What cycle allows the body to utilise muscle glycogen?

A

Glucose-Alanine Cycle

87
Q

How does the glucose alanine cycle work?

A

When muscles are being used glucose undergoes glycolysis and cellular respiration. However cellular respiration is slower than glycolysis and pyruvate can build up. Also when muscles are in high use they degrade and release amino acids.

So the pyruvate doesn’t sit around being wasted it can be transaminated to alanine using the released amino acids, alanine is then released into the body as an energy source. One of the main targets for alanine is the liver

88
Q

Give 2 functions of the glucose-alanine pathway

A

Provides indirect path for muscle glycogen to enter peripheral circulation as a source of energy

Allows for sparing of carbohydrate stores

Also allows for muscle to remove amino groups that need to be excreted / cleared by the liver

89
Q

Why would a high protein low carb meal technically cause hypoglycaemia

A

Amino acids stimulate insulin release & the low carbohydrate would mean you wouldnt replenish its levels and potentially result in too much glucose being taken up by muscle, liver etc and leave you in a hypoglycaemic state

90
Q

Why does a high protein low carb meal not leave you in hypoglycaemia

A

Amino acids stimulate both alpha and beta cells in the pancreas to release both hormones. This results in an increase in liver glucose output and counteracts the risk of hypoglycaemia

91
Q

How much energy does carbohydrates contribute to total energy intake globally?

A

Anywhere between 40-85%

92
Q

What are important about plants in relation to carbohydrates?

A

Plants are the main source of carbohydrates in the human diet.

Pants synthesise simple sugars from photosynthesis for energy, but extra is stored within the plant. The main storage substance being starch, but also cellulose and hemicellulose.

93
Q

What are the components of carbohydrates that humans can digest and absorb from animal products?

A

Animal glycogen & proteoglycans (important part of connective tissue)

94
Q

What are the main classifications of carbohydrates?

A

Sugars -> monos, di & sugar alcohols
Oligosaccharides (3-9)
Polysaccharides (>10)

95
Q

What is similar about sugars & carbs with aldehyde and/or ketone groups?

A

They are all reducing sugars -> i.e. they cause a reduction reaction in other molecules whilst they undergo oxidation

96
Q

What is the main functions of monosaccharides?

A

Principle dietary energy source

Building blocks of more complex carbs & molecules

97
Q

What are the main monosaccharides & their sources? Give 2 food sources each

A

Glucose -> fruit & veg & honey
Fructose -> fruit & veg
Galactose -> dairy & sugar beets

98
Q

What are the main disaccharides, componenets & their food sources?

A

Sucrose -> 1 fructose, 1 glucose -> Sugar cane & beet

Lactose -> 1 galactose, 1 glucose -> milk

Maltose -> 2 glucose -> degradated/fermented starch products

Trehalose -> 2 glucose -> insects and mushrooms

99
Q

What are the 3 main sources of starch

A

Seeds, grains, root veg

100
Q

What is the difference between maltose and trehalose

A

Both are disaccharides made up of 2 glucose monosacchairde molecules bound by alpha glycosidic bonds.

Difference is where the bonds take place:
Maltose -> alpha 1,4
Trehalose -> alpha 1,1

101
Q

What are the 3 types of sugars in the carbohydrate food category?

A

Sugar Alcohols / Polyols

102
Q

What are the main sources of sugar alcohols / polyols?

A

Diet -> asparagus, olives, pineapple

Synthetically produce and added to chewing gum, toffees, toothpaste, ice cream

103
Q

How are polyols synthetically produced?

A

Aldose reductase is an enzyme that can reduce the aldehyde group in a glucose molecule into a hydroxyl group making it a sugar alcohol

(remember an aldehyde group is just a double bound oxygen and the enzyme just breaks that bond and adds on a hydrogen to the carbon and a hydrogen onto the oxygen)

104
Q

Give examples of sugar alcohos

A

Mannitol, Sorbitol, Xylitol

105
Q

Given examples of polyols

A

Mannitol, Sorbitol, Xylitol

106
Q

What sources of oligosaccharides do we have?

A

Natural, Synthetic, Derivatives from enzymatic or microbial fermentation processes

107
Q

What are the two ways to characterise / classify an oligosaccharide?

A
  1. A molecule that has 3-10 monosaccharides

2. Carbohydrates that are not monosac or disac that remain in solution in 80% ethanol

108
Q

What are the two main ways to classify food derived oligosaccharides? Give an example of a type in each group.

A

Alpha-Glucans - maltodextrins (maltotriose)

Non-Alpha Glucans - inulin and fructo-oligosaccharide

109
Q

What is one food source common in the human diet that is rich in oligosaccharides?

A

Milk

110
Q

What is the main way to classify polysaccharides?

A

Alpha-Glucans (i.e. starch)

Non-Alpha Glucans (i.e. NSPs)

111
Q

Give three polysaccharides that are alpha-glucans.

A

Starch (+modified starches)
Dextrins
Resistant Starches

112
Q

Describe the structure of starch.

A

Made up of two glucose derived polymers - amylose and amylopectin.

Amylose is a straight helical chain of glucose monomers connected via alpha 1,4 bonds

Amylopectin is highly branched glucose polymers. The polymer is made up of alpha 1,4 bonds with alpha 1,6 bonds forming the branches every 12 units

113
Q

What is the usual amylose and amylopectin ratio?

A

Amylose 30%, Amylopectin 70%

114
Q

If a starch has increased amylose what feature would it have?

A

Waxy

115
Q

If a starch has increased amylopectin what feature will it have?

A

Sticky

116
Q

How is starch stored in plants?

A

Semi-crystaline Structures

117
Q

What is important about the semi-crystaline structure starch has in plants?

A

Raw, these are quite undigestible / inaccesable to enzymes in the gut

118
Q

How can you make semi-crystaline strcutured starch more accessible to digestion?

A

Heating with Water

119
Q

Explain the process involved when you heat starches in water?

A

Heating the semi-crystaline structured starchin water causes gelatinisation. This is where the water destabilises the intermolecular bonds, water ingress and granule swelling. This results in the irreversible breakdown of the structure & makes the molecule amorphous (less defined in shape).

This helps digestion of starches

120
Q

What happens when you cool boiled starch?

A

Retrogradation/Staling -> the a,ylose molecules rearrange to form a new crystaline structure

121
Q

What temperature range enhances staling?

A

-8 to +8

122
Q

What type of carbohydrate is a dextrin?

A

Polysaccharide

123
Q

What is the main source of dextrins?

A

Starch - dextrins is partially hydrolysed starch into smaller glucose polysaccharides

124
Q

What clinical use is there for dextrins?

A

Good for semi-elemental feeding / tube feeding

125
Q

Why is dextrins good for semi-elemental feeding?

A

Partially digested so makes digestion easier on the gut and also doesn’t have the osmotic pull glucose and disacchairdes have so therefore wouldn’t cause dehydration & diarrhoea

126
Q

What are resistant starches?

A

These are polysaccharides belonging to the alpha-glucan group. However these are the odd ones out as these also belong to the dietary fibre group as these are non-digestible. There are many reasonsfor this hence why there are many types (examples in lectures was RS1-4)

127
Q

What two common techniques are employed to modified starches?

A

Chemical Processes

Plant Breeding Plans

128
Q

What two chemical processes are commonly used in modifying starches?

A

Substitution & cross-linking

129
Q

What is the common aim to plant breeding in modifying starch?

A

altering the amylose : amylopectin ratio

130
Q

Give 3 reasons why you would want to modify starch?>

A

Reduce staling

Lower the gelatinisation point

Improve the stability of the molecule

Alter the viscosity properties

131
Q

Give 5 examples of NSPs

A 
Cellulose
Hemicellulose
Pectins
Plant Gums 
Plant Mucilages
132
Q

What is the main 2 NSPs in the diet and what are their structures?

A

Cellulose & Hemicellulose

Cellulose makes up 10-30% of NSPs consumed
This is an unbranched liner chain connected by beta-1,4 and forms tightly packed lattices

Hemicellulose are the second most common, but is a diverse group of highly branched polymers containing pentoses (C5) and hexoses (C6)

133
Q

Give the 3 main groups of dietary fibre in the human diet

A

NSPs

The non-alpha glucan oligosaccharrides - i.e. inulin and fructo-oligosaccharide

Lignin

134
Q

What is lignin and what is its relevance to health?

A

Lignin is a plant cell wall substance that isn’t actually a carbohydrate as it is a polymer of aromatic alcohols.

This is believed to have no benefits to health as they leave the body unaltered

135
Q

Give two examples of synthetically made dietary fibres

A

Methylcellulose & Polydextrose

136
Q

How may you classify dietary fibres?

A

Soluble and insoluble

137
Q

Give 4 food sources of dietary fibres?

A

Cereals, Cereal Products
Root crops
Fruit & Veg

138
Q

Give 6 main sources of carbohydrates?

A 
Cereals, Cereal Products
Bread
Root crops, Sugar Cane, Sugar Beet
Fruit & Veg
Milk
139
Q

What is the recommended daily intake of dietary fibre?

A

30g/day

140
Q

What is the UK average daily intake of dietary fibre?

A

Approx. 19g /day

141
Q

What gives rise to different structures of carbohydrates?

A

Isomers of monosaccharides

142
Q

What are the 3 main types of isomers concerning carbohydrate structure?

A

Constitutional
Geometric
Optical

143
Q

What is constitutional isomers?

A

molecules with same components but in different orders

144
Q

What is geometric isomers?

A

molecules which differences in placement of chemical groups with regards to double bonds (i.e. cis or trans)

145
Q

What is optical stereoisomers?

A

molecules with same number of atoms, chemical groups, and bonding but do not have superimposable images -> i.e. chiral molecules

146
Q

What is the term used to describe a molecule that is the mirror image of it?

A

Enantiomer

147
Q

What role does the mouth have in the digestion of carbohydrates?

A

Mastication - mechanical digestion

Salivary alpha-amylase - chemical digestion of starch & carbohydrates

148
Q

What products may be yielded by by the action of salivary alpha amylase?

A

I.e. what can be produced from the breakdown of starch

Glucose, Maltose, Maltotriose, & Dextrins

149
Q

What role does the stomach have in the digestion of carbohydrates?

A

Has no role in the digestion, only deactivates the amylase from the mouth

150
Q

What role does the small intestine play in the digestion of carbohydrates (ignore brush border for this question)

A

Receives pancreatic alpha amylase which continues breaking down starch into oligosaccharides, di’s & mono’s -> includes glucose, maltose, maltotriose and possibly some dextrins (but doubt it)

151
Q

Name 4 brush border enzymes and the items they work on and their products for disaccharide digestion

A

Maltase -> maltose -> 2 glucose
Sucrase -> sucrose -> 1 fructose, 1 glucose
Lactase -> lactose -> 1 galactose 1 glucose
Trehalase -> Trehalose -> 2 glucose

152
Q

WHat is the fancier terminologies for the enzymes in the brush border involved in carbohydrate metabolism

A

Maltase = alpha-glucosidase

Lactase = beta-galactosidase

Trehalase = Trehalase

Sucrase & Isomaltase = Sucrase-isomaltase

153
Q

What mechanism does each sugar absorb into the epithelial cell?

A

Galactose, Glucose = indirect active transport
Fructose = facilitated diffusion/transport

Polyols = simple diffusion

154
Q

What mechanism do sugars leave epithelial cells?

A

Facilitated diffusion

155
Q

What are the key transporters for the 4 sugars in absorption of carbohydrates

A

SGLT1 - two Gs
GLUT5 - F
GLUT2 - all 3

Polyols / Sugar Alcohols have no specific transporters

156
Q

Explain the absorption of sugar alcohols / polyols?

A

Only partially absorbed via non specific diffusion, most stays in lumen & is fermented by bacteria

157
Q

What does a large consumption of sports drinks do?

A

Laxative effect due to sugar alcohols commonly used

158
Q

What NSPs are not fermented by bacteria usually?

A

Lignin & Cellulose

159
Q

Why is NSPs / Dietary Fibre essential for large bowel health?

A

These can undergo bacterial fermentation to produce SCFAs including butyrate & propionate which the epithelial cells of the colon can absorb and use for energy, cell repair and growth via a process known as intestinal gluconeogenesis

The quantity and quality of NSPs consumed can affect the quantity and quality of the gut microbiome. And also the quant and qual of the GM alters the fermentation of NSPs

160
Q

What is the typical fate of glucose once absorbed?

A

Post-prandial glucose is stored as glycogen in muscles and liver & converted to triglycerides in liver or adipose tissues

161
Q

How is glucose available to the body via skeletal muscle glycogen?

A

Skeletal muscle glycogen is directly used for energy for the muscle but also indirectly available to the body via the glucose-alanine pathway

162
Q

What is the fate of fructose once absorbed?

A

Oxidated more quickly that glucose.
First converted to F1P by fructokinase then converted to glyceraldehyde-3-phosphate (G3P) which is an intermediate of glycolysis

163
Q

What has a diet high in fructose been associated with?

A

Lipogenesis, NAFLD, Interference of appetite and satiety control mechanisms

164
Q

What is the fate of galactose one absorbed?

A

Converted to G1P then G6P through the leloir pathway and then enters glycolysis

165
Q

What is the energy associated to digestible and non-digestible carbs (in cals and j)

A 
digestible = 4kcal/g or 16kj/g
non-digestible = 2kcal/g or 8kj/g
166
Q

How much of total daily energy intake should be made up of carbohydrates?

A

Between 40-65%

167
Q

What is the typical carbohydrate intake of a UK adult?

A 
27% = starch
10% = intrinsic sugars
11-12% = extrinsic sugars
168
Q

How much percent of total energy intake does extrinsic sugars make up in the average child in the UK?What should we be aiming for?

A

16% when should be aiming for 5-10%

169
Q

Why is it important to note food processing in reference to intrinsic and extrinsic sugars?

A

Processes like juicing release intrinsic sugars from cell walls that usually would not be digested/act like intrinsic sugars but because they are released they are then considered to be more like and extrinsic sugars

170
Q

What term denotes the fact humans require to consume carbohydrates?

A

Obligate Carbohydrate Metabolisers / Metabolites

171
Q

Why do humans rely on carbohydrates?

A

Some cells have little to no mitochondria so require glucose for energy

172
Q

Give 5 examples of cell types that are obligatory carbohydrate metabolisers

A

Neurones/Brain Cells, Erythrocytes, Leukocytes, Cornea, Lens, Retinal Cells, Renal Medulla

173
Q

What is the minimal amount of glucose our body relies on a day?

A

180g

174
Q

What is the minimal carbohydrate intake required per day?

A

50g (this is because the body can make up to 130g glucose via gluconeogenesis)

175
Q

What would a person complain / present with if low/lack of carbohydrates in the diet?

A

Lack of exercise tolerance and fatigue

176
Q

When the body is short on glucose what can it do to provide energy for the body?

A

Gluconeogenesis & Glycogenolysis

177
Q

When you consume no carbohydrates what may happen?

A

Enter ketosis - body utilises ketones derived from fatty acid oxidation as a source of energy

178
Q

Why is ketosis bad?

A

Detrimental to health -> cognitive impairment & foetal development issues

179
Q

Name 3 substrates used in gluconeogenesis?

A

Lactate, Pyruvate, Glycerol from TAGs, Carbon Skeleton of amino acids

180
Q

How can you assess carbohydrate levels in the body?

A

Biopsies or isotopic methods

181
Q

Name 3 roles of carbohydrates in the body other than energy metabolism?

A

Synthesis of molecules -> RNA / DNA
Synthesis of glucuronic acid -> facilitates toxin excretion
Synthesis of amino acids & glycoproteins

182
Q

Name 3 roles of glycoproteins

A

Mucous Production
Plasma Proteins -> Immunoglobulins, Prothrombin
Peptide Hormones
Cell Signalling

Foundations of Nutrition (13 decks)

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