Glucose & Carbohydrates Flashcards
1
Q
What is the usual fasting range of glucose?
A
4-6 mmol/l
2
Q
How long after eating does it take for glucose levels to normalise?
A
2-3 hours
3
Q
Name 3 glucose dependant cell types
A
Neurons, Erythrocytes, Mammary Glands, Testis
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
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)
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
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
8
Q
Give the 3 ways of how to get glucose levels to increase?
A
Digestion & Absorption of dietary carbs
Glycogenolysis
Gluconeogenesis
9
Q
Give the 3 ways to reduce glucose levels
A
Glycolysis
Glycogenesis
Conversion of glucose into fat acids and amino acids
10
Q
What does an item with a high glycaemic index mean?
A
Contains a greater proportion of digestible carbohydrates than non-digestible
11
Q
What transporter is involved in monosaccharide absorption?
A
SGLT-1 = glucose and galactose
GLUT 5 = fructose
12
Q
What is the difference between SGLT1 & GLUT5?
A
SGLT-1 is active transport
GLUT5 is facilitated transport
13
Q
Where does absorbed monosaccharides go from the enterocyte?
A
Portal vein via GLUT2
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
15
Q
How many steps are there to glycolysis?
A
10
16
Q
What is the start and end of glycolysis
A
1 glucose -> pyruvate
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
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
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
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
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
22
Q
Other than glycolysis what other pathway is glucose commonly used in?
A
Pentose Phosphate Pathways
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
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
25
How does glucose enter the PPP?
Glucose is converted to G6P in the first step of glycolysis and then this is 2 routes -> either enter the glycolysis or PPP pathway
26
Give a cell that depends on the PPP in practise?
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
27
What is gluconeogenesis?
Formation of glucose from non-carbohydrate sources
28
What are the main sources of substrates used in gluconeogenesis?
Lactate -> cori cycle
Alanine / Amino acids
Glycerol from fatty acids
29
How does lactate become glucose in gluconeogenesis?
Cori Cycle -> lactate can be converted back to pyruvate and move up the glycolysis pathway
30
How does amino acids become glucose in gluconeogenesis?
Alanine is the main amino acids and this like lactate can be converted to pyruvate and move u[ the glycolytic pathway
31
How does fatty acids convert to glucose in gluconeogenesis?
The glycerol from FAs can be converted to acetyl CoA and then converted to pyruvate and move up the glycolytic pathway
32
Where does gluconeogenesis take place in the body?
Liver and Kidneys
33
What does the "reverse of glycolysis" mean in reference to gluconeogenesis
The reverse of glycolysis is how non-carbohydrate compounds are converted to glucose once they become pyruvate
34
How is gluconeogenesis regulated?
3 types of mechanisms:
Allosteric
Genetic Expression Mechanisms
Covalent Phosphorylation
35
What do the regulating mechanisms do to allow or gluconeogenesis to take place?
Forms key enzymes / allows for access of key enzymes that can reverse the 3 steps that are 'non-reversible' oin the normal glycolysis pathway
36
Name 2 key enzymes in gluconeogenesis
Glucose-6-phosphatase
Fructose-1,6-biphosphatase
PEP carboxykinase
Pyruvate Carboxylase
37
What is glycogenesis
Synthesis of glycogen
38
Where does glycogenesis take place?
Liver & Skeletal Muscle
39
What is glycogen?
A branched polysaccharide / polymer of glucose
40
What is the structure of glycogen
Straight chains of alpha-1,4- glycosidic bonds with alpha 1-6 glycosidic bond branching every 9-10 units
41
What are the two key enzymes in glycogen synthesis and degradation?
Glycogen Synthase
| Glycogen Phosphorylase
42
What is the detailed explanation of glycogen synthesis?
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)
43
What is important to remember about glycogen and glycogen synthesis?
High energy costs
| High water binding capacity
44
Where is glycogen stored?
Cytosol of cells
45
What is the main stimulator for glycogenesis?
Insulin
46
What is glycogenolysis
Glycogen degradation to produce glucose
47
WHat enzyme mediates glycogenolysis
Glycogen phosphorylase
48
How is glucose produced from glycogen?
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
49
Name 2 things that down regulates glycogenolysis
Glucose, G6P, F1P, ATP, ADP,
50
What is the difference between liver and skeletal muscle glycogenolysis?
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.
51
What situations upregulates glycogenolysis?
Stress -> exercise, hypoglycaemia, hypoxia
52
How does catelcholamines upregulate glycogenolysis?
Catecholamines are able to phosphorylate glycogen phosphorylase to its active form via activation of PKA - protein kinase A
53
What is the endocrine proportion of the pancreas collectively called?
Islet of Langerhans
54
What do alpha, beta and delta cells produce in the pancreas?
```
Alpha = Glucagon
Beta = Insulin
Delta = Somatostatin
```
55
What is the structure of the insulin hormone?
51 amino acids in two polypeptide chains
56
What is the half life of insulin
5mins
57
How is insulin secreted into the blood?
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
58
How is insulin secretion stopped?
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
59
What pattern can be used to describe insulin secretion?
| Explain the theory behind it
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
60
How else does glucose and carbs help regulate insulin secretion?
Theory is that glucose and carbs can directly impact insulin gene expression & increase synthesis
61
How does fatty acids and amino acids affect insulin secretion?
```
FAs = short term increases, long term inhibits
AAs = increases secretion
```
62
What are the functions of the incretin hormones?
GLP-1 & GIP indirectly stimulate insulin secretion via g-protein coupled receptors when glucose levels are high
63
What is GLP-1 and GIP?
Glucagon-Like-Peptide-1
| Gastric inhibitory peptide
64
Give 3 sites of action for insulin
Liver, Skeletal Muscle, Adipose Tissue
65
What is insulins activity in skeletal muscle? (2)
Increases glucose uptake via GLUT4 (insulin dependant transporter) and promotes glycogenesis.
66
What is insulins activity in liver? (3)
Promotes glycogenesis, glycolysis
Promotes lipogenesis, TAG & Cholesterol synthesis
Suppresses gluconeogenesis, beta-oxidation. ketogenesis
67
What is insulins activity in adipose tissue? (3)
Aids TAG removal from plasma
Aids TAG synthesis
Prevents fat mobilisation
68
What is the structure of the glucagon hormone?
29 AA single polypeptide chain
69
What is the intermediate compound called that is actually secreted from the pancreatic cells?
Proglucagon
70
How does glucagon act on cells (generically)
Via transmembrane G protein coupled receptors
71
What stimulates glucagon release?
Low glucose and amino acids
72
Name 3 actions of glucagon
Glycogenolysis
Gluconeogenesis
Ketogenesis
73
What is the key determininent in the glucagon : insulin ratio and why?
Insulin because glucagon secretion is normally stable where as insulin is much more variable, therefore having more of an effect on overall ratio
74
Name 5 hormones, other than insulin and glucagon, that may impact glucose homeostasis
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
What main organs uptake glucose and which ones requires insulin?
> 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
What role does the kidney have in glucose homeostasis?
Gluconeogenesis, Glucose Uptake, Glucose Reabsorption, Excretion of glucose excess
77
What are the 5 outcomes of being in a fasted state in relation to the hormone ratio balance
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
In the fed state what two key points results in the many outcomes of glucose homeostasis?
Increase glucose concentration in the plasma
| Increased I:G ratio
79
How does the increase in glucose concentration in plasma result in changes in glucose homeostasis
Stimulates insulin release and more glucose can be uptaken by insulin independant organs (i.e. liver)
80
What changes occur when the ratio of I:G increases?
Suppression of FA mobilisation
FA synthesis in adipose tissues
Increased AA uptake & protein synthesis
Increased lactate production
81
What is the glucose/lactate paradox in fed states?
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
What is the link between excess carbohydrate and fat metabolism?
Excess glucose (and AAs that can convert to acetyl-CoA) can be converted to TAGs & FAs in adipose tissue and the liver
83
What role does insulin have in fat metabolism?
Insulin reduces fat mobilisation & promotes FA synthesis from citrate via activating acetyl-CoA carboxylase
84
What is the key enzyme insulin works on in converting carbohydrates to FA's
Acetyl CoA carboxylase
85
How does the glucose-fatty acid cycle link to post-absorptive and fasted states?
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
What cycle allows the body to utilise muscle glycogen?
Glucose-Alanine Cycle
87
How does the glucose alanine cycle work?
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
Give 2 functions of the glucose-alanine pathway
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
Why would a high protein low carb meal technically cause hypoglycaemia
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
Why does a high protein low carb meal not leave you in hypoglycaemia
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
How much energy does carbohydrates contribute to total energy intake globally?
Anywhere between 40-85%
92
What are important about plants in relation to carbohydrates?
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
What are the components of carbohydrates that humans can digest and absorb from animal products?
Animal glycogen & proteoglycans (important part of connective tissue)
94
What are the main classifications of carbohydrates?
Sugars -> monos, di & sugar alcohols
Oligosaccharides (3-9)
Polysaccharides (>10)
95
What is similar about sugars & carbs with aldehyde and/or ketone groups?
They are all reducing sugars -> i.e. they cause a reduction reaction in other molecules whilst they undergo oxidation
96
What is the main functions of monosaccharides?
Principle dietary energy source
| Building blocks of more complex carbs & molecules
97
What are the main monosaccharides & their sources? Give 2 food sources each
Glucose -> fruit & veg & honey
Fructose -> fruit & veg
Galactose -> dairy & sugar beets
98
What are the main disaccharides, componenets & their food sources?
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
What are the 3 main sources of starch
Seeds, grains, root veg
100
What is the difference between maltose and trehalose
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
What are the 3 types of sugars in the carbohydrate food category?
Sugar Alcohols / Polyols
102
What are the main sources of sugar alcohols / polyols?
Diet -> asparagus, olives, pineapple
Synthetically produce and added to chewing gum, toffees, toothpaste, ice cream
103
How are polyols synthetically produced?
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
Give examples of sugar alcohos
Mannitol, Sorbitol, Xylitol
105
Given examples of polyols
Mannitol, Sorbitol, Xylitol
106
What sources of oligosaccharides do we have?
Natural, Synthetic, Derivatives from enzymatic or microbial fermentation processes
107
What are the two ways to characterise / classify an oligosaccharide?
1. A molecule that has 3-10 monosaccharides
| 2. Carbohydrates that are not monosac or disac that remain in solution in 80% ethanol
108
What are the two main ways to classify food derived oligosaccharides? Give an example of a type in each group.
Alpha-Glucans - maltodextrins (maltotriose)
Non-Alpha Glucans - inulin and fructo-oligosaccharide
109
What is one food source common in the human diet that is rich in oligosaccharides?
Milk
110
What is the main way to classify polysaccharides?
Alpha-Glucans (i.e. starch)
Non-Alpha Glucans (i.e. NSPs)
111
Give three polysaccharides that are alpha-glucans.
Starch (+modified starches)
Dextrins
Resistant Starches
112
Describe the structure of starch.
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
What is the usual amylose and amylopectin ratio?
Amylose 30%, Amylopectin 70%
114
If a starch has increased amylose what feature would it have?
Waxy
115
If a starch has increased amylopectin what feature will it have?
Sticky
116
How is starch stored in plants?
Semi-crystaline Structures
117
What is important about the semi-crystaline structure starch has in plants?
Raw, these are quite undigestible / inaccesable to enzymes in the gut
118
How can you make semi-crystaline strcutured starch more accessible to digestion?
Heating with Water
119
Explain the process involved when you heat starches in water?
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
What happens when you cool boiled starch?
Retrogradation/Staling -> the a,ylose molecules rearrange to form a new crystaline structure
121
What temperature range enhances staling?
-8 to +8
122
What type of carbohydrate is a dextrin?
Polysaccharide
123
What is the main source of dextrins?
Starch - dextrins is partially hydrolysed starch into smaller glucose polysaccharides
124
What clinical use is there for dextrins?
Good for semi-elemental feeding / tube feeding
125
Why is dextrins good for semi-elemental feeding?
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
What are resistant starches?
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
What two common techniques are employed to modified starches?
Chemical Processes
| Plant Breeding Plans
128
What two chemical processes are commonly used in modifying starches?
Substitution & cross-linking
129
What is the common aim to plant breeding in modifying starch?
altering the amylose : amylopectin ratio
130
Give 3 reasons why you would want to modify starch?>
Reduce staling
Lower the gelatinisation point
Improve the stability of the molecule
Alter the viscosity properties
131
Give 5 examples of NSPs
```
Cellulose
Hemicellulose
Pectins
Plant Gums
Plant Mucilages
```
132
What is the main 2 NSPs in the diet and what are their structures?
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
Give the 3 main groups of dietary fibre in the human diet
NSPs
The non-alpha glucan oligosaccharrides - i.e. inulin and fructo-oligosaccharide
Lignin
134
What is lignin and what is its relevance to health?
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
Give two examples of synthetically made dietary fibres
Methylcellulose & Polydextrose
136
How may you classify dietary fibres?
Soluble and insoluble
137
Give 4 food sources of dietary fibres?
Cereals, Cereal Products
Root crops
Fruit & Veg
138
Give 6 main sources of carbohydrates?
```
Cereals, Cereal Products
Bread
Root crops, Sugar Cane, Sugar Beet
Fruit & Veg
Milk
```
139
What is the recommended daily intake of dietary fibre?
30g/day
140
What is the UK average daily intake of dietary fibre?
Approx. 19g /day
141
What gives rise to different structures of carbohydrates?
Isomers of monosaccharides
142
What are the 3 main types of isomers concerning carbohydrate structure?
Constitutional
Geometric
Optical
143
What is constitutional isomers?
molecules with same components but in different orders
144
What is geometric isomers?
molecules which differences in placement of chemical groups with regards to double bonds (i.e. cis or trans)
145
What is optical stereoisomers?
molecules with same number of atoms, chemical groups, and bonding but do not have superimposable images -> i.e. chiral molecules
146
What is the term used to describe a molecule that is the mirror image of it?
Enantiomer
147
What role does the mouth have in the digestion of carbohydrates?
Mastication - mechanical digestion
| Salivary alpha-amylase - chemical digestion of starch & carbohydrates
148
What products may be yielded by by the action of salivary alpha amylase?
I.e. what can be produced from the breakdown of starch
| Glucose, Maltose, Maltotriose, & Dextrins
149
What role does the stomach have in the digestion of carbohydrates?
Has no role in the digestion, only deactivates the amylase from the mouth
150
What role does the small intestine play in the digestion of carbohydrates (ignore brush border for this question)
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
Name 4 brush border enzymes and the items they work on and their products for disaccharide digestion
Maltase -> maltose -> 2 glucose
Sucrase -> sucrose -> 1 fructose, 1 glucose
Lactase -> lactose -> 1 galactose 1 glucose
Trehalase -> Trehalose -> 2 glucose
152
WHat is the fancier terminologies for the enzymes in the brush border involved in carbohydrate metabolism
Maltase = alpha-glucosidase
Lactase = beta-galactosidase
Trehalase = Trehalase
Sucrase & Isomaltase = Sucrase-isomaltase
153
What mechanism does each sugar absorb into the epithelial cell?
Galactose, Glucose = indirect active transport
Fructose = facilitated diffusion/transport
Polyols = simple diffusion
154
What mechanism do sugars leave epithelial cells?
Facilitated diffusion
155
What are the key transporters for the 4 sugars in absorption of carbohydrates
SGLT1 - two Gs
GLUT5 - F
GLUT2 - all 3
Polyols / Sugar Alcohols have no specific transporters
156
Explain the absorption of sugar alcohols / polyols?
Only partially absorbed via non specific diffusion, most stays in lumen & is fermented by bacteria
157
What does a large consumption of sports drinks do?
Laxative effect due to sugar alcohols commonly used
158
What NSPs are not fermented by bacteria usually?
Lignin & Cellulose
159
Why is NSPs / Dietary Fibre essential for large bowel health?
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
What is the typical fate of glucose once absorbed?
Post-prandial glucose is stored as glycogen in muscles and liver & converted to triglycerides in liver or adipose tissues
161
How is glucose available to the body via skeletal muscle glycogen?
Skeletal muscle glycogen is directly used for energy for the muscle but also indirectly available to the body via the glucose-alanine pathway
162
What is the fate of fructose once absorbed?
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
What has a diet high in fructose been associated with?
Lipogenesis, NAFLD, Interference of appetite and satiety control mechanisms
164
What is the fate of galactose one absorbed?
Converted to G1P then G6P through the leloir pathway and then enters glycolysis
165
What is the energy associated to digestible and non-digestible carbs (in cals and j)
```
digestible = 4kcal/g or 16kj/g
non-digestible = 2kcal/g or 8kj/g
```
166
How much of total daily energy intake should be made up of carbohydrates?
Between 40-65%
167
What is the typical carbohydrate intake of a UK adult?
```
27% = starch
10% = intrinsic sugars
11-12% = extrinsic sugars
```
168
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?
16% when should be aiming for 5-10%
169
Why is it important to note food processing in reference to intrinsic and extrinsic sugars?
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
What term denotes the fact humans require to consume carbohydrates?
Obligate Carbohydrate Metabolisers / Metabolites
171
Why do humans rely on carbohydrates?
Some cells have little to no mitochondria so require glucose for energy
172
Give 5 examples of cell types that are obligatory carbohydrate metabolisers
Neurones/Brain Cells, Erythrocytes, Leukocytes, Cornea, Lens, Retinal Cells, Renal Medulla
173
What is the minimal amount of glucose our body relies on a day?
180g
174
What is the minimal carbohydrate intake required per day?
50g (this is because the body can make up to 130g glucose via gluconeogenesis)
175
What would a person complain / present with if low/lack of carbohydrates in the diet?
Lack of exercise tolerance and fatigue
176
When the body is short on glucose what can it do to provide energy for the body?
Gluconeogenesis & Glycogenolysis
177
When you consume no carbohydrates what may happen?
Enter ketosis - body utilises ketones derived from fatty acid oxidation as a source of energy
178
Why is ketosis bad?
Detrimental to health -> cognitive impairment & foetal development issues
179
Name 3 substrates used in gluconeogenesis?
Lactate, Pyruvate, Glycerol from TAGs, Carbon Skeleton of amino acids
180
How can you assess carbohydrate levels in the body?
Biopsies or isotopic methods
181
Name 3 roles of carbohydrates in the body other than energy metabolism?
Synthesis of molecules -> RNA / DNA
Synthesis of glucuronic acid -> facilitates toxin excretion
Synthesis of amino acids & glycoproteins
182
Name 3 roles of glycoproteins
Mucous Production
Plasma Proteins -> Immunoglobulins, Prothrombin
Peptide Hormones
Cell Signalling
