Carbs Flashcards
Polysaccharides subgroups (2)
Starch (a-glucans) Non starch (non a-glucans)
Examples of monosaccharides (3)
Glucose
Fructose
Galactose
How are monosaccharides linked together?
Glycosidic bonds
What are the subgroups of sugar?(3)
Monosaccharides Disaccharides Polyols (sugar alcohols)
Oligosaccharides subgroups (2)
Malto-oligos
Non digestible-oligos
Explain the structure of starch (4)
Consists of linear amylose and branched amylopectin
Linear amylose - chain of glucose linked together by 1,4 bonds
Branched amylopectin - glucose also linked by 1,4 however branch points are 1,6 bonds
Which bonds cannot be broken down by the small intestine?
B- bonds
What determines whether a carb is digestible by enzymes?
Type of bond
Disaccharides examples (3)
Lactose
Maltose
Sucrose
What determines the nutritional properties of a carb?(2)
Monosaccharide composition
Type of bond
What are glycaemic carbs?(2)
They provide glucose for metabolism
As a result of digestion in absorption in small intestine
What are non glycaemic carbs?(2)
Not absorbed in small intestine
Fermented in large intestine
What are carbs composed of?(3)
Carbon, hydrogen, oxygen
What is the enzyme that hydrolyses glycaemic carbs?
a-amylase
How are monosaccharides aborted across the basolateral membrane?(2)
Facilitated diffusion
GLUT2
What is the brush border?
Microvilli on the small intestine wall
Name the brush border enzymes involved in digestion (3)
Glucosidases (Maltase)
Disaccharidases
Oligosaccharidases
Explain the digestion process in the stomach (3)
Chewing and salivary a-amylase partially breakdown starch
Starch enters the stomach
Salivary amylase is inactivated by stomach acid
Explain digestion in the small intestine (3)
Food reaches the lumen of the small intestine
Pancreatic a-amylase further breaks down starch
Brush border/enterocyte enzymes breaks down starch to monosaccharides
What do the a-amylase enzymes do?(2)
Break down alpha 1-4 glycosidic bonds of starch
Which microvilli enzyme hydrolyses both 1,4 and 1,6 glycosidic bonds?
Sucrase-isomaltase
Explain the absorption of fructose process within the intestine (3)
Fructose crosses enterocyte apical membrane via facilitated diffusion
Using GLUT5
Fructose then crosses the the basolateral membrane into the blood via GLUT2
What are some of the reasons why some carbs enter the large intestine (colon) (6)
Enzymes required are not present within the small intestine
Cant gain access to carb
Does not hydrolyses carb fast enough
Monosaccharide transporters not available or do not function at a high enough rate
Beta bonds
Fermentation process (3)
Bacteria produces hydrolytic enzymes
Carbs are broken down into monosaccharides
Monosaccharides are used as energy for growth by bacteria
What are the products of fermentation (2)
Short chain fatty acids
Gases
Name the SCFA products of fermentation (3)
Acetate
Propionate
Butyrate
What is the fate of each SCFA (3)
Butyrate - used as predominant energy source by colon cells
Propionate - absorbed and transported to liver
Acetate - absorbed and metabolised by peripheral tissues
What is the range of blood glucose?
3-5.5 mmol/l
Glycogenesis process (6)
G6P converted to G1P Using phosphoglucomutase G1P converted to UDP-glucose Using G1P uridyltranferase Glucose from UDP-glucose added to glycogen chain Using glycogen synthase UDP is released
Glycogenolysis initial process (4)
Glycogen to G1P
By glycogen phosphorylase
G1P to G6P
By phosphoglyceromutase
Glycogenolysis process in liver (3)
G6P converted to glucose
Via G6 phosphatase
Glucose then enters blood
Glycogenolysis in muscle (3)
G6P to pyruvate
Via glycolysis
Pyruvate is transaminated to alanine
What are low carb diets associated with?(3)
High concentrations of ketone bodies
Depleted glycogen stores
Hypercholesterolaemia
What are intrinsic sugars?
Naturally incorporated into cellular structure of food
What are extrinsic sugars?
Not contained within cellular structure of foods
What are free sugars?(4)
Sugar added to food
Explain the absorption of glucose and galactose across apical membrane (4)
Decreased sodium within cell draws sodium across apical membrane with glucose
This occurs via active transport
Using sodium-glucose transport protein 1
Sugar then crosses the the basolateral membrane into the blood via GLUT2 (facilitated diffusion)
What determines the rate of glucose uptake from the intestine?(2)
Rate of hydrolysis of oligosaccharides and polysaccharides
Glucose formula
C2H12O6
Degree of polymerisation for each class of carbs (3)
Sugars 1-2
Oligo 3-9
Poly 9+
Example of malto-oligosaccharides
Maltodextrins
Examples of starch (3)
Amylose
Amylopectin
Modified starches
Examples of non digestible oligosaccharides (3)
Ruffinose
Fructo-oligo
Galacto-oligo
Examples of non starch polysaccharides (4)
Cellulose
Hemicellulose
Pectin
Hydrocolloids
Where is glucose found?(3)
Fruits
Plant juices
Honey
Where is fructose found?(3)
Free state alongside glucose in:
Ripening fruits
Honey
Where is galactose found?(2)
In combination with glucose as lactose
In milk
Composition of sucrose (2)
Alpha 1, 2 linked
Glucose-fructose
Composition of lactose (2)
Beta 1, 4 linked
Galactose-glucose
Maltose composition (2)
Alpha 1, 4 linked
Glucose-glucose
Sucrose sources (3)
Sugar cane
Sugar beet
Fruit
Lactose sources
Milk and dairy produce
Maltose sources (2)
Spotted grain
Malt beverages
What is the most common natural sweetener?
Sucrose
_______ is produced during the digestion of starch
Maltose
Sources of starch (3)
Cereals
Root veg
Legumes
Glycogen is a form of ______
Starch
What is the optimal pH range for alpha amylase?
6.6-6.8
Where is alpha amylase produced?
Acinar cells in the pancreas
Define glycogenesis
Synthesis of glycogen from glucose
Define glycogenolysis
Stored glycogen is converted to glucose
Define gluconeogenesis
Synthesis of glucose from non-carb sources
Main substrates involves in gluconeogenesis (3)
Lactate
Glycerol
Alanine
How many molecules of ATP per glucose is produced?
38
DRV for free sugars
5% of energy intake
DRV for total carbs
50%
Non starch polysaccharide RDA
30 g/day
Why is it recommended that 50% of energy intake comes from carbs?(2)
Too much may be associated with inadequate intakes of essential nutrients
Too little may be associated with excess intake of sat fats
How can extrinsic sugars cause dental carries?
Fermented in mouth to yield acidic products
Lactose is an example of an _____ sugar
Extrinsic
Where are free sugars found?(3)
Honey, syrups and unsweetened fruit juices
