Carbohydrates and dietary starch Flashcards
Carbohydrates
What are the roles of carbs?
Metabolic fuel and energy store
Structural component of cell walls
Component of nucleic acids
Link with proteins and lipids
Carbohydrates
What are single units of carbs classed as?
Monosaccharides
Carbohydrates
What are 2 units of carbs classed as?
Disaccharides
Carbohydrates
What are 3-9 units of carbs classed as?
Oligosaccharides
Carbohydrates
What are 10+ units of carbs classed as?
Polysaccharides
Carbohydrates
What is the degree of polymerisation?
Number of carbon atoms
Carbohydrates
What parts of DNA and RNA are carbs?
Deoxyribose
Ribose
Carbohydrates
What is the main way the body stores carbs?
Glycogen
Carbohydrates
What are isomers?
Molecules with the same molecular structure but different chemical structures
Carbohydrates
How are glucose and fructose related?
They’re isomers
Carbohydrates
Which form of glucose can humans digest and why?
α-glucose
Human digestive enzymes can only digest α-linkages
Carbohydrates
What’s the difference between α and β glucose?
α glucose: H is up on 1C, OH bottom
β glucose: OH is up on 1C, H bottom
Carbohydrates
What are the uses for fibre?
Doesn’t cause a blood glucose spike (good for diabetics)
Can be used by bacteria in the large intestines
Carbohydrates
Cariogenic
Produces or promotes the development of tooth decay
Carbohydrates
What is a non-cariogenic alternative to sugar?
Polyols (sugar alcohols)
Carbohydrates
Polyols
Occur naturally in fruits
Water soluble
Vary in sweetness
Non-cariogenic
Carbohydrates
Are most ogliosaccharides digestible?
No
Carbohydrates
Which is easier to break down, branched or linear structures, and why?
Branched
Linear structures can become more compact
Carbohydrates
What is a digestible ogliosaccharide?
Maltodextrin
Carbohydrates
What food contains ogliosaccharides?
Soybeans
Lentils
Legume seeds
Carbohydrates
What happens when the ogliosaccharides in beans aren’t broken down?
Causes flatulence
Carbohydrates
Name two digestible polysaccharides
Starch
Glycogen
Carbohydrates
Name 3 non digestible polysaccharides
Cellulose
Pectin
β-glucan
Carbohydrates
What is the composition of starch?
Linear amylose (20-30%) Branched amylopectin (70-80%)
Carbohydrates
What are good sources of starch?
Potato
Rice
Wheat
Carbohydrates
Glycogen
The way excess glucose is stored in the liver
Carbohydrates
Glycemic carbohydrates
Can be hydrolysed by enzymes in gastrointestinal tract to monosaccharides
Absorbed in small intestine
Used in CHO metabolism
Carbohydrates
Non-glycemic carbohydrates
Not hydrolysed by enzymes in gastrointestinal tract
May ferment in the large intestine
Carbohydrates
What is amylose broken down into?
Maltotriose
Maltose
Carbohydrates
What is amylopectin broken down into?
Maltotriose
Maltose
Dextrins
Carbohydrates
What enzymes (in order) digest ogliosaccharides?
Maltase Maltase α-dextrinase α-dextrinase Maltase Sucrase
Carbohydrates
How are ogliosaccharides digested?
In steps using enzymes that remove one glucose molecule at a time
Carbohydrates
What do sugar transporters do?
Have individual roles
But together they move sugar from the intestine lumen into the blood
Carbohydrates
What does SGLT1 do?
Sugar transporter
Moves Na+ and glucose/galactose in the enterocyte
Carbohydrates
What are the cells of the intestinal lining called?
Enterocytes
Carbohydrates
Where do you find the GLUT variety of sugar transporters?
All cells
Carbohydrates
Where do you find GLUT 4?
Adipose tissue
Skeletal muscle
Carbohydrates
Which sugar transporter is controlled by a hormone?
Which hormone?
GLUT 4
Insulin
Carbohydrates
What does GLUT 5 do?
Moves fructose into the enterocyte
Carbohydrates
What does GLUT 2 do?
Transports sugars from the enterocyte into the blood
Carbohydrates
Ways that CHO can be metabolised in tissues
Glycolysis
Tricarboxylic acid (TCA) cycle
Anaerobic respiration
Carbohydrates
What is the overall effect of glycolysis?
6C glucose broken down into two lots of 3C pyruvic acid
Some ATP produced
Carbohydrates
High fructose corn syrup
Less expensive sweetening agent
Health concern about the amount of fructose present
Carbohydrates
Why is digesting large amounts of fructose bad?
In large amounts it is converted directly into fat
Can cause obesity
Carbohydrates
What happens when there is excess glucose in the blood?
Triggers release of insulin from the pancreas
Excess glucose converted into glycogen
Carbohydrates
What does glycogenin do?
Starts glucogen production in the muscles
Carbohydrates
Glycogenolysis
Regulated by hormones
Glycogen is broken down into glucose
Carbohydrates
What hormones control glycogenolysis?
Glucagon
Adrenaline
Carbohydrates
Gluconeogenesis
Glucose synthesis from non-carbohydrate sources
Carbohydrates
What sources are used in gluconeogenesis?
Lactate
Pyruvate
Glycerol
Amino acids
Carbohydrates
Cori cycle
Lactate is produced in the muscles during exercise and transported to the liver
This is converted to glucose which can then be used by the muscles
Carbohydrates
Glucose-Alanine cycle
The pyruvate created in muscles when glucose is broken down is further broken down to alanine
This is transported in the blood to the liver
Alanine converted back into pyruvate to be used to make glucose
Carbohydrates
Which metabolic pathway creates glucose from non-carbohydrate sources?
Gluconeogensis
Carbohydrates
Which metabolic pathway converts glucose to glycogen?
Glycogenesis
Carbohydrates
Which metabolic pathway converts glycogen to glucose?
Glycogenolysis
Carbohydrates
Which metabolic pathway converts glucose to pyruvate which can then be used in further steps of ATP production?
Glycolysis
Carbohydrates
Krebs cycle
Pyruvic acid from glycolysis enters mitochondrial fluid matrix
Produces NADH-H+, FADH2 some ATP
Carbohydrates
Dietary fibre
Edible parts of plants or analogous carbs
Are resistant to digestion and absorption in the small intestine
Completely or partially ferment in large intestine
Carbohydrates
What can dietary fibre promote?
Laxation
Blood cholesterol attenuation
Blood glucose attenuation
Carbohydrates
What are the two types of dietary fibre?
Soluble
Insoluble
Carbohydrates
Which type of fibre ferments?
Soluble dietary fibre
Carbohydrates
Which type of dietary fibre is more viscous?
Soluble
Carbohydrates
Lignin
Dietary fibre
Present in plants
Polyphenol (not a carb)
Carbohydrates
What does hydration and viscosity result in?
Delayed gastric emptying Reduced mixing of GI contents with digestive enzymes Reduced enzyme function Decreased nutrition diffusion rate Altered transit time
Carbohydrates
Gastric emptying
Movement of food from stomach to intestines
Carbohydrates
Hypoglycaemic
Low blood sugar levels
Carbohydrates
Hypolipodemic
Low lipid content
Carbohydrates
Bile acids
Emulsifies fat - makes it soluble
Carbohydrates
How are bile acids made?
With cholesterols in the liver
Carbohydrates
What happens if lignins, gums, pectins and/or hemicelluloses bind enzymes and nutrients?
Diminished absorption of lipids
Increased faecal bile acid excretion
Lowered serum cholesterol concentration
Altered mineral and carotenoid absorbtion
Carbohydrates
What fibres are fermentable?
Fructans Pectin Gums Psyllium Polydextrose Resistant starch
Carbohydrates
What type of fibre increases faecal bulk?
Non-digestible
Carbohydrates
Resistant starch
Starch and products of starch
Not absorbed in the small bowel
Carbohydrates
RS1
Physically inaccessible starch
Present in most grains
Carbohydrates
RS2
Resistant starch granules
Found in raw potato and green bananas
Carbohydrates
RS3
Retrograde starch
Caused by some food processing techniques
Carbohydrates
RS4
Modified starches
Carbohydrates
Low density lipoproteins
Transports cholesterol from the liver to the tissues
Carbohydrates
High density lipoproteins
Transports cholesterol from the tissue to the liver to be used by the liver
Carbohydrates
Which type of lipoprotein is the bad one?
LDL
Carbohydrates
What value equates to low GI?
~50 and less
