Lecture 13 Flashcards
What are the functions of carbohydrates?
- Energy stores, fuels, metabolic intermediates
- Protein sparing
- Prevents ketosis
- Ribose and deoxyribose sugars are part of the structural framework of RNA and DNA
- Cellulose makes up most of plant cell walls
- Carbs are linked to many proteins and lipids, where they are vitally involved in cell interactions
What are the two basic compounds that carbohydrates consist of?
Aldehydes and ketones
Give examples of 3 monosaccharides and what food they are found within.
Glucose
Galactose: milk and dairy products
Fructose: vegetable and fruit
Give three examples of disaccharides
Lactose: glucose and galactose
Maltose: glucose and glucose
Sucrose: glucose and fructose
Are starches water soluble?
NO
What are sources of starch for humans?
Potatoes, rice, wheat
What is another name for dietary fibre?
Non-starch polysaccharides
Why isn’t dietary fibre digestible?
Their glucose links can’t be broken
What are the properties of soluble fibre?
Dissolves in water to form gel and easily digested by bacteria in the colon (fermentable)
What are the properties of insoluble fibre?
Does no dissolve in water. Does not form gel and is less readily fermented
What happens to starch in the mouth?
Salivary enzyme amylase begins digestion
Starch is broken down to small polysaccharides and maltose
What happens to starch in the stomach?
Stomach acid inactivates salivary enzymes, halting starch digestion.
What happens to starch in the small intestine?
Starch is broken down to small polysaccharides and maltose by pancreatic amylase Disaccharide enzymes (maltase, sucrase, lactase) hydrolyse the disaccharides to monosaccharides
What is another name for disaccharidase?
Oligosaccharidase
Where are disaccharidases found?
On the microvilli of enterocytes
What happens in coeliac disease?
Microvilli are sloughed off and flattened. No brush border so can’t produce disaccharidases. Consumption of milk will result in inability to digest. Severe gastroenteritis from bacteria can also cause temporary lactase deficiency.
What are final products of complete alpha-amylase digestion?
Maltose
Maltotriose
Alpha-limit dextrins
What is related to total activity of oligosaccharidase and total transport capacity?
Surface area of small intestine
What are glucose and galactose absorbed by?
The same Na+ linked transport protein: the sodium-glucose co-transporter 1. (Active transport)
How is fructose absorbed?
By facilitated transport down a conc. gradient
What are the symptoms of lactose intolerance?
Bloating, abdominal discomfort (bacteria ferment undigested lactose, producing gas), diarrhoea
What are the causes for primary and secondary lactase deficiency?
Primary: genetic predisposition
Secondary: caused by bacteria (gastroenteritis) or autoimmune disease (coeliac)
What are the management options for lactase deficiency?
- Remove milk products
- Increase consumption gradually (secondary lactase deficiency)
- Spreading dairy intake throughout the day
- Use of enzymes
Where does the absorption of carbs primarily take place?
Small intestine
