Module 04 - Introduction to Carbohydrates and Carbohydrate Digestion (Section 01) Flashcards
What are the 5 main cellular functions of Carbohydrates?
- Provide energy in the diet
- Provide a storage form of energy (glycogen, starch)
- Form of componenets of mammalian cell membranes
- Comprise the cell wall in plants and bacteria
- Form components of insect chitin exoskeleton
Monosaccharides: 3 Carbon generic name & example?
triose, glyceraldehyde
Monosaccharides: 4 Carbon generic name & example?
tetrose, erythrose
Monosaccharides: 5 Carbon generic name & example?
pentose, ribose
Monosaccharides: 6 Carbon generic name & example?
hexose, glucose
Monosaccharides: 7 Carbon generic name & example?
heptose, sedoheptulose
Monosaccharides: 9 Carbon generic name & example?
nonose, neuraminic acid
What are Aldoses?
contain an aldehyde which has a hydrogen , R group, and =O attached to the carbon
What are Ketoses?
contain a keto group, which has 2 other carbons attached to the C and =O
How do monosaccharides form their ring?
the aldehyde or keto group react with an alcohol on the same molecule, closing the molecule into a ring
What happens to the carbonyl carbon (C1) when a monosaccharide forms its ring structure? What does the position of
the hydroxyl determine?
it becomes the anomeric carbon, which is a stereocentre; the position of the hydroxyl on the anomeric carbon determines whether the molecule is in the alpha (down) or beta (up) conformation
What is a Stereocentre? (aka chiral centre)
an atom with three or more different attachments where interchanging of two of these attachments leads to another stereoisomer
How many monosaccharides does a Disaccharide have? What are some examples of Disaccharides?
- two
- lactose, sucrose, maltose
How many monosaccharides does a Oligosaccharide have?
3-10
How many monosaccharides does a Polysaccharide have?
10+
- can be 100s sugars long
How many types of sugar does a Homopolysaccharide have? What is an example of a Homopolysaccharide?
- one
- glycogen
How many types of monosaccharides does a Heteropolysaccharide have?
- more than one
What is a Complex Carbohydrate?
sugars that are attached to non-carbohydrate stuctures by glycosidic bonds
What is a Glycosyl Residue?
- the sugar that participates in the complex carbohydrate glycosidic bond
What are sugars found to bind to? (4)
- purine/pyrimidine bases in nucleotides
- aromatic rings in steroids and bilirubin
- proteins to form glycoproteins
- lipids to form glycolipids
What is the bond called when it binds to and NH2 group? What amino acid is used for this bond?
- N-glycoside
- asparagine
What is the bond called when it binds to and OH group? What two amino acids are used for this bond?
- O-glycoside
- serine or threonine
What is an Isomer? Give examples
- compounds that have the same chemical formula but different structures
- glucose, mannose, galactose, fructose (C6H12O6)
What is an Epimer? Give examples
- compounds that differ in configuration at one specific carbon atom
- type of isomer
- e.g. glucose and mannose (C-2)
What is an Enantiomer?
- structures that are mirror images of each other (D- or L- conformations)
- type of isomer
What is a Hydrolysis Reaction?
a reaction where a molecule of water is added or consumed
What is Carbohydrate Digestion? Where does it occur?
- the process by which the body breaks down food into usable subunits
- the mouth and small intestine
What is released during chewing at the beginning of carbohydrate digestion? What does this do?
- alpha-amylase is released by the salivary glands
- begins to break apart the polysaccharide starch by cleaving alpha (1–>4) bonds
Why can humans not digest cellulose?
we lack enzymes that can cleave beta-(1–>4) bonds between glucose molecules in the polysaccharide
Where does digestion of carbohydrates stop? Why?
- in the stomach
- acidic environment of the stomach causes amylase to denature
What happens in the intestines during carbohydrate digestion?
- pancreatic alpha-amylase continues digestion
How is final carbohydrate digestion completed?
- by enzymes made by the intestinal mucosal cells lining the jejunum
- these enzymes are specific to a particular disaccharide, referred to as brush border enzymes
Where does intestinal absorption occur?
in the duodeum and upper jejunum, where the monosaccharides are passed into the circulatory system to be used by the body
What is Lactose Intolerance cause by?
a loss of lactase activity, either through lactase deficiency or through age-dependent loss of lactase activity
