Chapter 11: Carbohydrates Flashcards
Carbohydrates
A group of organic compounds occurring in foods and living tissues primarily used for fuel and structural components for cells
Carbohydrates can also be located on ____
proteins
What kind of bonds do carbohydrates contain ?
Bonds between carbon, hydrogen and oxygen
How are carbohydrates named ?
Names end in -ose
What are the three classes of carbohydrates ?
- monosaccharides
- oligiosaccharides
- polysaccharides
Monosaccharides
Simplest form of sugars
Oligiosaccharides
Have 2-1 0 sugars bound together
Polysaccharides
Large polymers or chains of sugars. Can be linear or branched
How many carbons can monosaccharides contain ?
3-7 carbons
What are the two types of monosaccharides ?
1) Aldoses ( contains aldehyde )
2) Ketoses ( contains ketone)
How are monosaccharides named ?
- by the number of carbons ( root end )
- Aldose or ketose
Ex) aldopentose
Aldoses have at least
3 carbons
Ketoses have at least
4 carbons
True or false, aldoses and ketoses contain no chiral centers
False
Enantiomers
Mirror image of original molecule
What are the two types on enantiomers found in organic compounds ?
L or D
Do L or D enantiomers specify the direction of rotated light
No they do not. The direction of rotated light is indicated by (+) or (-)
Diastereomers
Opposite configurations at one or more of the chiral centers of the original molecule
Epimers
diastereomers that differ at only one chiral center
Examples of monosaccarides
Glucose, fructose, galactose
What is the relation between glucose, mannose and galactose ?
Diastereomers
Examples of aldose monosaccharide
glucose or galactose
Example of a ketose monosaccharide
fructose
What are the two ways that carbohydrates can be drawn
Linear structure or cyclic form
How can hemiacetals or hemiketals be formed from linear form ?
Reactions from the C5 alcohol group
Anomeric carbon
The carbon that carries the carbonyl group
How are configuration of the anomeric carbon indicated
They are either indicated by α or β configuration.
What percentage of glucose molecules are in linear form ?
Less than 1 %
What percentage of glucose molecules are in α form ?
33 %
What percentage of glucose molecule are found in β form ?
66 %
What two locations can fructose form a ring ?
Either on C6 or C5
Haworth projection
Sugars drawn in ring structure projection
O-glycosidic bonds
Reaction between C1 carbon and O atom in an alcohol group . The bond is used to form long polymers of carbohydrates
N-glycosidic bonds
Reaction between C1 and the N of an amine
Where can N-glycosidic bonds be found ?
On cell surfaces
Why are phosphate groups often added to sugars ?
- it makes sugars anionic and prevent passive diffusion through the membrane
- it makes sugars more reactive
Disaccharides
Two monosaccharides linked by a glycosidic bond
Where does the O-glycosidic bond occur between two monosaccharides ?
Between C1 and on C6 or C4
Examples of dissacharides
Sucrose, Maltose, and lactose
Enzymes that digest disaccharides are usually found
In the cells of the small intestine
Sucrose is a disaccharide with bonds formed between
glucose and fructose
Maltose is a disaccharide with bonds formed between
Two glucose molecules
Lactose is a disaccharide with bonds formed between
Glucose and galactose
How are linkages in oligosaccharides indicated ?
Designated by the number of carbons linked
1-> 4 linkage
Linkage between the C1 of one monosaccharide nd the C4 of the other
1->6 linkage
Linkage between the C1 of one monosaccaride and the C6 of the other
Examples of polysaccharides
Starch or cellulose
What are the two forms of starch
α-amylose and amylopectin
What percentage of starch is α-amylose ?
10-30 %
What percentage of starch is amylopectin ?
70-90 %
What is the main storage molecule in animals ?
glycogen
Cellulose
A polysaccharide of glucose found in plants. It is linear , unbranched and gives plants structure
The chains in cellulose are
parallel which allows hydrogen bonds to form sheets resistant to hydrolysis
Why can’t mammals digest cellulose?
They do not have the enzyme to break down the linkages
What are the 3 classes of carbohydrate proteins ?
glycoproteins , proteoglycans , mucins
Glycoproteins
- carbohydrate group attached to protein
- mostly protein by weight
- most are part of the cell membrane for recognition and signaling
Proteoglycans
- Proteins that are bonded to particular sugars called glycoaminoglycans
- mostly carbohydrates by weight
- work as structural components or lubricants
Mucins
- mucoproteins
- mostly carbohydrate weight
- function as lubricants
The O-linkages on glycoproteins are linked by glycosidic bonds to protein chains with either
serine or threonine
The N- linkages are linked through an amide bond to a nitrogen through an _____ residue
Asparagine
N- linked oligoosaccarides have a common core of two ________ and three ______
- 2 N- acetylglucosamine residues
- mannose residues
Glycosylation
a controlled enzymatic modification of an organic molecule, especially a protein , with a sugar molecule
EPO
Erythropoetin , a hormone that stimulates the production of red blood cells
True or false, glycosylation decreases the stabiity of a protein
False, enhances
Recombinant EPO
Used to treat anemia , kidney disease, or chemotherapy
The properties of proteoglycans are determined by the
glycoaminoglycans
Examples of common glycoaminoglycans
- heparin sulfate
- chondroitin sulfate
- keratan sulfate
- dermatan sulfate
- hyaluronate
Glycoaminoglycans
complex polysaccarides containing repeating amino groups
Examples of proteoglycans
- cartilage
Role of mucins
- serve as a protective barrier
- cell adhesion
Human ABO blood groups are determined by
Glycosylation of surface proteins
Importance of glycosylation
- Helps to process and stabilize proteins
Lectin
Large class of glycan binding proteins that help with cell to cell contact. The proteins are found in every single organism
The C class of lectins require
Calcium
Selectins
Members of the Lectin C class that are involved in binding immune cells to sites of injury during inflammatory responses
Pathogens can gain entry into cells by
binding to lectins to carbohydrates
What is the difference between O and N inked glycosylation ?
O linked glycosylation are sugars that are attached to proteins through a hydroxyl group of serine or threonine .
N linked glycosylation are attached to proteins via amine group of an asaparagine residue
Describe the structure of a glycoaminoglycan
A long stretch of sugars consisting of alternating hexose and hexosamine residues. They also have many negatively charged sulfate groups on them
Describe how aggrecan , glycoaminoglycans and hylauronic acid make up the structure of cartilage
Many long strands of glycoaminoglycans, chondroitin sulfate and keratan sulfate are attatched to the aggregan moledcule. Then many aggrecan moleculles are attatched to strands of hylauronic acid
What are lectins ?
Molecules that bind carbohydrates on other cells involved with cell to cell interaction , immune responses and fertilization
