Carbohydrates

Carbohydrates

• Major energy source; made of carbon, hydrogen, and oxygen.

• Also called saccharides (sugars).

• Classified as monosaccharides, disaccharides, and polysaccharides.

Monosaccharides

• Simplest carbohydrates with 3-8 carbon chains and a carbonyl group.

• Aldoses: contain an aldehyde group.

• Ketoses: contain a ketone group.

• Classified by carbon atoms: triose (3C), tetrose (4C), pentose (5C), hexose (6C).

Chiral Molecules

• Chiral molecules have non-superimposable mirror images.

• Structural isomers: same molecular formula, different bonding.

• Stereoisomers: same formula, different spatial arrangement.

• Chiral carbon: bonded to four different groups.

• Enantiomers: stereoisomers that are non-superimposable mirror images.

• Achiral: superimposable mirror images.

Fischer Projections & D/L Notations

• 2D representation of 3D molecules with most oxidized carbon at the top.

• D/L isomers determined by the (\text{--OH}) group position on chiral carbon farthest from carbonyl carbon.

  • L: (\text{--OH}) on the left.

  • D: (\text{--OH}) on the right.

Important Monosaccharides

• Glucose: aldohexose, dextrose, blood sugar ((C6H{12}O_6)); building block for many larger saccharides.

• Fructose: ketohexose ((C6H{12}O_6)); sweetest carbohydrate.

• Galactose: aldohexose ((C6H{12}O_6)); from lactose; similar to glucose except for the (\text{--OH}) on carbon 4.

Haworth Structures

• Cyclic structures of pentose and hexose sugars.

• Formed by reaction of carbonyl and hydroxyl groups in the same molecule.

• Glucose forms a six-atom ring; fructose forms a five-atom ring.

• (\alpha) and (\beta) isomers exist due to (\text{--OH}) group position on carbon 1.

• Mutarotation: cyclic structures open and close in solution, converting between (\alpha) and (\beta) forms.

Disaccharides

• Two monosaccharides linked by a glycosidic bond via dehydration reaction.

• Common disaccharides: maltose, lactose, sucrose.

• Maltose: two D-glucose molecules linked by (\alpha)-1,4-glycosidic bond.

• Lactose: (\beta)-D-galactose and glucose linked by (\beta)-1,4-glycosidic bond.

• Sucrose: glucose and fructose linked by (\alpha), (\beta)-1,2-glycosidic bond; non-reducing sugar.

Polysaccharides

• Polymers of monosaccharides.

• Include amylose, amylopectin, glycogen, and cellulose (all polymers of glucose).

• Amylose: straight-chain of glucose units with (\alpha)-1,4-glycosidic bonds (20% of starch).

• Amylopectin: branched chain of glucose with (\alpha)-1,4- and (\alpha)-1,6-glycosidic bonds (80% of starch).

• Glycogen: glucose polymer stored in liver and muscle; highly branched with (\alpha)-1,4- and (\alpha)-1,6-glycosidic bonds.

• Cellulose: unbranched chains of glucose with (\beta)-1,4-glycosidic bonds; indigestible by humans.

Practice tests can help you prepare for exams by familiarizing you with the format, types of questions, and time constraints. To effectively use practice tests:

1. Simulate Exam Conditions: Take the test in a quiet environment, without distractions, and within the allotted time.

2. Review Material Beforehand: Ensure you have studied the relevant material before taking the test to get an accurate measure of your understanding.

3. Analyze Your Results: After the test, review each question, especially those you answered incorrectly, to understand the correct solution and why your answer was wrong.

4. Focus on Weak Areas: Identify the topics or types of questions you struggle with and focus your studying on those areas.

5. Use Multiple Resources: Utilize a variety of practice tests from different sources to get a broad exposure to potential questions.