3: CHO & Lipids Introduction

Carbohydrates and Lipids Introduction

• The overall goal is to evaluate the structure and function of carbon-based molecules and identify features enabling unique chemical behaviors.

• Carbohydrates

  • Summarize common carbohydrates in the body and diet.
  • Explain carbohydrate structure through linear and cyclic forms, identifying the anomeric carbon.
  • Differentiate between aldehydes and ketones, and describe the bonds formed between monosaccharides.
  • Explain the difference between alpha and beta conformations in monosaccharides and alpha and beta linkages in polysaccharides.

• Lipids

  • Compare and contrast types of lipids and their uses in biological systems.
  • Compare and contrast saturated and unsaturated forms of lipids.
  • Compare and contrast types of adipose tissue and explain the role of adipose in energy storage.
  • Explain how lipid structure contributes to lipid behavior, location, storage, and usage in biological systems.

Macromolecules

• Macromolecules are large carbon-containing molecules held together by covalent bonds.
• Examples include proteins, RNA, and DNA.
• Bonds between atoms within polymeric macromolecules are covalent.
• Bonds across polymeric macromolecules (between molecules) are often hydrogen bonds.

Carbohydrate Basics

• Polyhydroxy aldehydes and polyhydroxy ketones are both types containing a carbonyl group (C=O).
• In the carbohydrate with the carbonyl group, if the other bond is to a hydrogen instead of carbon, it's an aldehyde.
• Nearly all sugars in the body have a D configuration.

Key Carbohydrate Processes

• Carbohydrates are essential for key processes.
• They play a key structural role.
• They are a source of carbon skeletons for new molecules.
• They are useful for storing energy (glycogen).
• They are useful for transporting energy (blood glucose).

Stereochemistry and Sugars

• Sugars are optically active due to asymmetric carbon centers.
• While many possible configurations exist, only a few are present/important in the body and diet.

Natural Configuration

• Aldehyde residues are easily oxidized, but in aqueous environments, glucose exists mostly in a cyclic configuration, making it resistant to oxidation and less reactive.
• It does not readily react with protein.
• Cyclic configuration is ideal for transport/blood sugar.

Simplification of Ring Structure

• Carbohydrates, specifically sugars, come in different carbon structures (3, 5, and 6 carbon sugars).
• Carbon structures have linear and ring forms.
• The ring forms are more stable, especially when hydrated.
• Examples include glucose, fructose, ribose, and deoxyribose.

Actual Ring Structures

• Ring formation for glucose and fructose involves different configurations and carbon numbers.
• This can lead to new asymmetric carbons, called the anomeric carbon.
• The anomeric carbon arises because the carbonyl was involved in a new bond
• Examples include glucose and fructose in various ring forms.

Polysaccharides

• Differences in sugar linkages affect the chemical behaviors of polysaccharides.
• Links between sugar molecules are glycosidic linkages/glycosidic bonds.
• Hemiacetal carbon of one sugar links to the hydroxyl of another.
• If composed of only one type of monosaccharide, it's a homoglycan.
• If composed of different monosaccharides, it's a heteroglycan.
• Example linkages include those connecting glucose molecules in starch, glycogen, and cellulose.

A Few Quick Reminders

• Alpha and beta forms have different stereochemistry regarding the hydroxyl group location on the anomeric carbon.
• O-bonds involve oxygen; N-bonds involve nitrogen.

Storage Structures

• Storage structures, such as plastids containing starch granules in potato tuber cells, store carbohydrates.
• Other examples include glycogen granules in muscle tissues and cellulose microfibrils in plant cell walls.

Lipids

• Lipids are non-polar and hydrophobic hydrocarbons, composed of carbons and hydrogens.
• Functions include storing energy (fats, oils), forming cell membranes (phospholipids), acting in regulatory roles (steroids), aiding in photosynthesis (chlorophylls), providing thermal insulation (fat), electrical insulation (myelin), and repelling water (oil, wax).

Saturated vs. Unsaturated

• Saturated fats have fully bound hydrogens, are linear, and typically solid at room temperature.
• Unsaturated fats have double bonds, causing bends in the structure, and are typically liquid at room temperature.

Lipids (Specific types)

• Fatty acids, the simplest forms, are found in plasma.
• Triglycerides are the storage form primarily in adipose tissue.
• Phospholipids are amphipathic and crucial to cell membranes.

Fatty Acids

• Fatty acids are a smaller source of energy (except in the brain and red blood cells).
• They aren't typically found free in the body, but are bound to albumin in the blood or fatty acid binding proteins in the cytosol.
• Fatty acids are categorized by their carbon chain length. Different lengths are distributed to different metabolic functions in the body.

Triacylglycerols (Triglycerides)

• Triglycerides are the storage form of lipids in adipose tissue.
• They are formed by the esterification of fatty acids to glycerol.

Adipose Tissue

• Adipose tissue is an active endocrine organ impacting energy balance.
• It produces hormones (e.g., leptin, adiponectin, resistin).
• Fat is stored in subcutaneous, visceral, and ectopic locations.
• Adipose tissue has complex roles in energy balance and influencing metabolic function in the body.

Phospholipids

• These are complex lipids with hydrophobic hydrocarbons and a polar head group, often involving a phosphate linking the glycerol.
• Variations in hydrocarbon and polar head groups lead to variations in behavior.
• They contribute to membrane charge and fluidity.

Proteins vs. Carbohydrates

• Both are polymers built from monomers.
• Proteins are composed of amino acids, while carbohydrates are composed of sugars.
• Proteins can have nitrogen and sulfur.