Biochemistry Quiz: Carbohydrates and Fats

Lipids - Introduction

• Lipids are a class of large biological molecules, not polymers, and generally not considered macromolecules.
• They are grouped together based on a shared trait: poor to no interactions with water (hydrophobic).
• Lipids have a wide variety of forms and functions.
• The most biologically important are phospholipids, glycolipids, and steroids.

Learning Outcomes

• Describe the structure of fat molecules.
• Understand how fat types differ due to their structure, resulting in varied properties.
• Briefly describe the fat naming and numbering systems.
• Describe phospholipid structure and understand how their molecular diversity arises.
• Define glycolipids and cholesterol importance in membrane lipids.
• Describe amphipathic properties and their role in bilayer formation.

Carbohydrates (Previously covered)

• Carbohydrates have a minimum of 3 carbon atoms and a (CH₂O)n ratio .
• They, except for dihydroxyacetone, can exist as isomers.
• Common monosaccharides include glucose, fructose, ribose, mannose, and galactose.
• They can exist in linear or cyclic forms as alpha or beta.
• They form hemiacetals or hemiketals, depending on the OH orientation.
• Disaccharides are formed through glycosidic bonds and may be reducing or non-reducing.
• Complex polysaccharides include glycogen, starch, and cellulose.
• Glycoproteins are common in the body and are classified into three categories.

Fats - Fatty Acids

• Fats are not polymers, yet are large molecules assembled from smaller molecules via dehydration.
• Fats are constructed from glycerol and fatty acids.
• Glycerol is an alcohol with three carbons and each with a hydroxyl group.
• Fatty acid chains vary in length (14-24 carbons) with 16 and 18 carbons being most common.
• Fatty acid chains can be saturated or unsaturated based on the presence of double bonds.
• Saturated fats are solid at room temperature and have no double bonds, allowing for tight packing.
• Unsaturated fats are liquid at room temperature and have one or more double bonds, resulting in kinks that prevent tight packing.

De Novo Lipogenesis

• De novo lipogenesis (DNL) is a metabolic process that converts non-lipid carbon precursors into lipids using glucose as a starting point
• Glucose is used to form citrate and then acetyl-CoA.
• Acetyl-CoA leads to the activation of fatty acid synthase from CoA.

Fatty Acid Saturation

• Fatty acids vary in length and in the presence and location of double bonds.
• Saturated fatty acids have no double bonds, while unsaturated fatty acids have one or more double bonds in their hydrocarbon chains.
• Saturated fatty acids generally have higher melting points than unsaturated fatty acids.
• Unsaturated fatty acids typically are in liquid form.

Animal Fats

• Animal fats are primarily composed of saturated fatty acids.
• The hydrocarbon chains of their fatty acids allow them to tightly pack together, characteristic of solids at room temperature.

Vegetable/Fish Fats

• Vegetable and fish fats are typically unsaturated, meaning that they are built of one or more types of unsaturated fatty acids.
• The unsaturated fatty acids are liquid at room temperature.
• The kinks of double bonds result in less tight packing, characteristic of fluids at room temperature.

Science Behind Observations

• The melting point of fatty acids depends on chain length and degree of saturation; unsaturated fatty acids have lower melting points compared to saturated ones.
• Shorter chain length suggests a lower melting point compared to longer chains.

Hydrogenated Fats

• "Hydrogenated vegetable oils" are unsaturated fats that have been synthetically converted to saturated fats by adding hydrogen.
• A catalyst is often required for a hydrogenation reaction.
• The hydrogenation reaction reduces the number of double bonds in the fatty acid.

Diet and Atherosclerosis

• A diet rich in saturated fats can contribute to atherosclerosis.
• Deposits called plaque develop within blood vessel walls and affect blood flow.
• Vegetable and fish oils and hydrogenation are methods for producing unsaturated fats

Fats: An Overview

• The most common types of fats are saturated, trans, monounsaturated, and polyunsaturated.
• Different fats have different health impacts and should be consumed in appropriate amounts as per healthy recommendations.
• Saturated fats are usually solid at room temperature, while unsaturated fats are typically liquid or semi-solid.

Phospholipids

• Essential components of cell membranes
• Constructed from four components: one or more fatty acids, a platform to which the fatty acids are attached, a phosphate group, and an alcohol group attached to a phosphate group.
• These structures are crucial for the form and function of the membranes, providing a classic example of form-function interplay.

Phosphoglycerides

• Consist of a glycerol backbone to which two fatty acid chains and a phosphorylated alcohol are attached.
• The hydroxyl groups at positions C-1 and C-2 of glycerol are esterified to the carboxyl groups of two fatty acid chains.
• The hydroxyl group at position C-3 of glycerol is esterified to phosphoric acid.

Phosphatidate

• The simplest phosphoglyceride formed from diacylglycerol and phosphorus.

Alcohol Groups

• Essential components of phosphoglycerides
• Common phosphoglyceride alcohols are amino alcohols (ethanolamine, serine), choline, and inositol.

Phospholipid head dive

• Structural formulas of the head groups attached to phospholipids.
• Include various important classifications of phospholipids (Phosphatidylcholine, Monoacyl PC, Phosphatidylethanolamine, Phosphatidylglycerol, Phosphatidylinositol, Phosphatidylserine).

Sphingomyelin

• A phospholipid not derived from glycerol but from sphingosine which is an amino alcohol with a long, unsaturated hydrocarbon chain.
• Sphingomyelin's structure involves sphingosine, a fatty acid, and phosphate, with choline or ethanolamine.

Membrane Lipids with Carbohydrates (Glycolipids)

• These lipids include sugar molecules attached to the backbone.
• Derived from sphingosine.
• Like sphingomyelin, they can be positioned asymmetrically within the membrane, with sugars facing outwards (extracellularly).
• The simplest glycolipid is cerebroside.
• More complex ones such as gangliosides may include multiple sugar residues.

Steroids

• Lipids characterized by a carbon skeleton consisting of four fused rings
• Cholesterol is a significant example, commonly occurring in animal cell membranes.
• Cholesterol functions as a precursor for other steroids, including hormones like cortisol, testosterone, and estrogen.

Summary

• Fats are composed of glycerol and fatty acid chains and are frequently found in food.
• The degree of saturation (amount of double bonds of unsaturated lipids) and presence of these bonds affect the physical properties of the lipid, including melting, solidifying, and flexibility properties.
• Various fatty acids have specific properties, and the degree of saturation and chain length influence those properties.
• Common lipids are constructed from combinations of these components, and their classifications are based on these structural differences.

Test your knowledge on key concepts related to carbohydrates and fats in biochemistry. This quiz covers topics such as the reactivity of glucose with proteins, types of bonds in sugars, classifications of fatty acids, and more. Perfect for students of biochemistry looking to reinforce their understanding.