Biochemistry: Carbohydrates and Macromolecules Quiz

Biological Molecules Overview

• Biological molecules are categorized into four major classes: carbohydrates, lipids, proteins, and nucleic acids.
• Nucleic acids, while important, are discussed later in a different course (General Biology 2).
• Organic molecules all contain carbon and often include hydrogen, oxygen, nitrogen, and other minor elements.

Macromolecule Structure

• Macromolecules are composed of smaller subunits called monomers.
• Monomers are linked together by covalent bonds to form polymers.
• Dehydration synthesis is the process by which monomers are joined to form polymers; a water molecule is released during this process.
• Conversely, hydrolysis breaks polymers down into monomers and requires a water molecule in the process.

The Miller-Urey Experiment

• The Miller-Urey experiment simulated early Earth conditions to investigate the possible origin of life.
• The experiment used gases (water, methane, ammonia, and hydrogen) to recreate the primitive Earth's atmosphere.
• An electrical spark simulated lightning.
• The experiment showed that amino acids, the building blocks of proteins, could form under these conditions.

Enzymes in Biological Reactions

• Enzymes are biological molecules that catalyze or speed up biochemical reactions.
• Each enzyme is specific to its substrate.
• Enzymes accelerate both hydrolysis and dehydration reactions.
• Dehydration reactions form bonds, requiring energy.
• Hydrolysis reactions break bonds, releasing energy.
• An enzyme changes slightly as it binds its substrate to facilitate this action.
• Many different kinds of enzymes exist (e.g., amylase, sucrase, maltase, lipases, pepsin, peptidases).

Carbohydrates

• Carbohydrates are found in grains, fruits, and vegetables
• They provide glucose, a primary source of energy for the body.
• They have a general formula (CH₂O)ₙ.
• The ratio of carbon, hydrogen, and oxygen is 1:2:1.
• Carbohydrates are categorized into three subtypes:
  • Monosaccharides
  • Disaccharides
  • Polysaccharides

Monosaccharides

• Monosaccharides typically contain 3-7 carbon atoms.
• They end with the suffix "-ose".
• They contain a carbonyl group (C=O).
• Aldoses have a carbonyl group at the end of the carbon chain.
• Ketoses have a carbonyl group in the middle of the chain
• Examples include triose, pentose (5C), and hexose (6C) sugars like glucose, fructose, and galactose.
• Glucose, fructose, and galactose are all structural isomers, having shared molecular formulas (C₆H₁₂O₆).

Disaccharides

• Disaccharides are formed when two monosaccharides are linked through a dehydration reaction.
• A water molecule forms as the glycosidic bond, connecting the two molecules is formed.
• This linkage forms between carbon 1 on one sugar and carbon 2 on the other sugar (1,2 glycosidic linkage).
• Common disaccharides include sucrose, maltose, and lactose.

Polysaccharides

• Polysaccharides are long chains of monosaccharides linked by glycosidic linkages.
• These chains can be branched or unbranched.
• They can contain different types of monosaccharides
• Their molecular weights can exceed 10,000 daltons.
• Examples include starch, glycogen, and cellulose.

Starch

• Starch is composed of amylose and amylopectin.
• Amylose is unbranched and contains 1-4 glycosidic bonds.
• Amylopectin is branched and contains 1-4 and 1-6 glycosidic bonds.

Cellulose

• Cellulose is a polysaccharide found in plant cell walls.
• It is unbranched and composed of glucose monomers linked by β-1,4-glycosidic linkages.
• The orientation of glucose monomers in cellulose gives it a strong, fibrous structure.

Chitin

• Chitin is a tough polysaccharide that forms the exoskeleton of arthropods.
• It also contains nitrogen.

Lipids

• Lipids are a diverse group of non-polar hydrophobic hydrocarbons.
• They include fats, oils, waxes, phospholipids, and steroids.
• Functions of lipids include long-term energy storage and insulation, serving as building blocks for some hormones, and forming important parts of cellular membranes.

Fats and Oils

• Fats and oils are made up of glycerol and fatty acids (triacylglycerol—three fatty acids linked to a glycerol molecule)
• Fatty acids can be saturated or unsaturated, depending on the presence or absence of double bonds in their carbon chain backbones.
• Saturated fats are typically solid at room temperature, while unsaturated fats are typically liquid at room temperature (oils).
• Oils can contain one (monounsaturated) or more than one (polyunsaturated) carbon-carbon double bond.

Trans Fats

• Trans fats are unsaturated fats that have been processed to change their structure.
• The hydrogen atoms are on opposite sides of the double carbon bond, which gives trans-fatty acids a linear structure and makes them capable of stacking tightly.
• Trans fats are solid at room temperature and can contribute to heart disease.

Essential Fatty Acids

• Essential fatty acids are required for human health but cannot be synthesized by the body.
• Omega-3 fatty acids are essential and are found in salmon, trout and tuna fish.
• Essential fatty acids can play a role in reducing the risk of heart disease.

Waxes

• Waxes are esters of long-chain fatty acids and long-chain alcohols.
• They are hydrophobic and prevent water from sticking to surfaces.
• They are found on the feathers of some aquatic birds and on the surfaces of leaves from certain plants.

Phospholipids

• Phospholipids have a hydrophilic head and two hydrophobic tails.
• The head is a modified phosphate group (often containing choline or serine), attached to a glycerol backbone.
• The two hydrophobic tails are fatty acids.
• Phospholipids are major components of cell membranes.
• The hydrophilic heads face the aqueous solution, and the hydrophobic tails are sequestered in the middle of the bilayer.

Steroids

• Steroids have a characteristic structure: four linked carbon rings.
• Cholesterol is an example of a steroid and is the most prevalent steroid in the human body.
• Steroids also include other important hormones such as testosterone and estradiol, as well as precursors for vitamin D and bile salts.

Proteins

• Proteins are the most abundant organic molecules in living organisms.
• They have a wide array of functions, including regulatory functions, structural functions, protective functions, transport functions, enzymatic functions, and as toxins.
• Enzymes are proteins that act as biological catalysts, speeding up chemical reactions.
• Proteins are composed of amino acids.

Amino Acids

• Amino acids are the building blocks of proteins.
• They have a central carbon atom (α-carbon) bonded to an amino functional group (-NH₂) , a carboxyl functional group (-COOH), a hydrogen atom, and a side chain (R-group) which makes each amino acid different.

Peptide Bonds

• Peptide bonds link amino acids together to form polypeptide chains.
• A peptide bond forms through a dehydration reaction between the carboxyl group of one amino acid and the amino group of the next. A water molecule is eliminated during this process.

Polypeptides vs. Proteins

• A polypeptide is a chain of amino acids linked by peptide bonds.
• A protein is a polypeptide (or multiple polypeptides) that may be modified by the addition of non-peptide prosthetic groups, sometimes resulting in a unique function depending on the amino acid sequence.

Protein Synthesis

• Protein synthesis is the process of building proteins from amino acids.
• The sequence of amino acids is determined by a gene encoding that protein.

Protein Structure

• Protein shape is central to its function.
• Four levels of protein structure:
  • Primary - linear amino acid sequence dictated by DNA.
  • Secondary - local 3D folding of the polypeptide chain (alpha-helix or beta-pleated sheet) stabilized by hydrogen bonding between backbone atoms.
  • Tertiary – overall 3D structure of the entire polypeptide, determined by interactions such as hydrophobic interactions, ionic bonding, hydrogen bonding, and disulfide bridges between amino acid side chains.
  • Quaternary – the arrangement of multiple polypeptide chains (subunits) that form the final functional protein structure. These interactions frequently involve weak interactions between subunits.

Protein Denaturation

• Denaturation is a process where a protein's structure changes and loses its function, usually due to alterations in temperature, pH, or by chemical agents.
• When proteins denature, the structure they create is disrupted, unraveling the protein. This often leads to a change in protein function.