Monosaccharides and Polysaccharides

• Biochemistry deals with macromolecules within cells and organisms

Macromolecules

• Large molecules are composed of repeating subunits
• Four major classes include carbohydrates, proteins, lipids, and nucleic acids

Carbohydrates

• Used for energy, building materials, cell identification, and communication
• Contain carbon, hydrogen, and oxygen in a 1:2:1 ratio
• Divided into three groups: monosaccharides, disaccharides, and polysaccharides

Monosaccharides

• These are simple sugars and the one subunit of carbohydrates
• Two types exist: aldose and ketose

Aldose

• All carbons have hydroxyl groups attached
• A carbonyl group is present on a terminal carbon

Ketose

• All carbons have hydroxyl groups attached
• A carbonyl group is present on a central carbon

Monosaccharides - Glucose

• Sugars with five or more carbons form ring structures when dissolved in water
• Glucose forms a ring structure when two of its functional groups interact
• Two possible arrangements exist: alpha and beta glucose
• Glucose, fructose, and galactose are isomers, possessing the same chemical formula but different structures

Disaccharides

• Combine two subunits of simple sugars
• A glycosidic linkage forms between two monosaccharides through a condensation reaction (dehydration synthesis)
• Maltose has two a glucose molecules linked by an a-1-4 glycosidic linkage
• Sucrose and lactose are other common disaccharides

Polysaccharides

• Complex carbohydrates contain many subunits, ranging from hundreds to thousands
• Hydrophilic but very large, therefore they can attract water but do not dissolve
• Four types include starch, glycogen, cellulose, and chitin

Starch

• Plants use starch for energy Storage
• Composed of amylose (a1-4 links) and amylopectin (a1-4 links, a1-6 links where it branches)

Glycogen

• Used as animal energy storage is stored in the liver and muscle cells
• Composed of a1-4 links and a1-6 links where it branches
• More branched than starch

Cellulose

• Composed of B1-4 links
• Every other glucose subunit becomes inverted to accommodate this link
• Not coiled or branched
• Used in plant cell walls

Chitin

• Cellulose-like polymer of N-acetylglucosamine
• A glucose molecule with a nitrogen-containing group attached at second C-position is a monomer
• Forms hard exoskeletons in insects and crustaceans
• Exists in fungal cell walls

Lipids

• Hydrophobic molecules ("water fearing")
• Nonpolar and insoluble in water
• Fats, phospholipids, steroids, and waxes are examples
• A gram of fat has 9 calories of energy (compared to 4 calories in carbohydrates and proteins)
• Functions include energy storage, cushioning, and insulation
• Excess carbohydrates are converted to fat and stored as droplets in adipose (fat) tissue in animals

Fats

• They are trigylcerides
• Glycerol is the backbone, it contains 3 hydroxyls
• Each fatty acid is between 14 and 22 carbons and has a terminal carboxylic acid
• A condensation reaction attaches 3 fatty acids to glycerol, forming ester linkages (esterification)

Saturated Fats

• Generally come from animals
• Used for insulation, protection, and long-term energy storage.
• Helps dissolve fat-soluble vitamins
• Solid at room temperature due to straight chains
• Fatty acids are closer together because of strong intermolecular forces
• Diets high in these fats can lead to heart disease
• No double bonds are found between carbon atoms in the fatty acids

Unsaturated Fats

• Generally comes from plant oils
• One or more double bonds are found between carbon atoms in fatty acids
• Liquid at room temperature
• Diets high in these fats can improve health
• Double bonds form kinks and produce more space between fatty acids, this reduces the number of intermolecular interactions

Phospholipids

• Composed of one glycerol, two fatty acids, and a polar phosphate group
• Considered amphipathic, containing both polar and non-polar parts
• Form cellular membranes (phospholipid bilayer)
• The phospholipid bilayer is virtually impermeable to macromolecules
• It is relatively impermeable to charged ions
• Quite permeable to soluble molecules and small lipids
• O₂ and CO₂ diffuse through with very little resistance
• The most common phospholipids are phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine

Steroids

• Hydrophobic molecules
• Have four fused hydrocarbon rings with many functional groups attached
• Cholesterol and some hormones (e.g. cortisol, estrogen, testosterone, progesterone) are steroids

Cholesterol

• Cholesterol is converted by the body into bile salts and vitamin D
• Also essential for functioning cell membranes and comes from the food consumed or synthesized in the liver
• A high bloodstream level of cholesterol is linked to atherosclerosis
• Bloodstream cholesterol is transported as spherical particles called lipoproteins
• The two most commonly known lipoproteins are low-density lipoproteins (LDL) and high-density lipoproteins (HDL)

Waxes

• Bees wax, paraffin, and cutin
• Consist of alcohol or carbon rings with an ester linkage to a fatty acid
• Act as waterproof coatings on various plant and animal parts
• Hydrophobic and non-polar

Proteins

• A polymer contains many subunits folded into a 3D structure that specifies its function
• Complex and diverse group of molecules in living systems and are involved in almost everything cells do
• Examples include enzymes, immunoglobulins, hemoglobin, keratin, and fibrin

Types of Proteins

• Structural proteins such as hair, tendons, and ligaments provide framework support
• Defensive proteins such as antibodies act as infection fighters
• Signal proteins such as hormones act as messengers
• Carrier proteins such as hemoglobin transport materials
• Recognition and Receptor proteins are cellular markers which are major histocompatibility complex
• Enzyme proteins such as amylase act as a catalyst
• Motile proteins such as actin and myosin cause movement

Amino Acids

• Monomers are made of proteins (polypeptides)
• There are 20 different amino acids, eight of which are essential
• Essential amino acids, which cannot be made in human cells, must be obtained from the diet
• The R groups (side chains) contained in the 20 amino acids make each one unique
• These side chains can make the amino acid polar (hydrophilic), non-polar (hydrophobic), or charged (acidic/basic)

Nonpolar Amino Acids

• Glycine (gly), alanine (ala), valine (val), leucine (leu), isoleucine (ile), methionine (met), phenylalanine (phe), tryptophan (trp), and proline (pro)

Polar Amino Acids

• Serine (ser), threonine (thr), cysteine (cys), tyrosine (tyr), asparagine (asn), and glutamine (gln)

Charged Amino Acids

• Acidic amino acids are aspartic acid (asp) and glutamic acid (glu)
• Basic Amino Acids are lysine (lys), arginine (arg), and histidine (his)

Protein Structure

• Peptide bonds hold amino acids together
• A condensation reaction forms peptide bonds
• A polypeptide must be more than 50 amino acids in length to then fold into a 3D shape
• Proteins are only functional after folding

Protein Conformation

• Also called conformation
• Depends on the amino acids it contains, and the interaction between those amino acids, the interaction between those amino acids

Primary Structure

• The unique sequence of amino acids in the polypeptide
• Determined by the nucleotide sequence of a particular gene
• In a protein with 'X' number of amino acids, number of possibilities is 20x

Secondary Structure

• The folding and coiling of the polypeptide chain as it grows
• Formed by hydrogen bonds between oxygen atoms of a carboxyl group and hydrogen atoms of the same amino acid backbone
• Two types exist which include a helix and B pleated sheets
• α helix – Is a tight coil produced by H-bonds repeated every four peptide bonds
• β pleated sheets – H-bonds formed between parallel stretches of a polypeptide

Tertiary Structure

• Polypeptide chains undergo additional folding due to side chain (R-group) interactions
• Interactions between side chains include hydrogen bonds, hydrophobic inter-actions, and disulfide bridges
• Disulfide bridges are bonds that form when the -SH groups of two cysteine amino acids line up and react to form a S-S covalent bond
• This is a strong bond that stabilizes the shape of the protein

Quaternary Structure

• Two or more polypeptide chains come together, such as in collagen and hemoglobin

Protein Prosthetic Groups

• Many proteins require non-protein components called prosthetic groups to function
• Hemoglobin is composed of four polypeptides chains that include a heme group which is a ring with a single Fe+2 ion
• The heme group binds oxygen

Denaturation

• Proteins unravel due to temperature and pH changes (denature)
• Caused by the disruption of hydrogen bonds, etc
• A denatured protein cannot carry out its biological function
• A denatured protein can revert to its original shape if removed from the extreme environment, provided it does not destroy the primary sequence

Nucleic Acids

• Composed of nucleotides
• Nucleotides consist of a nitrogenous base, a five-carbon sugar, and a phosphate group
• Nitrogenous bases include adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U)
• DNA and RNA are nucleotide polymers that serve as the assembly instructions for proteins in living organisms
• ATP and GTP are nucleotides that take part in cell metabolism along with nucleotide coenzymes (NAD+, NADP+ and FAD)

Nucleotides

• A phosphodiester linkage is made of a link between a phosphate group and hydroxyl group at an adjacent sugar’s carbon 3
• Sugars found in nucleic acids either take the form of deoxyribose (in DNA) or ribose (in RNA)

Nitrogenous Bases

• Pyrimidines include cytosine (C), thymine (T), and uracil (U)
• Purines include adenine (A) and guanine (G)

DNA

• In DNA, A connects with T with 2 hydrogen bonds
• G connects with C with 3 hydrogen bonds
• The two strands are antiparallel with one strand upside down compared to the other