Biology Notes Ch. 5 Macromolecules

What are macromolecules?

• All living things are made of four classes of large molecules: carbs, proteins, lipids, and nucleic acids

• Macromolecules are large molecules composed of thousands of covalently connected atoms and their molecule structure and function are inseparable

What is a polymer?

• a long molecule consisting of many similar building blocks called monomers

• Carbs, proteins, and nucleic acids are polymers 

What are the monomers of carbs, proteins, and nucleic acids? 

• Carbs: monosaccharide (such as glucose, fructose, and galactose) 

• Proteins: amino acids 

• Nucleic acids: nucleotides 

Dehydration Synthesis vs. Hydrolysis 

• Dehydration Synthesis: Removal of water to bond two monomers together 

• Hydrolysis: the addition of water to break two monomers apart 

Carbohydrates

• include sugars and the polymers of sugars 

• Simplest carbs are monosaccharides, then disaccharides, then oligosaccharides, and polysaccharides 

• Glucose is the most common and is C6H12O6

• Monosaccharides are classified by the location of the carbonyl group (aldose or ketose) and the number of carbons in their carbon skeleton (3 carbons= triose, 5 carbons=pentose)

• Are often drawn linearly, but in aqueous solutions sugars form rings 

• They serve as a major fuel for cells and as raw material for building molecules 

• Disaccharides include maltose and sucrose (maltose = 2 glucose/ sucrose = glucose+fructose)

Structure of Polysaccharides

• polysaccharides are the polymers of sugars, they have storage and structural roles 

• The structure and function of polysaccharides are determined by its sugar monomers and the positions of glycosidic linkages

  • Example: Starch is the storage polysaccharide of plants whereas glycogen is the storage polysaccharide in animals. Starch consists entirely of glucose monomers (stored within chloroplasts and other plastids). The simplest form of starch is amylose

    • Amylose vs. Amylopectin: Amylose is a mostly linear, helical polymer of glucose, while amylopectin is a highly branched polymer, together forming starch. Amylose is less soluble then amylopectin

  • Glycogen in humans and other vertebrates is located in the liver and muscle cells

Cellulose

• The polysaccharide cellulose is a major component of the tough wall of plant cells 

• Like, starch, cellulose is a polymer of glucose, but the glycosidic linkages differ 

• The difference is based on two ring forms for glucose: alpha and beta 

  • Starch is made of 1-4 linkages of alpha glucose monomers, cellulose is made of 1-4 linkages of beta glucose monomers 

• Starch is the sugar storage for plants while cellulose is the structural component. 

Polymers with alpha vs. Polymers with beta

• Polymers with alpha glucose are helical

• Polymers with beta glucose are straight 

• In straight structures, H atoms on one strand can bond with OH groups on other strands 

• Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants 

• Beta glucose monomers → cellulose molecules → microfibrils → cellulose microfibrils in a plant cell wall → cell wall

Cellulose in humans

• Enzymes that digest starch by hydrolyzing alpha linkages can’t hydrolyze beta linkages in cellulose

• Cellulose in human food passes through the digestive tract as insoluble fiber

• Some microbes use enzymes to digest cellulose and many herbivores from cows to termites have symbiotic relationships with these microbes.

Chitin

• Another structural polysaccharide found in the exoskeleton of arthropods 

• Provides structural support for the cell walls of many fungi

• Is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals. 

Lipids

• do not form polymers and don’t have monomers

• have little or no affinity for water, they are hydrophobic because they consist mostly of hydrocarbons which are non-polar covalent bonds

• Consist of fats, phospholipids, and steroids

Fats

• Constructed from two types of smaller molecules: glycerol and fatty acids 

• Glycerol is a three carbon alcohol with a hydroxyl group attached to each carbon

• A fatty acid consists of a carboxyl group attached to a long carbon skeleton

• Separate from water because water molecules form hydrogen bonds with each other and exclude the fats

• Mainly used for energy storage as adipose tissue

Saturated vs. Unsaturated Fatty Acids

• Fatty acids differ in number and locations of double bonds

• Saturated have the maximum number of hydrogens possible and no double bonds (solid foods like butter at room temp, comes from animal products)

• Unsaturated have one or more double bonds (liquid at room temp like oil, comes from plant and fish fats)

Fats and Health

• May contribute to cardiovascular disease through plaque deposits 

• Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen 

• Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds 

• trans fats contribute more than saturated fats to cardiovascular disease, certain unsaturated fatty acids are not synthesized in the human body

• essential fats are omega 3 fatty acids which are required for growth and thought to protect against cardiovascular disease 

Phospholipids

• two fatty acids and a phosphate group are attached to glycerol 

• The two fatty acid tails are hydrophobic but the phosphate group and its attachments form a hydrophilic head 

• When added to water, they self-assemble into a bilayer with the hydrophobic tails pointing toward the interior 

• Make up the phospholipid cell membrane bilayer

Steroids

• lipids characterized by a carbon skeleton consisting of 4 fused rings 

• cholesterol, an important steroid, is a component in animal cell membranes

• Although cholesterol is essential in animals, high levels in the blood may contribute to cardiovascular disease

Protein functions

• account for more than 50% of the dry mass of most cells 

• Protein functions include: structural support, storage, transport, cellular communications, movement, and defense against foreign substances

• they’re the workers of the cell

  • Enzymatic proteins: selective acceleration of chemical reactions 

  • Defensive Proteins: protection against disease 

  • Storage proteins: storage of amino acids 

  • Transport proteins: transport of substances (like hemoglobin which is an iron containing protein of blood that transports oxygen) 

  • Hormonal Proteins: coordination of an organism’s activities

  • Receptor Proteins: response of cell to chemical stimuli

  • Contractile and Motor Proteins: movement

  • Structural Proteins: support

What are polypeptides? What is their basic structure?

• Polypeptides are unbranched polymers built from the same set of 20 amino acids

• A protein is a biologically functional molecule that consists of one or more polypeptides

• Amino acids are organic molecules with carboxyl and amino groups 

• Amino acids differ in their properties due to differing side chains, called R groups

• linked by peptide bonds and a polypeptide is the polymers of amino acids

• Each polypeptide has a few to a thousand monomers that have a carboxyl end (c-terminus) and an amino end (N-terminus)

What are the four levels of Protein structure?

• A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape (3D)

• The sequence of the amino acids determines a proteins structure which determines its functions

1) Primary structure of a protein is its unique sequence of amino acids 

2) Secondary Structure: found in most proteins, consists of coils and folds in the polypeptide chain 

3) Tertiary structure is determined by interactions among various side chains (R groups) 

4) Quaternary structure results when a protein consist of multiple polypeptide chains

Primary Structure

• the sequence of amino acids in a protein, is like the order of letters in a long word and is determined by inherited genetic information

Secondary Structure

• The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone 

• Creating a helix or beta pleated sheet 

Tertiary Structure

• determined by interactions between R groups, rather than interactions between backbone constituents - include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der waals interactions

• strong covalent bonds called disulfide bridges may reinforce the protein’s structure 

Quaternary Structure

• results when two or more polypeptide chains form one macromolecule 

  • includes collagen: a fibrous protein consisting of 3 polypeptides coiled like a rope 

  • Hemoglobin: a globular protein consisting of four polypeptides — two alpha and two beta chains (and a heme/iron deposit) 

What affects protein structure?

• Physical and chemical conditions can affect structure

  • alterations in pH

  • salt concentration

  • temperature

  • environmental factors

  • genetic anomalies (even one amino acid in a chain can change a protein entirely, this is how you get sickle cell disease where the hemoglobin capacity to carry oxygen is greatly reduced and you have sickle shaped blood cells that are extremely painful)

• Causes denaturation which makes a protein biologically inactive

Protein Folding

• it is difficult to predict a protein’s structure from tis primary structure and most proteins go through several structures on their way to stable structure 

• Chaperonins: proteins that assist the proper folding of other proteins 

• Alzheimer’s, parkinson’s, and mad cow disease are associated with misfolded proteins 

How to Study Protein Structure 

• X-ray crystallography 

• Nuclear magnetic resonance (NMR) spectroscopy 

• Bioinformatics: uses computer programs to predict protein structure from animo acid sequences  

Nucleic Acids basic info and where does protein synthesis occur?

• The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene 

• monomers are called nucleotides which make up DNA which makes up genes

• Nucleic acids include DNA and RNA (deoxyribonucleic acid and ribonucleic acid 

• DNA provides directions for its own replication and DNA directs synthesis of messenger RNA which controls protein synthesis

• Protein Synthesis occurs in ribosomes

Protein Synethesis

• occurs in ribosomes primarily 

• first DNA synthesizes mRNA which then exits the nucleus and enters the cytoplasm and then it synthesizes proteins at the ribosome. 

How are nucleic acids polymers? What is the makeup of the monomer?

• they are polymers called polynucleotides and each polynucleotides is made of monomers called nucleotides 

• Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups 

• The portion of a nucleotide without the phosphate group is called a nucleoside 

• Adjacent nucleotides are joined by covalent phophodiester bonds. They form between the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon on the next.

• This creates a sugar phosphate back bone with the nitrogenous bases as appendages

• the sequence of the bases are unique for each gene