Chapter 4 - Nucleic Acids and the Origins of Life Flashcards
All living things are made up of these four classes of large biological molecules:
- carbohydrates
- lipids
- proteins
- nucleic acids
Macromolecules
large molecules composed of thousands of covalently connected atoms.
polymer
A long molecule consisting of many similar or identical monomers linked together by covalent bonds.
monomer
The subunit that serves as the building block a polymer
dehydration reaction
occurs when two monomers bond together through the loss of a water molecule.
hydrolysis
Polymers are disassembled to monomers. Hydrolysis adds a water molecule, breaking a bond.
Carbohydrates
include sugars and the polymers of sugars. Though often drawn as linear skeletons, inaqueous solutions many sugars form rings.
monosaccharides
- The simplest carbohydrates.
- Also known as “single sugars”.
- have molecular formulas that are usually multiples of CH₂O
- Glucose (C₆H₁₂O₆) is the most common monosaccharide
- serve as a major fuel for cells and as raw material for building molecules
Monosaccharides are classified by…
- The location of the carbonyl group (as aldose or ketose)
- The number of carbons in the carbon skeleton
polysaccharides
- A polymer of many monosaccharides, formed by dehydration reactions.
- The polymers of sugars have storage and structural roles.
- Structure and function determined by its sugar monomers and the positions of glycosidic linkages
disaccharide
A double sugar, consisting of two monosaccharides joined by a glycosidic linkage formed by a dehydration reaction.
Glycosidic linkage
A covalent bond formed between two monosaccharides by a dehydration reaction.
- Polymers with α glucose are helical
- Polymers with β glucose are straight
- H atoms on one strand can bond with OH groups on other strands
Starch
A storage polysaccharide in plants, consisting entirely of glucose monomers joined by α glycosidic linkages.
- Plants store surplus starch as granules within chloroplasts and other plastids
- The simplest form of starch is amylose
Glycogen
An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.
Cellulose
A structural polysaccharide of plant cell walls, consisting of glucose monomers joined by β glycosidic linkages. In these β structures, H atoms on one strand can bond with OH groups on other strands. Parallel cellulose held together this way are grouped into microfibrils, which form strong building materials for plants.
- 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
- Difference is based on two ring forms for glucose: alpha (α) and beta (β)
- Enzymes that digest starch by hydrolyzing α linkages can’t hydrolyze β linkages in cellulose
- Passes through the digestive tract as insoluble fiber, or like in many herbivores, microbes use enzymes to digest the cellulose.
Chitin
A structural polysaccharide, consisting of amino sugar monomers, found in many fungal cell walls and in the exoskeletons of all arthropods.
Lipids
Any group of large biological molecules, including fats, phospholipids, and steroids, that mix poorly, if at all, with water.
- Do not form polymers
- Lipids are hydrophobic because they consisty mostly of hydrocarbons, which form nonpolar covalent bonds.
Fat
A lipid consisting of three fatty acids linked to one glycerol molecule; also called a triacylglycerol or triglyceride.
- Fats separate from water because water molecules form hydrogen bonds with eachother and exclude the fats
- In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylclycerol, or triglyceride.
- Ester linkage: any of a class of compounds produced by reaction between acids and alcohols with the elimination of water. Esters with low molecular weights, such as ethyl acetate, are usually volatile fragrant liquids; fats are solid esters
- The major function of fats is energy storage
- Humans and other mammals store their fat in adipose cells
- Adipose tissue also cushions vital organs and insulates the body
- Humans and other mammals store their fat in adipose cells
Glycerol
A three-carbon alcohol with a hydroxyl group attached to each carbon.
Fatty Acid
A carboxylic acid with a long carbon chain. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form a fat molecule, also known as a triacylglycerol or triglyceride.
- Fatty acids vary in length (number of carbons) and in the number and locations of double bonds.
Saturated fatty acid
A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that are attached to the carbon skeleton.
- Solid at room temperature
- Most animal fats are saturated
- Diets rich in this may contribute to cardiovascular disease through plaque deposits
Unsaturated fatty acids
A fatty acid that has one or more double bonds between carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.
- Also known as oils because they are liquid at room temperature
- Plant fats and fish fats are usually unsaturated
- Certain unsaturated fatty acids are not synthesized in the human body and must be supplied in the diet
- Omega-3 fatty acids: required for normal growth and thought to provide protection against cardiovascular disease
Phospholipid
- A lipid made up of glycerol joined to two fatty acids and a phosphate group.
- The hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails, while the rest of the molecule acts as a polar, hydrophilic head.
- Phospholipids form bilayers that function as biological membranes.
- When added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior. This results in a bilayer arrangement found in cell membranes
- Phospholipids are the major component of all cell membranes
Steroid
A type of lipid characterized by a carbon skeleton consisting of four fused rings with varius chemical groups attached.
Enzymatic Proteins
- A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed by the reaction.
- Can perform their functions repeatedly, functioning as workhorses that carry out the processes of life
Storage Proteins
Hormonal Proteins
Contractile and Motor Proteins
Defensive Proteins
Transport Proteins
Receptor Proteins
Structural Proteins
Polypeptides
- A polymer of many amino acids linked together by peptide bonds.
- Range in length from a few to more than a thousand monomers
- Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus)
Amino Acid
- An organic molecule possessing both a carboxyl and an amino group.
- Serve as the monomers of polypeptides
- Differ in their properties due to differing side chains, called R groups
- Linked by peptide bonds
Peptide Bond
The covalent bond between the carboxyl group on one amino acid and the amino group on another, formed by a dehydration reaction.
Primary Protein Structure
- A protein’s unique senquence of amino acids.
- Like the order of letters in a long word
- Determined by inherited genetic information
- A slight change in primary structure can affect a protein’s structure and ability to function
- Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
Secondary Protein Structure
- Found in most proteins
- Consists of coils and folds in the polypeptide chain
- These coils and colds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone
- Typical secondary structures are a coil called an α helix and a folded structure called a β pleated sheat
Tertiary Protein Structure
- Determined by interactions among various side chains (R groups), rather than interactions between backbone constituents
- These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions
Quaternary Protein Structure
Results when a protein consists of myltiple polypeptide chains
- Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
- Hemoglobin is a glubular protein consisting of four polypeptides: two alpha and two beta chains
Chaperonins
- Protein molecules that assist the proper folding of other proteins
- Diseases such as Alzheimer’s, Parkinson’s, and mad cow diease are associated with misfolded proteins
X-Ray Crystallography
A technique used to study the three-dimensional structure of molecules. It depends on the diffraction of an X-ray beam by the individual atoms of a crystallized molecule.
Deoxyribonucleic Acid (DNA)
- A nucleic acid molecule, usually a double-stranded helix, in which each polynucleotide strand consists of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T)
- The nitrogenous bases in DNA pair up and form hydrogen bonds. Called complementary base pairing.
- Adenine is always with thymine
- Guanine is always with cytosine
- The nitrogenous bases in DNA pair up and form hydrogen bonds. Called complementary base pairing.
- Capable of being replicated and determining the inherited structure of a cell’s proteins.
- Directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis
- Protein synthesis occurs on ribosomes
- In the DNA double helix, the two backbones run in opposite 5’ to 3’ directions from each other, an arrangement referred to as antiparallel
- One DNA molecule includes many genes.
Polynucleotide
- A polymer consisting of many nucleotide monomers in a chain. The nucleotides can be those of DNA or RNA.
- Adjacent nucleotides are joined by covalent bonds that form between the -OH group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon on the next
- These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages
