Biochemistry & The Molecules of Life Chapters 2 & 3 Biochemistry & The Molecules of Life

At the cellular level, are we really what we eat? What evidence do we have? What do we still need to find out?

Carbohydrates, Lipids, Proteins, and Nucleic Acids: Larger Molecules from Smaller Building Blocks Macromolecules: DNA, Carbohydrates,

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids L-O-N-G starch molecules short sugar molecules

short sugar molecules Monosaccharides “mono” means “one” “monosaccharide” means “one sugar” Monosaccharides are simple sugars. Glucose is found in sports drinks. Fructose is found in fruit. Monosaccharides are the main fuel that cells use to do work.

Disaccharides “di” means “two” “disaccharide” means two sugars. short sugar molecules “di” means “two” “disaccharide” means two sugars. It is constructed from two monosaccharides. The most common disaccharide is sucrose, common table sugar. It consists of a glucose linked to a fructose. The average American consumes about 64 kg of sugar per year.

Polysaccharides L-O-N-G starch molecules “poly” means “many” “saccharide” means “sugar” polysaccharide - means “many sugars” one sugar unit Complex carbohydrates are called polysaccharides. They are long chains of sugar units.

Where are carbohydrates in a cell? In the cytosol in animals as glycogen In the cell wall in plants as cellulose In amyloplasts in plants as starch (organelle not shown) In the cytosol of plants and animals as both simple and complex carbohydrates

Carbohydrate Review So carbohydrates are long or short molecules that are made by joining together different numbers of a small subunit called a monosaccharide. Monosaccharide = one sugar Disaccharide = two sugars Polysaccharide = many sugars They are found in many cellular structures and are a major energy source for the cell.

So how are monosaccharides joined together to make polysaccharides?

Polysaccharides are polymers. Polymers are made by stringing together many smaller molecules called monomers. Enzymes in cells link monomers by dehydration reactions. (Enzyme)

Monomer - means “one unit” (Enzyme)

Monomer - means “one unit” Dimer - means “two units” (Enzyme)

Monomer - means “one unit” Dimer - means “two units” Polymer - means “many units” (Enzyme)

Monomer - means “one unit” Dimer - means “two units” Polymer - means “many units” For carbohydrates, the “unit” is the monosaccharide! (Enzyme)

Organisms also have to break down polymers. Enzymes in cells do this by a process called hydrolysis. (Enzyme)

Monomer - means “one unit” Dimer - means “two units” Polymer - means “many units” (Enzyme)

Monomer - means “one unit” Dimer - means “two units” (Enzyme)

Monomer - means “one unit” (Enzyme)

Lactose is another type of disaccharide found in milk. Some people lack the enzyme that hydrolyzes lactose, and, therefore, have trouble digesting lactose, a condition called lactose intolerance.

Dehydration and Hydrolysis Chemical Reactions are the exact opposites H2O Hydrolysis + Dehydration polymer monomers

Chemical Reactions Cells constantly rearrange molecules by breaking and forming chemical bonds. These processes are called chemical reactions. Chemical reactions cannot create or destroy matter, They only rearrange it.

Before we continue looking at biological molecules let’s take an even closer look at our carbohydrates to review some essential chemistry

Chemical Bonds, Molecules, and Atoms Here is a dehydration reaction joining two monosaccharide molecules to form one disaccharide molecule. A chemical bond is formed between the two monosaccharides keeping these two molecules close together to form the disaccharide. 25

Chemical Bonds, Molecules, and Atoms Abbreviated structure Molecules are two or more atoms bonded together. Here you see the atoms (letters) of a glucose monosaccharide molecule held together by chemical bonds (lines) =

Atoms Atoms are composed of subatomic particles. A proton is positively charged. An electron is negatively charged. A neutron is electrically neutral. Check out: http://www.chem4kids.com/files/atom_intro.html Example: a helium atom 27

Electron Arrangement and the Chemical Properties of Atoms Electrons determine how an atom behaves when it encounters other atoms. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings 28

Electrons orbit the nucleus of an atom in specific electron shells. The number of electrons in the outermost shell determines the chemical properties of an atom. 29

Chemical Bonds Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells. These interactions usually result in atoms staying close together. The atoms are held together by chemical bonds. Three main types of chemical bonds: Ionic bonds Covalent bonds Hydrogen bonds Stronger bonds Weaker bonds 30

Ionic Bonds When an atom loses or gains electrons, it becomes electrically charged. Charged atoms are called ions. Ionic bonds are formed between oppositely charged ions. 31

Covalent Bonds A covalent bond forms when two atoms share one or more pairs of outer-shell electrons. 32

What happens when the electrons in a covalent bond are shared unequally? Water is a compound in which the electrons in its covalent bonds are shared unequally. Oxygen is greedy for electrons and keeps their negative charge closer to itself. This causes it to be a polar molecule, one with opposite charges on opposite ends. + Covalent bonds where electrons are shared unequally - 33

Hydrogen Bonds The polarity of water results in weak electrical attractions between neighboring water molecules called hydrogen bonds. Covalent bond with unequally shared electrons 34

Simple sugars and double sugars dissolve readily in water. They are hydrophilic, or “water-loving.” Slight negative charge of oxygen in water and sugar molecules are attracted to Slight positive charges of hydrogen in water and sugar molecules. Hydrogen bond! Covalent bonds! I Love You!

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids L-O-N-G starch molecules Polymers of monosaccharides held together by covalent bonds short sugar molecules Monosaccharides And disaccharides

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids fats steroids Lipids are hydrophobic. They do not mix with water

Fats Functions: energy storage, cushioning, insulation Fats are formed by linking fatty acid molecule subunits onto a glycerol molecule subunit by dehydration reactions

Dietary fat consists largely of the molecule triglyceride. Triglyceride is a combination of glycerol and three fatty acids. Run Away! No charge! Cannot interact with water! (hydrophobic)

Unsaturated fats Saturated fats Have less than the maximum number of hydrogens bonded to the carbons. Saturated fats Have the maximum number of hydrogens bonded to the carbons. (double and triple bonds) (all single bonds)

Too much of a good thing can be bad Saturated Fatty Acids: Too much of a good thing can be bad Most animal fats have a high proportion of saturated fatty acids, which can be unhealthy. Example: butter Most plant oils tend to be low in saturated fatty acids. Example: corn oil WHY are too many saturated fats unhealthy?

Not all fats are unhealthy. Some fats perform important functions in the body and are essential to a healthy diet.

Special Lipid: Phospholipids Phospholipids form a two-layered membrane, the phospholipid bilayer. Negative charge interacts with water! (hydrophilic) Water! No charge! Cannot interact with water! (hydrophobic)

Other Lipids: Steroids Steroids are very different from fats in structure and function. The carbon skeleton is bent to form four fused rings. Cholesterol is the “base steroid” from which your body produces other steroids. Example: sex hormones Cholesterol is a key component of cellular membranes…

Synthetic anabolic steroids are controversial. They are variants of testosterone.

Where are lipids in a cell? In the smooth ER where lipids are synthesized In all membranes as phospholipids Triglycerides (Ex: fat in animal cells, seed oils in plant cells) stored in cytoplasm (not shown)

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids Molecules of fatty acid and glycerol subunits held together by covalent bonds fats steroids Lipids are hydrophobic. They do not mix with water Phospholipids are special They allow water and lipids to interact.

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids

Proteins A protein is a polymer constructed from amino acid monomers. Proteins perform most of the tasks the body needs to function. Structural Proteins Receptor Proteins Storage Proteins Enzymes Contractile Proteins Hormonal Proteins Transport Proteins Sensory Proteins Defensive Proteins Gene Regulatory Proteins

Structure of an Amino Acid

Structure of an Amino Acid I Love You! Run Away!

The Monomers: Amino Acids All proteins are constructed from a common set of 20 kinds of amino acids. Some fear water (hydrophobic) Some love water (hydrophilic) Structure gives Function!

Proteins as Polymers Cells link amino acids together by dehydration reactions. The resulting covalent bond between them is called a peptide bond.

Structure gives Function!! Your body has tens of thousands of different kinds of protein. The arrangement of amino acids makes each one different. Structure gives Function!!

Protein Shape Proteins have four levels of structure. Primary 1st level Secondary 2nd level Tertiary 3rd level Quaternary 4th level

Primary structure The specific sequence of amino acids in a protein

A slight change in the primary structure of a protein affects its ability to function. The substitution of one amino acid for another in hemoglobin causes sickle-cell disease.

Protein Shape Primary structure held together by covalent bonds Secondary structure held together by hydrogen bonds

A protein’s shape is sensitive to the surrounding environment Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape. This happens by disrupting the hydrogen bonds that hold together the shape of a protein. This is called denaturation. If the shape unfolds, the function is destroyed…

The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins The membranes of cells are composed mostly of: Lipids Proteins Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

The lipids belong to a special category called phospholipids. Phospholipids form a two-layered membrane, the phospholipid bilayer.

Most membranes have specific proteins embedded in the phospholipid bilayer.

Membrane phospholipids and proteins can drift about in the plane of the membrane This behavior leads to the description of a membrane as a fluid mosaic: Molecules can move freely within the membrane. A diversity of proteins exists within the membrane.

Where are proteins in a cell? Everywhere!! Proteins are enzymes, and structural, transport, receptor, regulatory, contractile proteins, etc, and perform most of the functions of a cell! In the all membranes as integral membrane proteins

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids

Biological Molecules There are four categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids DNA, deoxyribonucleic acid RNA, ribonucleic acid

Nucleic Acids Nucleic acids are information storage molecules. They provide the directions for building proteins. Transcription Translation

Nucleic acids are polymers of nucleotides. I Love You! Nucleic acids are hydrophilic!

Each DNA nucleotide has one of the following bases:

Nucleotide monomers are linked into long chains. These chains are called polynucleotides, or DNA strands. A sugar-phosphate backbone joins them together.

Two strands of DNA join together to form a double helix.

RNA, ribonucleic acid, is different from DNA. Its sugar has an extra OH group. It has the base uracil (U) instead of thymine (T).

Where are nucleic acids in a cell? DNA is in the nucleus, mitochondria, and chloroplasts RNA is in the nucleus, mitochondria, chloroplasts, cytosol, and ribosomes!