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Cells and Cell Chemistry Level of Chemical Organization of the Body • Matter is anything that occupies space and has mass • In the body, most chemicals are in the form of molecules. Molecules are particles of matter that are composed of atoms. – Elements are pure substances. – Compounds are substances whose molecules have more than one element. • Atoms: the smallest particle of an element that has the chemical properties of the substance – Are composed of protons, electrons, and neutrons BIO 006 Lec 2:Cell & Cell Chemistry 1 The core of the atom is the nucleus. • It consists of: – Protons: + (positive) charge, have mass; number of protons in the nucleus is the atom’s atomic number. – Neutrons: have no charge (neutral particle) The number of protons and neutrons combined is the atomic mass of an atom. • Electrons: - (negative) charge, surround the nucleus in a circle which is called an orbital. Have no measurable mass. • Orbitals are arranged into energy levels BIO 006 Lec 2:Cell & Cell Chemistry 2 • The first energy level of an atom can hold 2 electrons • The second level can hold up to 8 electrons Electrons have potential energy • Each orbital further away from the nucleus has a higher level of energy -- When an electron moves to an orbital closer to the nucleus it loses energy --When an electron moves to an orbital further away from the nucleus, it gains energy • In an electrically neutral atom, there is one electron for every proton. BIO 006 Lec 2:Cell & Cell Chemistry 3 • Atoms are chemically stable when the outer occupied energy level is completely filled – Atoms react with one another in ways to make their outermost energy level full. To do this, atoms can share, donate, or borrow electrons. – The first shell can hold 2 electrons; the second can hold 8 electrons; few atoms have a third shell • These interactions cause the atoms to bind to each other; this is called a “chemical bond” • Types of chemical bonds: – Covalent – Ionic BIO 006 Lec 2:Cell & Cell Chemistry 4 • Covalent Bond – Formed by the sharing of electrons with another atom (in order to fill the outermost shell) – Sharing of 1 pair of electrons (one electron from each atom) is a single bond – Sharing of 2 pairs of electrons is a double bond – Because atoms involved in a covalent bond must stay close to each other, covalent bonds are strong and normally don’t dissociate (break apart) in water. – Example: Hydrogen gas BIO 006 Lec 2:Cell & Cell Chemistry 5 • Ionic bond- bond which is formed between an atom that has 1-2 electrons in its outer energy shell and an atom that needs only 1-2 electrons to fill its outer level. – The atom with 1-2 electrons transfers its outer shell electron(s) to the other atom. • + charge for each electron lost • - charge for each electron gained – An electrically charged atom or molecule is called an ion. Examples: Na+, Cl– The bond is of moderate strength and dissolves easily in water (called dissociating). – Molecules that form ions when dissolved in water are called electrolytes. BIO 006 Lec 2:Cell & Cell Chemistry 6 Compounds • Compounds are substances whose molecules have more than one element. – Organic compounds are composed of molecules that contain carbon – Inorganic compounds do not contain carbon BIO 006 Lec 2:Cell & Cell Chemistry 7 Life depends on water. • Water is essential to life. – It is the most abundant compound in the body – Water is a solvent (liquid into which solutes are dissolved)and forms aqueous solutions in the body – Water is involved in chemical reactions within the body. • Chemical reactions are interactions among molecules in which atoms group into new combinations. BIO 006 Lec 2:Cell & Cell Chemistry 8 Acids, bases, and salts Are compounds that affect chemical reactions in the body + Water molecules dissociate to form equal amounts of H (hydrogen ions) and OH– (hydroxide ions) Acid—substance that shifts the H+/OH– balance in favor of H+; opposite of base + – Base—substance that shifts the H /OH balance against H+; also known as an alkaline substance; opposite of acid pH—expression of H+ concentration in a solution 7 is neutral pH values above 7 are basic; pH values below 7 are acidic BIO 006 Lec 2:Cell & Cell Chemistry 9 • • Neutralization occurs when acids and bases mix together Buffers are chemical systems that absorb excess acids or bases and thus maintain a relatively stable pH BIO 006 Lec 2:Cell & Cell Chemistry 10 Basic Structure and Function of each major organic compound in the body • Carbohydrates • Lipids (fats) • Proteins • Nucleic acids BIO 006 Lec 2:Cell & Cell Chemistry 11 Carbohydrates—sugars and complex carbohydrates Contain carbon (C), hydrogen (H), oxygen (O) Made up of carbon subunits called: Monosaccharides or single sugars (e.g., glucose) Disaccharide—double sugar made up of two monosaccharide units (e.g., sucrose, lactose) --Polysaccharide—complex carbohydrate made up of many monosaccharide units (e.g., glycogen made up of many glucose units) • Function of carbohydrates is to store energy for later use --liver and muscle cells form glycogen when there is an excess of glucose in the blood. BIO 006 Lec 2:Cell & Cell Chemistry 12 • Lipids—fats and oils Trigylcerides Made up of one glycerol unit and three fatty acids Store energy for use later • Phospholipids ---Similar to triglyceride structure, except with only two fatty acids, and with a phosphorus-containing group attached to glycerol ---The head attracts water and the double tail does not, thus forming stable double layers (bilayers) in water ---Phospholipids form cell membranes BIO 006 Lec 2:Cell & Cell Chemistry 13 Cholesterol – a steroid lipid Molecules have a steroid structure made up of multiple rings Cholesterol stabilizes the phospholipid tails in cell membranes and is converted into steroid hormones (estrogen, testosterone, cortisone) by the body BIO 006 Lec 2:Cell & Cell Chemistry 14 • Proteins Very large molecules made up of amino acids held together in long folded chains by peptide bonds Structural proteins Form structures of the body Collagen is a fibrous protein that holds many tissues together Keratin forms tough waterproof fibers in the outer layer of the skin BIO 006 Lec 2:Cell & Cell Chemistry 15 Functional proteins Participate in the body’s chemical processes Examples: hormones, cell membrane channels and receptors, enzymes Enzymes o o Are Catalysts—help chemical reactions occur but remain unchanged Lock-and-key—each enzyme fits a particular molecule that it acts on as a key fits into a lock – Proteins can combine with other organic molecules to form glycoproteins or lipoproteins BIO 006 Lec 2:Cell & Cell Chemistry 16 • Nucleic acids-DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) – Made up of nucleotide units, each consisting of • • • • Sugar (ribose or deoxyribose) Phosphate Nitrogen bases: adenine, thymine or uracil, guanine, cytosine Nucleotides bind to one another to form strands or similar structures – DNA (deoxyribonucleic acid)-double helix • Used as the cell’s “master code” for assembling proteins • Uses deoxyribose as the sugar and Adenine, Thymine and Guanine and Cytosine (no uracil) • Forms a double helix BIO 006 Lec 2:Cell & Cell Chemistry 17 RNA (ribonucleic acid) Used as a temporary “working copy” of a gene (portion of the DNA code) Uses ribose as the sugar and Adenine, Uracil, Cytosine, and Guanine as bases (no thymine) By directing the formation of structural and functional proteins, nucleic acids ultimately direct structure and function of the entire body BIO 006 Lec 2:Cell & Cell Chemistry 18