Biology: How Life Works Active Lecture Slides PDF

Morris Hartl Knoll Lue Michael Heitz Hens Lozovsky Merrill Phillis Pires Liu Biology: How Life Works Active Lecture Slides Chapter 2 The Molecules of Life Copyright © Macmillan Learning  Chapter 2 The Molecules of Life ...

Morris Hartl Knoll Lue Michael Heitz Hens Lozovsky Merrill Phillis Pires Liu Biology: How Life Works Active Lecture Slides Chapter 2 The Molecules of Life Copyright © Macmillan Learning  Chapter 2 The Molecules of Life  Atoms and Elements Atoms consist of protons, neutrons, and electrons. The atom’s nucleus is formed by protons and neutrons. The atom’s electrons move in orbitals around the nucleus. Elements contain only one type of atom.  Atomic Mass The atomic number is specified by the number of protons. For example, an atom with six protons is always carbon. The atomic mass is the number of protons plus the number of neutrons.  Isotopes In isotopes, the proton number stays the same, but the neutron number is different. Carbon Atom Carbon Isotopes  Orbitals and Shells Electrons occupy regions of space called orbitals. Atoms with more than two electrons have at least two orbitals.  Valence electrons Valence electrons are the electrons in the outermost electron shell. Valence electrons often participate in reactions or bond forming.  Losing or Gaining Electrons If an atom gains or loses an electron, then it can carry a charge.  Chemical Bonds Atoms can combine with one another to form molecules, which are held together by chemical bonds. The number of valence electrons (or number of electrons in the outermost shell) affects the number of bonds that can be formed. Covalent Bonds  Polar Covalent Bonds Polar covalent bonds occur when electrons that are shared between two atoms are not equally shared. In a molecule of water, the electrons will be closer to the oxygen most of the time because the electronegativity of oxygen is greater than that of hydrogen. The unequal sharing of electrons results in partial negative charges on the oxygen and partial positive charges on the hydrogen. Nonpolar covalent bonds form when atoms share electrons equally. Which option accurately describes a polar covalent bond? A. the unequal sharing of electrons between an atom with a partial positive charge and an atom with a partial negative charge B. the interaction of an atom with very high electronegativity and an atom with very low electronegativity C. the interaction of a hydrogen atom connected to an atom with a high electronegativity and an electronegative atom of another molecule D. the equal sharing of electrons between atoms of identical or similar electronegativities E. None of the other answer options is correct. The oxygen and hydrogen atoms of a water molecule contain what type of bond? A. polar covalent B. ionic C. hydrogen D. van der Waals interactions  Ionic Bonds The electronegativity of chlorine is much greater than sodium. When ionic bonds between the two form, the chlorine takes an electron from sodium, and the result is a negatively charged chlorine atom and a positively charged sodium atom. The interaction between the two occurs because opposite charges attract one another. Why do salts dissolve in water? In water, the partial positive charge on the hydrogen ions associate with the negative charge on the chloride ions, and the partial negative charge on the oxygen ions associates with the positive charge on the sodium ions. Chemical reactions involve breaking and making chemical bonds.  Water Chemistry Water is a polar molecule. Water is a good solvent. Molecules can be described as hydrophilic or hydrophobic depending on how they react with water. The pH of water is 7. pH is a measurement of the concentration of protons in solution.  Hydrogen Bonds in Water: The Importance of Polar Covalent Bonds  Water has unusual properties. Water is less dense when solid (frozen) than when liquid. Water resists decreases or increases in its temperature because in order for its temperature to change hydrogen bonds must be broken.  Carbon: Life’s Chemical Backbone The four major elements that make up the human body are: carbon oxygen hydrogen nitrogen Molecules containing carbon are called organic molecules. Carbon and Covalent Bonds  Carbon-Containing Molecules This arrow represents the The molecule can rotate sharing of the about the plane of the single electron in the bond. covalent bond. Carbon-containing molecules can be very diverse. They can contain many carbons in a linear or ring arrangement.  Carbon Double Bonds Sometimes adjacent carbon atoms can share two pairs of electrons, forming a double bond.  Structure and Function These two molecules are isomers because they have the same chemical formula but different arrangements of atoms (structure). The difference in structure can affect how the molecules interact with other molecules, resulting in each molecule having a potentially different function from the other.  Organic Molecules https://www.youtube.com/watch?v=MqO3_270X-s Please watch the video above. (less than 3 min long) Proteins are made of amino acid subunits.  Proteins are also called polypeptides. When amino acids (figs. a and b) are linked together in a chain, they form a protein. Amino acids are joined through a covalent bond called a peptide bond (fig. c). The carboxyl group releases an oxygen atom, and the nitrogen loses two hydrogen atoms to form a molecule of water when peptide bonds are formed. Nucleotides have three main components and are the building blocks of nucleic acids. A five-carbon One or more sugar phosphate groups A base containing nitrogen Nucleotide Bases This base is only This base is only found in DNA. found in RNA.  Bonds Between Nucleotides The phosphodiester bond joins two nucleotides together. The bond is formed between the phosphate group of each nucleotide and the 3′-OH of the last nucleotide. Structure of DNA  Carbohydrates (C6H12O6) These carbohydrates (sugars) are monosaccharides. They all have the same formula, but they are isomers of each other, which means they are functionally different from one another. Types of Sugar Molecules Monosaccharide Polysaccharide  Lipids: Fatty Acids Lipids are grouped together because they share the same physical property—they are all hydrophobic. Fatty acids, a type of lipid, are long chains of carbon with a carboxyl group at the end.  Lipids: Structure Saturated versus unsaturated fatty acids have different structure based on the presence of C-C double bonds. Triacylglycerols are uncharged and hydrophobic and can often form oil droplets within the cell. Van der Waals The hydrocarbon chains in Forces fatty acids have non-polar covalent bonds. Electrons are still moving around the atoms in the fatty acids, creating short- lived regions with slight negative charges. These are attracted to slight positive regions in another atom. The longer the hydrocarbon tail, the greater the strength of van der Waals forces. Saturated vs. Unsaturated Fats Animal fats are saturated. Without double bonds causing kinks in the structure, animal fats can stack closely together and are stabilized by more van der Waals interactions than unsaturated fats. This also contributes to the quality of animal fats, where they are solid at room temperature.  Lipids: Steroids This steroid is a cholesterol. It is found in the lipid bilayer of animal cell membranes. Cholesterol also serves as a precursor in the synthesis pathway producing estrogen and progesterone. Could water vapor, methane, ammonia, and hydrogen gas been the building blocks of life on early Earth? How did the building blocks of life form macromolecules? Clay minerals in volcanic rocks can bind and stabilize nucleotides on their surface and Leslie Orgel put bring nucleotides close enough short single- that small polymers could form. strand nucleic acids in a reaction chamber. The nucleotides formed the complementary sequence and a double-stranded nucleic acid.