2.1 What Does Life Require?

2.1 What Does Life Require? A Definition of Life There is no simple definition of life. Instead there is a list of characteristics. Growth Movement Reproduction Response to external environmental stimuli Metabolism

A Definition of Life All living Earth organisms… have a common set of biological molecules Are composed of cells can maintain homeostasis can evolve require liquid water

Elements: fundamental forms of matter Atoms: the smallest units of an element Atoms are composed of Protons (positive charge) and neutrons in the nucleus of the atom Electrons (negative charge) are found in an “electron cloud” surrounding the nucleus Ions are atoms with an electrical charge.

Atomic number is determined by the number of protons in the nucleus

Molecule: two or more atoms held together by chemical bonds Water molecule: two hydrogen atoms bonded to one oxygen atom

The Properties of Water Water is a polar molecule: Oxygen side is slightly negative Because it is more electronegative than hydrogen Hydrogen side is slightly positive When molecules have no charges, they are nonpolar. Toward which atom are the electrons of a water molecule pulled?

Water is a good solvent (helps chemical reactions). Solute: what is being dissolved in the solvent Solvent: what dissolves the solute Solution: solutes added to a solvent

The Properties of Water Hydrogen bond: the weak attraction between the hydrogen atom of one water molecule and the oxygen atom of another Hydrogen bonds are what makes sugar water sticky

The Properties of Water Water can dissolve salts and hydrophilic(water–loving) molecules because it is polar. Nonpolar molecules such as oil are hydrophobic (water-fearing) they do not easily dissolve in water they instead aggregate into a single large oil “drop” Can you think of an example of a hydrophobic substance? What happens to it in water?

Water can dissolve acidsand bases. The pH scale is a measure of the relative amounts of acids and bases in a solution. pH greater than 7 = basic pH lower than 7 = acidic Pure water = 7 – neutral We tolerate pH’s between 4 and 10 Our stomach goes from pH 7 to 2-0 for a meal and then back to 7 again

Organic Chemistry • All life on Earth is based on organic chemistry: the chemistry of the element carbon. • Carbon makes up most of the mass of living organisms. • Why?

Organic Chemistry • Carbon: a molecular TinkerToy • Can bond to 4 different atoms at once • Covalent bonds: strong bonds from sharing electrons • Carbon makes 4 bonds • Nitrogen makes 3 bonds; 1 lone pair – hydrogen bonding • Oxygen makes 2 bonds; 2 lone pairs – hydrogen bonding • Hydrogen makes 1 bond

Carbon can make macromolecules • Carbohydrates • Proteins • Lipids • Nucleic Acids

Structure and Function of Macromolecules Carbohydrates: molecules of carbon, oxygen, and hydrogen Major source of energy for cells Monosaccharides or simple sugars are building blocks for carbohydrates Examples - glucose, fructose, maltose, galactose, ribose Disaccharides are composed of two monosaccharides Examples - sucrose, lactose Polysaccharides are composed of many monosaccharides

Structure and Function of Macromolecules Carbohydrates

Structure and Function of Macromolecules Proteins: polymers of amino acids; joined by peptide bonds Proteins are made up of carbon (4 bonds), oxygen (2 bonds), hydrogen (1 bond), and nitrogen (3 bonds). There are 20 different amino acids, with different chemical properties. Different combinations of amino acids give proteins different properties. (like how shuffling a deck gives different poker hands each time)

Proteins • Functions: • Enzymes are proteins: carry out all the important chemical reactions in all cells • Cell structures • Movement of cells, cell replication, structural support of cells, communication, defense (antibodies) • Proteins are encoded for by genes!

Structure and Function of Macromolecules

Figure 2.13a General formula for amino acid Amino group Carboxyl group Side group

Figure 2.13b Peptide bond formation Peptide bond Peptide bond Valine Alanine Phenylalanine

Figure 2.13c Protein Protein Folding and Denaturing

Structure and Function of Macromolecules Lipids: (mostly) hydrophobic; composed mostly of carbon and hydrogen Three types: Fat is composed of a glycerol molecule joined with 3 fatty acid tails – no hydrophilic portions Steroids are a four carbon ring structure such as cholesterol, estrogen, testosterone, bile salts – minor hydrophilic portion Phospholipids are composed of a glycerol molecule, 2 fatty acid tails and a phosphate group – significant hydrophilic portion

Structure and Function of Macromolecules Lipids: • Why is this molecule hydrophobic? • What happens to it in water?

Structure and Function of Macromolecules Nucleotide ribose + a phosphate + a nitrogenous base Used to build nucleic acids (DNA/RNA) and for cellular metabolism (ATP, NAD, FAD) Nucleic acids: polymers of nucleotides, metabolism The nucleotide: Figure 2.15c

Structure and Function of Macromolecules Nucleotides are of two types: RNA and DNA, depending on the sugar. DNA is the stored and protected hereditary material in all knownliving organisms. The structure of a DNA molecule is a double helix. RNA is used to make proteins

2.2 Life on Earth Prokaryotic and Eukaryotic Cells A cell is the fundamental structural unit of life All cells on Earth are either prokaryotic or eukaryotic.

Prokaryotic Cells Prokaryotic cells are smaller and simpler in structure. Prokaryotic cells probably resemble the earliest cells to arise on Earth. Some structures in the famous Martian meteorite resemble Prokaryotic cells. Prokaryotes do not have a true nucleus. Prokaryotes do have cell wall

Eukaryotic Cells Eukaryotic cells are much more complex. Have a true nucleus surrounded by a membrane Also have membrane-bound organelles with specialized jobs

Cell Structure All cells are surrounded by a plasma membrane. Like walls of a house, they keep things contained and protected from the other side of the wall Made of a phospholipid bilayer: hydrophobic tails orient inside the membrane, away from water Semipermeable: some molecules can cross and some can’t (like a door, a window, a vent, or a window screen on a house)

Cell Structure Nucleus: surrounded by a double nuclear membrane which houses DNA Ribosomes: assembly proteins can be attached to membranes or free floating Cytosol: watery substances that surrounds the nucleus and organelles Mitochondria: provide energy for the cell, using oxygen Chloroplasts: sites of photosynthesis in plant cells Lysosomes: contain digestive enzymes to break down substances Endoplasmic reticulum: extra membrane; site of lipid synthesis and some protein synthesis

Cell Structure Be able to recognize the major ones!

Plasma membrane Sugar chains Cholesterol Phospholipid bilayer Head Tail Protein

Table 2.1.2 Nucleus SKIP details Nucleus Nuclear pore Nuclear envelope Nucleolus Chromatin

Table 2.1.3 Lysosome Lysosome Membrane Digestive enzymes and digested material

Table 2.1.4 Chloroplast Chloroplast Outer membrane Inner membrane Stroma Thylakoids Granum

Table 2.1.5 Ribosomes Ribosomes Ribosomes

Table 2.1.6 Endoplasmic reticulum (ER) Endoplasmic reticulum (ER) Nuclear envelope Rough endoplasmic reticulum Ribosomes Vesicle Smooth endoplasmic reticulum

Table 2.1.7 Golgi apparatus SKIP details Golgi apparatus Vesicle from ER arriving at Golgi apparatus Vesicle departing Golgi apparatus

Table 2.1.12 Mitochondrion SKIP details Mitochondrion Outer membrane Intermembrane space Inner membrane Matrix

2.2 Life on Earth Eukaryotic Cells Describe major similarities and differences. Why are there similarities and differences? Figure 2.18

The Tree of Life and Evolutionary Theory This unity of lifeis best explained by a tree of life, with modern species having evolved from common ancestors.

Now let’s review

Which of the following would not be considered an element? • oxygen • iron • water • nitrogen

An atom’s atomic number refers to its __________. • electrons • nucleus • protons • neutrons

Which of the following statements is correct? • Water is a good solvent because it is polar. • Water is a bad solvent because it is polar. • Water is a good solvent because the electrons are shared equally. • Water is a bad solvent because the electrons are more attracted to oxygen.

What type of chemical bond in this diagram causes different water molecules to be attracted to one another? • covalent bonds • ionic bonds • double bonds • hydrogen bonds

What class of biological macromolecules are typically hydrophobic? • polysaccharides • proteins • nucleic acids • lipids

2.1 What Does Life Require?