Biology unit 2

What eight characteristics do living systems have in common?

1. They are capable of movement 2. Complex and highly ordered 3. Can respond to stimuli 4. Composed of one or more cells 5. Use energy to accomplish work 6. Maintain relatively constant internal conditions (homeostasis) 7. Can grow, develop, and reproduce 8. Can transmit genetic information to their offspring, making them capable of evolutionary adaptation to the environment

What is a hypothesis?

A hypothesis is constructed based on observations, and it must generate experimentally testable predictions.

The electron transport chain produces a proton gradient

A proton gradient forms as electrons move through electron carriers. NADH is oxidized to NAD+. The electrons move to cytochrome oxidase, where they join with H+ and O2 to form H2O. This results in three protons being pumped into the intermembrane space.

The potential energy stored in organic molecules resides largely in C-H bonds

Aerobic respiration uses oxygen as the final electron acceptor for redox reactions. Anaerobic respiration utilizes inorganic molecules as electron acceptors, and fermentation uses organic molecules.

What laws are living systems subject to?

All living systems function based on the laws of chemistry and physics

Cell conditions determine enzyme activity

An enzyme's functionality depends on its ability to maintain its three-dimensional shape, which can be disrupted by temperature and pH. The activity of enzymes can be decreased by inhibitors. Competitive inhibitors compete for the enzymes active site. Noncompetitive inhibitors bind to the allosteric site, changing the structure of the enzyme to inhibit it. Allosteric binding can also activate an enzyme.

Cell size is limited

As cell size increases, diffusion becomes inefficient.

The periodic table reflects the electronic structure of atoms

Atoms tend to establish completely full outer energy levels (the octet rule). Elements with filled outermost orbitals are inert. Twelve of these elements are found in living organisms in greater than trace amounts: C, H, O, N, P, S, Na, K, Ca, Mg, Fe, and CI. Compounds of carbon are called organic compounds. The majority of molecules in living systems are composed of C bound to H,O and N.

Environmental changes can cause a loss of protein structure

Changes to the environment, such as temperature, pH, and salt concentration, can denature proteins by interfering with the weak forces holding proteins together. Some proteins will regain their structure when returned to normal conditions, showing that amino acid sequence strongly influences structure.

Water molecules are both cohesive and adhesive

Cohesion is the tendency of water molecules to adhere to one another due to hydrogen bonding. The cohesion of water is responsible for its surface tension. Adhesion occurs when water molecules adhere to other polar molecules. Capillary action results from water's adhesion to the sides of narrow tubes, combined with its cohesion.

Covalent bonds build stable molecules

Covalent bonds are formed by atoms sharing electrons. This forms stable molecules by filling outer electrons shells with no net charge. Covalent bonds may be single, double, or triple, depending on the number of electrons shared. Nonpolar covalent bonds involve equal sharing of electrons between atoms. Polar covalent bonds involve unequal sharing of electrons.

The information molecules of the cell are long chains of nucleotides

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are polymers composed of nucleotide monomers. Cells use nucleic acids for information storage and transfer. Nucleic acids contain four different nucleotide bases. In DNA these are adenine, guanine, cytosine, and thymine. In RNA, thymine is replaced by uracil.

Atoms are composed of three kinds of subatomic particles

Each element is defined by its atomic number, the number of protons in the nucleus. Electrically neutral atoms have the same number of protons as electrons. Atoms that gain or lose electrons are ions. Atomic mass is the sum of the mass of protons and neutrons. Isotopes are forms of an element with different numbers of neutrons, and thus different atomic mass. Radioactive isotopes are unstable.

Electron carriers transfer electrons from one molecule to another

Electron carriers can be reversibly oxidized and reduced. for example, NAD+ is reduced to NADH by acquiring two electrons; NADH is oxidized when it transfers their electrons to other molecules.

Animals regulate body temperature in a variety of ways

Endotherms have high metabolic rates and generate heat internally; ectotherms do not.

Endotherms create internal metabolic heat for conservation or dissipation

Endotherms regulate temperature by physiological changes; ectotherms use behavior

Energy may be stored or used to do work

Energy is the capacity to do work. Potential energy is stored energy, and kinetic energy is the energy of motion. Energy takes many forms: mechanical, heat, sound, electric current, or light. Energy is measured in units of heat known as kilocalories. Photosynthesis stores light energy from the Sun as potential energy in the structure of sugar molecules. Breaking bonds requires energy, and making bonds releases energy.

What is included in an experiment?

Experiments involve a manipulated variable and a control

Fermentations donate electrons generated by glycolysis to organic molecules rather than oxygen

Fermentation is the oxidation of NADH and reduction of an organic molecule. In yeast, pyruvate is decarboxylated, then reduced to ethanol. In animals, pyruvate is reduced directly to lactate.

During photosynthesis, chloroplasts capture light energy and synthesize which organic molecule?

Glucose

Polysaccharides are building materials and energy-storage compounds

Glucose is used to make three important polymers: glycogen (in animals) and starch and cellulose (in plants). Chitin is a related structural material found in arthropods and many fungi.

Do living systems depend on information transactions?

Hereditary information found in the DNA molecule is passed on from one generation to the next. This information is read out to produce proteins, which themselves have information in their structures. Living systems can also acquire information about their environment.

Negative feedback mechanisms keep values within a narrow range

Homeostasis uses negative feedback loops to limit responses to deviations from a set point

Water's structure facilitates hydrogen bonding

Hydrogen bonds are weak interactions between a partially positive H in one molecule and a partially negative O in another molecule.

Hydrogen bonds can form between polar molecules

Hydrogen bonds occur when the positive end of one polar molecule is attracted to the negative end of another.

How do you know if the hypothesis is rejected?

Hypotheses are rejected if their predictions cannot be verified by observation or experiment

Cellular membranes are assembled from four major components

In eukaryotic cells, membranes have four components: a phospholipid bilayer, transmembrane proteins, an interior protein network, and cell-surface markers. The interior protein networks composed of cytoskeletal filaments and peripheral membrane proteins, which are associated with the membrane. Membranes contain glycoproteins and glycolipids on the surface that act as cell identity markers.

Continuous respiration requires the regeneration of NAD+

In the presence of oxygen, NADH passes electrons to the electron transport chain. In the absence of oxygen, NADH passes the electrons to an organic molecule such as acetaldehyde (fermentation).

Which direction is Na+ going to want to move?

Into the cell (influx)

Facilitated diffusion utilizes specific carrier proteins and ion channels

Ions and large hydrophilic molecules cross the phospholipid bilayer, with the help of proteins, in facilitated diffusion. These proteins can be channels or carriers. Channels are specific for different ions and allow diffusion based on concentration or electrical gradients across the membrane. Carrier proteins bind to the molecules they transport, much like an enzyme. The rate of transport by a carrier is limited by the number of carriers in the membrane.

Fats consist of fatty acids attached to glycerol

Lipids are insoluble in water, because they have a high proportion of nonpolar C-H bonds. Fats are excellent energy-storage molecules.

Do living systems transform energy and matter?

Living systems have a constant need for energy, which is ultimately provided by the sun. The nature of life is to constantly transform energy. We break down food molecules to provide energy to build up complex structures.

Biological membranes are fluid mosaics

Membranes are sheets of phospholipid bilayers with hydrophobic regions oriented inward and hydrophilic regions oriented outward. In the fluid mosaic model, proteins float on or in the lipid bilayer.

Biochemical pathways organize chemical reactions in cells

Metabolism is the sum of all biochemical reactions in a cell. Anabolic reactions require energy to build up molecules, and catabolic reactions break down molecules and release energy. Chemical reactions in biochemical pathways use the product of one reaction as the substrate for the next.

Mitochondria metabolize organic compounds to generate ATP

Mitochondria have a double-membrane structure, contain their own DNA, and can divide independently. The inner membrane is extensively folded. Proteins on the surface and in the inner membrane carry out metabolism to produce ATP.

Proteins have diverse functions

Most enzymes are proteins. Proteins also provide defense, transport, motion, and regulation, among many other roles.

Can K+ diffuse freely out of the cell?

No; it is charged. It needs to be transported (facilitated diffusion)

Can Na+ freely diffuse into the cell?

No; it is charged. It needs to be transported (facilitated diffusion)

Water organizes nonpolar molecules

Nonpolar molecules will aggregate to avoid water. This maximizes the hydrogen bonds that water can make. This hydrophobic exclusion can affect the structure of DNA, proteins, and biological membranes.

Which direction is K+ going to want to move?

Out of the cell (efflux)

Oxidation-reduction reactions transfer energy

Oxidation is a reaction involving the loss of electrons, and reduction is the gain of electrons. These two reactions take place together and are therefore termed redox reactions.

The lipid bilayer forms spontaneously

Phospholipids are composed of two fatty acids and a phosphate group linked to a 3-carbon glycerol molecule. The phosphate group is polar and hydrophilic; the fatty acids are nonpolar and hydrophobic, and they orient away from the hydrophilic environment. The nonpolar interior of the lipid bilayer impedes the passage of water and water-soluble substances. The phospholipid bilayer is fluid. Hydrogen bonding of water keeps the membrane in its bilayer configuration; however, phospholipids and unanchored proteins can diffuse laterally. Membrane fluidity can change and depends on the fatty acid composition of the membrane. Unsaturated fats tend to make the membrane more fluid. Temperature also affects fluidity.

Phospholipids form membranes

Phospholipids contain two fatty acids and one phosphate attached to glycerol. In phospholipid-bilayer membranes, the phosphate heads are hydrophilic and cluster on the two faces of the membrane, and the hydrophobic tails are in the center.

Disaccharides are transport sugars

Plants convert glucose into the disaccharide sucrose for transport without their bodies. Female mammals produce the disaccharide lactose to nourish their young.

There are four levels of protein structure

Protein structure is defined by the following hierarchy: primary (amino acid sequence), secondary (hydrogen bonding patterns), tertiary (three-dimensional folding), and quaternary (associations between two or more polypeptides).

Chemiosmosis utilizes the proton gradient to produce ATP

Protons diffuse back into the mitochondrial matrix via the ATP synthase channel, which uses the energy of the proton gradient to synthesize ATP.

Diffusion is the result of random molecular motion

Simple diffusion is the passive movement of a substance along a concentration gradient. Biological membranes pose a barrier to hydrophilic polar molecules, while they allow hydrophobic substances to diffuse freely.

Chemical reactions alter bonds

Temperature, reactant concentration, and the presence of catalysts affect reaction rates. Most biological reactions are reversible.

Pyruvate is converted to a 2-carbon acetyl group for what cycle?

The Krebs cycle

The Krebs cycle oxidizes 2-carbon acetyl groups

The Krebs cycle produces a small amount of ATP and potential energy in NADH and FADH2. Acetyl-CoA is oxidized to CO2.

The active sites of enzymes conform to fit the shapes of substrates

The binding causes the enzyme to adjust its shape to the substrate so that there is a better fit.

Osmosis is the movement of water across membranes

The direction of movement due to osmosis depends on the solute concentration on either side of the membrane.

The second law states that some energy is lost as disorder increases

The disorder, or entropy, of the universe is continuously increasing. In an open system like the Earth, which is receiving energy from the Sun, this may not be the case. To increase order, however, energy must be expended. In energy conversions, some energy is always lost as heat.

Monosaccharides are simple sugars

The empirical rule formula of a carbohydrate is (CH2O). Carbohydrates are used for energy storage and as structural molecules. Simple sugars contain 3 to 6 or more carbon atoms. The general formula for 6-carbon sugars is C6H12O6, and many isomeric forms are possible. Living systems often have enzymes for converting isomers from one to another.

Cells store and release energy in the bonds of ATP

The energy of ATP is stored in the bonds between its terminal phosphate groups. The negative phosphate groups repel each other, making the covalent bonds joining them unstable. Enzymes catalyze the hydrolysis of ATP to produce ADP and phosphate, which have less potential energy than ATP. ATP is continuously cycled. It is synthesized with energy from exergonic reactions, and ATP hydrolysis releases energy to drive endergonic processes.

Does structure determine function?

The function of macromolecules is dictated by and dependent on their structure. Similarity of structure and function may indicate an evolutionary relationship.

Atoms contain discrete energy levels

The potential energy of electrons increases as distance from the nucleus increases. Energy levels correspond to quanta (singular, quantum) of energy. The loss of electrons from an atom is called oxidation. The gain of electrons is called reduction. Electrons can be transferred from one atom to another in coupled redox reactions.

Does evolution explain the unity and diversity of life?

The underlying similarities in biochemistry and genetics support the contention that all life evolved from a single source. the diversity found in living systems arises by evolutionary change.

Membrane proteins have many functions

Transporters are integral membrane proteins that carry specific substances through the membrane. Enzymes often occur on the interior surface of the membrane. Cell-surface receptor respond to external chemical messages and change conditions inside the cell; cell identity markers on the surface allow recognition of the body's cells as "self." Cell-to-cell adhesion proteins glue cells together; surface proteins that interact with other cells anchor to the cytoskeleton.

Proteins are polymers of amino acids

Twenty common amino acids each contain amino and carboxyl groups that are joined by peptide bonds to make polypeptides. Unique R groups determine their properties.

The first law states the energy cannot be created or destroyed

Virtually all activities of living organisms require energy. Thermodynamics is the study of energy changes. Energy changes form as it moves through organisms and their biochemical systems, but it is not created or destroyed.

Water is a good solvent for polar molecules

Water's polarity makes it a good solvent for polar substances and ions. Polar molecules or portions of molecules are attracted to water (hydrophilic). Molecules that are nonpolar are repelled by water (hydrophobic).

A granum contains a few to several dozen

thylakoids