Chapter 9: Cells and Energy Fifteen Summary Facts

Worksheet 9.1

Chapter 9: Cells and energy – fifteen summary facts

1There are four levels of protein organization:

primary level – involves the sequence of amino acids
secondary level – involves hydrogen bonds between the carboxyl and amino groups of separate amino acids
tertiary level – involves interactions among R-groups of separate amino acids
quaternary level – involves multiple peptide chains which combine to form a single chain.

Not all proteins have quaternary level organization.

2Fibrous proteins produce long, narrow shapes; globular proteins are more three-dimensional in shape. Fibrous proteins are usually insoluble in water; globular proteins are usually water soluble. Actin is an example of a fibrous protein; haemoglobin is an example of a globular protein.

3Amino acids may be grouped according to the properties of their side chains (R-groups) into polar and non-polar amino acids. Polar amino acids have hydrophilic properties and occur near the exterior and interior of cell membranes. Polar and non-polar amino acids are important in determining the specificity of an enzyme. Active sites of enzymes often involve polar and non-polar amino acids in their make-up and this affects whether the substrate will ‘fit’ or not.

4Enzymes speed up both anabolic and catabolic reactions without being changed themselves. The way they work is explained by the induced-fit model. This model is different from the lock-and-key model in that the enzyme’s active site and the substrate change shape once they are in contact to bring about a closer fit for the lowering of the activation energy, which allows the reaction to proceed more rapidly.

5Activation energy is the energy necessary to destabilize chemical bonds in a substrate in order to bring about some change.

6In competitive inhibition, a molecule called a competitive inhibitor, competes directly for the active site of an enzyme. In non-competitive inhibition, the inhibitor does not compete for the enzyme’s active site. It combines with the allosteric site and brings about a change in conformation of the active site, thus inhibiting the enzyme. End-product inhibition involves non-competitive inhibition to stop a metabolic pathway.

7Oxidation and respiration are important to both cell respiration and photosynthesis. Oxidation involves loss of electrons, gain of oxygen, loss of hydrogen and a compound with lower potential energy. Reduction involves gain of electrons, loss of oxygen, gain of hydrogen, and a compound with higher potential energy. If a compound is oxidized, another substance must be reduced thus causing a redox reaction.

8Cell respiration includes glycolysis, anaerobic respiration and aerobic respiration. The link reaction, the Krebs cycle and oxidative phosphorylation occur in aerobic respiration within the mitochondrion. Glycolysis and anaerobic respiration occur in the cytosol.

9The electron transport chain and chemiosmosis are the processes by which most ATPs are produced. These processes occur on the inner mitochondrial membrane and on the membranes of the cristae. FADH2 and NADH bring the energy-rich electrons to the electron transport chain. Oxygen is the final acceptor of the chain’s energy-rich electrons to form ‘water of metabolism’.

10The final ATP net gain of aerobic cellular respiration is 36 ATPs. The cell is most efficient at breaking down the carbohydrate glucose; however, other organic compounds are commonly broken down by respiration.

11Photosynthesis occurs in the chloroplasts of autotrophic cells. The process of photosynthesis involves light-dependent and light-independent reactions. Thylakoids have photosystems that include chlorophyll a molecules, accessory pigments, and a protein matrix. Photosystem I and photosystem II both operate to carry out the light-dependent reaction of photosynthesis.

12Products of the light-dependent reaction are ATP, free oxygen, and NADPH. These products are then used by the light-independent reaction to form glucose and ultimately complex carbohydrates.

13The light-independent reaction involves the Calvin cycle and begins and ends with the compound RuBP (ribulose bisphosphate). Triose phosphate (TP) is the pivotal compound of the Calvin cycle, which produces glucose, disaccharides, polysaccharides, or RuBP.

14The absorption spectrum of photosynthesis represents the wavelengths of light absorbed by the pigments of the chloroplast. The action spectrum of photosynthesis represents the effectiveness of different wavelengths of light in carrying out photosynthesis. There is a strong positive correlation between the action spectrum and the absorption spectrum.

15Many factors may affect the rate of photosynthesis. These include temperature, light intensity, and carbon dioxide concentration. If any one of these factors is below a certain level and affects the rate of photosynthesis, it is called a limiting factor.