Chapter 4 Cellular Metabolism & Digestion Metabolism involves 2 processes: Anabolism- is the buildup of larger molecules from smaller ones and requires energy. Catabolism- is the breakdown of larger molecules into smaller ones, and releases energy. Anabolism-provides biochemicals needed for cell growth & repair. Dehydration Synthesis- Small molecules attach by sharing atoms (forming a covalent bond) and releasing water. Anabolism Catabolism

Dehydration Synthesis Three examples 1. Carbohydrates – following the removal of OH from one molecule and H from the other, monosaccharides are joined by sharing an oxygen atom. 2. Lipids – one glycerol and 3 fatty acids form fat (triglyceride) plus three H 2 O by dehydration synthesis.

Dehydration Synthesis 3. Proteins – amino acids are joined by a peptide bond using dehydration synthesis.

Catabolism – break large molecule into smaller molecules Hydrolysis – enzyme used to break bond between 2 portions of a molecule. A water molecule is split, and OH & H used in the process. -Complex carbohydrates broken down into monosaccharides. -Fats broken down into glycerol and fatty acids. -Proteins broken down into amino acids. -Nucleic acids into nucleotides. C 12 H 22 O 11 + H 2 O C 6 H 12 O 6 + C 6 H 12 O 6 sucrose waterglucose fructose -Hydrolysis is the opposite of Dehydration Synthesis. Hydrolysis Disaccharide + H 2 O monosaccharide + monosaccharide Dehydration Synthesis - Hydrolysis occurs during digestion, breaking down macromolecules.

Enzymes are complex molecules, usually proteins, that promote cellular chemical reactions by 1. lowering the amount of energy required to start reaction (activation energy). 2. increasing the rate of metabolic reactions 3. insuring specificity by only binding and reacting with specific molecules called substrates 4. not being altered by the reaction, enabling them to be used over and over again Peroxidase

During enzyme-controlled reactions,active sites combine with substrate(s). The ability to recognize a substrate depends on the shape of the enzyme molecule. The 3-D structure twists and coils so it fits the specific shape of the substrate. The active site is the place where the enzyme and substrate join.

The speed of enzyme-controlled reactions depends on the number of enzyme and substrate molecules. The higher the concentration, the faster the reaction rate. Enzymes can be deactivated (inactivated) by exposure to heat, radiation, electricity, certain chemicals, or extreme pH. Both excess heat and pH denature enzymes

Metabolic Pathway – a sequence of enzyme controlled reactions. 3 important pathways: 1. Carbohydrate pathways 2. Lipid pathways 3. Protein pathways

Carbohydrate Pathway -Carbohydrates are digested into monosaccharides such as glucose -Carbohydrates are used as a cellular energy source. -The 1 st phase (glycolysis) occurs in the cytoplasm and is anerobic. One glucose yields two pyruvic acids. - The 2 nd phase: Pyruvic acid is broken down to form a 2-carbon acetyl group. The 2-carbon acetyl group combines with Coenzyme A to form acetyl coenzyme A (acetyl CoA). Acetyl CoA is sent to the mitochondria where it enters the Krebs cycle, releasing energy which is transferred to ATP. Some energy is lost as heat. Mitochondria Excess glucose is stored as fat or glycogen.

Lipid Pathway -Fats contain more than twice the chemical energy as carbohydrates or proteins. -Fats must undergo hydrolysis before energy is released. Fats are broken down into glycerol and fatty acids. -Some of the fatty acid reacts to form acetyl CoA through beta oxidation. -Excess acetyl CoA is converted into ketone bodies such as acetone. -Resulting acetyl CoA is oxidized in the citric acid cycle. The result = energy.

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Lipid Pathway: continued -The glycerol part of triglyceride can also go into the citric acid cycle, resulting in energy production. -If ketone bodies form faster than they can be broken down, they are eliminated through the lung and kidney, giving breath and urine a fruity odor. Example 1: a person fasting to lose weight typically has an excess of ketone bodies. Example 2: a person with diabetes mellitus may metabolize excess fat, resulting in excess ketone bodies and potentially, acidosis.

Protein Pathway -When we eat, proteins are digested into amino acids which are transported by the blood to cells. -Inside our cells, many amino acids reunite to form the proteins which our bodies needs. -Some protein is broken down to supply energy. -The protein that is going to be used as energy is broken down into amino acids. -The amino acids undergo deamination which occurs in the liver and removes nitrogen-containing portions (NH 2 groups). These react to form urea which is eliminated in urine. -Some deamination leads to acetyl CoA and some to citric acid cycle. Energy is released and captured in ATP. Starving people deplete carbohydrates, and lipids before using protein for energy.

Summary of how food provides energy 1.Carbohydrates, the normal source of energy production, are 1 st converted to glucose. Glucose is broken down into pyruvic acid, then acetyl CoA, which enters the Krebs Cycle. 2.Similarly, fats and proteins are broken down into acetyl CoA, thereby providing energy.