Cellular Metabolism and Biological Cell Structures

Unit 1: Cellular Metabolism and Cell Types

Catabolism and Anabolism

Catabolism refers to all chemical reactions where substances are broken down into simpler ones, releasing energy.

• Cellular respiration: C₆H₁₂O₆ + 6O₂ (glucose) → 6CO₂ + 6H₂O + Energy (ATP)

Anabolism refers to all the chemical reactions where simple substances are joined together to form more complex ones.

• Photosynthesis: H₂O + CO₂ + Sunlight → C₆H₁₂O₆ + 6O₂

Heterotrophic Nutrition

Heterotrophic nutrition: Heterotrophic organisms cannot synthesize organic compounds from inorganic compounds. They incorporate organic matter which has been made by other organisms.

1. Some glucose molecules are used in cellular respiration and others are used in other processes.
2. Cellular respiration takes place inside the mitochondria, where glucose and oxygen molecules are converted into carbon dioxide and water. This process releases a lot of energy.
3. Part of this energy is used in carrying out cellular functions, such as movement. Part of this energy is lost as heat, and the rest is used in anabolic reactions.
4. The energy in anabolic reactions can be used to join several molecules of glucose to form more complex carbohydrates.

Autotrophic Nutrition

Autotrophic nutrition: Organisms that can synthesize organic compounds from inorganic compounds.

1. Autotrophic cells take in carbon dioxide and water.
2. Inside the chloroplasts, these molecules are joined to form glucose using energy from sunlight. The light energy is captured by the pigment chlorophyll. During this process, oxygen is released.
3. Some glucose molecules are used in catabolic reactions to obtain energy: cellular respiration.
4. As in heterotrophic cells, the energy obtained by catabolism is used in different cellular functions, part is lost as heat, and part is used in anabolic reactions, as in the example below, to build more complex carbohydrates.

Characteristics of Prokaryotic Cells

• No nucleus: The DNA is free in the cytoplasm.
• Only found in unicellular living things of the Monera kingdom.
• Never reproduce sexually, although they can perform some kind of genetic exchange.
• No membranous internal structures.
• Smaller ribosomes.
• Always have a cell wall.
• No cytoskeleton.
• DNA is just one circular molecule called a bacterial chromosome. They can also have plasmids.

Characteristics of Eukaryotic Cells

• Nucleus which contains DNA.
• They are found in both multi- and unicellular living things of all other kingdoms.
• Most often, eukaryotic living things can reproduce sexually.
• Large variety of membranous organelles.
• Larger ribosomes.
• Do not always have a cell wall.
• Cytoskeleton present.
• DNA is organized in several linear molecules called chromosomes. There are also circular DNA inside mitochondria and chloroplasts.