Cellular Metabolism and Energy Needs

Cellular Metabolism

• Cellular metabolism is the sum total of catabolic and anabolic reactions, regulated pathways.
• Organisms continuously replenish ATP through sugar or fat oxidation.
• Cells adjust metabolic pathways (anabolic or catabolic) based on cellular conditions.
• Storage molecules and feedback regulation influence metabolic pathways.
• Glycolysis and the citric acid cycle are a small part of overall cellular reactions.
• Food molecule breakdown in animals occurs in three stages: initial breakdown, intermediate breakdown, and final oxidation.
• Glycolysis, TCA cycle, oxidative electron transport, and fermentation are crucial for energy production.

Energy Needs of Living Cells

• Living cells require energy to grow, divide, and perform daily functions.
• Organic materials, particularly sugars and fats, provide the primary energy source.
• Plants produce their own sugars through photosynthesis.
• Animals obtain sugars from consuming plants or other organisms.
• Plants can also undergo respiration.
• Bacteria demonstrate a variety of energy acquisition methods, including photosynthesis, aerobic respiration, anaerobic respiration, and fermentation.

Anabolic and Catabolic Reactions

• Metabolism encompasses all chemical reactions, including anabolism and catabolism.
• Catabolism breaks down large molecules into smaller ones, releasing energy (exergonic).
• Anabolism uses energy to build larger molecules from smaller ones (endergonic).
• Some energy is lost as heat during these reactions.

Enzymes and Metabolic Reactions

• Enzymes are chemical agents that speed up metabolic reactions without being consumed.
• Enzymes speed up anabolic and spontaneous catabolic reactions.
• Enzyme activity is regulated in various ways, including covalent modification.
• Enzymes lower activation energy, accelerating reaction rates.

Cellular Energy Capture/Controlled Oxidation

• Living cells utilize a controlled, stepwise oxidation of glucose to efficiently capture useable energy.
• Glucose oxidation releases energy in smaller steps.
• The energy released is stored in activated carriers.

Energy Carrier Molecule

• Cells use energy carrier molecules (e.g., ATP) to store energy released from catabolic reactions.
• ATP transfers energy from catabolic to anabolic reactions, coupling energy production and consumption.

Glycolysis and the Citric Acid Cycle

• Glycolysis and the citric acid cycle constitute a small portion of overall cellular reactions.
• Glycolysis breaks down glucose into pyruvate, producing ATP and NADH.
• The citric acid cycle further oxidizes acetyl-CoA, generating NADH, FADH2 and ATP.
• The small number of initial ATP molecules produced in glycolysis and citric acid cycle are significant as they initiate the electron transport chain.

Regulation of Enzyme Activities

• Enzyme activity is regulated by a multitude of factors to ensure cellular reactions are balanced.
• Food availability and cellular conditions influence regulation.
• Metabolic pathways are regulated according to cellular needs.

Cellular Pathway Selection

• Cells, in response to their conditions, direct metabolic intermediates into anabolic or catabolic pathways.
• Muscle and brain cells rely primarily on glucose for energy.
• Feedback regulation allows cells to switch between glucose breakdown and synthesis based on needs (e.g., fasting conditions or strenuous exercise).
• Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources.

Feedback Regulation Mechanism

• Feedback regulation is a mechanism where the product of a pathway inhibits or stimulates its own production to maintain homeostasis.
• This mechanism controls process rates and final products in many cellular processes.

Where else have we seen feedback before?

• Blood glucose regulation is an example of feedback in action.
• High blood glucose levels lead to insulin secretion.
• Insulin promotes glucose uptake and storage, lowering blood sugar.
• Conversely, low blood sugar triggers glucagon production.
• This balance ensures glucose levels remain within the normal range for organ function.

Gluconeogenesis and Glycolysis Interplay

• Gluconeogenesis is the reversal of glycolysis.
• Specific enzymes are activated and deactivated to control whether glycolysis or gluconeogenesis occurs.

Glycogen Breakdown

• Glycogen, composed of glucose monomers, serves as a storage form.
• Synthesis and breakdown of glycogen are regulated, controlled by energy levels.

Fats as a Storage Source

• Fats store greater amounts of energy than glycogen.
• Breakdown of fat produces more energy than glycogen.

Food Molecule Breakdown in Animals (3 stages)

• Stage 1: Breakdown of large food molecules into simpler subunits (e.g., proteins to amino acids, polysaccharides to sugars, fats to fatty acids and glycerol).
• Stage 2: Further breakdown of those simpler subunits into Acetyl CoA.
• Stage 3: Complete oxidation of Acetyl CoA in the citric acid cycle to yield greater amounts of ATP and other molecules.

Plant Food Storage

• Plants store synthesized sugars as fats and starch to provide energy for plant embryo development and growth.
• Seeds, a component of the plant embryo, are often a significant food source for animals.
• Fats and starch are often stored in chloroplasts.

Pyruvate Oxidation

• Pyruvate, produced from glycolysis, is converted to acetyl-CoA in the mitochondrion.
• This process involves the release of CO2 and the production of NADH, which is a crucial component of energy production.

Citric Acid Cycle

• Acetyl-CoA enters the citric acid cycle (also known as the Krebs cycle.)
• The cycle releases CO2, produces NADH and FADH2, and generates a small amount of ATP. - It's a critical part of cellular respiration, as it fully oxidizes organic molecules to produce energy required for later processes.

Oxidative Phosphorylation

• Oxidative phosphorylation, occurs in the inner mitochondrial membrane.
• Electrons carried by NADH and FADH2 are used to create a proton gradient and drives ATP synthesis.
• Oxygen is crucial as the terminal electron acceptor.

This quiz explores cellular metabolism, including catabolic and anabolic reactions, energy production through glycolysis, and the citric acid cycle. It also covers how living cells obtain and utilize energy from organic materials. Test your knowledge on these essential biological processes.