Metabolism, Enzymes, and Digestive System: Key Concepts for Biology

What is metabolism?

The sum total of all chemical reactions that occur within an organism.

What is catabolism?

The breakdown of large molecules into smaller ones, releasing energy.

What is anabolism?

The synthesis of larger molecules from smaller ones, requiring energy.

What is the general function of enzymes in metabolism?

They control biochemical processes (both anabolic and catabolic reactions) by speeding them up.

How do enzymes affect activation energy?

Enzymes lower the activation energy required for a reaction to proceed.

Name four key features of enzymes.

1. They are proteins. 2. They are specific to their substrate. 3. They are not consumed in reactions. 4. They can be denatured.

Describe the 'Lock and Key' model of enzyme action.

The enzyme (lock) has a specific active site shape that only fits a specific substrate (key). When they bind, the reaction occurs.

What happens to an enzyme when it is denatured?

Its three-dimensional shape (especially the active site) is permanently altered, preventing substrate binding and stopping its function.

How does pH affect enzyme activity?

Each enzyme has an optimal pH. Deviation from this pH can cause denaturation, reducing activity.

How does temperature affect enzyme activity?

Increasing temperature increases activity up to an optimum point. Beyond that, heat denatures the enzyme, rapidly decreasing activity.

How do competitive inhibitors affect enzyme function?

They have a similar shape to the substrate and compete to bind to the active site, blocking the real substrate.

How do non-competitive inhibitors affect enzyme function?

They bind to a site other than the active site (allosteric site), changing the enzyme's shape and making the active site non-functional.

What are coenzymes and cofactors?

Non-protein molecules that help enzymes function properly (e.g., vitamins, minerals).

How does the concentration of reactants and products affect enzyme activity?

Increasing reactant concentration increases reaction rate (up to a limit). Increasing product concentration can slow the reaction (feedback inhibition).

Name the 6 basic activities of the digestive system.

1. Ingestion, 2. Mechanical digestion, 3. Chemical digestion, 4. Movement (peristalsis), 5. Absorption, 6. Elimination.

What is the difference between mechanical and chemical digestion?

Mechanical breaks food into smaller pieces (increases surface area). Chemical breaks down molecules into smaller, soluble nutrients via acids and enzymes

To what smaller molecule are carbohydrates broken down? Name an example.

Monosaccharides (simple sugars). Example: Glucose.

To what smaller molecule are proteins broken down?

Amino acids.

To what smaller molecule are lipids (fats) broken down?

Glycerol and fatty acids.

What is a peptide bond?

The chemical bond that links two amino acids together to form a dipeptide (2) or polypeptide chain (heaps, 20+).

What is the monomer (building block) of a nucleic acid?

A nucleotide.

Name the accessory organs of the digestive system.

Liver, gall bladder, and pancreas.

What is the function of the teeth?

Mechanical digestion (mastication/chewing).

What is the human dental formula?

2:1:2:3 / 2:1:2:3 (Incisors, Canines, Premolars, Molars per half-jaw).

What is the function of the oesophagus?

To move food from the mouth to the stomach via peristalsis.

What is peristalsis?

Rhythmic waves of muscle contraction that push food through the alimentary canal.

What is the main function of the stomach?

Mechanical churning and chemical digestion of proteins using pepsin and HCl.

Name the three sections of the small intestine.

Duodenum, jejunum, and ileum.

What is the primary function of the small intestine?

Chemical digestion and absorption of nutrients.

What is the function of the large intestine?

Absorption of water and electrolytes; formation and storage of faeces.

What is the function of the liver?

Produces bile (which emulsifies fats).

What is the function of the gall bladder?

Stores and concentrates bile.

What is the function of the pancreas?

Produces pancreatic juice containing many digestive enzymes (proteases, lipase, amylase) and bicarbonate to neutralize stomach acid.

Where is bile produced and where does it act?

Produced in the liver, stored in the gall bladder, and acts in the small intestine (duodenum) to emulsify fats.

What is the function of villi and microvilli in the small intestine?

They greatly increase the surface area for absorption.

During absorption, what is absorbed into the blood capillary inside a villus?

Monosaccharides (glucose) and amino acids.

During absorption, what is absorbed into the lacteal (lymph capillary) inside a villus?

Fatty acids and glycerol (which are reassembled into fats/lipids).

What is the difference between active and passive transport in nutrient absorption?

Active transport requires energy (ATP) to move nutrients against a concentration gradient. Passive transport (diffusion) does not require energy.

What is the function of the rectum?

Stores faeces before elimination.

What is elimination (defecation)?

The removal of undigested materials and some metabolic wastes from the body via the anus.

What is constipation?

Infrequent or difficult bowel movements, often due to low water or fibre intake.

What is diarrhoea?

Frequent, loose, watery stools, often due to infection or irritation.

What is bowel cancer?

A malignancy (cancer) of the large intestine or rectum.

What is soluble fibre and how does it help digestion?

Fibre that dissolves in water, forming a gel. It helps regulate blood sugar and lower cholesterol.

What is Coeliac disease?

An autoimmune disease where ingesting gluten damages the villi of the small intestine, leading to malabsorption.

What is the general word equation for aerobic cellular respiration?

Glucose + Oxygen → Carbon Dioxide + Water + ATP (energy).

What is the main purpose of cellular respiration?

To catabolise (break down) organic compounds to store energy in the form of ATP.

Where in the cell does glycolysis occur?

The cytosol (cytoplasm).

Where in the cell do the Krebs cycle and Electron Transport Chain (aerobic stages) occur?

The mitochondria.

What are the inputs and outputs of glycolysis (anaerobic stage)?

Input: Glucose. Output: 2 Pyruvate, 2 ATP, 2 NADH.

What is the net ATP yield from one glucose molecule during aerobic respiration?

Approximately 36-38 ATP.

What is the net ATP yield from one glucose molecule during anaerobic respiration (fermentation) in humans?

2 ATP.

What are the products of anaerobic respiration in humans (lactic acid fermentation)?

Lactic acid and 2 ATP.

What is oxygen debt?

The amount of oxygen needed to convert accumulated lactic acid back into glucose in the liver after intense exercise.

What is 'recovery oxygen'?

The extra oxygen you breathe in after exercise to repay the oxygen debt.

Compare the efficiency of aerobic vs. anaerobic respiration.

Aerobic is much more efficient (produces ~36-38 ATP). Anaerobic is inefficient (produces 2 ATP) but fast, and doesn't require oxygen.

What is the relationship between ATP and ADP?

ATP (Adenosine Triphosphate) is broken down into ADP (Adenosine Diphosphate) + P, releasing energy. ADP + P is recombined using energy to form ATP.

Outline three things a cell uses ATP energy for.

1. Active transport (pumping molecules across membranes). 2. Protein synthesis (anabolism). 3. Muscle contraction.