Biological Molecules
Water
Water as a Solvent
The oxygen atom in water attracts electrons more strongly than hydrogen atoms.
This unequal sharing of electrons generates a slight negative charge near the oxygen atom and a slight positive charge near the hydrogen atoms.
This results in a permanent dipole, leading to an uneven charge distribution which classifies water as a polar molecule.
Many substances, particularly inorganic ions, can dissolve in water due to the polar nature, allowing for chemical reactions to occur when dissolved substances can move.
Carbohydrates
General Overview
Carbohydrates are organic molecules solely composed of carbon, hydrogen, and oxygen, consisting of long chains of sugar units known as saccharides.
There are three types of saccharides: monosaccharides, disaccharides, and polysaccharides.
Monosaccharides can combine to form disaccharides and polysaccharides through glycosidic bonds formed during condensation reactions.
Monosaccharides
Definition
Monosaccharides are the monomers (building blocks) of carbohydrates.
They are water-soluble, small, and simple molecules.
Key Example: Glucose
A common monosaccharide with six carbon atoms.
Essential substrate for respiration, making it a critical biological molecule.
Disaccharides
Definition
Composed of two monosaccharides linked by a glycosidic bond via a condensation reaction.
Key Examples
Maltose: Formed by the condensation of two glucose molecules.
Sucrose: Formed by condensing glucose with fructose.
Lactose: Formed by condensing glucose with galactose.
Polysaccharides
Definition
Composed of many monosaccharides joined together, serving primarily as energy stores.
They have a large, compact structure minimizing space with many glucose molecules.
Easily hydrolyzed to release glucose for respiration, thus releasing energy.
They are insoluble, preventing osmotic effects in cells.
Key Example: Glycogen
The main energy storage molecule in animals.
Comprised of glucose molecules connected via 1,4 and 1,6 glycosidic bonds.
Highly branched structure allows rapid energy release.
Large but compact structure maximizing energy storage capacity.
Key Example 2: Starch
Primary energy store in plants, consisting of two polysaccharides: amylose and amylopectin.
Amylose: Unbranched chain of glucose linked by 1,4 glycosidic bonds, resulting in a coiled and compact structure for energy storage.
Amylopectin: Branched structure made of glucose linked by both 1,4 and 1,6 glycosidic bonds, allowing rapid enzymatic digestion and energy release.
Joining Monosaccharides
Process
Monosaccharides like glucose and galactose join through condensation reactions to form glycosidic bonds (single oxygen atom).
To hydrolyze polysaccharides, water is added to break the glycosidic bonds, splitting polysaccharides into smaller molecules or disaccharides into monosaccharides.
Lipids
General Overview
Biological molecules with diverse roles: energy storage, organ protection, thermal insulation, and forming cell membranes.
Non-polar molecules, thus insoluble in water but soluble in organic solvents.
Can be saturated or unsaturated.
Saturated Lipids
Found in animal fats, characterized by no carbon-carbon double bonds.
Unsaturated Lipids
Mostly found in plants and contain carbon-carbon double bonds, melting at lower temperatures than saturated fats.
Triglycerides
Essential lipids made up of one glycerol molecule and three fatty acids linked by ester bonds during condensation reactions.
Fatty acids vary in their chain lengths and the number of double bonds. Triglycerides serve as long-term energy reserves in cells.
Mass Transport
Need for a Transport System
In single-celled organisms, substances exchange quickly via simple diffusion due to a high surface area to volume ratio.
Larger organisms, like humans, have a low surface area to volume ratio, necessitating mass transport systems to efficiently supply nutrients.
Circulatory System
Components
Composed of the heart and three blood vessel types: arteries, veins, and capillaries, each with specific adaptations.
Arteries
Carry oxygenated blood away from the heart.
Have thick muscular and elastic walls to withstand high blood pressure.
Small lumen, no valves, and a folded inner lining for stretching.
Split into smaller arterioles leading to capillaries.
Capillaries
Arterioles branch into capillaries for substance exchange with cells.
Numerous and highly branched, providing a large surface area.
Walls are one cell thick for rapid diffusion and have narrow diameters to reach all cells.
Veins
Formed from capillaries, carrying deoxygenated blood back to the heart.
Thin walls for low pressure, wide lumen for maximizing blood flow, and contain valves to prevent backflow.
Structure of the Heart
Composed of four chambers: left and right atria, left and right ventricles.
Atria receive blood from veins; ventricles pump blood out to arteries.
The atrioventricular valves prevent backflow into the atria; semilunar valves prevent backflow from arteries into ventricles.
Double Circulatory System
Describes the blood's two-pass flow through the heart.
Blood enters the right atrium from the vena cava, moves to the right ventricle, and is sent to the lungs via the pulmonary artery.
Oxygenated blood returns to the left atrium via the pulmonary vein, and from there it is pumped to the body through the aorta.
Cardiac Cycle
Stages
Atrial Systole: Atria contract, forcing blood into ventricles; atrioventricular valves open due to greater atrial pressure.
Ventricular Systole: Ventricles contract, closing atrioventricular valves and opening semilunar valves to expel blood.
Cardiac Diastole: Atria and ventricles relax, decreasing chamber pressure allowing blood to flow in; semilunar valves close to prevent backflow.
Transport of Gases in the Blood
Haemoglobin
A water-soluble globular protein in red blood cells, made of two alpha and two beta polypeptide chains, and four haem groups.
Each haem group can bind one oxygen molecule, enabling a single haemoglobin molecule to carry four oxygen molecules, forming oxyhaemoglobin.
Transport Mechanism
The affinity of oxygen for haemoglobin changes with the partial pressure of oxygen (measure of concentration).
Higher partial pressure increases haemoglobin's affinity for oxygen, facilitating loading in the lungs and unloading in respiring tissues.
Carbon dioxide diffuses into capillaries from respiring tissues and binds to haemoglobin to form carboxyhaemoglobin.
Dissociation Curves
Illustrate the relationship between haemoglobin saturation and partial pressure of oxygen.
High partial pressure yields high haemoglobin saturation, whereas low pressure results in lower saturation.
Factors Affecting Affinity:
Saturation: Binding increases haemoglobin's affinity due to conformational change.
Fetal Haemoglobin: Higher affinity for oxygen than adult haemoglobin, allowing it to absorb more oxygen in low partial pressure environments (e.g., placenta).
The Bohr Effect: Increased carbon dioxide partial pressure decreases haemoglobin's affinity for oxygen, facilitating oxygen unloading in respiring tissues.
Cardiovascular Diseases (CVD)
Atherosclerosis
Hardening of arteries caused by plaque build-up (atheroma).
Progression:
Damage to endothelial lining (caused by factors such as high cholesterol, smoking, high blood pressure).
Inflammatory response attracts white blood cells to the site.
Plaque develops from white blood cells, cholesterol, calcium salts, and fibers.
Narrowing of arteries occurs, restricting blood flow which raises blood pressure, causing further endothelial damage and recurrent plaque formation.
Blood Clotting
Clots minimize blood loss and prevent pathogen entry into the bloodstream.
Process:
Platelets contact damaged vessel wall, changing to a spherical shape and clustering to form a temporary plug.
Platelets and damaged tissues release clotting factors, triggering prothrombin transformation into thrombin.
Thrombin catalyzes fibrinogen conversion to insoluble fibrin, creating a mesh that traps blood cells to form a clot.
Risk Factors for CVD
Various factors increase the risk of cardiovascular diseases, classified as modifiable or non-modifiable:
Genetics: Hereditary factors can contribute to higher blood pressure.
Diet: High cholesterol and fats contribute to plaque formation.
Age: Increased prevalence of CVD with age.
High Blood Pressure: Narrows and damages arteries.
Smoking: Damages artery linings, promoting atheroma formation.
Inactivity: Linked with higher blood pressure.
Mitigation strategies include quitting smoking, regular exercise, dietary adjustments, and maintaining a healthy weight.
Dietary Antioxidants
Oxidative Stress: Imbalance between antioxidants and free radicals, contributing to CVD.
Antioxidants can stabilize free radicals, potentially reducing the risk of CVD.
Blood Cholesterol Levels and CVD
Cholesterol is transported via high-density lipoproteins (HDLs) and low-density lipoproteins (LDLs), both having different effects:
High-Density Lipoproteins (HDLs):
Transport cholesterol to the liver for expulsion, reducing cholesterol levels.
Formed from unsaturated fats and proteins.
Low-Density Lipoproteins (LDLs):
Deliver cholesterol to arteries, potentially forming plaques and increasing cholesterol levels.
Formed from saturated fats and proteins.
Positive correlation exists between saturated fats and cholesterol levels, thus connecting saturated fat intake to increased CVD risk.
Treatment of Cardiovascular Diseases
Antihypertensives
Used to lower blood pressure.
Pros: Generally effective and cost-efficient.
Cons: Potential for side effects, though usually mild and reversible.
Statins
Reduce cholesterol levels, thereby decreasing plaque accumulation.
Pros: Mostly effective and beneficial in relaxing blood vessels.
Cons: Possible side effects include nausea, muscle aches, and rare severe effects like diabetes.
Anticoagulants
Prevent blood clots.
Pros: Lower the risk of thrombosis.
Cons: Risk of excessive bleeding in the event of vessel damage.
Platelet Inhibitors
Interrupt blood clot formation processes.
Pros: Effective in certain arteries where anticoagulants fail.
Cons: Risk of excessive bleeding similar to anticoagulants.
Obesity Indicators
Understanding of cardiovascular disease and its contributors has improved.
Recognizing overweight and obesity can encourage healthy lifestyle changes.
Body Mass Index (BMI)
Calculated as:
BMI = \frac{\text{Body mass in kilograms}}{(\text{Body height in metres})^2}Classification:
Under 18.5: Underweight
18.5 - 25: Normal
25 - 30: Overweight
Over 30: Obese
Waist to Hip Ratio (WHR)
Measures obesity risk.
Classification:
Male: WHR > 0.9 is considered obese.
Female: WHR > 0.85 is considered obese.
Perceived Risk
Defined as the likelihood of an unfavorable event.
Actual risk (quantified by research) may differ from perceived risk (based on personal factors), leading to potential misjudgment of health risks.
Exam Technique
Key specifications: Ability to analyze quantitative data related to health risks and distinguish between correlation and causation while recognizing conflicting evidence is essential.
Quantitative Data: Represented numerically (e.g., weight).
Correlation: Indicates the relationship between two variables (ranges from -1 to 1).
Value 1: Perfect positive correlation
Value 0: No correlation
Value -1: Perfect negative correlation
Example: Positive correlation exists between cholesterol levels and CVD cases.
Causation: One variable directly affects another.
Example: Increased cholesterol causes increased plaque formation (causation and correlation).
Evaluating Studies: Must avoid bias through random, representative sampling, sufficient sample size, and statistical analysis.
Reliable studies should include controls, have a placebo group, and ideally be double-blind.