Biomolecules and Cellular Structure

DNA and RNA: Structure and Function

DNA and RNA are nucleic acids essential for genetic information storage and transfer in cells. Their differences in structure and function are fundamental to molecular biology.

• DNA (Deoxyribonucleic Acid): More chemically stable than RNA due to its double-stranded structure and deoxyribose sugar.

• Complementary Base Pairing: DNA strands pair via specific hydrogen bonds: Adenine (A) with Thymine (T), and Cytosine (C) with Guanine (G).

• RNA (Ribonucleic Acid): Contains ribose sugar and uracil (U) instead of thymine.

• Function: DNA stores genetic information; RNA is involved in protein synthesis.

Example: DNA replication relies on complementary base pairing to ensure accurate copying of genetic material.

Proteins: Transport and Structure

Proteins serve diverse roles in cells, including transport, structural support, and catalysis.

• Transport Proteins: Facilitate movement of molecules across membranes (e.g., aquaporins, proton pumps, potassium channels).

• Structural Proteins: Provide support and shape to tissues (e.g., collagen).

Example: Collagen is a structural protein, not a transport protein.

Cellular Transport Mechanisms

Passive and Active Transport

Cells regulate the movement of substances across their membranes through various transport mechanisms.

• Simple Diffusion: Passive movement of molecules from high to low concentration, without energy or channels.

• Facilitated Diffusion: Passive transport via membrane proteins.

• Carrier-Mediated Transport: Involves specific proteins and may require energy.

• Osmosis: Diffusion of water across a semipermeable membrane.

Example: Oxygen enters cells by simple diffusion.

Chemical Bonds and Interactions

Hydrogen Bonding

Hydrogen bonds are weak interactions crucial for the structure of biomolecules.

• Definition: A hydrogen bond is a weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen, nitrogen).

• Intramolecular vs. Intermolecular: Hydrogen bonds can occur within a molecule (intramolecular) or between molecules (intermolecular).

• Relative Strength: Hydrogen bonds are weaker than covalent and ionic bonds.

Example: Hydrogen bonds stabilize the double helix structure of DNA.

Feedback Mechanisms in Physiology

Negative Feedback

Negative feedback mechanisms maintain homeostasis by counteracting changes in physiological systems.

• Definition: A process where a change in a variable triggers a response that opposes the initial change.

• Examples:

  • Narrowing of blood vessels when body temperature drops.

  • Regulation of blood glucose levels.

Example: Amplification of labor contractions is a positive feedback, not negative.

Cell Division and Cellular Respiration

Mitosis: Phases and Features

Mitosis is the process of cell division resulting in two genetically identical daughter cells.

• Telophase: The phase during which two nuclei start to form.

• Cytokinesis: In animal cells, characterized by the formation of a cleavage furrow.

Example: Plant cells form a cell plate during cytokinesis.

Aerobic Cellular Respiration

Aerobic respiration is the process by which cells generate ATP using oxygen.

• Stages (in order): Glycolysis → Pyruvate oxidation → Krebs cycle → Electron transport chain and chemiosmosis

Equation:

Enzymes and Biochemical Reactions

Enzyme Specificity

Enzymes are biological catalysts that accelerate chemical reactions with high specificity.

• Substrate Specificity: Each enzyme acts on a particular substrate due to its unique active site.

• Function: Enzyme specificity is crucial for proper metabolic regulation.

Example: Lactase specifically catalyzes the breakdown of lactose.

Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming chemical bonds.

• Examples: Burning paper and cooking are chemical reactions; water freezing is a physical change.

Oxidation and Reduction

Oxidation and reduction (redox) reactions are fundamental to energy transfer in cells.

• Oxidation: Involves the loss of electrons.

• Reduction: Involves the gain of electrons.

Equation:

Tissues and Organ Systems

Types of Tissues

Tissues are groups of cells with similar structure and function.

• Muscle Tissue: Responsible for movement.

• Nervous Tissue: Transmits signals and information.

• Connective Tissue: Supports and binds other tissues.

• Epithelial Tissue: Covers surfaces and lines cavities.

Example: Nervous tissue transmits electrical impulses throughout the body.

Stratified Epithelial Tissue

Stratified epithelial tissue consists of multiple layers of cells, providing protection.

• Primary Function: Protection against abrasion and pathogens.

Connective Tissue: Blood and Cartilage

Connective tissues provide structural and functional support in the body.

• Blood: Plasma is the extracellular matrix, supporting cells and transporting substances.

• Cartilage: Supports and cushions joints, providing flexibility and resistance to compression.

Example: Articular cartilage in joints reduces friction and absorbs shock.

Anatomical Terminology and Skeletal System

Directional Terms

Directional terms describe the locations of structures relative to each other.

• Ipsilateral: On the same side of the body.

• Contralateral: On opposite sides of the body.

• Medial: Toward the midline.

• Intermediate: Between two structures.

Example: The left and right elbows are contralateral.

Cranial Sutures

Sutures are immovable joints between skull bones.

• Coronal Suture: Located between the parietal bones and the frontal bone.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between parietal and occipital bones.

• Squamous Suture: Between parietal and temporal bones.

Cellular Organization and Function

Nucleosome Packaging

In eukaryotic cells, DNA is packaged into nucleosomes by histone proteins.

• Histones: Proteins that organize DNA into structural units called nucleosomes, facilitating compaction and regulation.

Example: Chromatin structure is determined by histone-DNA interactions.

Structure-Function Relationship

Design and Function of Biological Structures

Biological structures are adapted to perform specific functions, reflecting the principle of structure-function relationship in anatomy and physiology.

• Specific Functions: Organs and tissues are specialized for their roles (e.g., lungs for gas exchange, muscles for movement).

Example: The structure of alveoli in the lungs maximizes surface area for efficient gas exchange.

Table: Types of Transport Proteins

The following table summarizes the main types of transport proteins and their functions.

Table: Stages of Aerobic Cellular Respiration

Table: Types of Tissues and Their Functions