Title: Overview of Human Cell Structure and Functions

Cell and Tissue

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Introduction to Human Anatomy and Physiology

  • Anatomy and Physiology
    • Anatomy: The science of body structure.
    • Physiology: The science of body function.

Levels of Structural Organization

There are six levels of structural organization in the human body:

  1. Chemical Level

    • The smallest unit of human anatomy and physiology is the atom.
    • The human body comprises 26 essential elements, with oxygen (65%), carbon (18.5%), hydrogen (9.5%), and nitrogen (3.2%) being major components.
    • About 96% of body mass comprises major elements, while eight other elements are classified as lesser elements.

  2. Cellular Level

    • Molecules combine to form cells, the structural and functional units of life.

  3. Tissue Level

    • Groups of similar cells work together to perform specific functions known as tissues.

  4. Organ Level

    • Different tissues combine to form organs that serve specific functions.

  5. System Level

    • Related organs work together to form a system, such as the digestive system.

  6. Whole Body Level

    • All parts/systems work together to constitute the entire body.

Basic Life Processes

Life processes distinguish living organisms from non-living things:

  • Metabolism:

    • It includes all chemical processes in the body.
    • Catabolism: Breakdown of complex molecules into simpler ones.
    • Anabolism: Formation of complex molecules from simpler ones.

  • Responsiveness:

    • The ability to detect and respond to changes.

  • Movements:

    • Essential for growth and differentiation.

  • Growth and Differentiation:

    • Organism development processes.

  • Reproduction:

    • Essential for species continuation.

  • Stopping any life process can lead to cell death and ultimately death of the body.

Planes and Sections

There are three main types of anatomical planes and sections:

  1. Sagittal Plane

    • Divides the body or organ into right and left sides.

  2. Frontal or Coronal Plane

    • Divides the body or organ into anterior (front) and posterior (back) parts.

  3. Transverse or Horizontal Plane

    • Divides the body or organ into superior (upper) and inferior (lower) portions.

Cell Structure

  • A cell is the basic structural and functional unit enclosed by a membrane.

  • Main Parts of a Cell:

    1. Plasma Membrane
    2. Cytoplasm
    3. Nucleus

Plasma Membrane

  • Functions:

    • Acts as the outer boundary of the cell.
    • Selectively allows substances to enter or exit.

  • Composition:

    • Comprised of a lipid bilayer made of three types of molecules:
      • Phospholipids (75%)
      • Cholesterol (20%)
      • Glycolipids (5%)

Transportation Across Plasma Membrane

  • Movements of substances across the plasma membrane can be classified into several types, including passive and active transport mechanisms.

This structured outline captures essential concepts in human anatomy and physiology regarding the organization of the body, basic life processes, anatomy planes, and cell structure.

Extended readings:

openstax.org
1.2 Structural Organization of the Human Body - Anatomy and ...
byjus.com
Anatomy and Physiology of Human Body - BYJU'S
study.com
Levels of Organization in the Human Body | Definition & Examples

Cell Transport Mechanisms

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Passive Process

  • Definition: Substances move down their concentration gradient without the use of cellular energy.
  • Examples: Simple diffusion, facilitated diffusion, and osmosis.

(a) Simple Diffusion

  • Description: Movement of substances across the lipid bilayer of the cell membrane freely, without the aid of membrane transport proteins.
  • Insight: This process is crucial for small, non-polar molecules (e.g., oxygen and carbon dioxide) that can easily pass through the hydrophobic core of the membrane.

(b) Facilitated Diffusion

  • Description: Movement of substances (like glucose) through the lipid bilayer with the help of membrane proteins that act as carriers.
  • Insight: This process is important for larger or polar molecules that cannot easily cross the membrane. Examples of carrier proteins include glucose transporters.

(c) Osmosis

  • Description: A specific type of diffusion where only water molecules move across a semi-permeable membrane.
  • Insight: Osmosis is crucial for maintaining cell turgor pressure in plant cells and regulating the internal environment of cells.

Active Process

  • Definition: Cellular energy is used to move substances against their concentration gradient.
  • Mechanisms:
    • Primary active transport (requires ATP directly).
    • Secondary active transport (derives energy from the concentration gradient of another substance).

Examples of Active Transport

  • Endocytosis: The process of ingesting substances by cells (e.g., phagocytosis for solid particles).
  • Exocytosis: The process of expelling substances from the cell.

Cytoplasm

  • Definition: All cellular contents between the cell membrane and nucleus.
  • Components:
    • Cytosol: The fluid portion, making up about 55% of total cell volume, containing ions, glucose, amino acids, fatty acids, proteins, ATP, and waste.
    • Organelle: Specialized structures within the cell with specific shapes and functions.

(i) Cytosol (Intracellular Fluid)

  • Insight: Key site for many chemical reactions, including glycolysis, which converts glucose into pyruvate, yielding ATP.

(ii) Organelles

  • Examples:
    • Centrosome: Contains two centrioles, important for cell division.
    • Ribosomes: Sites of protein synthesis.
    • Endoplasmic Reticulum: Involved in protein and lipid synthesis.
    • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

(a) Centrosome

  • Description: An organelle that helps organize microtubules during cell division.
  • Function: Centrioles within the centrosome migrate to opposite poles of the cell, assisting in the formation of the spindle apparatus which enables proper chromosome distribution.

Extended readings:

www.khanacademy.org
Cellular organelles and structure (article) - Khan Academy
www.palmbeachstate.edu
[PDF] Cellular Level of Organization - Palm Beach State College
www.pvamu.edu
[PDF] Define Cell

Notes on Cell Organelles

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Ribosome

  • Definition: A cell organelle made up of ribosomal RNA (rRNA) and protein, involved in protein synthesis.
  • Function:
    • Site of protein synthesis (location where mRNA is translated into proteins).
  • Location:
    • Mainly situated on the rough endoplasmic reticulum (ER).
    • Free ribosomes (not attached to ER) synthesize proteins for the cytosol.
    • Ribosomes in mitochondria synthesize mitochondrial proteins.

Insight: Ribosomes are crucial for translating genetic information into functional proteins, forming the basis for cellular operations.

Lysosomes

  • Definition: An organelle involved in intracellular digestion.
  • Function:
    • Contains hydrolytic enzymes that break down proteins and carbohydrates.
    • Aids in the digestion of pathogens engulfed by the cell.
  • Importance: Essential for recycling cellular components and maintaining cellular health.

Insight: Lysosomal function is critical in preventing cellular buildup of waste and in immune response.

Endoplasmic Reticulum (ER)

  • Definition: A complex network of membranous tubules in the cytoplasm.
  • Forms:
    • Granular (Rough ER) : Studded with ribosomes; main site for protein synthesis and transportation.
    • Agranular (Smooth ER) : Lacks ribosomes; synthesizes lipids and steroids (e.g., estrogen, testosterone).

Insight: The smooth ER plays a vital role in lipid metabolism and detoxification processes within the cell.

Golgi Complex

  • Definition: A membranous sac organelle present in almost all cells.
  • Function:
    • Involved in the processing, packaging, and transport of proteins.

Insight: Functions like a post office for proteins, ensuring they reach their correct destination.

Mitochondria

  • Definition: Organelle with an oval shape, approx. 0.5 µm in diameter, known as the powerhouse of the cell.
  • Function:
    • Catalyzes aerobic processes for ATP synthesis in active organs like the liver and muscles.
  • Structure:
    • Has an outer and inner membrane.
    • The inner membrane contains folds known as cristae, which increase surface area for respiration.
    • Mitochondrial matrix: The fluid-filled space inside the inner membrane, contains enzymes for metabolic processes.
    • Mitochondria have their own DNA, which is inherited maternally and contains about 37 genes.

Insight: Mitochondrial health is essential for energy production, and mutations in mitochondrial DNA can lead to metabolic disorders.

Nucleus

  • Definition: The largest organelle containing genetic material (chromosomes).
  • Structure:
    • Surrounded by a nuclear envelope that separates it from the cytoplasm.
    • Contains nucleoli, which produce ribosomes.
  • Function:
    • Holds genetic information in the form of DNA, which is critical for cellular function and heredity.

Insight: The nucleus acts as the command center of the cell, regulating gene expression and maintaining the integrity of genes.

Additional Information

  • The complete genetic information in a cell (or organism) is referred to as the genome. In humans, it contains approximately 30,000 genes.

Summary: Understanding these organelles is vital for grasping cellular functions and the larger mechanisms that govern life at the microscopic level. Each organelle collaborates to maintain cellular health and ensure proper functioning within biological systems.

Extended readings:

www.khanacademy.org
Cellular organelles and structure (article) - Khan Academy
byjus.com
Cell Organelles - Types, Structure and their Functions - BYJU'S
study.com
Organelle Function Types & Importance - Lesson - Study.com

Nucleic Acid

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Overview

  • Definition: Nucleic acids are high-molecular-weight chemicals made of carbon, hydrogen, oxygen, nitrogen, and phosphorus. They carry genetic information necessary for replication and cellular processes.
  • Naming Origin: The term "nucleic acid" originated from the early discovery of these molecules within cell nuclei.
  • Structure: Nucleic acids are complex structures formed from sugars (pentoses), phosphoric acid, and nitrogen bases (purines and pyrimidines).

Types of Nucleic Acid

  1. Deoxyribonucleic Acid (DNA)

    • Composition: Made up of nucleotides that consist of a deoxyribose sugar, phosphoric acid, and one of four nitrogen bases (adenine, guanine, thymine, cytosine).
    • Base Pairing: Adenine pairs with thymine (A=T) and guanine pairs with cytosine (G=C).
    • Structure: DNA forms a double helix structure as proposed by Watson and Crick in 1953. The strands are held together by hydrogen bonds between complementary base pairs (A-T and C-G).

    Insights:

    • DNA’s double helix structure is crucial for its function in heredity and genetic information storage.
    • The sequence of bases along the DNA strand determines genetic information.

    Biological Importance of DNA:

    • Basic Molecule of Heredity: DNA is fundamental in the transmission of genetic traits.
    • Genes: Comprised of DNA, genes are the units of heredity.
    • Genetic Information: DNA stores, expresses, and transmits genetic information across generations.
    • Mutations: Changes in DNA sequence can lead to abnormal cell functions or malignant cells.
    • Protein Synthesis: RNA is synthesized from DNA to produce proteins.

  2. Ribonucleic Acid (RNA)

    • Composition: An important nucleic acid found in all living cells, RNA contains ribose sugar.
    • Functionality: RNA plays a key role in protein synthesis and can also act as genetic material in certain viruses.

    Insights:

    • RNA differs from DNA in that it contains ribose, which has one more oxygen atom than deoxyribose.
    • The presence of RNA viruses highlights the diversity of genetic material beyond DNA.

DNA Fingerprinting

  • Technique Usage: DNA fingerprinting is a method used in research, paternity testing, and forensic identification.
  • Identification: A small sample of DNA is sufficient for generating a fingerprint, making it a powerful tool for individual identification.

This structured note combines essential information on nucleic acids, their types, and their functionalities, enhancing comprehension through additional insights and explanations.

Extended readings:

pmc.ncbi.nlm.nih.gov
Understanding biochemistry: structure and function of nucleic acids
www.britannica.com
Nucleic acid | Definition, Function, Structure, & Types - Britannica
bio.libretexts.org
8.1: Nucleic Acids - Structure and Function - Biology LibreTexts

Notes on RNA and Cell Division

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Types of RNA

1. Messenger RNA (m-RNA)

  • Formation: Synthesized by transcription of DNA templates.
  • Function:
    • First step in protein synthesis.
    • Carries code for specific amino acid sequences from DNA to cytoplasm.
  • Proportion: Comprises 10% to 20% of total RNA.
  • Insight: Acts as a template for protein synthesis, translating genetic information into functional proteins.

2. Transfer RNA (t-RNA) or Soluble RNA (s-RNA)

  • Function:
    • Transports amino acids from cytoplasm to ribosomes for protein synthesis.
  • Proportion: Makes up 10% of total RNA.
  • Insight: Functions like an adapter molecule, linking amino acids to their corresponding codons on the mRNA strand.

3. Ribosomal RNA (r-RNA)

  • Location: Found within ribosomes.
  • Function:
    • Assists in protein synthesis.
    • Forms the core of ribosome's structure and catalyzes the assembly of amino acids into protein chains.
  • Proportion: Represents 60% to 80% of total RNA.
  • Insight: Crucial for the translation process, ensuring accurate protein synthesis by decoding the mRNA.

Cell Division

Overview

  • Definition: The process by which cells reproduce themselves.
  • Types:
    • Mitosis
    • Meiosis

Mitosis (Somatic Cell Division)

  • Chromosome Count: Daughter cells contain the same number of chromosomes (diploid) as the parent cell.

  • Cycle Phases:

    i. Interphase
    • Purpose: Cells replicate DNA, organelles, and grow.
    Phases of Interphase
    • G1 Phase:
      • Cells prepare most organelles needed for division.
    • S Phase:
      • DNA replication occurs, resulting in new DNA formation.
    • G2 Phase:
      • Enzymes and other proteins are synthesized.

ii. Mitotic Phase

  • Sub-phases:
    1. Prophase
    2. Metaphase
    3. Anaphase
    4. Telophase
  • Process: Involves the separation of duplicated chromosomes and the completion of cellular division.

Diagram Overview

  • Cell Cycle: Represents stages including G1, S, G2, and M phases, illustrating how the cell checks for errors and prepares for division.

Extended readings:

www.britannica.com
RNA | Definition, Structure, Types, & Functions - Britannica
www.genome.gov
Ribonucleic Acid (RNA) - National Human Genome Research Institute
www.nature.com
RNA Functions | Learn Science at Scitable - Nature